TASK 600 TECHNICAL MEMORANDUM NO. 607 LONG-TERM BIOSOLIDS MANAGEMENT PLAN

Transcription

1 City and County of San Francisco 2030 Sewer System Master Plan TASK 600 TECHNICAL MEMORANDUM NO. 607 LONG-TERM BIOSOLIDS MANAGEMENT PLAN FINAL DRAFT August YGNACIO VALLEY ROAD SUITE 300 WALNUT CREEK, CALIFORNIA (925) FAX (925)

2 CITY AND COUNTY OF SAN FRANCISCO 2030 SEWER SYSTEM MASTER PLAN TASK 600 TECHNICAL MEMORANDUM NO. 607 LONG-TERM BIOSOLIDS MANAGEMENT PLAN TABLE OF CONTENTS Page No. 1.0 BACKGROUND WASTEWATER SYSTEM OVERVIEW Southeast Water Pollution Control Plant Oceanside Water Pollution Control Plant North Point Water Pollution Control Plant Solids Processing Facilities Recent Biosolids Quantities Current Biosolids Management Practices Recent Solids Characteristics Current Solids Management Costs Biosolids Management Program Goals Previous Biosolids Management Planning for San Francisco References SOLIDS PROJECTIONS Future Raw Wastewater Solids Quantities and Characteristics Future Digested Solids Quantities Product Quantity Projections for Alternative Treatment Options Future Biogas Production Rates Fats, Oils, and Grease Quantities Organic Waste Material References REGULATORY AND PUBLIC FRAMEWORK Regulatory Considerations Policy Considerations Recent Contracts Annual 40 CFR 503 Report Public Input and Involvement Industry Trends BIOSOLIDS MARKETS AND DISPOSITION Biosolids Products Agricultural Land Application Market Class B Biosolids Agricultural Land Application Market Improved Biosolids Products DRAFT - September 14, 2009 i

3 5.4 Landfill Markets Horticulture and Silviculture - Product Distribution and Marketing Land and Mine Reclamation Market Construction Products Market Fuel and Energy Markets Dedicated Disposal Overall Market and Product Assessment References STATUS ON ORGANIC WASTE PROCESSING Organic Waste Situation at San Francisco Digestion of Organic Waste Economic and Non-economic Assessment for Organic Waste Processing/Digestion Summary References PROCESSING TECHNOLOGIES Thickening Technologies Digestion Stabilization Technologies Non-Digestion Stabilization Technologies Dewatering and Drying Technologies Other Solids Processing Technologies Biogas Processing and Use Technologies Screening Criteria Screening to Identify Viable Technologies Recommendations on Viable Technologies Solids Processing Approach References SOLIDS PROCESSING SITES Dispersed Versus Centralized Solids Processing Land Area Needs for Centralized Processing Bayside Solids Site Alternatives Oceanside Solids Siting Evaluation of Bayside Site Options References EVALUATION OF BIOSOLIDS MANAGEMENT ALTERNATIVES Alternative B-1 - Retain/Upgrade Existing Class B Program Alternative B-2 - Upgrade To Class A Program and Expand Uses Alternative B-3 - Create Marketable Products for ~Half of the Production Alternative B-4 - Create Marketable Products for Entire Production Alternative B-5 - Utilize Thermal Processing Economic Comparisons Evaluation of the Alternatives Recommendations References DRAFT - September 14, 2009 ii

4 10.0 IMPLEMENTATION PROGRAM Program Description Site Selection for BBC Products and Markets Technology Follow-Up LIST OF TABLES Table 1 Recent San Francisco Biosolids Production Table 2 San Francisco Biosolids Management Summary, Table 3 San Francisco Biosolids Beneficial Use, Table 4 Average 2005 SEWPCP Biosolids Metal Concentrations Table 5 Class B Pathogen Density Compliance at SEWPCP, Table 6 Vector Attraction Reduction Compliance at SEWPCP, Table 7 SEWPCP Nutrient Monitoring Results, Table 8 Average 2005 OSWPCP Biosolids Metal Concentrations Table 9 Class B Pathogen Density Compliance at OSWPCP, Table 10 Vector Attraction Reduction Compliance at OSWPCP, Table 11 OSWPCP Nutrient Monitoring Results, Table 12 Estimated Current Annual Solids Management Costs Table 13 Current Hauling and Tipping Fees Table 14 Bayside Raw Wastewater Solids Projections, Year Table 15 Oceanside Raw Wastewater Solids Projections, Year Table 16 Bayside Digested Solids Projections, Year Table 17 Oceanside Digested Solids Projections, Year Table 18 Comparison of Current and Future Biosolids Production Rates Table 19 Average Annual Product Quantities, Year Table 20 Biogas Production Estimates, Year Table 21 San Francisco FOG Estimates Table 22 Estimated Organic Waste Quantities in San Francisco Table 23 Local Regulation of Biosolids Land Application in Northern California Table 24 Current San Francisco Biosolids Management Practices Table 25 Available Landfill Options Table 26 Potential Demand for Biosolids Product Within San Francisco Table 27 Market Assessment Table 28 Product and Market Compatibility Table 29 Technology Screening Table 30 Technology Recommendations Summary Table 31 Sites Considered for BBC Table 32 BBC Siting Criteria Table 33 BBC Site Screening Evaluation Table 34 Suitable Bayside Sites - Advantages and Disadvantages Table 35 Outline of Five Categorical Biosolids Alternatives Table 36 Costs for Biosolids Management Alternatives Table 37 Evaluation Criteria for the Biosolids Management Alternatives Table 38 Ratings of Biosolids Management Alternatives DRAFT - September 14, 2009 iii

5 LIST OF FIGURES Figure 1 The San Francisco Wastewater System Figure 2 SEWPCP Process Flow Diagram Figure 3 OSWPCP Process Flow Diagram Figure 4 Temperature Phased Anaerobic Digestion Figure 5 Acid/Gas Phased Digestion Options Figure 6 Class A Thermophilic Digestion Options Figure 7 Belt Filter Press Figure 8 Centrifuge Figure 9 Screw Press Figure 10 Direct Thermal Drum Dryer Producing Graded Pellet Product Figure 11 Indirect Thermal Dryer Producing Ungraded Product Figure 12 Sites Considered for Bayside Biosolids Center (1) Figure 13 Sites Considered for Bayside Biosolids Center (2) Figure 14 Price Range for Biosolids Cake Disposition in California Figure 15 Biosolids Management Alternatives Figure 16 BBC/OBC Simplified Solids Process Schematic Figure 17 OSWPCP Simplified Solids Process Schematic Figure 18 Potential Sites for Bayside Biosolids Center DRAFT - September 14, 2009 iv

6 Technical Memorandum No. 607 LONG-TERM BIOSOLIDS MANAGEMENT PLAN Please note this memo was created in February of 2007 and was not updated. It was determined by the SFPUC and the consultants that it was important to capture the information at the time of development so the reviewers could see the progression of information and decisions made at the time of the memo development. Please also note that the word 'alternative' was used instead of 'configurations' for the memos reflecting the existing wording at the time it was written. In the Summary Report, the term was updated to 'configuration' so as not to confuse the CEQA review process. The configurations mentioned herein may have changed or been eliminated and are not considered full CEQA alternatives. 1.0 BACKGROUND Wastewater treatment plants serve to remove the waste from wastewater, so that clean plant effluent can be safely discharged to waterways or be reused for beneficial purposes. The wastewater treatment process concentrates the waste materials present in sewage, creating wastewater solids or sewage sludge as a residual material. The wastewater solids are processed to create biosolids. Biosolids are wastewater solids that comply with standards developed by the United States Environmental Protection Agency (USEPA) for beneficial use. This technical memorandum addresses wastewater solids processing needs to create biosolids products, evaluates alternative biosolids management methods and approaches for San Francisco, and includes recommendations for improvements and future needs relating to San Francisco s wastewater solids processing and biosolids management. 2.0 WASTEWATER SYSTEM OVERVIEW The San Francisco sewer system is primarily a combined sewer system whereby storm water and wastewater are conveyed in the same pipes. Many cities, including New York, Philadelphia, Boston, Seattle, and Sacramento, have combined sewers. Other cities have one system of pipes for sewage and another system of pipes for storm water. San Francisco developed a relatively unique system of transport/storage boxes and related infrastructure for the City s combined wastewater system in the 1970s and 1980s. Transport/storage boxes collect the combined wastewater and stormwater and transport it to pumping stations, which deliver it to three treatment plants shown in Figure 1. Combined sewer discharges (CSDs) occur when the flows exceed the treatment and storage capacity of the system. The three treatment plants are described below. DRAFT - September 14,

7 Figure 1 The San Francisco Wastewater System 2.1 Southeast Water Pollution Control Plant The Southeast Water Pollution Control Plant (SEWPCP) has a dry weather average flow capacity of 85 million gallons per day (mgd). During wet weather conditions plant can provide up to 150 mgd of secondary treatment, and an additional 100 mgd of primary treatment. Flows up to 110 mgd are discharged through an outfall to San Francisco Bay. Flows greater than 110 mgd are discharged to Islais Creek. Only secondary effluent is discharged to Islais Creek; all primary effluent discharges are routed to the San Francisco Bay outfall. The liquid treatment processes include screening, grit removal, primary sedimentation, pure oxygen activated sludge, secondary clarification, and sodium hypochlorite disinfection, and sodium bisulfite dechlorination, as shown in Figure Oceanside Water Pollution Control Plant The Oceanside Water Pollution Control Plant (OSWPCP) has a dry weather average flow capacity of 21 mgd and peak wet weather flow capacity of 65 mgd. Treated water is discharged through an ocean outfall. The liquid treatment processes include screening, grit removal, primary sedimentation, pure oxygen activated sludge, secondary clarification, and sodium hypochlorite disinfection, as shown in Figure 3. DRAFT - September 14,

8 Figure 2 SEWPCP Process Flow Diagram Figure 3 OSWPCP Process Flow Diagram DRAFT - September 14,

9 2.3 North Point Water Pollution Control Plant The North Point Water Pollution Control Plant (NPWPCP) provides wet weather treatment only. The peak wet weather capacity is 150 mgd. The effluent is discharged to the San Francisco Bay through four outfalls. The NPWPCP provides primary level treatment only for wet weather flows. 2.4 Solids Processing Facilities The existing processes used to turn wastewater solids into biosolids are described below Southeast Water Pollution Control Plant The existing SEWPCP solids processing facilities are shown in Figure 2. Primary sludge is thickened in the primary clarifiers. Waste activated sludge (WAS) is thickened using gravity belt thickeners. The two thickened sludges are mixed in a solids blending tank prior to being fed to the anaerobic digestion system. The anaerobic digestion system consists of ten tanks. Seven tanks are active digesters, and two tanks are storage digesters. One digestion tank is currently out of service due to a collapsed roof. The sludge within the tanks is heated to mesophilic temperatures (95 to 100 degrees Fahrenheit) and continuously mixed. The typical sludge residence time within the anaerobic digestion system exceeds 15 days. Anaerobic bacteria in the tanks degrade volatile solids in the sludge. The wastewater solids are stabilized in the anaerobic digestion process and pathogen densities are significantly reduced. Water is removed from the biosolids that exit the digesters using centrifuges. The dewatered biosolids have a gelatinous consistency and are called biosolids cake. The cake is loaded into covered trucks for transport to the end-use or disposal sites. The anaerobic bacteria in the digestion system create biogas as a byproduct of the digestion process. The biogas is a mixture of methane and carbon dioxide. The biogas is collected and used as fuel for boilers, and as fuel for a cogeneration system that uses an internal combustion engine and generator for electrical power production with waste heat from the engine providing heat for the digestion process. In addition, the SFPUC is implementing a 600 kw molten carbonate fuel cell project at the SEWPCP to convert biogas into electricity Oceanside Water Pollution Control Plant The OSWPCP solids processing facilities are shown in Figure 3. Primary and waste activated sludges are mixed and co-thickened using gravity belt thickeners prior to being fed to the anaerobic digestion system. The anaerobic digestion system consists of four eggshaped digesters. Biogas from the anaerobic digestion process fuels boilers and a cogeneration system that supplies about 30 percent of the electricity needs of the DRAFT - September 14,

10 wastewater treatment plant. Digested biosolids are dewatered using belt filter presses prior to being loaded into covered trucks for transport to the end-use or disposal sites North Point Water Pollution Control Plant Solids from the NPWPCP are returned to the combined sewer system during and following wet weather events for transport to the SEWPCP. 2.5 Recent Biosolids Quantities Table 1 presents the quantity of biosolids produced by San Francisco during the period 2003 through Table 1 Recent San Francisco Biosolids Production 2030 Sewer System Master Plan City and County of San Francisco SEWPCP OSWPCP Total City Year Wet Tons Dry Tons Wet Tons Dry Tons Wet Tons Dry Tons ,558 17,189 22,261 3,613 88,819 20, ,138 14,535 21,401 3,293 81,539 17, ,269 13,738 24,845 3,814 83,114 17,552 Annual average 61,655 15,154 22,836 3,573 84,491 18,727 Daily Average Current Biosolids Management Practices San Francisco has beneficially reused all of the biosolids produced in recent years. The biosolids are transported to Alameda, Contra Costa, Solano, and Sonoma Counties for agricultural land application, use as landfill alternative daily cover (ADC), or other landfill beneficial use. Agricultural land application occurs during the months of April through October each year. Landfill use occurs throughout the year. Table 2 provides a summary of biosolids management practices in Table 3 summarizes the 2005 data by beneficial use. 2.7 Recent Solids Characteristics The solids characteristics most pertinent to biosolids recycling include solids concentration, metals concentrations, pathogen densities, and vector attraction reduction. Recent solids characteristics from the San Francisco Water Pollution Control Plants are described below. DRAFT - September 14,

11 Table 2 San Francisco Biosolids Management Summary, Sewer System Master Plan City and County of San Francisco Tons Percent County Site Beneficial Use (wet weight) of Total Alameda Vasco Road Landfill ADC Contra Costa Solano Sonoma Western Contra Costa County Landfill ADC 9, Hay Road Landfill ADC + other 43, Potrero Hills Landfill ADC 4, Synagro Land 19, Application Synagro Land Application 6, Totals 83, Table 3 San Francisco Biosolids Beneficial Use, Sewer System Master Plan City and County of San Francisco Beneficial Use Tons (wet weight basis) Percent of Total Landfill ADC and other uses 57, Land Application 25, Totals 83, Southeast Water Pollution Control Plant The total solids concentrations for biosolids from the SEWPCP averaged 23.6 percent during Average metal concentrations for 2005 are shown in Table 4, along with the 40 CFR Table 3 pollutant concentrations. As shown in Table 4, the biosolids produced at the SEWPCP have low metals concentrations, well below Table 3 limits, which are the most stringent established by the USEPA. The SEWPCP achieved compliance with 40 CFR 503 Class B pathogen density requirements during 2005 by maintaining anaerobic digestion detention times greater than 15 days and digestion temperatures above 95 F. Table 5 summarizes the 2005 results. DRAFT - September 14,

12 Table 4 Average 2005 SEWPCP Biosolids Metal Concentrations 2030 Sewer System Master Plan City and County of San Francisco Constituent SEWPCP 2005 Average (mg/kg (1) ) Pollutant Concentration Limit (2) (mg/kg (1) ) Compliance? Arsenic < Yes Cadmium < Yes Copper Yes Lead Yes Mercury Yes Molybdenum (3) Yes Nickel Yes Selenium < Yes Zinc Yes Source: SFPUC, February 20, (1) Milligrams per kilogram, dry weight basis. (2) From 40 CFR , Table 3. (3) Limit is under reconsideration by USEPA. Biosolids may not exceed 75 mg/kg molybdenum until a new pollutant concentration limit is established. Table 5 Class B Pathogen Density Compliance at SEWPCP, Sewer System Master Plan City and County of San Francisco Month Digestion Detention Time (days) Average Digester Temperature ( F) Class B Compliance? (1) Jan Yes Feb Yes Mar Yes Apr Yes May Yes Jun Yes Jul Yes Aug Yes Sep Yes Oct Yes Nov Yes Dec Yes Source: SFPUC, February 20, (1) 15 days detention time at or above 95 F required per 40 CFR (b)(3). DRAFT - September 14,

13 The SEWPCP achieved compliance with 40 CFR 503 vector attraction reduction requirements during 2005 by reducing volatile solids concentrations by 38 percent or greater in the anaerobic digestion process. Table 6 summarizes the 2005 results. Table 6 Vector Attraction Reduction Compliance at SEWPCP, Sewer System Master Plan City and County of San Francisco Average Volatile Solids Month Reduction (1) Compliance? (2) Jan 40.1 Yes Feb 56.3 Yes Mar 45.9 Yes Apr 51.5 Yes May 52.3 Yes Jun 43.4 Yes Jul 45.2 Yes Aug 48.5 Yes Sep 47.6 Yes Oct (3) Yes Nov 51.2 Yes Dec 51.5 Yes Source: SFPUC, February 20, (1) Van Kleeck Method used to calculate volatile solids reduction, except where noted. (2) 38 percent or greater reduction required per 40 CFR (b)(1). (3) Approximate mass balance method used to calculate volatile solids reduction. Nutrient monitoring is required for the land application of biosolids, so that the biosolids loading rate to the soil can meet the fertilizer needs of the crop that is grown. Table 7 summarizes the 2005 nutrient monitoring results for the SEWPCP. Table 7 SEWPCP Nutrient Monitoring Results, Sewer System Master Plan City and County of San Francisco Average Concentration Parameter (% (1) ) Total Kjeldahl Nitrogen (2) 5.65 Ammonia 1.54 Total Phosphorus 1.56 Source: SFPUC, February 20, (1) Dry weight basis. (2) Measurement of organic nitrogen plus ammonia nitrogen. DRAFT - September 14,

14 2.7.2 Oceanside Water Pollution Control Plant The total solids concentrations for biosolids from the OSWPCP averaged 15.4 percent during Average metal concentrations for 2005 are shown in Table 8, along with the 40 CFR Table 3 pollutant concentrations. As shown in Table 8, the biosolids produced at the OSWPCP have low metals concentrations, well below the Table 3 limits, which are the most stringent established by the USEPA. Table 8 Average 2005 OSWPCP Biosolids Metal Concentrations 2030 Sewer System Master Plan City and County of San Francisco Constituent SEWPCP 2005 Average (mg/kg (1) ) Pollutant Concentration Limit (2) (mg/kg (1) ) Compliance? Arsenic < Yes Cadmium Yes Copper Yes Lead Yes Mercury Yes Molybdenum 13 - (3) Yes Nickel Yes Selenium Yes Zinc Yes Source: SFPUC, February 20, (1) Milligrams per kilogram, dry weight basis. (2) From 40 CFR , Table 3. (3) Limit is under reconsideration by USEPA. Biosolids may not exceed 75 mg/kg molybdenum until a new pollutant concentration limit is established The OSWPCP achieved compliance with 40 CFR 503 Class B pathogen density requirements during 2005 by maintaining anaerobic digestion detention times greater than 15 days and digestion temperatures above 95 F. Table 9 summarizes the 2005 results. The OSWPCP achieved compliance with 40 CFR 503 vector attraction reduction requirements during 2005 by reducing volatile solids concentrations by 38 percent or greater in the anaerobic digestion process. Table 10 summarizes the 2005 results. Table 11 summarizes the 2005 nutrient monitoring results for the OSWPCP. DRAFT - September 14,

15 Table 9 Class B Pathogen Density Compliance at OSWPCP, Sewer System Master Plan City and County of San Francisco Average Digester Temperature ( F) Class B Compliance? (1) Digestion Detention Month Time (days) Jan Yes Feb Yes Mar Yes Apr Yes May Yes Jun Yes Jul Yes Aug Yes Sep Yes Oct Yes Nov Yes Dec Yes Source: SFPUC, February 20, (1) 15 days detention time at or above 95 F required per 40 CFR (b)(3). Table 10 Vector Attraction Reduction Compliance at OSWPCP, Sewer System Master Plan City and County of San Francisco Month Average Volatile Solids Reduction (1) Compliance? (2) Jan 58.5 Yes Feb 62.3 Yes Mar 66.9 Yes Apr 66.2 Yes May 70.2 Yes Jun 66.1 Yes Jul 68.8 Yes Aug 62.0 Yes Sep 65.2 Yes Oct 70.8 Yes Nov 65.1 Yes Dec 57.3 Yes Source: SFPUC, February 20, (1) Van Kleeck Method used to calculate volatile solids reduction. (2) 38 percent or greater reduction required per 40 CFR (b)(1). DRAFT - September 14,

16 Table 11 OSWPCP Nutrient Monitoring Results, Sewer System Master Plan City and County of San Francisco Average Concentration Parameter (% (1) ) Total Kjeldahl Nitrogen (2) 7.17 Ammonia 2.19 Total Phosphorus 1.50 Source: SFPUC, February 20, (1) Dry weight basis. (2) Measurement of organic nitrogen plus ammonia nitrogen. 2.8 Current Solids Management Costs Estimated current annual solids management costs (excluding amortized capital) for the SEWPCP and OSWPCP are summarized in Table 12. The costs reflect the thickening, digestion, and dewatering processes at the wastewater treatment plant sites, as well as offsite hauling and final disposition of the biosolids by contractors. The current offsite hauling and tipping fees are summarized in Table 13 (SFPUC, 2005). Table 12 Estimated Current Annual Solids Management Costs 2030 Sewer System Master Plan City and County of San Francisco Description SEWPCP OSWPCP Labor $3,814,000 $1,653,000 Energy $1,174,000 $402,000 Chemicals $983,000 $265,000 Materials and Services $452,000 $128,000 Contract Hauling and End Use $2,050,000 $888,000 Total Annual Cost $8,473,000 $3,336,000 Table 13 Current Hauling and Tipping Fees 2030 Sewer System Master Plan City and County of San Francisco Hauling ($/ wet ton) Tipping Total ($/wet ton) County Reuse Site SEWPCP OSWPCP ($/ton) SEWPCP OSWPCP Alameda Vasco Road Landfill $16.01 $17.34 $15.95 $31.96 $33.29 Contra Western Contra Costa $14.34 $15.93 $19.00 $33.34 $34.93 Costa County Landfill Hay Road Landfill $24.50 $25.72 $10.75 $35.25 $36.47 Solano Potrero Hills Landfill $22.46 $24.97 $15.95 $38.41 $40.92 Synagro Land $23.78 $25.57 $12.95 $36.73 $38.52 Application Sonoma Synagro Land $22.70 $18.74 $22.50 $45.20 $41.24 Application DRAFT - September 14,

17 2.9 Biosolids Management Program Goals The SFPUC has established the following goals for its biosolids management program: Create a sustainable, flexible and diversified program of biosolids management. Maximize beneficial and cost-effective reuse of the City s biosolids and any system byproducts (i.e., digester gas or biogas). Maximize energy efficiency and recovery in the processing of biosolids. Provide a high degree of protection for health and safety. Evaluate Class A treatment processes and techniques to determine feasibility and cost-effectiveness for City facilities. Evaluate the complete range of environmental impacts of biosolids management and choose options that minimize negative impacts. Manage biosolids operations (treatment processing, transportation and reuse) in a manner consistent with being a good neighbor to the local community. Complete & certify Biosolids Environmental Management System. Investigate feasible markets for biosolids reuse within the City and County of San Francisco. Consider opportunities for co-management with other waste streams (grease, food waste, etc.). Develop a ten-year maintenance plan for the existing solids handling facility to ensure reliability and compliance Previous Biosolids Management Planning for San Francisco Several biosolids management and sludge processing studies have been conducted by San Francisco over the past 25 years. The current biosolids management system of the City has evolved from a variety of activities and studies over many years. The Long-Term Biosolids Management Plan, prepared by Carollo Engineers in 1997 (Carollo Engineers, 1997) is the most recent long-term, overall study for the City. The 1997 Long-Term Biosolids Management Plan recommended a diversified biosolids management strategy that included Class B biosolids recycling as ADC at landfills and agricultural land application. DRAFT - September 14,

18 2.11 References Carollo Engineers. City and County of San Francisco, Long-Term Biosolids Management Plan. December SFPUC. City and County of San Francisco Cost and Solids Information for SFPUC. City and County of San Francisco, Annual Report for Sludge Generators. February 20, SOLIDS PROJECTIONS Future wastewater solids quantities and characteristics are discussed in this section, so that alternatives can be sized and evaluated for appropriate future needs. Also estimated here are quantities of trucked grease and related wastes which are likely to be co-processed along with the wastewater solids. A third type of material is the separately-collectable organic waste material from City residential and commercial sources. This organic waste material is discussed here because there is also potential for this material to be processed with wastewater solids. 3.1 Future Raw Wastewater Solids Quantities and Characteristics Future raw wastewater solids quantities were developed by the SFPUC based on population projections, water supply projections, pollutant load projections, and historical treatment plant performance data (SFPUC, May 25, 2006). The raw solids projections are shown in Tables 14 and 15 for the Bayside and Oceanside, respectively. The projections assume continued use of primary sedimentation tanks and high-purity oxygen activated sludge system biological treatment at the City s wastewater plants. Alternate treatment methods for wastewater processing could occur in the future, which would alter these projections. To provide a safety factor for this eventuality, a 10 percent contingency is added into the year 2030 projections, as indicated in the tables in this section. Table 14 Bayside Raw Wastewater Solids Projections, Year Sewer System Master Plan City and County of San Francisco Description Peaking Factor Total Solids (1) (klbs/d) Volatile Solids (2) (klbs/d) Fixed Solids (3) (klbs/d) Average annual Peak month Peak 2-week Peak day Notes: (1) 10 percent contingency factor was added as a safety factor (2) Volatile solids assumed to be 78 percent of total solids, based on historical data. (3) Total solids less volatile solids. DRAFT - September 14,

19 Table 15 Oceanside Raw Wastewater Solids Projections, Year Sewer System Master Plan City and County of San Francisco Description Peaking Factor Total Solids (1) (klbs/d) Volatile Solids (2) (klbs/d) Fixed Solids (3) (klbs/d) Average annual Peak month Peak 2-week Peak day Notes: (1) 10 percent contingency factor was added as a safety factor (2) Volatile solids assumed to be 78 percent of total solids, based on historical data. (3) Total solids less volatile solids. The characteristics of the future raw sludge/solids are assumed at this time to be similar to current characteristics. It is possible that, in the future, alternate wastewater treatment methods such as using a membrane bioreactor (MBR) might be used which would change the characteristics of the biological solids to some extent. Also, effluent filtration could be added which would increase quantities slightly. If chemical precipitation was added, this would create more inorganic sludge quantities but would not cause much change in the total organic wastewater solids. The potential changes in wastewater processing and the resulting impact on sludge characteristics, are not so severe as to cause a problem in the evaluation of sludge/biosolids alternatives or in the development or recommendations of this Biosolids Management Plan. It is possible that eventual design and operating criteria for solids processing facilities could be impacted by such changes in sludge characteristics. 3.2 Future Digested Solids Quantities Assuming that anaerobic digestion will be used to stabilize the raw wastewater solids in the future, quantities are developed here. (A section evaluating sludge stabilization options is included in Section 5 of this Report.) Stabilization reduces the odor of the solids and makes them less attractive to vectors such as flies and rodents. The digestion process greatly reduces the volatile content of the solids, thereby reducing the total mass of solids. Future digested solids quantities are shown in Tables 16 and 17 for the Bayside and Oceanside, respectively. The digestion and solids processing system provides equalization of sludge production to some extent, and, therefore, peak day production is not presented for digested quantities. DRAFT - September 14,

20 Table 16 Bayside Digested Solids Projections, Year Sewer System Master Plan City and County of San Francisco Description Volatile Solids (1) (klbs/d) Fixed Solids (klbs/d) Total Solids (2) (klbs/d) Average annual Peak month Peak 2-week Notes: (1) Assumes 55 percent volatile solids reduction in an anaerobic digestion process. (2) Volatile solids + fixed solids. Table 17 Oceanside Digested Solids Projections, Year Sewer System Master Plan City and County of San Francisco Description Volatile Solids (1) (klbs/d) Fixed Solids (klbs/d) Total Solids (2) (klbs/d) Average annual Peak month Peak 2-week Notes: (1) Assumes 55 percent volatile solids reduction in an anaerobic digestion process. (2) Volatile solids + fixed solids. Table 18 presents comparisons of current and future biosolids production rates. Significant increases in biosolids quantities are expected during the planning period. Table 18 Comparison of Current and Future Biosolids Production Rates 2030 Sewer System Master Plan City and County of San Francisco Source Current Average (dry tons/d) Year 2030 Projection (1) (dry tons/d) Increase (%) Bayside Oceanside Total City Note: (1) Assumes 95 percent capture rate in dewatering process. 3.3 Product Quantity Projections for Alternative Treatment Options Digested solids receive further treatment to reduce water content and change the product characteristics so that it will be suitable for the end use or disposition. Table 19 presents the average annual product quantities from the Bayside and Oceanside for various product moisture contents. The table also shows the total number of truckloads per day required to transport the entire mass of processed solids from the City. DRAFT - September 14,

21 Table 19 Average Annual Product Quantities, Year Sewer System Master Plan City and County of San Francisco Bayside (wet tons/ day) Oceanside (wet tons/ day) Total City (truckloads/ day) (1) Moisture Product Content Dewatered cake 85% Dewatered cake 75% Thermally dried product 10% Combustion ash 0% Note: (1) Assumes 20 wet tons per truckload. 3.4 Future Biogas Production Rates Biogas production estimates from the anaerobic digestion process are summarized in Table 20. This projection assumes 55 percent volatile solids reduction. Somewhat greater gas production is likely to occur from advanced digestion processes and Class A anaerobic digestion processes. Table 20 Biogas Production Estimates, Year Sewer System Master Plan City and County of San Francisco Description Bayside(KSCF/d) (1) Oceanside (KSCF/d) (1) Average annual Peak month Peak 2-week Peak day Note: (1) Assumes 16 cubic feet per pound of volatile solids destroyed. 3.5 Fats, Oils, and Grease Quantities Fats, oils, and grease (FOG) consist of both yellow grease and brown grease. Yellow grease is FOG waste generated by restaurants and collected for recycling by rendering companies, which use it to make tallow and other products. Therefore, yellow grease quantities are not expected to be available for use within the sludge processing system at the City. Brown grease is FOG discharged to sewers or collected from grease traps, and it becomes contaminated with sewage. The City is expecting to institute additional rules in the near future to minimize the amount of brown grease that is discharged to the sewers. In the future, the brown grease is expected to be collected separately in trucks to prevent its potential clogging and other negative impacts in the sewers. Trucks that collect brown grease could be logically directed to bring this material to the anaerobic digestion system for wastewater solids. This has proven cost-effective at other wastewater agencies in DRAFT - September 14,

22 California. The quantity of brown grease is not added onto the raw solids quantities presented in Tables 1 and 2, since this material has largely been accounted for already in those projections. Table 21 presents estimates of the FOG material quantities produced in San Francisco, based on typical FOG production rates (National Renewable Energy Laboratory). Table 21 San Francisco FOG Estimates 2030 Sewer System Master Plan City and County of San Francisco Location Yellow Grease (1) (lbs/d) Brown Grease (2) (lbs/d) Total City 19,000 27,000 Bayside n/a 22,000 Oceanside n/a 5,000 Notes: (1) Assumes 9 lbs per person per year (National Renewable Energy Laboratory, 1998), and population of 750,000 persons. (2) Assumes 13 lbs per person per year (National Renewable Energy Laboratory, 1998). The brown grease, in the future, may be trucked to the City s wastewater sludge digesters for processing. 3.6 Organic Waste Material Organic waste materials represent a major potential digestion feedstock to greatly increase biogas production and produce renewable energy. Norcal collects organic wastes within the City and County of San Francisco as part of the solid waste collection system. Norcal estimates that about 400 wet tons per day of organic waste material could be collected in the future. Table 22 summarizes the organic waste materials potentially available. Comparison with Table 1 shows that the quantity of organic waste volatile solids is similar to the year 2030 city-wide volatile solids projections for wastewater solids; therefore, these organic wastes represent a major potential source of biogas and energy production. Table 22 Estimated Organic Waste Quantities in San Francisco 2030 Sewer System Master Plan City and County of San Francisco Description Quantity 1 % Solids % VS/TS Separated Source Organics wet tons/day ~30 85 Mixed Organics wet tons/day ~50 80 Notes: (1) 6 day/week basis (2) SSO = mostly commercial food waste (3) MO = food and yard waste, plus miscellaneous other wastes including paper These organic waste materials would need pre-processing before they could be fed to anaerobic digestion systems, and these costs need to be determined to evaluate the overall DRAFT - September 14,

23 economics of digesting this material. Discussions between the SFPUC staff and Norcal are ongoing to further discuss and evaluate options of processing and handling these organic waste materials in San Francisco, and to discuss potential for co-locating such digestion and biogas utilization facilities along with wastewater solids processing facilities. Chapter 5 of this technical memorandum provides further details on conceptual planning on potential organic waste processing and digestion at San Francisco. 3.7 References National Renewable Energy Laboratory. Urban Waste Grease Resource Assessment. November SFPUC. Wastewater Flow and Load Projections SFPUC Wastewater Master Plan. May 25, Norcal, Estimates of organic waste production within the City and County of San Francisco. 4.0 REGULATORY AND PUBLIC FRAMEWORK This section addresses regulatory, policy, and public perception issues associated with biosolids management. 4.1 Regulatory Considerations There are a number of regulatory considerations associated with biosolids management. Detailed descriptions of the regulatory requirements are provided in a separate Project Memorandum (REFERENCE). Brief discussion is presented below to provide a regulatory context to the biosolids planning efforts described in this report. Biosolids use and disposal is regulated at the Federal, State, and local levels, as described below United States Environmental Protection Agency The USEPA regulates biosolids use under Section 503 of Chapter 40 of the Code of Federal Regulations (40 CFR 503). The 40 CFR 503 regulations address land application, surface disposal, and incineration of biosolids. The 40 CFR 503 regulations are selfimplementing and include monitoring, certification, and reporting requirements. Although a permit application must be submitted, USEPA Region 9 does not typically issue permits. Agencies are required to send an annual report to USEPA Region 9 summarizing and certifying their compliance with the rule. The 40 CFR 503 regulations establish metal concentration limitations, pathogen density reduction requirements, vector attraction reduction requirements, and site management practices for land application of biosolids. Land application refers to the beneficial use of biosolids for their nutrient and organic matter content. Biosolids land application rates DRAFT - September 14,

24 cannot exceed the fertilizer (nitrogen) needs of the vegetation that will be grown. The metal concentration limitations are based on a risk assessment prepared by USEPA. The pathogen density and vector attraction reduction requirements are based on past successful experience. Biosolids are classified as either Class B or Class A with respect to pathogen density. Class B biosolids have significantly reduced pathogen densities (as compared to raw sludge), but require application site management to ensure protection of public health and the environment. Class A biosolids have further reduced pathogen densities and do not require application site management to ensure protection of public health and the environment. Biosolids that meet the pollutant concentration, Class A pathogen, and vector attraction reduction requirements in 40 CFR 503 are typically called Exceptional Quality Biosolids, and can be sold or given away in bulk or bags without additional regulation by USEPA. The 40 CFR 503 regulations also establish requirements for surface disposal of biosolids. Surface disposal includes monofills, surface impoundments, lagoons used for final disposal as opposed to treatment, waste piles, dedicated disposal sites, and dedicated beneficial use sites. In general, surface disposal of biosolids refers to application at high rates in excess of crop nutrient requirements, if a crop is grown as a management practice. The regulation establishes metal concentration limitations, pathogen density reduction requirements, vector attraction reduction requirements, and site management practices. Incineration refers to combustion of sewage sludge or biosolids at high temperatures in an enclosed device. The 40 CFR 503 regulations establish metals concentration limits, total hydrocarbon emission limits, and management practices. The use or disposal of nonhazardous incinerator ash is not covered by 40 CFR 503; other Federal regulations (40 CFR 257 and 40 CFR 258) cover these practices United States Department of Agriculture The United States Department of Agriculture (USDA) has established national organic food standards (7 CFR 205) that govern the production and marketing of fresh and processed food that is labeled organic. Although biosolids are essentially all organic matter, biosolids or products containing biosolids may not be used in organic food production State Water Resources Control Board State regulation of biosolids land application is more stringent than Federal regulation. The California State Water Resources Control Board (SWRCB) has adopted General Waste Discharge Requirements (WDRs) for the Discharge of Biosolids to Land for use as a Soil Amendment in Agricultural, Silvicultural, Horticultural, and Land Reclamation Activities (Biosolids General Order). The Biosolids General Order can be used by Regional Water Quality Control Boards (RWQCBs) for streamlined permitting of biosolids land application sites. The RWQCBs may also elect to create site-specific WDRs for biosolids land application sites. The Biosolids General Order applies to Class B land application sites and DRAFT - September 14,

25 sites where Class A Exceptional Quality biosolids will be applied at rates greater than 10 dry tons per acre per year to a field that is larger than 20 acres in size. The Biosolids General Order goes beyond the requirements of 40 CFR 503 by requiring additional biosolids testing, soil testing, and groundwater sampling Regional Water Quality Control Boards The RWQCBs protect water quality within their jurisdictions by issuing WDRs to regulate the discharge of waste to land, including agricultural land application of biosolids and biosolids co-disposal in landfills. The RWQCBs regulate biosolids use or disposal by issuing WDRs for sites where biosolids are to be applied. The adoption of the Biosolids General Order has led to increased consistency between WDRs, however, the RWQCBs can adopt site-specific WDRs if conditions warrant. The SWRCB and the RWQCBs generally recognize that highly treated Class A, Exceptional Quality biosolids products such as heat dried pellets or properly prepared composts are commercial products and their use is not regulated. Landfills are classified by the nature of their lining systems and the types of waste they can accept. Class III landfills are designed to accept typical municipal solid waste, whereas Class I landfills are designed for hazardous waste. Non-hazardous biosolids can be co-disposed at a Class III landfill if: The biosolids are at least 20% solids for primary sludge only, or at least 15% solids if a mixture of primary and secondary sludges; and, The landfill maintains a minimum 5:1 solids to liquids ratio in the co-disposed waste; and, The landfill has a leachate collection and removal system. Most Class III landfills do not have leachate collection and removal systems, and therefore cannot accept dewatered cake biosolids for co-disposal. The RWQCBs can allow codisposal of biosolids greater than 50 percent solids in Class III landfills without leachate collection and removal systems. Class III landfills may also have site-specific waste acceptance criteria established in their WDRs. Biosolids that exceed the acceptance criteria cannot be co-disposed at that particular landfill California Integrated Waste Management Board The California Integrated Waste Management Board (CIWMB) is responsible for reducing California s use of landfills for waste disposal by increasing waste diversion for recycling. DRAFT - September 14,

26 The CIWMB regulates co-disposal of biosolids in landfills, use of biosolids for Alternative Daily Cover (ADC), and biosolids composting facilities. Some landfills are permitted to use biosolids as Alternative Daily Cover (ADC). At these landfills biosolids are mixed with other materials to serve as a daily cover for the solid waste placed in the landfill, reducing the need to use soil for that purpose. ADC is considered to be a beneficial use, even though the materials are ultimately entombed in a landfill. ADC use is regulated by the California Integrated Waste Management Board, and is limited to 25 percent of the total landfill cover requirements. Bioreactor landfills are designed and operated in ways to rapidly degrade organic waste. The increase in waste degradation and stabilization is accomplished through the addition of liquid and air to enhance microbial processes and increase the production of landfill gas. The bioreactor landfill concept is very different from conventional sanitary landfilling practices and regulations that emphasize minimizing liquid addition and creating dry tomb conditions within landfills. The addition of the moisture, organic matter, and nutrients in biosolids to bioreactor landfills can potentially increase landfill gas production, which in turn can be used to produce electricity. There is currently only one bioreactor landfill project in California, located in Yolo County, but the California Integrated Waste Management Board reports significant interest in utilizing bioreactor landfill technologies at other locations in California. The USEPA has proposed to issue a Federal rule that will allow states to issue site-specific research, development, and demonstration permits to landfills that will allow the addition of liquids to landfills. If the proposed regulations are adopted there may be more bioreactor landfill projects in California, which in turn could increase the number of landfills that accept biosolids Air Quality Management Districts Air Quality Management Districts (AQMDs) are regional agencies tasked with reducing air pollution within their jurisdictions. AQMD regulations can affect biosolids management programs by requiring permits and emission control systems at cogeneration, heat drying, composting, and thermal conversion facilities California Department of Food and Agriculture The California Department of Food and Agriculture (CDFA) regulates nutrient guarantees of fertilizer materials and agricultural minerals. CDFA licensing is required for all producers of fertilizing materials and agricultural minerals. San Francisco biosolids can either be classified as a fertilizer material or an agricultural mineral, depending on the moisture content. Heat dried biosolids will qualify as a fertilizing material under the CDFA regulations. Dewatered cake biosolids are considered to be an agricultural mineral. DRAFT - September 14,

27 4.1.8 Delta Protection Commission The Delta Protection Commission is a state agency tasked with regional planning for the Sacramento/San Joaquin River Delta area, a large, fertile agricultural area located relatively close to the Bay Area. The Delta Protection Commission has adopted regulations that prohibit biosolids land application within the Primary Zone of the Delta, as defined in Section of the California Water Code. The Primary Zone includes portions of Solano, Yolo, Sacramento, San Joaquin, and Contra Costa counties. The five counties have incorporated the requirements of the Delta Protection Commission within their land use plans and zoning codes Local Regulation Northern California counties have enacted local regulation of biosolids land application in various forms, as summarized in Table 23. Some counties require a Conditional Use Permit (CUP) be obtained for a site, which triggers an environmental review in accordance with the California Environmental Quality Act (CEQA) and allows the county to apply site-specific conditions to the proposed operation. Other counties have enacted biosolids ordinances to address local concerns. The ordinances range from complete banning of biosolids land application to allowing Class A or Class B biosolids to be applied. Each county s requirements are unique and must be studied carefully; some ordinances even ban the use of high quality products like compost or fertilizer pellets derived from biosolids. In general, the trend in California has been towards increasingly restrictive local regulation or bans of biosolids land application. Table 23 Local Regulation of Biosolids Land Application in Northern California 2030 Sewer System Master Plan City and County of San Francisco Biosolids Ordinance County CUP Required Ban Class A Only Class B Allowed Alameda Merced Sacramento San Joaquin Solano Sonoma Stanislaus Yolo 4.2 Policy Considerations There are policies established by non-governmental organizations that should be considered for biosolids management planning purposes. DRAFT - September 14,

28 4.2.1 Food Processor Policies A number of food processors will not accept crops that are grown using biosolids. Some company policies go so far as not accepting crops grown on land where biosolids have ever been applied. The food processing companies are concerned that their products could be viewed as tainted by human waste, even though extensive research has shown that the use of biosolids in accordance with the established regulations is safe for human health and the environment California Farm Bureau The California Farm Bureau Federation urges a cautious approach to biosolids use, due to the presence of heavy metals and pathogens and perceived questions over the safety of the material. While heat dried biosolids address the pathogen issue by sterilizing the product, heavy metals will still be present. Local, including County, Farm Bureaus are free to establish their own policies towards biosolids use, and established policies range from support for biosolids recycling to calls for bans on the practice. 4.3 Recent Contracts All San Francisco biosolids are currently hauled by Sunset Scavenger, a subsidiary of Norcal Waste Systems. Table 24 summarizes the current biosolids management practices. As shown in the table, biosolids are used as ADC during the wet season, when land application is not permitted due to wet field conditions. During the dry season land application sites are used as much as possible, and any excess material is sent to landfills for use as ADC. Table 24 Current San Francisco Biosolids Management Practices 2030 Sewer System Master Plan City and County of San Francisco Disposition Perio88d Weekdays Weekends Wet Season Hay Road Landfill ADC + other uses (Solano County) (November April) Dry Season (May October) Synagro Land Application (Solano County) (1) Landfill ADC as needed (Alameda, Contra Costa, and Solano Counties) Note: (1) Strategy is to maximize use of this outlet Synagro Land Application (Sonoma County) During the summer of 2006 San Francisco also began transporting small (pilot) quantities of biosolids to Merced County land application and composting sites. The land application sites are managed by Synagro and Solid Solutions. The composting facility is operated by Synagro. DRAFT - September 14,

29 4.4 Annual 40 CFR 503 Report San Francisco submits an annual report to USEPA each February that documents the biosolids management practices for the previous year and demonstrates compliance with the 40 CFR 503 regulations, including pollutant concentrations, pathogen requirements, and vector attraction reduction requirements. The report is certified by the SFPUC management prior to submittal to USEPA. 4.5 Public Input and Involvement Significant outreach efforts have been made by SFPUC staff in recent years to address issues and concerns expressed in the counties where land application of San Francisco biosolids is taking place, particularly Solano County. The outreach efforts have included contact with members of the Board of Supervisors, discussions with Solano County Environmental Management staff, attendance at public meetings and hearings, providing information to interested members of the public, etc. 4.6 Industry Trends General industry trends towards biosolids management in California s more urban locations include the following: Biosolids quantities are increasing due to population growth and increasingly tighter clean water regulations. Most wastewater agencies remain committed to recycling biosolids rather than disposing of them. There is a general recognition that agricultural land application of Class B dewatered cake is not a long-term biosolids management solution. Local ordinances increasingly limit the practice or ban it outright. Some county bans include Class A biosolids products. The shrinking inventory of permitted land application sites and increasing county restrictions in California have forced wastewater agencies to haul biosolids greater distances, raising transportation costs. Increased competition for available sites has increased application costs. Large wastewater agencies are increasingly turning to high-solids centrifuges for dewatering to reduce the moisture content of their biosolids and reduce hauling costs. Some wastewater agencies are converting to advanced anaerobic digestion processes, such as thermophilic or temperature-phased digestion, to achieve Class A pathogen status, increase volatile solids destruction, and increase biogas production. DRAFT - September 14,

30 Large wastewater agencies in California are often relying on private sector involvement in their biosolids management programs downstream of the dewatering function, including hauling, land application, composting, heat drying, product marketing and distribution, and thermal conversion processes. Wastewater agencies are increasingly considering production of biosolids products with improved aesthetic qualities, such as compost or heat dried pellets, for their recycling programs. Wastewater agencies are pursuing other, sometime unique, outlets for biosolids besides agriculture, including biosolids as renewable fuel in cement kilns, or deep well injection in petroleum oil fields to enhance natural gas production. Wastewater agencies are identifying the need for, and pursuing, regional solutions to biosolids management. 5.0 BIOSOLIDS MARKETS AND DISPOSITION This section considers potential outlets for biosolids products produced by San Francisco; whether for beneficial use or disposal. The discussion begins with consideration of the characteristics of the products that could potentially be produced, followed by discussion of the potential markets for the products. 5.1 Biosolids Products Biosolids products can take a number of different forms, as described below Dewatered Cake Dewatered cake represents the most basic and most common form of biosolids products. Dewatered cake is produced using mechanical dewatering technologies, such as belt filter presses or centrifuges. Dewatered cake products typically consist of 85 to 70 percent moisture (15 to 30 percent solids) and have a gelatinous, bread dough consistency. The color, odor, and pathogen density characteristics of dewatered cake products are a function of the processes used to treat the biosolids prior to dewatering. Dewatered cake products can be produced that have pathogen densities that achieve Class A standards. The typical reaction by the general public to the overall appearance of dewatered cake varies widely from curiosity and fascination to suspicion and revulsion Soil Amendments Dewatered cake biosolids can be mixed with various other materials and processed to create soil amendments (such as compost) or topsoil replacement products. The list of potential feedstock materials that can be used include green waste, wood chips, sawdust, sand, lime, cement kiln dust, wood ash, and others. Soil amendment products are generally DRAFT - September 14,

31 treated to Class A pathogen density standards. The soil amendment class of products usually has a pleasant, earthy odor and pleasing overall appearance to the general public Dried Products and Fertilizers Dewatered cake biosolids can be dried to form fertilizer products. Drying methods include solar drying and thermal drying. This class of products can take a wide variety of forms. Solar dried biosolids typically contain less than 40 percent moisture and can have a dusty, soil-like appearance. Solar dried products may meet Class A pathogen density standards. Solar drying is usually land-intensive and therefore may not be a practical option for an urbanized city such as San Francisco. Thermally dried biosolids products generally contain less than 10 percent moisture. The product appearance is a function of the drying technology used, and can range from uniform spherical pellets with little dust to angular, non-uniform, dusty products. The thermally-dried biosolids products generally have a slightly stronger, more pungent odor than the soil amendment products, but fewer odors than dewatered cake. The overall appearance of thermally-dried products is generally acceptable to the general public. Uniform, spherical products with low dust content are generally preferred over angular, nonuniform, dusty products Other Products Several other types of biosolids products can result from specific biosolids treatment processes, including: Ash: The end product of biosolids combustion for energy recovery or disposal is ash. Lightweight Aggregate: Vitrification processes (e.g., Minergy) create a lightweight glass aggregate product. Fuel: Pyrolysis processes create char or oil fuel products. 5.2 Agricultural Land Application Market Class B Biosolids Agricultural land application refers to the use of biosolids in bulk as a soil amendment or fertilizer to grow agricultural crops. Biosolids are applied at or below the agronomic rates to ensure that the nutrients in the biosolids are used up by the crop, rather than accumulating in the soil and leaching to groundwater. The biosolids add organic matter to the soil, which is a valuable addition to many California soils that are typically very low in organic matter. Class B biosolids that are to be recycled through agricultural land application generally take the form of dewatered cake. San Francisco biosolids are currently Class B dewatered cake. Land application of Class B dewatered cake has been attractive to wastewater agencies because it has been one of the lowest cost ways to manage biosolids. It has also become DRAFT - September 14,

32 increasingly controversial in California and has been banned or restricted by a number of counties, as described in the previous section. In light of the food processor policies towards biosolids, a farmer s use of biosolids could potentially affect the value of prime farmland where vegetables could be grown and marketed to food processors. Many farmers perceive that the potential benefits from using biosolids do not outweigh the risks associated with crop and land values. Therefore, much of the agricultural land application occurs on marginal ground where the growth of highvalue crops is not possible due to soil quality characteristics. Low value crops, such as hay used for animal feed, are typically grown. Land application of Class B biosolids is mostly accomplished by firms that specialize in biosolids management. The firms are under contract with the municipal wastewater agencies. The firms solicit interested farmers and obtain the required permits. The firm spreads the biosolids and completes the monitoring required by the permits. The farmer receives free fertilizer, but is generally not paid a tipping fee. Proactive public outreach is generally required in communities where land application is to occur because dewatered cake biosolids do not look or smell like materials commonly used in agriculture. Neighbors of land application sites may react with fear and concerns about the practice if not given proper information on the safety and benefits. Agricultural land application is a seasonal market in Northern California. Land application activities are generally not possible (and may be prohibited by local regulations) during the wet season, November through April. Farm fields are usually too wet during this time of the year to allow access to the heavy equipment needed to spread biosolids. Dry season application (May through October) must be scheduled around the growth cycle of the crops; biosolids cannot be applied while a crop is being grown. Farm land that is not irrigated (dryland farming) is ideal for biosolids land application because biosolids can be applied throughout much of the dry season; the farmer plants his crop just prior to the wet season and harvests the crop in late spring or early summer. Agricultural land application does not appear to be a sustainable biosolids management practice for wastewater agencies that serve large urban areas, such as the San Francisco Bay area and the greater Los Angeles area. Rural communities in California are becoming increasingly resistant to accepting waste products that are transported from distant urban centers, particularly with dewatered cake products. Agricultural land application of dewatered cake may provide a short-term outlet for San Francisco biosolids, but should not be considered a permanent biosolids management solution. As counties located close to the Bay Area place greater restrictions on agricultural land application of Class B biosolids the SFPUC will be forced to haul dewatered cake longer distances. Counties that ban or restrict Class B biosolids reuse may also limit Class A biosolids products. It is prudent for San Francisco to focus efforts on creating higher-quality biosolids products that are morereadily accepted by the communities that receive and use them, rather than focusing on DRAFT - September 14,

33 maximizing the short-term economic advantages provided by Class B biosolids recycling in agriculture Dedicated Land Application Sites Land application on land owned by wastewater agencies appears to be more sustainable than land application on distant private property. Many small wastewater agencies in California apply their biosolids to property they own that is adjacent to or near the wastewater treatment plant of origin. Often these dedicated land application sites are located within the incorporated limits of the city that operates the site. Dedicated land application sites are generally accepted by the local agricultural community, provided that they remain a good neighbor with respect to odors, dust, and other nuisance conditions. The agricultural community s concern over the fate of heavy metals in biosolids and soil contamination is addressed by permanent public agency ownership of the land. Purchase of farmland outside the wastewater agency s county presents greater risk than development within the city or county of origin. Vallejo Sanitation and Flood Control Agency owns and operates a farm on Tubbs Island, located in adjacent Sonoma County. The award-winning project has a long, successful operating history. However, the City of Los Angeles purchase of an established site in Kern County has not appeared to reduce Kern County resident s resistance to land application of biosolids originating from urban Southern California. The Green Acres farm is located within unincorporated Kern County, and is subject to the provisions of a land application ban that was approved by Kern County voters through the local initiative process in June Therefore, development of a dedicated land application site by San Francisco in another county presents considerable risk and is not considered feasible Exportation Out-of-State Exporting biosolids out of the state of origin is or has been practiced by a number of large wastewater agencies, including the City of New York, District of Colombia Water and Sewage Authority, City of Los Angeles, and Orange County Sanitation District. Transport can be by truck or rail, depending on the haul distance. Biosolids from Southern California have been successfully exported by truck to several Arizona counties for beneficial use. However, Orange County Sanitation District encountered significant local opposition in 2003 when it began exporting biosolids by truck to Nye County, Nevada. The Sacramento Regional County Sanitation District received a proposal from a large, fully-permitted ranch located north of Reno (in Nevada) to accept biosolids transported by rail as a long-term (15 year) solution. The proposal was not accepted, however it demonstrates that out-of-state exportation may be a viable alternative for Northern California wastewater agencies. Pursuit of out-of-state markets for San Francisco Class B biosolids is not recommended at this time, but should be considered in the future if solutions located within California become infeasible or prohibitively expensive. DRAFT - September 14,

34 5.3 Agricultural Land Application Market Improved Biosolids Products Biosolids can be processed to create products with improved characteristics when compared with the existing Class B dewatered cake. The improved products can range from Class A dewatered cake to heat dried pellets, compost, or other soil amendments. The aesthetic qualities of this broad category of improved products vary widely, as will the marketability of the products for agricultural land application Class A Dewatered Cake Upgrading treatment to produce Class A dewatered cake reduces the pathogen density in the biosolids, but does not improve the aesthetic qualities of the product. From a State and Federal regulatory perspective Class A dewatered cake is a product that does not require regulation to protect human health and the environment. However, some counties in California have chosen to regulate (or ban) the use of Class A biosolids in agriculture within their jurisdictions. Similarly, food processing company policies against biosolids apply equally to all products irrespective of pathogen density or product aesthetic qualities. Therefore, the market for Class A dewatered cake is somewhat similar to the market for Class B dewatered cake, although with less regulation. Neighbors of land application sites cannot distinguish between Class A and Class B dewatered cake products, because they look and smell the same. Therefore, production of a Class A dewatered cake product does not relieve responsibility for providing proactive public outreach to communities where application will occur Dried Biosolids - Pellets and Granules The only Northern California heat drying facility in operation is located at the Sacramento Regional Wastewater Treatment Plant. Fertilizer pellets produced at the facility are used in bulk for agricultural purposes to grow animal feed crops within Sacramento County. The pellets are similar in size and shape to conventional granular fertilizer materials, and conventional spreading equipment is used. The use of the product is not regulated at the Federal, state, or local (Sacramento County) levels. The contractor that produces and distributes the product maintains a low profile. Nearby local biosolids bans (e.g., San Joaquin County, Delta Protection Commission) and food processing company policies do not discriminate between types of biosolids products and therefore apply to the heat dried pellet product. Nevertheless, use of the product in bulk agriculture appears to be successful. The market potential for heat dried pellets in agriculture appears to be greater than for Class A dewatered cake due to the improved aesthetic qualities of the product. The product appearance and use resembles fertilizer rather than manure. The pellets can be produced to be similar in size and shape to conventional fertilizer materials. The product contains minimal moisture, so truck traffic is minimized. Conventional spreading equipment is used to apply the product. Neighbors of sites where the product is used are less likely to react DRAFT - September 14,

35 negatively. The target market for the product would be similar to dewatered cake biosolids; marginal soils used to grow animal feed crops. Product revenue is expected to be minimal due to the low cost of competing conventional fertilizing materials, but the use of the product will likely prove to be more-acceptable to the receiving communities than dewatered cake Compost and Other Soil Amendments State mandates to divert waste from landfills has resulted in large quantities of green waste compost flooding the soil amendment markets. Soil amendments are generally only used in agriculture to correct soil problems. The market for compost and other soil amendment products derived from biosolids in agriculture is expected to be limited due to the availability of competing products. A subclass of biosolids soil amendment products has high residual ph values due to the use of alkaline materials (e.g., lime) in the treatment process. In some parts of the country high ph biosolids products are popular with growers due to their need to raise the ph of acidic soils and the low cost of biosolids products compared with other liming agents. However, there is little market in Northern California for high ph biosolids products due to generally calcareous soils and availability of low cost liming products (e.g., sugar beet lime) that are more-readily accepted by the agricultural community than biosolids. 5.4 Landfill Markets Biosolids products may be either disposed or put to beneficial use in landfills, as described below. A dewatered cake product is generally the most economical form of biosolids to dispose or use at landfills Disposal Some landfills allow disposal of biosolids. Each landfill has its own requirements for biosolids disposal with respect to total solids content and specific chemical constituent concentrations. SFPUC staff conducted a survey to determine landfill availability for biosolids disposal within 200 miles of San Francisco (Jones and Schepis, 2006). The results of the survey are summarized in Table 25. DRAFT - September 14,

36 Table 25 Landfill Name Altamont Landfill Available Landfill Options 2030 Sewer System Master Plan City and County of San Francisco Vasco Road Sanitary Landfill Keller Canyon Landfill Salinas Valley Solid Waste Authority Forward Landfill Newby Island Sanitary Landfill Potrero Hills Landfill Hay Road Landfill Yolo County Landfill Source: Jones and Schepis, Alternative Daily Cover County Dispo sal ADC Alameda Alameda Contra Costa Monterey San Joaquin Santa Clara Solano Solano Yolo Permitted Biosolids Capacity Not specified 500 tons/day Not specified 250 tons/day 40,000 tons/yr Not specified Unused Biosolids Capacity 1,000 tons/week 1,000 tons/week 1,000 tons/week Some landfills are permitted to use biosolids as Alternative Daily Cover (ADC), as shown in Table 25. At these landfills biosolids are mixed with other materials to serve as a daily cover for the solid waste placed in the landfill, reducing the need to use soil for that purpose. ADC is considered to be a beneficial use, even though the materials are ultimately entombed within the landfill. ADC use is regulated by the California Integrated Waste Management Board, and is limited to 25 percent of the total landfill cover requirements. Therefore, there is limited ADC capacity available for use by Bay Area wastewater agencies Bioreactor Landfills Bioreactor landfills are operated in ways to rapidly degrade organic waste. The increase in waste degradation and stabilization is accomplished through the addition of liquid to enhance microbial processes and increase the production of landfill gas. Air is also sometimes added to bioreactor landfills to enhance aerobic decomposition of organic wastes. The bioreactor landfill concept is very different from conventional sanitary landfilling practices and regulations that emphasize minimizing liquid addition and creating dry tomb conditions within landfills. The addition of the moisture, organic matter, and nutrients in DRAFT - September 14,

37 biosolids to bioreactor landfills can potentially increase landfill gas production, which in turn can be used to produce electricity. There is currently only one bioreactor landfill project in California, located in Yolo County, but the California Integrated Waste Management Board reports significant interest in utilizing bioreactor landfill technologies at other locations in California. The USEPA has proposed to issue a Federal rule that will allow states to issue site-specific research, development, and demonstration permits to landfills that will allow the addition of liquids to landfills. If the proposed regulations are adopted there may be more bioreactor landfill projects in California, which in turn could increase the number of landfills that accept biosolids. 5.5 Horticulture and Silviculture - Product Distribution and Marketing High quality Class A biosolids fertilizer or soil amendment products can be distributed and marketed to horticulture and silviculture (tree farming) users. This broad category of users comprises most other users besides commercial agriculture Dried Pellet Products The Bay Area Clean Water Agencies (BACWA, 2006) and Sacramento Regional County Sanitation District (SRCSD, 1996) have both conducted extensive studies to investigate potential markets for heat dried pellet biosolids products in Northern California. Both studies identified substantial market potential for high quality heat dried biosolids pellets. The potential markets include: Fertilizer blending operations; Parks and golf courses; and, Bagged retail sales. Both studies identified potential market opportunities that far exceed the annual volume of biosolids produced by San Francisco. Furthermore, heat drying removes most of the moisture from the biosolids, reducing the total mass of product and therefore substantially increasing the radius of economical truck transport. The SRCSD is currently the only producer of heat dried biosolids pellets in Northern California. The entire SRCSD product is used in bulk use in agriculture within Sacramento County; therefore substantial market potential remains for other wastewater agencies Soil Amendment Products The City of Santa Rosa currently operates the only biosolids composting operation in the Bay Area, processing approximately 5 dry tons of biosolids daily in an agitated bed system (City of Santa Rosa, 2003). The product is marketed in bulk to local users. Another notable compost producer historically was the East Bay Municipal Utility District, which operated a DRAFT - September 14,

38 successful composting program for many years until their aerated static pile composting facility was shut down in the 1990s, primarily due to nuisance odor conditions. Biosolids soil amendment products must compete with similar products produced from other feedstock, such as green waste compost. Some existing products are labeled as not produced from biosolids. The potential markets for biosolids soil amendment products include: Soil blending operations; Landscape contractors; Parks and golf courses; and, Bagged retail sales. Solid waste agencies have been required to divert green waste from landfills to achieve mandated diversion goals. The result has been a major increase in the volume of compost produced in California, which in some cases has flooded markets. Further market study is advised prior to substantial investment in a soil amendment production system to manage San Francisco biosolids Markets within San Francisco High quality biosolids products could potentially be used on parks, golf courses, playgrounds, schools and other landscaped areas within San Francisco. The SFPUC inventoried publicly-owned irrigated acreage as part of its recycled water master planning efforts. The inventory results are summarized in Table 26, along with the theoretical and realistic demands for biosolids, based on average annual nitrogen fertilizer demands of 100 lbs. N per acre per year. As shown in Table 26, the theoretical demand is between 2,000 and 2,100 dry tons per year; however, for planning purposes no more than about 50 percent of the theoretical demand for parks, golf courses, and playgrounds can be realistically relied upon. Because the theoretical school use is small and potentially controversial it is excluded from the estimated demand. Therefore, a reasonable expectation is for a demand of approximately 1,000 dry tons per year. Some additional private use could also occur, increasing the total demand to perhaps 1,100 to 1,200 dry tons per year which represents less than five percent of the total mass of biosolids produced by the City. The information in Table 26 assumes that a well-digested, Class A, high-quality, heat dried biosolids fertilizer product is produced, bagged, and actively marketed. The demand would likely be highly seasonal, with most use occurring during the spring and autumn months. There would likely be less demand for a soil amendment product such as compost, due to the difficulty in effectively using compost products on established turf areas. DRAFT - September 14,

39 Table 26 Potential Demand for Biosolids Product Within San Francisco 2030 Sewer System Master Plan City and County of San Francisco Annual Biosolids Demand Irrigated (dry tons/year) Description Area (1) Theoretical (2) Realistic (3) Parks, golf courses, and playgrounds 2038 acres Schools 44 acres 44 0 Total 2083 acres Notes: (1) Source: San Francisco Department of Public Works (March 2006). (2) Assumes 5% N guaranteed analysis. Corresponding product application rate is 1 dry ton per acre per year. (3) Approximately 50 percent of theoretical demand, excluding school use. 5.6 Land and Mine Reclamation Market Biosolids have been used successfully to reclaim land damaged by mining operations, particularly in the mid-atlantic area (Pennsylvania) and in British Columbia (Canada). The biosolids add vital nutrients and organic matter to the damaged soils, enhancing restoration efforts. Class B dewatered cake biosolids are added in a one-time application prior to seeding with a mixture of grasses and legumes. Research has found that a high application rate of biosolids is required to provide sufficient organic matter and nutrients to ensure a sustainable vegetative cover. The high application rate can result in a nitrate spike in underlying groundwater, but this is seen as less of a water quality problem in the states where the land reclamation activities are pursued than the surface water quality problems caused by lands disturbed by the mining activities. There are currently no land or mine reclamation projects using biosolids in California, although significant land areas exist that are disturbed by mining operations. California has an anti-degradation policy towards groundwater that could prove to be an obstacle to the high rates of biosolids application found to be successful in the mid-atlantic area. Significant effort would be required to obtain regulatory approvals in California, due to the lack of project precedent. 5.7 Construction Products Market Potential markets for products created from vitrification processes are specific to the characteristics of the materials. Lightweight glass aggregate products from vitrification can be used in the manufacture of ceramic floor tile, abrasives, concrete additives, asphalt paving mixtures, or composite roofing shingles. Generally these types of processes have been implemented by private companies with long-term contracts to receive dewatered cake biosolids from wastewater agencies. The implementing companies are responsible for DRAFT - September 14,

40 marketing the products they produce. Additional market study is highly recommended prior to substantial investment by San Francisco in a publicly owned and operated facility of this nature. Beneficial uses for non-hazardous ash from biosolids incineration include use as an additive in the production of blocks used for erosion prevention, bricks, and novelty products. Neither of the two agencies using incinerators located in Northern California uses their ash in these ways. The two agencies are the Central Costa County Sanitary District (CCCSD) and the City of Palo Alto. The CCCSD disposes its incinerator ash in a landfill. The Palo Alto incinerator ash contains sufficient phosphorus to make it attractive as a soil amendment additive. Palo Alto therefore recycles its incinerator ash by transporting it to a soil blender, who mixes it with compost to form a soil amendment product. 5.8 Fuel and Energy Markets Energy can be derived from biosolids or from biogas generated from biosolids processing, as described below Markets for Biosolids Potential markets for products created from pyrolysis processes are specific to the characteristics of the materials. Char or oil fuel products from pyrolysis can potentially be used for energy production or in cement kilns. Generally these types of processes have been implemented by private companies with long-term contracts to receive dewatered cake biosolids from wastewater agencies. The implementing companies are responsible for marketing the products they produce. Additional market study is recommended prior to substantial investment by San Francisco in a publicly owned and operated facility of this nature. Dried biosolids pellets have an energy content of approximately 9,500 BTU per pound and can potentially be used as fuel. Potential future markets for dried biosolids pellets include waste-to-energy facilities and cement kilns. The cement industry has recently become interested in biosolids as a renewable fuel source. User requirements are specific to each cement kiln. The combustion ash is integrated into the cement product. Increasing interest in renewable energy sources could lead to increased production of biomass and bioenergy crops, such as hybrid poplar trees, corn for ethanol production, or seed crops to create the vegetable oils used in the production of biodiesel. The use of biosolids to grow these crops would be subject to local agricultural regulations and use restrictions. DRAFT - September 14,

41 5.8.2 Markets for Biogas Anaerobic digestion processes create a biogas product, which is a mixture of methane and carbon dioxide. Biogas can be used as fuel in internal combustion or gas turbines that are connected to generators that produce electricity. Fuel cells are another technology that can be used to create electricity from biogas. Biogas is considered to be a renewable energy source, and increasing awareness of global warming issues and rising fossil fuel prices is leading to increased interest in creating new sources of biogas and enhancing biogas production at existing anaerobic digestion facilities. Programs are being developed to enhance biogas production in wastewater treatment plant anaerobic digestion systems by direct addition of fats, oils, and grease (FOG) and liquefied food wastes. EBMUD has a successful program that incorporates trucked-in FOG and food processing wastes. South Bayside System Authority in Redwood City has been adding trucked-in FOG directly to anaerobic digesters since the 1990s. 5.9 Dedicated Disposal Surface disposal of biosolids is practiced by several wastewater agencies in Northern California, including Sacramento Regional County Sanitation District, Dublin-San Ramon Services District, and Las Gallinas Valley Sanitation District. All of the surface disposal sites are located on treatment plant property. Biosolids are mixed into the soil at these dedicated land disposal sites at high rates. Vegetation is not grown, but soil microbes decompose the biosolids and use or transform much of the nutrients. The dedicated land disposal sites are lined or otherwise highly controlled, depending on the subsurface geological conditions. Surface disposal is not considered to be feasible for San Francisco due to the landintensive nature of the process. Development of a surface disposal site in another county is not viewed to be politically feasible Overall Market and Product Assessment Table 27 presents a simplified assessment of the current markets for biosolids products in Northern California, as well as opinions of the future market potential. The table reflects the increasing wastewater industry awareness of limits to agricultural land application of biosolids and a needed shift to other markets. Table 28 presents the compatibility of various biosolids products with the future markets. A product that is compatible with multiple markets presents lower risk to the wastewater agency than a product that is compatible with only a few. The table shows that heat dried pellets and compost (including compost-like soil amendments) have the greatest compatibility with multiple markets. DRAFT - September 14,

42 Table 27 Market Assessment 2030 Sewer System Master Plan City and County of San Francisco Market Current Market Assessment Opinion of Future Market Potential Agricultural Land Application Increasingly problematic, trending towards increased local restrictions and/or bans. Food processor policies render prime farmland unavailable. Best opportunities are on marginal soils growing animal feed crops. Dewatered Cake Products Trends towards local restrictions and/or bans likely to continue. Class A cake market potential somewhat better than Class B cake due to reduced regulatory burden. Improved Products More-likely to be accepted by receiving communities (compared to dewatered cake products) due to improved product aesthetics. Local restrictions and/or bans may apply to improved products. Dried products can be economically hauled further than cake products. Landfill ADC Good, but limited ADC capacity Increasing demands for limited capacity likely to continue as Landfill Bioreactors Landfill Co-disposal Horticulture and Silviculture Distribution and Marketing Land and Mine Reclamation Construction Products available. Currently no available projects in California. Limited availability. Good backup option. High quality product and active marketing required Currently no projects in California. Currently no projects in California. agricultural land application becomes less feasible. Interest in renewable energy could increase number of bioreactor landfills. Proposed regulatory changes could increase number of bioreactor landfills available. Limited availability. Good back-up option. High quality product and active marketing required. Lack of precedent in California. Regulatory hurdles to implementation. Lack of precedent in California. Markets are product-specific. Active marketing required. DRAFT - September 14,

43 Table 27 Market Assessment 2030 Sewer System Master Plan City and County of San Francisco Market Current Market Assessment Opinion of Future Market Potential Fuel and Energy - Biosolids Currently no projects in California. Projects currently being developed in California. Regulatory mandates for power companies to increase renewable energy portfolios combined with rising prices for fossil fuels could significantly increase interest in biosolids as a fuel source. Cement industry interest in biosolids as renewable fuel source Fuel and Energy - Biogas Dedicated Disposal Color Key: Highest potential Medium potential, some concerns Lowest potential, significant barriers Biogas commonly used to cogenerate electric power and provide heat. Currently no projects available to San Francisco is increasing. Increasingly valuable biogas uses for co-generation systems, fuel cells, and direct energy to dry biosolids. Implementation by San Francisco considered infeasible. DRAFT - September 14,

44 Table 28 Product and Market Compatibility 2030 Sewer System Master Plan City and County of San Francisco Markets Agricultural Landfill Horticulture and Silviculture Products Land Application ADC Bioreactors Co- Disposal Distribution and Marketing Class B dewatered cake Class A dewatered cake Compost Alkaline soil amendment Land and Mine Reclamation Construction Energy Heat dried pellets Construction products Char and/or oil Ash DRAFT - September 14,

45 5.11 References Bay Area Clean Water Agencies. Bay Area Regional Biosolids Management Program Initial Market Assessment. April Jones, Bonnie M., Gerald Schepis. Review of Current Landfill Options for Reuse and Disposal of Bay Area Biosolids Sacramento Regional County Sanitation District. Biosolids Heat Drying/Chemical Treatment Project. May San Francisco Department of Public Works. Recycled Water Master Plan for the City and County of San Francisco. March Santa Rosa, City of. Laguna Subregional Water Reclamation Facility, Biosolids Program Phase 2. July STATUS ON ORGANIC WASTE PROCESSING This section is prepared based on conceptual information available on potential organic waste processing and digestion at San Francisco. There are several factors coalescing to push this concept forward. There are also factors that suggest a combined anaerobic digestion and biogas utilization facility for organic wastes and wastewater solids could be a cost-effective and sensible approach at San Francisco. This section is a status report on the conceptual planning to date. 6.1 Organic Waste Situation at San Francisco Norcal handles, by charter, solid waste collection and solid waste management for the City and County of San Francisco (City). The Department of Public Works and a Charterestablished Rate Board oversee rates for solid waste services, and the City s Department of the Environment undertakes planning services (with Norcal) for solid waste recycling. Norcal already provides a high degree of solid waste recycling activities for the City; however, there are additional City-established diversion goals Norcal is facing: 75 percent landfill diversion by percent landfill diversion by 2020 The major category of waste material that needs to be recycled to reach these extreme diversion goals is the category of organic wastes (typically wet or partially wet materials). This includes a large quantity of food waste material in San Francisco from restaurants, but also from grocery stores and other commercial establishments, along with yard wastes and other mixed organic materials. DRAFT - September 14,

46 Currently, about 300 wet tons/day of these organic wastes are transported from the San Francisco Recycling and Disposal Facility (SFRD) to various composting facilities. The primary food waste composting occurs at a Norcal facility in the Central Valley. This facility s ability to increase capacity is restricted due to air emission limitations (VOC emission limits), yet there is a need to handle perhaps 600 wet tons/day or more. Furthermore, this is a large quantity of waste to transport out of San Francisco. Therefore, alternative processing of organic wastes to reduce volume and extract energy appears advantageous. If the wastes were anaerobically digested at San Francisco to produce biogas/energy, the residual digested (and dewatered) material could be transported to the Valley for composting. In this manner, Norcal indicates the composting operation would be more manageable and cost-effective and the final composting product would be significantly improved. Also, air emissions would be significantly reduced, and a major renewable energy supply created at the digestion/biogas facility. 6.2 Digestion of Organic Waste The approach conceptualized here for organic waste processing has evolved from Europe over the last 10 to 15 years. Process technologies have been developed and patented and are licensed for use in various countries around the world. The technologies are still not extensively used, even world-wide. North America has only a tiny number of examples of such organic waste processing/digestion for biogas production. This situation makes it challenging to develop decisions quickly at San Francisco. The most pertinent North American location using this concept full-scale is at Toronto, Canada, where two facilities have been operating for a few years (See Van Opstal references for Toronto-Dufferin facility). At some facilities world-wide such as at Toronto-Dufferin, only certain organic fractions of municipal solid waste (MSW) are digested. At other facilities, co-digestion is used, whereby organic fractions of MSW are digested along with materials such as cow manure, wastewater sludges, or other organic feedstock. Fortunately, work on organic waste digestion has been underway the past several years by Norcal, in preparing food waste material for digestion at the EBMUD wastewater plant digesters in Oakland (see Yoloye et al article, 2006). A pilot program has been underway since 2004, and Norcal has provided up to one truckload per day of pre-sorted, screened food waste to EBMUD with many of the contaminants removed. At EBMUD, plant staff conduct additional screening and mashing/pulping, and dilute the material to about 6 or 8 percent solids for feeding to the anaerobic digesters. At EBMUD, the relatively limited quantity of food waste in this pilot program is mixed with the sludges and other organic wastes fed to all digesters at the plant. EBMUD indicates this program is highly successful in producing additional biogas which has helped them greatly boost their power production in recent years. At EBMUD, the biogas is used in cogeneration engines (internal combustion engines) to produce electrical power and hot water for digester heating. EBMUD intends to expand this program of processing/digesting food waste materials and DRAFT - September 14,

47 bring other organic waste materials to the digestion facility to further increase biogas production and electrical power production over the next 5 years Organic Waste Quantities and Characteristics at San Francisco The organic wastes under consideration here are the wet or partially wet organic waste materials collected. San Francisco currently has basically a 3-can/bin system for solid waste collection all collected on a weekly basis: Organics bin (yard waste, food waste, etc.) Recycle bin (plastics, glass, metals, etc.) Trash bin In this arrangement, it is the Organics bin that is collecting the potential waste of interest. In the future, however, San Francisco may change to a 2-bin arrangement which would likely involve the following: (1) a wet bin (containing all food/yard waste and other organic wastes); and (2) a dry bin containing mostly dry recyclables. Obviously, collection details, public education, and other factors affect quantities and characteristics of the wastes, and the estimates provided here are the best available at this time. The quantities/characteristics estimated by Norcal for organic waste collection in the nearterm future (within about 5 years) are broken into two source categories: Source Separated Organics (SSO), which is largely commercial food waste. 200 wet tons/day (6 day/week basis), with 30 % solids content, and 85 % VS/TS. Mixed Organics (MO), which is food/yard waste, plus miscellaneous other organic wastes including paper). 200 wet tons/day (6 day/week basis), with 50 % solids content, and 80 % VS/TS. In total, this is 125,000 tons of organic wastes per year. The two source categories above are estimated to have somewhat different moisture content as indicated, and, therefore, initial processing of the as-received wastes could be different for these two organics streams. Norcal is currently evaluating options to initially process these materials at its SFRD facility in the southeast portion of the City. The SFRD is currently a large transfer and recycling facility for San Francisco solid wastes. Initial processing of these organic streams needs to include pre-sorting and screening to remove large material perhaps over 4 in size. This would include removal of obvious large items, large yard wastes (limbs/sticks/etc), larger wood wastes, as well as some plastics, rags, metals, and miscellaneous debris. When coupled with other reject materials below, Norcal believes about 10 percent of the as-received material will not proceed to digestion. DRAFT - September 14,

48 6.2.2 Pre-Processing and Digestion After the initial presorting/screening described above, the organic wastes can be further processed within one of several optional technologies and fed to anaerobic digesters. The functions of these pre-processing steps are to further remove contaminants from the waste stream (especially plastics, grit, glass, and metal), shred and/or pulp the material to much smaller particle sizes for effective digestion, and dilute the relatively thick material received down to a slurry that digesters can handle typically 6 to 10 percent solids for feeding. The Toronto Dufferin example (see references) indicates 6 to 7 percent solids feed has been their common feed thickness. These final pre-processing steps (including pulping/slurrying) probably need to be located adjacent to the digesters because the organic waste slurry is likely to be difficult to pump or transport long distances. The layout and sizing of a pre-processing facility located at the digester complex has not been completed. However, it would need to encompass functions including the following: truck delivery/storage of initially-processed organic wastes, equipment for the preprocessing described above, loadout for reject material, handling and storage for recycle process liquids, tankage for storing processed and slurried material ready for digestion, as well as all support facilities necessary including odor control. As indicated, the quantity of contaminants and debris (i.e., rejects) from the initial processing and pre-processing steps is estimated by Norcal to be 10 percent based on wet weight of as-received material. This would eliminate 40 wet tons/day from the total of 400 wet tons/day of as-received wastes. Therefore, digester feed material would be as follows on a 6 day/week basis: SSO 200 wet tons/day = 60 dry tons/day of solids. After rejects = 54 dry tons/day digester feed. MO 200 wet tons/day = 100 dry tons/day of solids. After rejects = 90 dry tons/day digester feed. These two streams total 144 dry tons/day. Assuming 7 to 8 percent solids feed to digestion, this would be a flowrate of about 400,000 to 500,000 gallons/day. For a 15- to 18-day Hydraulic Residence Time for digestion, this would require between 6 and 9 million gallons of digestion volume. If feedrates were equalized throughout the week (for a 7 day/week basis versus 6 day/week basis), these quantities would be reduced by about 15 percent. Volatile solids loading rates to digestion would be within acceptable ranges. At least one of the prominent technologies from Germany promotes recuperative thickening on the digestion process, so that the Solids Residence Times are boosted to perhaps 25 to 30 days, while the Hydraulic Residence Time remains in the 15 to 18 day range. The reason for this is to achieve greater volatile solids reduction and gas production, and perhaps to keep higher solids content or solids density within the digester for improved performance. DRAFT - September 14,

49 Bayside Biosolids Center (BBC) planning indicates that 15 million gallons of digester volume (6 tanks at 2.5 mil gal each) is needed for wastewater solids digestion. Therefore, addition of organic waste digestion would require 3 or 4 similar-sized digester tanks to be added to the digester complex. Digesting the organic waste materials within separate digesters would keep the organic waste materials segregated from wastewater-derived biosolids, In this manner, two separate digestion facilities would be operated at the same site, and the digested products would need to be separately handled, dewatered, and loaded out to avoid crosscontamination. The digesters built and used for organic waste digestion might be somewhat different in design than the sludge digesters, and contain different mixing systems. The organic waste digestion system that is envisioned would use mesophilic digestion, not the higher-temperature thermopohilic operation being planned for the wastewater solids. All digesters need to be fed 7 days per week and 24 hours per day, and, therefore, storage of processed organic waste feedstock would be required for night-time feeding and to allow Sunday/weekend feeding of digesters. Feedrates may be somewhat reduced below average on the weekend, however, consistent feeding of digesters produces consistent biogas production, which is critical for maximum biogas utilization Biogas Production and Utilization If loading to the organic waste digesters is fully equalized on a 7-day/week basis, then average volatile solids (VS) loading would be about 201,000 lbs/day (91,000 kg VS/day). All additional information below assumes that loading is equalized for 7 day/week feeding. The destruction of volatile solids within digestion is subject to many variables and there are significant different percentages reported in the literature for similar types of feedstocks. Some of this work is from full-scale, operating facilities, and some is from pilot or lab-scale research and development. Due to the conceptual nature of this work, an estimated range of VS reduction (VSR) is used as follows for the two wastestreams: For SSO, VSR is estimated to be 60 percent (low end) and 80 percent (high end) to encompass the likely range. The quantity of VS reduced or destroyed would then range from 47,000 to 62,000 lbs/day for the SSO material. For MO, VSR is estimated to be 55 percent (low end) and 70 percent (high end). The slightly reduced VSR range for MO is due to expected paper and other fractions in this waste. The quantity of VS reduced or destroyed would then range from 68,000 to 86,000 lbs/day for the MO material. Total VS reduced or destroyed in the organic waste digesters would be the sum of these, or 115,000 to 148,000 lbs/day of Volatile Solids. It should be noted that Norcal is undertaking additional testing work currently to better determine digestability of the waste steams, volatile solids reduction, and gas production rates. DRAFT - September 14,

50 As for biogas production rates for these organic wastes, a reasonable range for estimating purposes would be between 12 and 16 cubic feet of biogas per pound of VS destroyed. When these assumptions are used for calculations, the biogas production estimates are a range as follows: 1.4 million cubic feet per day of biogas (low end average condition) 2.4 million cubic feet per day of biogas (high end average condition) Gas production can vary considerably, of course, based on loading rates, characteristics of feedstocks, and operating conditions. However, based on the loads provided, the above biogas estimates are reasonable. The biogas is estimated to contain about 64 percent methane and have an energy value of about 600 BTU per cubic foot. Biogas processing would likely need to include the following, assuming that biogas is used in engine cogeneration equipment: Hydrogen sulfide removal (perhaps iron chloride addition to digestion, and perhaps iron sponge treatment of the biogas) Moisture removal through condensation Possible siloxane removal (via activated carbon) Compression for feeding engines Biogas storage of perhaps 1 hour or less of biogas production volume The two different biogas streams (from the two different digestion processes), will have somewhat different characteristics. Co-treatment of the biogas from wastewater solids digestion and organic waste digestion is likely to be cost-effective, but this needs to be evaluated. Once treated, the biogas from both digestion processes is likely to be used within a common cogeneration system. However, again, the details of this need to be evaluated. Based on recent cogeneration engine performance, a value of 9000 BTU per KW-hr is used here for estimating power production. Using the total gas production quantities from above, and an energy value of 600 BTU per cubic foot, the biogas from organic waste digestion would provide between 4 and 6½ megawatts (MW) of continuous electrical power production. Waste heat from the engines would likely be used to produce hot water which is then used in digester heating and perhaps for other purposes in the facility. This power production estimate does not include the biogas energy from wastewater solids digestion that information is contained within other SSMP documentation, which shows that the sludge digestion biogas can also produce a few megawatts of electrical power. DRAFT - September 14,

51 6.2.4 Solids Dewatering Operation Digested organic wastes would need to be mechanically dewatered, and the dewatered material would be trucked to composting facilities. Dewatering equipment options are being evaluated, however, centrifuges can probably perform this dewatering operation effectively and would probably achieve 25 to 30 percent solids content material, assuming appropriate polymer conditioning dose. Quantities of dewatered material would vary depending on the volatile solids reduction actually achieved within digestion. Based on the VSR estimates provided in this memorandum, the range of dewatered material would be between 160 and 260 wet tons per day. This would require about 7 to 11 truckloads per day. Part of the centrate from the dewatering operation would be recycled for use in slurrying the organic waste material for digestion. The remaining portion of the centrate would be discharged to the sewer system. 6.3 Economic and Non-economic Assessment for Organic Waste Processing/Digestion Cost estimates have not yet been determined for the construction or operation of facilities needed to process/digest these organic waste streams or for the biogas utilization system. Electrical power production economics will also require assessment. Overall economic assessment will need to consider multiple issues associated with this conceptual approach. And non-economic factors will also be crucial to further evaluation. 6.4 Summary This section is a status report as of March 30, 2007 for conceptual work to date on organic waste processing, digestion and biogas utilization at San Francisco. It is intended as information to be used in the development of the SFPUC Sewer System Master Plan. Projections of solids reduction and biogas production within the digestion process are presented here as a range because limited testing results are available to date on the specific organic wastestreams. Additional data should be available soon to help narrow the range in these projections, and allow more detailed evaluation of processing issues. 6.5 References Van Opstal, Evaluating AD System Performance for MSW Organics. Article from November 2006 Biocycle magazine. (Toronto Dufferin facility) Van Opstal, Managing AD System Logistics for MSW Organics. Article from December 2006 Biocycle magazine. (Toronto Dufferin facility). Norcal, Discussions with Norcal representatives over the period late 2006 through March DRAFT - September 14,

52 Yoloye, O., Kiang, D., Gray, D., and Hendry T., Don t Waste Your Food! Article in the Water Environment Federation Biosolids Technical Bulletin, Vol. 11, No. 2, March/April PROCESSING TECHNOLOGIES This section describes and evaluates a wide range of technologies that are available in the field of wastewater sludge processing. Some or many of these may be feasible for use in San Francisco. The processing technologies are discussed within the following categories: Thickening Technologies Digestion Stabilization Technologies Non-Digestion Stabilization Technologies Dewatering and Drying Technologies Other Solids Processing Technologies Biogas Processing and Use Technologies The technologies discussed and evaluated here include those that are commonly used in the industry (either in North America or in Europe). This evaluation also includes technologies that are considered innovative and are undergoing further improvement/development, as long as they have promising features and there are examples of full-scale experience. In general, processes that are at the research or embryonic stage of their development are not included here, since it is too early to determine if these processes will ever move to full-scale use. Screening criteria are established later in this section. These criteria are applied to the processes described to develop technology recommendations. 7.1 Thickening Technologies A common first step in processing wastewater solids is to conduct thickening operations to bring thin solids slurries up to several percent solids. Thickened sludges are still slurries and are almost always pumped to move or convey them Thickening Primary Sludge in the Primary Clarifier Thickening of primary sludge within the primary clarifier is a very common technique at wastewater treatment plants, and is currently the method used at the SEWPCP. There are, however, some drawbacks to this option. Thickening performance varies and often the thickened solids are less than four percent solids. Limited thickening makes the following processes larger and more costly, so that thickening has become a much more important DRAFT - September 14,

53 process than it was historically. There are processes described below that can be used to thicken primary sludge to a higher degree. An advantage of thickening within the primary clarifier is that no polymer is required Gravity Belt Thickener A gravity belt thickener (GBT) consists of a fabric belt that rotates slowly around a series of rollers driven by electric variable speed motors. The top surface is flat, and slopes gradually upward from the feed end to the discharge end of the machine. A series of plows suspended from a frame above the belt gently mix the sludge as it passes to separate water from the flocculated solids. Water is separated from the solids by gravity drainage, and also by the capillary suction forces exerted by the belt pores. Thickened sludge typically discharges to a hopper from where positive displacement pumps convey it downstream to the next process. Polymer must be added to the sludge for the proper operation of a GBT. It can be fed to the sludge in a small mixing chamber directly upstream of the sludge feed point, into the sludge feed box, or at a point in the feed piping upstream of the unit. Having several injection points allows optimization of polymer performance. Through adjustment of the operating variables such as belt speed, polymer dosing, and sludge feed rate, thickened sludge concentrations of 4 to 7 percent are commonly achievable. Thickening of waste activated sludge (WAS) is very common with GBTs, and this is the method currently used at the SEWPCP to thicken the WAS. However, cothickening of primary and WAS on GBTs has been conducted successfully, and is used currently by the City at the OSWPCP Dissolved Air Flotation In dissolved air flotation thickening (DAFT) the solids are floated to the surface of the tank by using air bubbles to alter their specific gravity. In the DAFT process, a source of air for flotation is provided by pressurizing a stream of liquid (process water or DAFT effluent) and saturating the liquid with air. When the pressurization system is discharged into the tank, the pressure is reduced and turbulence is created. Air in excess of that required for saturation at atmospheric pressure leaves solution as very small bubbles (the effect is similar to that of removing the cap from a bottle of seltzer water). A key requirement is a depressurizing zone at a location where the bubbles that form upon release of pressure contact the solids entering the DAFT. The bubbles adhere to the suspended particles or become enmeshed in the solids matrix. Since the average density of the solids-air aggregate is less than that of water, the agglomerate floats to the surface and is skimmed off the top. Polymer is commonly used to enhance the performance of the DAFT. DAFTs typically achieve thickened sludge solids concentrations ranging from 4 to 6 percent, depending upon the characteristics of the sludge, the air to solids (A/S) ratio, polymer dosage, and DRAFT - September 14,

54 various design and operating refinements. WAS is commonly thickened in DAFT units, but DAFTs are also effective in co-thickening of primary and WAS together Centrifuge Thickening Centrifuges are typically used for thickening applications where high capacity is required within a small footprint, or where fully-contained thickening is critical for odor control. The machines use more electrical power than other thickening options and usually require more maintenance. Thickened solids of five percent or more can be achieved, and polymer conditioning is required. Centrifuge thickening is used for biological sludges, and has also been used by a few agencies to thicken primary solids, and even for co-thickening service. The very large City of Los Angeles Hyperion plant uses centrifuges for WAS thickening Gravity Thickening Separate gravity thickeners have been most often used to thicken primary sludge. They are used less often today than historically, mostly because of improved thickening performance of other processes. Gravity thickening for primary sludge might be able to achieve five percent solids at San Francisco, but the thickening is likely to be variable in performance. It is also an odorous process, as the sludge is retained within the thickener for several hours. Thickening of biological sludge within gravity thickeners is not advisable because thickening performance would deteriorate and increased odors are likely. The gravity thickening process offers little advantage at San Francisco and is not considered further Rotary Drum Thickening Rotary drum thickening, sometimes called rotary screen thickening, has been used primarily at smaller wastewater plants. It functions similar to gravity belt thickening, in that free water from a flocculated sludge is drained through porous media. Polymer use is required, and in general, better performance is achieved on sludges with more fiber content. An advantage is its small footprint requirement. Concerns for the process include odor control, sensitivity to polymer type, operator attention needs, and use primarily at smaller scale plants than San Francisco Membrane Thickening Membrane thickening has been tested for waste activated sludge and implemented at a few wastewater plants in the USA. This approach involves the use of membranes to separate liquid from a WAS slurry. Thickening to over four percent solids has been reported. For the type of sludge currently produced in San Francisco, this would not be an acceptable option. However, if membrane bioreactors were utilized in the future for wastewater treatment, then membrane thickening could be considered. DRAFT - September 14,

55 7.2 Digestion Stabilization Technologies Both anaerobic and aerobic digestion technologies have a long history of use in sludge processing in North America, although anaerobic digestion is much more common at larger wastewater treatment plants of the size at San Francisco. There are several distinctive digestion processes which are discussed in this section Anaerobic Digestion Mesophilic Mesophilic anaerobic digestion is the most common stabilization process used in North America (and in Europe), and is the process that has been used at the SEWPCP and the OSWPCP. Anaerobic digesters are large covered tanks equipped with mixing, heating, and biogas collection systems. Anaerobic bacteria in the digesters convert organic matter into methane, carbon dioxide, and water; pathogen densities are reduced; and a stabilized sludge is produced. Modern high-rate digesters are typically single-stage reactors. Mesophilic anaerobic digesters are typically operated at temperatures between 35 and 38 C. USEPA estimates that over 50 percent of the wastewater treatment plants in the United States use this process. Mesophilic digestion systems produce a Class B biosolids product if the solids retention time is greater than 15 days. Two-stage mesophilic anaerobic digestion, where digesters are operated in series, improves process performance. The second-stage anaerobic digester generally has less solids retention time (SRT) than the first stage. The advantages of this process configuration are slightly improved volatile solids reduction, a product with reduced pathogen content, and less product odor potential Pasteurization/Mesophilic Anaerobic Digestion Pasteurization consists of heating sludge to 70 C or greater for 30 minutes or longer to inactivate bacteria, enteric viruses, and other pathogens this definition by the USEPA describes a process that will produce Class A biosolids. Pasteurization is almost always accomplished in batches to prevent short-circuiting of pathogens through the process. Pasteurization temperatures are achieved using heat exchangers or with direct steam injection. Mesophilic digestion follows the pasteurization step to stabilize the solids. Pasteurization as described here is quite limited in North America but is gaining more interest. It has been implemented more in Europe Anaerobic Digestion Thermophilic Thermophilic anaerobic digestion is similar to mesophilic anaerobic digestion except that the reactors are operated at temperatures ranging from 50 to 57 degrees C. In general, different categories of microorganisms are working at these different temperature ranges (thermophilic versus mesophilic). At present, there are at least a dozen full-scale wastewater plants using thermophilic anaerobic digestion in the US and Canada. California DRAFT - September 14,

56 installations include the City of Los Angeles Hyperion and Terminal Island treatment plants and one of the Inland Empire Utilities Agency plants. The major differences between thermophilic and mesophilic digestion are the requirements for sludge heating, feed control, and digester gas management. Mixing and temperature control also become more important for thermophilic digestion. The major advantages of thermophilic digestion are faster reaction rates, additional volatile solids reduction and gas production, and the potential to meet Class A pathogen density requirements depending on process configuration. Thermophilic digestion can be undertaken in single-stage systems or in multiple-stage systems. Multiple stage systems have advantages in pathogen control Temperature Phased Anaerobic Digestion The temperature phased digestion process includes two anaerobic digestion systems - one operating at thermophilic temperature and one operating at mesophilic temperature. Since each phase has largely different sets of bacteria and since thermophilic reactions proceed at a faster rate, greater overall volatile solids reduction can be achieved. Within each phase, all digestion processes (hydrolysis, acidification, and methane formation) occur and should be in balance. Therefore, the ph is not depressed and acid/alkalinity ratios are monitored to show proper health of each phase of the process. The phases can be in either order, but sufficient solids retention time must be provided in each phase for full methane production. The more common process order for temperature phased digestion is for the thermophilic system to be used before the mesophilic system, as shown in Figure 4. This is primarily because of the desire to reduce volatile acids concentrations as low as possible, and thereby have a digested product with minimum odor level. This process arrangement may also add to the energy efficiency by allowing for heat recovery between the two phases. A minor variation of this arrangement would be to operate the first phase in the thermophilic range, and then leave the second phase unheated, allowing it to cool down naturally and operate between mesophilic and thermophilic temperatures. However, performance may suffer at some operating temperatures. Figure 4 Temperature Phased Anaerobic Digestion DRAFT - September 14,

57 The process of thermophilic followed by mesophilic digestion evolved in Germany in the 1980s and some process developers there have promoted minimum solids retention times in the thermophilic phase of only 2 to 3 days. However, essentially all German facilities using the process (about 10 are reported to exist) have thermophilic phase solids retention times greater than this (Dichtl, 1997). In the United States, the process has been promoted by Iowa State University (ISU), which holds a patent on it. ISU calls the process Temperature Phased Anaerobic Digestion or TPAD. About a dozen TPAD systems are now operating in the USA; however, several of these have just recently come on-line and data at others are quite limited. Many of the USA plants are located in the Upper Midwest and Great Plains states. Omaha Nebraska s Papillion Creek WWTP (about 55 mgd) has one of the largest temperature phased digestion systems in the United States. Significant increases in volatile solids reduction are being achieved by moving from a single-stage mesophilic system to a temperature phased process. Plants seem to be achieving between 15 and 20 percent additional volatile solids reduction by making this change. For instance, a plant which had been recording 50 percent volatile solids reduction with single-stage mesophilic digestion, may achieve about 58 to 60 percent volatile solids reduction by changing to this temperature phased process, assuming total SRT remains similar. An advantage of the process is that it operates well at a wide variety of retention times for each phase. To implement the process in the USA, existing digesters have often been converted from mesophilic to thermophilic service, thereby providing fairly long retention times for thermophilic digestion (greater than 12 to 15 days, typically). For plants wishing to maximize performance, thermophilic retention times in the range of 5 to 10 days may be more appropriate. Mesophilic retention times may be reduced to as low as 8 to 10 days. The above-described temperature phased digestion system produces a material that would not meet Class A, Alternative 1 requirements of 40 CFR 503 because the thermophilic digester is not operated in a batch mode. With continuous or near-continuous feeding and withdrawal from a digester, short-circuiting of pathogens through the reactor prevents Class A designation of the process. Therefore, additional tanks are required to meet the Class A Alternative 1 standards. Thermophilic batch tanks can be expected to meet the Class A requirement, as described in Section below Acid/Gas Phased Digestion The anaerobic digestion process proceeds through definable phases. These phases include: (1) hydrolysis the solubilization of particulate material; (2) acidification production of volatile acids; and (3) methanogenesis the production of methane gas. Each phase has groups of micro-organisms that are primarily responsible for these activities. To some extent, these phases can be separated so that the bacteria are grown within desirable or even optimum conditions. The most workable process separation developed to DRAFT - September 14,

58 date is to utilize an acid-phase and a methane or biogas-production phase, as shown in Figure 5. The primary characteristics of this phasing approach are the following: The first phase (acid generation) has a short SRT and high volatile loading to maximize acid production within an acidic environment generally ph 6 or less. The result is that little methane gas and relatively little total gas is produced. High concentrations of volatile acids occur in this phase. The second phase (methane gas generation) has a considerably longer SRT because methane-generating bacteria require longer growth times. The ph is typically at or slightly above neutral and the vast majority of methane, and total gas, is produced in this phase. Figure 5 Acid/Gas Phased Digestion Options DRAFT - September 14,

59 The primary advantage of this approach is that greater volatile solids reduction is possible (compared to single stage mesophilic digestion) and the approach helps to limit foam production within the process. The process was originally developed at mesophilic temperatures for both phases, but either phase can be at thermophilic temperatures. This process evolved in the 1970s under the name Acimet, and patents were developed for the process. The treatment plant that has the longest history of using this process is the Woodridge-Greene Valley WWTP in DuPage County, Illinois. For over 10 years this plant has operated with acid/gas phased digestion. More recently, a few other facilities in the USA are moving toward using the process or are pilot testing the process. For instance, the Inland Empire Utilities Agency in California has tested and implemented the process at its Regional Plant 1. A specially built and specially operated acid phase reactor may be required to achieve the short SRTs and the maximum benefit from the process. The gas from the first phase reactor in DuPage County contains about 3,000 to 10,000 ppm of hydrogen sulfide. This gas is burned directly in a flare. Other options may be required at plants located in air basins where SOx limits are more severe. Also, any leakage of the gas from the acid-phase reactor is likely to be a significant odor problem, due to its extremely high odor level (much more odorous than typical digester gas from mesophilic digestion). Three-phase digestion is a variant of the acid-gas phased digestion process. This process is also shown in Figure 6. The three-phase process is used at the Inland Empire plant as follows: (1) acid phase at mesophilic temperature: (2) methane phase at thermophilic temperature: and (3) methane phase at a variable temperature regime, which is sometimes thermophilic and sometimes between thermophilic and mesophilic Class A Thermophilic Digestion Options Several options have been developed and implemented to provide Class A biosolids from thermophilic digestion configurations. Figure 7 presents three different configurations that have been developed. The first option shown on the figure meets the USEPA Class A Alternative 1 (time/temperature equation) in a direct manner with required batch step at the necessary time/temp. This is used at the City of Los Angeles Terminal Island Plant. The second option was developed through research and testing at Columbus, Georgia and has a Conditional PFRP-Equivalency status from the USEPA. The third option is used at Vancouver, Canada, and has 4-stages of thermophilic digestion to minimize short-circuiting of sludge through the process train. Each of these options has shown its ability to meet Class A biosolids requirements. There are pros and cons to each one of these options. The first option is obviously easiest to meet EPA s regulatory requirements, but requires the use of frequent valve changes for the batch-operated tankage. From an operational standpoint, it is better to avoid valve changes, and have a process (such as options 2 and 3) that is operating continuously and has the needed flexibility to handle all loading variations. DRAFT - September 14,

60 Figure 6 Class A Thermophilic Digestion Options DRAFT - September 14,

61 7.2.7 Thermal Hydrolysis/Anaerobic Digestion Thermal hydrolysis is a sludge pre-digestion process aimed at achieving more efficient anaerobic digestion and producing Class A digested biosolids and a well-dewatered product. The Cambi Process is the thermal hydrolysis process that has been developed and marketed world-wide. It was developed by a Norwegian company and has been implemented full-scale at several plants in Northern European countries (UK, Ireland, Norway, Denmark, etc.). Cambi thermal hydrolysis consists of first dewatering the sludge (raw primary and WAS) to about 15 percent solids content. The dewatered sludge is fed into a batch hydrolysis vessel, where it is subjected to high heat (320 F) and pressure (100 psi). The pressure is released in a flash tank which helps destroys pathogens and breaks down the cell structures in the sludge. Following hydrolysis, the sludge is anaerobically digested usually at mesophilic temperature. Digestion feedstock for this process is typically about 9 percent solids, thus reducing the digestion tankage requirements. This is one of the key advantages of the process. Another key advantage is a very well-dewatered product (typically 30 to 35 percent solids), and a product that is well-stabilized. The Cambi process was pilot tested at San Francisco s SEWPCP in The pilot test was successful and achieved increased volatile solids reduction over mesophilic, Class B digestion Aerobic Digestion Aerobic digestion consists of aerating thickened or unthickened sludge in a tank for an extended period of time. Volatile solids are oxidized in the process, stabilizing the sludge and reducing the total mass of solids that must be managed by recycling or disposal. Pathogen densities are also reduced. The process does not produce a methane-rich biogas. Many small (less than 5 mgd) wastewater treatment plants in the United States use aerobic digestion to stabilize solids, due to its relatively low capital costs, simplicity, and compatibility with the certain liquid treatment processes. The aerobic digestion process requires substantial energy input in the form of aeration blowers, and therefore is not typically used at larger wastewater plants Auto-thermal Thermophilic Aerobic Digestion The Auto-thermal Thermophilic Aerobic Digestion (ATAD) process uses the energy released from the oxidation process to raise the temperature of the sludge above 50 to 55 degrees C. The process is effective at volatile solids reduction and greatly reduces pathogen densities. Sludge is first thickened prior to the ATAD process to about 5 to 6 percent solids. The ATAD process typically consists of at least two covered reactors in series. Air is mixed with the sludge to maintain vigorous mixing and to insure maximum DRAFT - September 14,

62 aerobic conditions and oxidation to achieve thermophilic temperatures. The detention time is typically 8 to 10 days. Process temperature is controlled by adjusting the amount of air/oxygen added. The ATAD process has been used primarily at small plants it has rarely been used at plants over about 5 to 10 mgd in size. There are significant odor issues to overcome in the design and operation since maintaining truly aerobic conditions within the reactors under all conditions is challenging. For these reasons, it is not considered appropriate for San Francisco Dual Digestion Dual digestion is a combination of aerobic and anaerobic digestion processes. The first stage consists of high-purity oxygen aerobic digestion with about a one-day detention time, which heats the sludge to thermophilic temperatures. Process temperature is controlled by adjusting the amount of oxygen added to the reactor. The first-stage thermophilic aerobic digestion provides a high-degree of pathogen reduction and conditions the sludge to provide a more-stable and reliable second-stage anaerobic process. The second-stage of the dual digestion process consists of an anaerobic digestion system with typically 15 days of SRT. Sludge can be cooled to mesophilic temperatures prior to introduction to the second-stage anaerobic digestion system. The dual digestion process can be designed to produce a Class A biosolids product. The only West Coast plant to employ this process is at Tacoma, Washington. Tacoma staff developed a multi-stage anaerobic digestion portion of the process which includes thermophilic, then mesophilic, anaerobic digestion Anaerobic/Aerobic Digestion Recent research by Virginia Polytechnic Institute and State University (Virginia Tech) has investigated the concept of anaerobic digestion followed by aerobic digestion. Virginia Tech has found that some sludge solids are degraded only or primarily by anaerobic digestion, and some solids are digested primarily during aerobic digestion. Providing an aerobic digestion process following conventional mesophilic anaerobic digestion has been found to achieve up to 65 percent volatile solids reduction. The studies also suggest that providing aerobic digestion after anaerobic digestion can remove significant amounts of ammonia and total nitrogen from the biosolids, thus greatly limiting the recycle stream impact from dewatering. The process is in the development stage. 7.3 Non-Digestion Stabilization Technologies There are a host of non-digestion processing technologies which are used to stabilize sludge. These range from alkaline processes to composting, and also include many thermal processes. Some of these processes are quite specific in terms of producing a certain product (such as a fuel product or construction aggregate). Other processes are more general in terms of the final product and its end use or disposition. DRAFT - September 14,

63 7.3.1 Alkaline Stabilization (PSRP, or Class B process) Alkaline stabilization consists of adding sufficient quantities of quicklime (CaO) or other alkaline materials to sludge to raise the ph of the mixture above 12 for two hours or more. The high ph significantly reduces or eliminates biological activity and destroys pathogens. Biological activity in the mixture can resume if the ph of the mixture is allowed to decline over time, so alkaline-stabilized biosolids cannot be stored for long periods of time. Raising the ph of sludge releases ammonia; therefore, air collection and odor control equipment is frequently required for an alkaline stabilization process. Alkaline stabilization is not a common practice in California due to product market limitations Alkaline Treatment (Class A process) Several proprietary processes are available that use a combination of heat and high ph to create Class A soil amendment products. Quicklime, cement kiln dust, or other alkaline materials are mixed with dewatered biosolids in heated or insulated reactors. The high heat of the chemical reaction (or supplemental heat addition) destroys pathogens. Raising the ph of biosolids releases ammonia and sometimes other odorous compounds; therefore, air collection and odor control equipment is frequently required for an alkaline stabilization process. The appearance of the finished product varies with each proprietary process; some products are significantly more aesthetically agreeable than others. As indicated above, alkaline stabilization is not common in California Composting Unconfined Composting is the controlled aerobic decomposition of organic matter to produce a humuslike material. Thermophilic temperatures are achieved through auto-heating during the composting process, destroying pathogens. Bulking agents are mixed with dewatered cake to increase the porosity of the mixture and add carbon. Typical bulking agents include wood chips or sawdust. In some co-composting operations the bulking agent is municipal green waste. Unconfined composting is accomplished outside of an enclosed building or vessel. The lowest-cost composting technique is normally the use of mixed windrows, however, this technique has high odor emissions. Open windrow composting should therefore not be considered unless a very remote site can be located and odor transport potential carefully evaluated. In San Francisco, this is not considered possible Composting Confined Confined composting is composting within an enclosed building or vessel. The advantage of confined composting is that odors can be controlled. There are many different arrangements for confined composting as simple as aerated static pile composting within a building, to systems using automated, mechanical mixing and transport during the process. DRAFT - September 14,

64 One proven process is the agitated bed system manufactured by a number of companies. With this technology the composting takes place within concrete bays that measure approximately 10 feet wide by 6 feet deep by 200 feet long. Automated machinery periodically mixes and moves the composting mixture. Feed materials are introduced at one end of the bay and the finished compost is removed at the other end. The system is enclosed within a building so that foul air can be collected and treated in a biofilter. The City of Santa Rosa has had a successful agitated bed biosolids composting program for many years. Finding adequate space/footprint within San Francisco is likely to be one of the key challenges for a local composting facility, and insuring that odors are adequately controlled. Also, bulking agent would need to be brought in for the operation. The market for a compost product is probably one of the first things to be evaluated before proceeding further with evaluations Vermiculture Vermiculture is the process of converting biosolids into soil conditioner material using earthworms. The earthworms consume the biosolids and produce castings (earthworm feces). Earthworm castings have a mild odor and are similar in appearance to high-quality topsoil. Biosolids are mixed with a bulking agent, such as green waste or wood chips, to increase porosity and create an ideal aerobic environment suitable for the earthworms. The mixture is typically spread in low windrows on top of a mixture of castings and earthworms. The earthworms migrate vertically into the biosolids and begin making castings and reproducing. After a period of time (depending on the volume of biosolids and the earthworm density) the earthworms are separated from the castings and the process begins again. There are significant space requirements and related odor control issues to be resolved. Work to date has been on smaller scale facilities. For these reasons, vermiculture is not recommended for further evaluation in San Francisco Slurry-Carb Process EnerTech Environmental, Inc. has patented their Slurry-Carb process to create renewable fuel from biosolids. Dewatered biosolids are subjected to high heat and pressure to break down the cellular structure of the material, releasing carbon dioxide gas. After depressurization and partial cooling the resulting slurry is dewatered using centrifuges to about 50 percent total solids content, and then dried to over 90 percent total solids content to create E-Fuel. The E-Fuel is considered to be a renewable fuel in California, and can be used in cement kilns and coal-fired processes. EnerTech Environmental, Inc. claims the process uses less energy to create renewable fuel than the heat drying processes described above. DRAFT - September 14,

65 The first full-scale Slurry-Carb facility is being planned for a site at Rialto, California adjacent to the Rialto Wastewater Treatment Plant. Several Southern California wastewater agencies have signed contracts to provide dewatered biosolids to the privately-owned, operated, and financed facility at negotiated tip fees, if the facility is actually implemented in a timely fashion. The cost to these agencies is expected to be in the range of $70 to $80 per wet ton. The Rialto facility is expected process 675 wet tons of biosolids cake daily, and occupies approximately 2 acres. The facility is currently being designed and site permits negotiated. EnerTech indicates the facility could be operating by All of the E-Fuel produced at the Rialto facility will be used at a nearby cement kiln, and the fuel residuals would become part of the cement product Pyrolysis Pyrolysis processes consist of subjecting dried biosolids to very high temperatures in the absence of oxygen. Unlike the Slurry-Carb process described above, the biosolids are first dried to remove most of the moisture. The dried biosolids are then heated to 1200 F to 1800 F in a reactor, creating a char product that can be used as a fuel Gasification Gasification is also called starved air combustion. Gasification consists of exposing biosolids to high heat and pressure without adequate oxygen to complete combustion. The biogas that is produced has heating value. Other products from the process include char and/or oil, depending on the temperature and pressure used. There are currently no biosolids gasification facilities in the United States Sludge-to-Oil Technology The Enersludge process, a proprietary system by Environmental Solutions International, Ltd., of Australia is a pyrolysis process designed to create an oil product. Dried biosolids are subjected to a temperature of 850 F for 30 minuets, creating oil, biogas, and char. The char and biogas are burned to provide energy for the process. The low-grade oil product is marketed. There is currently one facility operational in Australia Thermal Depolymerization and Thermal Conversion Process Changing World Technologies, Inc. offers a patented technology called thermal depolymerization or thermal conversion that converts complex organic materials into a light crude oil. Potential feedstock materials for the process include food processing wastes, sewage sludge, mixed plastics, and old tires. The feedstock is ground into small pieces and mixed with water, if dry. The feedstock is fed into a reactor and subjected to high temperature and pressure (250 C and 600 psi, respectively) for about 15 minutes, after which the pressure is rapidly reduced to boil off most of the water. The end result is a mixture of crude hydrocarbons and solid minerals that are separated out. The hydrocarbons DRAFT - September 14,

66 are refined further in a second reactor that is heated to 500 C. The oil product is suitable for use in electrical generation equipment. The first full-scale facility is operating in Carthage, Missouri, processing turkey offal from an adjacent slaughterhouse. The facility has experienced odor complaints since its startup in February There are currently no full-scale facilities that process sewage sludge Thermal Processing with Energy Recovery The most direct method of exploiting the energy value of biosolids is thermal processing with energy recovery. Thermal processing with energy recovery consists of the complete combustion of biosolids in fluidized bed or multiple hearth incinerators. Exhaust from the combustion reaction passes through heat exchangers to recover energy. Usually the energy that is recovered is directed back to the combustion process to reduce or eliminate supplemental fuel requirements. Supplemental fuel requirements are very low if raw sludge is dewatered to about 30 to 32 percent solids. For digested sludge, higher solids content would be required to avoid supplemental fuel needs. Air pollution control devices, such as wet scrubbers, dry and wet electrostatic precipitators, fabric filters, and afterburners are used to reduce emissions to acceptable levels. The USEPA estimates that approximately 20 percent of the biosolids generated in the United States are combusted for disposal. In California biosolids incinerators are operated by the City of Palo Alto and the Central Contra Costa Sanitary District Thermal Conditioning and Heat Treatment Organic matter can be oxidized in the presence of water by subjecting it to high temperatures, pressure, and sufficient oxygen. The end product of wet air oxidation is a sterile ash that can be readily dewatered. The Zimpro process was installed at a number of wastewater treatment plants in the 1970s and 1980s. Thickened sludge and air were pumped into a reactor, and subjected to temperatures and pressures of up to 500 F and 1,800 psi for 40 to 60 minutes. The oxidized slurry was then cooled in a heat exchanger, and the gases reduced to atmospheric pressure through a pressure control valve. The processed sludge could then be dewatered using conventional methods, such as centrifuges or belt filter presses (USEPA, September 1979). Unfortunately, the Zimpro process, which operated at subcritical temperatures and pressures proved to be very odorous, and this technology is being phased out. Two manufacturers are developing wet air oxidation systems that operate at super critical temperatures and pressures. The HydroProcessing and Chematur Engineering AB systems operate at temperatures and pressures up to 1,100 F and 3,700 psi to achieve greater oxidation than the older Zimpro process with less odors. Neither process has an operational full-scale facility. DRAFT - September 14,

67 Wet Air Oxidation in Deep Well A variant of the wet air oxidation concept uses a deep well to achieve high pressure and temperature, rather than pumps. GeneSyst International Inc. offers a technology that consists of two concentric tubes that extends to a depth of 6,000 to 8,000 feet in the ground. Thickened sludge is pumped down the outer tube, and the treated product is withdrawn from the top of the inner tube. The sludge is subjected to increasing temperature and pressure as it travels down the outer tube. Oxygen is injected to the bottom of the well, where the temperature and pressure is the highest, causing the oxidation reaction to occur. The treated slurry cools as it travels up the inner tube. The chief advantage of the system is that it does not require the use of high pressure sludge pumping systems. Unfortunately, maintenance of deep well structures is difficult and specialized. In addition, the well cannot be installed across an earthquake fault. There are no full-scale installations in operation in North America Irradiation Sludge can be disinfected to Class A standards by subjecting it to beta or gamma radiation. The 40 CFR 503 regulations require a 1.0 megarad dose at room temperatures. Beta rays can be generated by a particle accelerator. Gamma rays are emitted by radioactive isotopes like Cobalt 60 or Cesium 137. Additional treatment is required after irradiation to achieve vector attraction reduction requirements (USEPA, July 2003). There are no fullscale applications of this technology in North America High-Temperature Melting and Vitrification The Minergy process is designed to create a glass aggregate product from biosolids. The Minergy process is owned by the Minergy Corporation, a subsidiary of Wisconsin Energy Corporation. Biosolids are first dried to 90 percent solids and then combusted in an oxygenrich atmosphere at temperatures of 2,600 F to 2900 F. At those high temperatures the ash from the biosolids melts and is subsequently cooled to create an inert glass aggregate product that is black in color. Air emissions control equipment includes a condenser, carbon bed, and particulate, NOx and SOx control equipment. A full-scale (1,200 wet tons per day) Minergy facility has been in operation at Neenah, Wisconsin since In addition, a smaller (187 wet tons per day) facility located at Zion, Illinois started operation in Bio-Brick Production Bio-bricks are created by mixing dewatered biosolids with the conventional clay and shale ingredients used to make bricks. The resulting mixture is formed into brick shapes, dried, and then fired in the conventional brick-making manner. The kiln temperatures reach 1,100 C during the firing process, causing the combustion of the organic matter in the biosolids. Therefore, the biosolids provide some energy value to the kiln. The interstitial voids in the bio-bricks add to the freeze-thaw durability of the bricks and improve mortar adhesion. DRAFT - September 14,

68 Pilot testing is required to determine the acceptable quantity of biosolids that can be incorporated into a brick mixture while maintaining acceptable compressive strength, water absorption, and freeze-thaw resistance criteria. The chemical characteristics of the biosolids can also affect the color of the bio-bricks. Upgraded emission control equipment may be required for the bio-brick kiln Lagooning Plants with sufficient area have lagooned their digested biosolids for months or even years to achieve further stabilization and destruction of volatile solids. Pathogen reduction to Class A standards has also been accomplished. The San Jose/Santa Clara WPCP continues to use large-scale lagooning and air drying on a large site with several hundred acres for this type of operation. The Dublin San Ramon Services District also uses lagooning for biosolids processing. These are unique sites with sufficient land and buffer area. Since the land and buffer area required are not available in San Francisco, lagooning is not considered a viable option. 7.4 Dewatering and Drying Technologies Dewatering technologies remove water from biosolids to create materials having about 15 to 30 percent solids content. Drying can involve a number of options, and the solids content of dried biosolids can range from 40 or 50 percent for partially dried, and up to 95+ percent solids for fully-dried material Belt Filter Press Belt filter presses employ moving porous belts to continuously dewater sludge. Belt filter presses are currently used at the OCWPCP to dewater biosolids, and are capable of achieving approximately 15 percent total solids content. Figure 7 illustrates the belt filter press process. The process consists of three distinct phases. In the first phase, polymer is mixed with the sludge for conditioning purposes. The second phase consists of gravity drainage through a single belt to a non-fluid consistency. The sludge is pressed between two belts and rollers in the third stage to produce the dewatered cake. Belt widths of 1.0 and 2.0 meters are generally used, although machines using belts up to 3.0 meters wide are manufactured. High pressure water sprays continuously clean the belts. Required ancillary equipment includes polymer feed systems, wash water systems, sludge feed pumps, odor containment and control systems, and dewatered cake conveyance systems. Belt filter press dewatering has worked satisfactorily in San Francisco, however, if prices for transport and product use continue to rise, it may be more economical to consider technologies that provide a higher cake solids content. DRAFT - September 14,

69 Figure 7 Belt Filter Press Centrifuge Centrifuges are another commonly used dewatering technology. Centrifuges are currently used at the SEWPCP to dewater biosolids. The newer high-solids centrifuge machines typically achieve dewatered cake of approximately 23 to 28 percent total solids content. The process is illustrated in Figure 8. Centrifugal force of 500 to 3,000 times the force of gravity is applied to the biosolids within the centrifuge, separating liquid from the solids. The centrifuge has a solid bowl that spins at a high rate. Liquid sludge, conditioned with polymer, is introduced within the rotating bowl. The sludge spins with the bowl, separating into liquid and solid fractions. A screw conveyor mechanism spins within the rotating bowl at a slightly faster or slower speed than the bowl to facilitate moving the solids fraction towards one end of the bowl, where it is discharged. The centrate (removed liquid) is discharged through another port. The process operates continuously. Required ancillary equipment includes sludge feed pumps, polymer feed systems, and sludge cake conveyance systems. Centrifuges are sized based on hydraulic and solids throughput. Machines are available to dewater sludge flow rates ranging from 25 gpm to 700 gpm. Newer high-solids machines can produce a very well-dewatered material Screw Press The screw press represents a relatively new technology for dewatering municipal wastewater solids, although the technology has been used successfully in industrial, pulp and paper production, chemical, and food processing applications. DRAFT - September 14,

70 Figure 8 Centrifuge Figure 9 is a diagram of a screw press. Thickened sludge, conditioned with polymer, is introduced to the machine in the head box at the inlet end. The mixture is conveyed from the inlet end to the outlet end of the press by the rotating screw. As the material is conveyed along the length of the press it is squeezed between the tapered screw shell and the screen drums. The dewatered solids exit the press at the discharge end and fall down the discharge box. The adjustable pressure cone provides back pressure within the machine, particularly when the machine is initially filled. For municipal wastewater solids applications the pressure cone is typically not needed after the machine is filled; the dewatered sludge provides sufficient back pressure. The liquid that was forced out through the screens is returned to the liquid treatment process. Figure 9 Screw Press Unlike the centrifuge, the screw press operates at a very slow rotational speed. The screw rotation is usually one-half of a revolution per minute or less for municipal wastewater solids. Water is slowly forced from the sludge by squeezing action similar to a belt filter press but for much longer periods of time. The solids retention time in a screw press can be on the order of two hours. The long solids retention time make screw presses practical for small wastewater treatment plants only, due to the large size of the machine relative to DRAFT - September 14,

71 amount of biosolids throughput. Therefore, screw presses are likely not a practical solution for San Francisco Rotary Press The rotary press technology operates by feeding flocculated sludge between two parallel, 4- foot diameter rotating, chrome-plated, stainless steel fine screens which rotate very slowly on a single shaft (typically between 1 to 3 rpm). Each disk set is called a channel. Filtrate passes through the screens as the sludge advances around the channel. The frictional force at the sludge/screen interface coupled with increased pressure caused by an outlet restriction produces the dewatered sludge cake. The rotary press has proven to be an effective dewatering device for blends of primary and secondary sludge as well as digested sludge. Developed in Canada, there are several plants running for over ten years with proven performance. The rotary press can typically achieve higher solids content than belt filter presses with only slightly higher polymer and power requirements. The low rotational speed has resulted in low maintenance requirements. The rotary press has enclosed dewatering channels minimizing odor control requirements. As with the screw press, the rotary press has a relatively long solids retention time, resulting in a large machine relative to the amount of biosolids throughput. Therefore, rotary presses are not a practical solution for San Francisco Plate and Frame Pressure Filter A plate and frame pressure filter consists of a series of metal plates sandwiched together in a heavy steel frame. Pressure filters operate by using a positive pressure differential as the driving force to separate water from the sludge slurry. Conditioned sludge is pumped into the pressure filter (between the plates) until the pressure reaches 100 lbs/in2, at which time pumping is discontinued and the press plates are separated and the dewatered sludge is normally scraped off and falls into a truck trailer below. The use of pressure filters has fallen out of favor for dewatering municipal wastewater sludges for a variety of reasons. The traditional process requires addition of large amounts of lime and ferric chloride that increases the volume of sludge that must be disposed. Many installations modified their operation years ago to use polymer to condition sludge instead of lime and ferric chloride, creating a lower solids content cake. Filter presses are a batch process requiring more operator attention than the favored continuous-flow processes described above. A typical problem has been the labor required to scrape the dewatered material off the plates. A fairly recent variation of the plate and frame pressure filter is the vacuum/heat filter press. Following the pressure dewatering described above, steam or hot water is circulated inside the plates to heat the biosolids. At the same time a vacuum is pulled on the biosolids, DRAFT - September 14,

72 causing the water in the biosolids to evaporate. When the solids are dry (upwards of 80 percent solids is reported), the vacuum and heat are removed and the plates are separated to allow the dried product to be removed from the press. The process should be capable of producing a Class A biosolids product, but long-term maintenance issues remain and the process has not been proven at large scale Air/Solar Drying Open Systems Biosolids can be dewatered and dried using open system drying beds. Drying bed area requirements are a function of the mass of water that must be removed and the climatic characteristics of the site. Covers to limit rainfall on the bed can be used in areas of higher precipitation. Regulatory agencies typically require that newly constructed drying beds be lined to prevent groundwater contamination by nutrients or salts in the biosolids. Asphalt concrete pavement and other materials have been used successfully for this purpose. Paved beds work well as they allow mechanical equipment to work on the beds. Biosolids must be stabilized prior to air drying to limit odor emissions. And in more urban areas, uncovered/uncontained drying beds are usually limited in size. Sometimes, dewatering precedes drying beds to limit the area required. Open system drying beds are not a practical solution for San Francisco due to the landintensive nature of the process and odor emissions Air/Solar Drying Within Structure Recent innovations in air/solar dewatering/drying operations involve handling biosolids within a greenhouse or hot-house structure equipped with forced-air ventilation and automatic mechanical mixing. Humidity and air temperature are monitored within the greenhouse and ventilation fans are energized as needed to maintain suitable drying conditions. The mechanical mixing systems vary in type and complexity. Treatment of the discharged airstream is required for sites with close neighbors. One small system has been successfully implemented at the Town of Discovery Bay in Northern California. Air/solar drying within a structure is probably not a practical solution for San Francisco due to the area requirements and odor issues. However, advancements in the technology are making evaporation more efficient and cost-effective, and there could be a future option, depending on space requirements, for a portion of the City s biosolids product to be dried or partially dried with a technology in this category Heat Drying Graded Pellet Product Heat drying technologies use thermal energy to evaporate almost all moisture from biosolids to create a Class A product. There are wide varieties of dryer technologies available; for master planning purposes the technologies can be divided into processes that create graded pellet products similar to commercial fertilizer products, and those that create ungraded products. DRAFT - September 14,

73 Most of the heat drying technologies that create graded pellet products are direct dryers. In direct dryers, moisture removal is achieved predominantly by convective heat transfer. A hot air/gas mixture is generated by a fuel-burning furnace, which exhausts the hot gases directly into the drying vessel. The hot gases come into direct contact with the dewatered sludge, causing the water to evaporate. Direct drum dryers are capable of making a highquality biosolids product consisting of uniform, hard, spherical pellets similar in appearance (with the exception of color and odor) to commercial inorganic fertilizer products. Most of the largest thermal drying operations in the United States use direct drum dryers to create their biosolids products. A process schematic of a direct thermal drum dryer system is shown in Figure 10. Dewatered biosolids are first mixed with already-dried biosolids pellets upstream of the drying drum to control the moisture content of the mixture within the dryer. This first step in the drying process accomplishes two important functions. First, it provides a means of reincorporating fines and undersized particles that are separated from the product in the screening step following the dryer. Second, the physical form of the biosolids is altered so it does not stick to the internal parts of the drying drum. This preliminary mixing step is critical to producing a pellet product from the dryer. The triple-pass drying drum rotates as hot air and the sludge particles pass through. The biosolids particles exiting the drum are screened to separate product of the desired particle size for cooling and temporary storage while awaiting distribution to market outlets. Oversized particles are crushed and returned to the head-end of the process, along with undersized particles and fines. The dryer off-gases are treated with a condenser prior to recycling back to the furnace or discharging to the atmosphere following treatment in a regenerative thermal oxidizer. Recycling a large portion of the process air serves to decrease the volume of air requiring treatment prior to discharge and to increase the thermal efficiency of the process. Heat dried biosolids products must be stored properly or they can catch on fire. If a pile of heat dried biosolids absorbs moisture it can autoheat and combust, therefore, proper design of product storage facilities is vital. Product storage silos are generally equipped with temperature sensors and inert gas blanketing to reduce fire potential Heat Drying Ungraded Product Heat drying technologies are also available that produce ungraded products containing wider variation in particle sizes and shapes. In general, ungraded heat dried biosolids products contain higher percentages of fines, creating dustier products. Ungraded product particles tend to be more angular in appearance and therefore less-similar to commercial fertilizer than graded products. Ungraded products will be more-difficult to market as fertilizer than graded products because of these differences. Most of the ungraded products are produced using indirect drying technology. DRAFT - September 14,

74 Figure 10 Direct Thermal Drum Dryer Producing Graded Pellet Product Indirect dryers achieve moisture removal predominantly by conductive heat transfer, and the biosolids are kept separate from the primary heated drying medium (typically oil or steam). The drying medium is heated in a boiler or heat exchanger by the hot combustion gases from a fuel-burning furnace. An indirect dryer consists of a stationary vessel with an internal agitator and stirring assembly. The dewatered biosolids cake enters the stationary vessel of the indirect dryer and is continuously agitated and stirred during the drying cycle. The heat is then transferred from the drying medium to the sludge by circulating the medium through the stirring mechanisms, augers, shafts, disks, dryer casing, or other equipment that comes into contact with the sludge. A process diagram of a typical indirect thermal drying system is shown in Figure 11. Dewatered biosolids are introduced to the drying chamber, which is heated with hot oil or steam. Moisture evaporates from the biosolids as they move through the machine. Dried biosolids exit the dryer, and are cooled prior to temporary storage in a silo while awaiting distribution to market outlets. Vapor from the dryer passes through a condenser prior to treatment in a biofilter or other odor control process and discharge to the atmosphere. The volume of air that must be treated is significantly smaller than the direct drying systems because the furnace air does not come into contact with the drying biosolids. DRAFT - September 14,

75 Figure 11 Indirect Thermal Dryer Producing Ungraded Product Unlike the direct dryers, the indirect drying systems generally do not include product screening and recycle. The product storage silo must include temperature sensors and provisions for inert gas blanketing for fire prevention purposes. Indirect dryers may be operated on a continuous or batch basis, depending on the manufacturer Innovative Biosolids Drying Several innovations in drying technology are occurring, often in an attempt to reduce the energy requirements. These technologies are largely being developed in Europe, and they include the following: Belt drying. This method includes lower temperature drying typically using hot air at 350 to 400 degrees F. Biosolids are spread onto belts to maximize surface area exposed to warm air. The system uses energy at almost the same level as the moreconventional heat dryers, and is geared toward producing a dry (i.e., 90 percent solids) Class A product. The system has been geared to smaller operations, but larger operations are possible. Microwave drying. High-efficiency multi mode microwaves are used to heat the material from within. Heated air is used to carry away the moisture. Again, smaller plants have been targeted to date, but larger operations are possible. The major factor that is likely to be available at the San Francisco facilities is a large hot water stream (at perhaps 180 degrees F) from the cogeneration facilities. This waste heat hot water stream needs to be explored for use in innovative drying applications such as the DRAFT - September 14,

76 above, and also together with solar technology, to determine if a biosolids drying operation could be developed with much lower purchased energy use Combined Centrifuge/Dryer Centrifuge technology has been combined with thermal drying technology in the Centridry process to enhance dewatering. Dewatered cake from the centrifuge system drops into a chamber where hot air contacts the material and quickly evaporates moisture so that the product is typically about 60 to 70 percent solids. The heating of the biosolids is not sufficient to provide Class A (pathogen-free) biosolids. A portion of the exhaust air is recycled to increase thermal efficiency and reduce the volume of air that is treated discharged. The process was pilot tested in King County, Washington several years ago and produced a semi-dry product that had some odor emissions. The process is used at several European plants prior to combustion of the sludge/biosolids. 7.5 Other Solids Processing Technologies Technologies that do not fit in the previous categories are described below. These are not stand-alone processes, but are typically used in association with previously-discussed processes Disintegration Processes Waste activated sludge (WAS) is primarily composed of cell tissue that is more-difficult to digest than primary sludge. Disintegration processes are available that are designed to break the walls of the WAS cells, or in some cases break apart large agglomerations of cells called bioflocs, thus making them more readily digestible. The potential benefits include higher volatile solids reduction, increased biogas production, reduced digested solids quantities, and better dewatering performance. The disintegration processes manufactured by Sonico and IWE Tech use ultrasonic waves to break cell walls. The MicroSludge process uses chemicals and pressure/heat to achieve disintegration goals. Disintegration processes have been successfully implemented in Europe in the last 5 years. Research continues in North America, including full-scale demonstrations. The costs to operate disintegration processes must be carefully evaluated in conjunction with demonstrated benefits to determine if a net financial gain will be realized Nutrient Removal Processes Biosolids dewatering and other processes can create waste side streams containing high concentrations of ammonia, phosphorus, and other nutrients. Under certain conditions a chemical precipitate (scale), called struvite, can form in piping and mechanical equipment. Struvite is difficult to remove, and can cause significant pipeline restrictions or complete clogging. One technique for controlling struvite formation is to remove the phosphorus from the waste side stream. The Crystalactor process, offered by DHV Water BV, is a fluidized bed reactor designed to precipitate phosphorus from a liquid waste stream, creating crystal DRAFT - September 14,

77 pellets. Chemicals are added to the liquid waste stream to adjust the ph and create suitable conditions for phosphorus precipitation. The reactor contains sand or minerals to provide suitable seed material for crystal growth. The crystals become heavier as they grow, moving to the bottom of the reactor. The finished pellets are removed from the bottom of the reactor, air dried, and sold as fertilizer Cannibal Process The Cannibal process is a proprietary solids reduction process offered by USFilter Corporation. The process combines fine screening and a proprietary bioreactor to significantly reduce the mass of biological solids requiring disposal. Return activated sludge is passed through a 250-micron screen to remove grit, inorganic trash (plastics, etc.), and organic materials that are not readily degradable, such as hair and lint. The screenings are sent to landfill. A portion of the screened return activated sludge is sent to a proprietary side-stream interchange bioreactor. The bioreactor is a batch-fed anoxic process designed to reduce the mass of solids through digestion by facultative bacteria. The effluent from the bioreactor is best returned to an anoxic zone within the liquid treatment process. The manufacturer claims sludge yields of 0.1 pounds per pound of BOD5 removed in the liquid treatment process, plus 0.2 to 0.25 pounds of screenings per pound of BOD5 removed in the liquid treatment process. The Cannibal process is designed for wastewater treatment plants that do not have a primary clarification process. Existing plant capacities range from 0.75 to 16 million gallons per day. 7.6 Biogas Processing and Use Technologies With anaerobic digestion of wastewater solids and other organic feedstocks, an energy-rich gas is produced which usually contains between 60 and 70 percent methane. This gas is often called digester gas or biogas, and we refer to it as biogas in this report. The biogas is increasingly valuable in today s energy markets and is a renewable fuel which has important implications for sustainability goals. Capturing methane and using it wisely minimizes methane emissions to the atmosphere a critical greenhouse gas concern. Biogas can be used wherever natural gas is used; however, required gas characteristics vary depending on the combustion method/device. Characteristics required for stationary biogas applications at the treatment plant are much less stringent than required to meet pipeline quality natural gas or vehicle fuel needs. Options for biogas use are presented and discussed here along with technologies for biogas processing and handling On-Site Electric Power Generation and Cogeneration Electrical power is a highly valued and flexible commodity in California and elsewhere. Therefore, on-site power generation or cogeneration is very popular at California wastewater treatment plants when considering options for using the biogas from anaerobic digestion of solids. The heat byproduct from cogeneration facilities is also valuable in heating the digesters and providing heat for buildings, and even for building cooling via DRAFT - September 14,

78 absorption chillers. Biogas power generation via internal combustion engines is a mature and well proven technology. Gas turbine technology is also used for electric power production from biogas. Several major reciprocating engine and gas turbine manufacturers have dozens of successful operating projects. Biogas to electricity projects have been more risk-free than some of the other biogas use options, and the power that is created is fully usable. The optional technologies for power generation and cogeneration are: Internal combustion engines are the most frequently-used technology for biogas cogeneration at wastewater plants. Heat recovery from the engine is almost always implemented, creating a hot water system for heating purposes. Engine development has produced greater efficiency over the years. Gas turbines are also used for biogas cogeneration, particularly at larger treatment plants. For combustion gas turbines, slightly less biogas energy goes to electric power production and somewhat more waste heat energy is produced. Turbines are more sensitive to gas moisture content and characteristics such as siloxane. Gas turbines also require higher pressure biogas than most other gas use technologies often 150 to 250 psi. Therefore, gas pretreatment becomes more critical. Fuel cells produce electric power and some waste heat with no moving parts. Fuel cells combine hydrogen (extracted from the biogas) and oxygen (from air) in an electrochemical reaction and represent a very clean technology from the standpoint of air emissions. The technology is now available, but is very costly and still undergoing additional development. San Francisco has had engine-based cogeneration facilities at both the SEWPCP and the OSWPCP. And, a fuel cell project is being developed by the City. Therefore, electric power generation and cogeneration technologies are well-known to City staff On-Site Direct Engine Drives Some plants operate biogas engines to directly drive aeration blowers, large pumps, or other large mechanical equipment that has constant or near-constant load. Waste heat can be recovered and used as described previously. There is likely to be limited cost-effective opportunity for this option at the City s treatment plants because major changes would be required in powering this type of equipment Sell Biogas to Local User If a local user for the biogas was available in San Francisco, the biogas could be piped directly to the user and the biogas sold directly. Unfortunately, no known user is available that fits this situation in San Francisco. At Sacramento and Los Angeles (Hyperion Plant), biogas produced in the digesters is piped to immediately-adjacent electric power or cogeneration plants owned or operated by power utilities. In both these cases, the biogas represents a relatively small portion of the total energy used in the power/cogen plants. DRAFT - September 14,

79 Steam from these power/cogen plants is piped back to the digestion facility for heating purposes. Contracts between the wastewater plant utility and the power utility were negotiated in the 1990s to handle these transfers of gas and steam. This option could arise in the future at San Francisco, but currently there is no plan for this type of arrangement Clean the Biogas and Sell to Utility With the price of natural gas rising in recent years in the US and worldwide, the concept of cleaning the biogas to pipeline or utility-quality natural gas is gaining interest, however, currently there are very few wastewater digestion plants using this approach. Various technologies are available for biogas cleaning and scrubbing, but removing carbon dioxide and various pollutants is a major task involving capital facilities and additional operating cost. This may be an option to evaluate in the future if technology improves and economics of options change Clean the Biogas and Use for Vehicle Fuel An option being used in Europe and gaining some momentum there, is to clean the biogas and compress it to high pressures (2000 to 3000 psi) that are required for use in compressed natural gas (CNG) vehicles. Typically, a CNG fleet vehicle organization is required at close proximity to the digestion plant to make this option work. Cleaning the biogas to high quality standards is required for the high pressure compressors and to protect vehicle engines. This option is expected to be difficult for San Francisco because of the need to find a CNG user/organization and contract for the use of the fuel on a very reliable basis. Also, the economics of this approach have been evaluated by others in the US, and it does not appear favorable for San Francisco Use for Heat-Drying Biosolids A few wastewater treatment plants, mostly in the Eastern US, have used their biogas to provide energy to thermally dry their dewatered biosolids. Sometimes a mixture of biogas and other fuels is used to provide the required hot air for direct dryers or provide hot steam/oil for indirect drying systems. This option becomes more workable if the drying operation is conducted continuously (24/7 on a reliable basis) so that the biogas can be used continuously in the drying system. If heat drying is only conducted 6 days per week or the drying system frequently goes down for maintenance, then the biogas would be flared during these periods unless there was another use for the biogas during dryer down-times Boiler Use for Heating The most common use of biogas has been, and continues to be, for heating of sludge in the anaerobic digesters. There are several methods used for such digester heating, but the most common method is to use biogas as fuel in a hot water boiler, and the hot water is then used in heat exchangers to heat the sludge/biosolids slurry. Steam boilers are also used at some plants to provide steam for heating (and, through absorption chillers, for cooling uses in buildings). Even if the digestion plant uses cogeneration or other methods of DRAFT - September 14,

80 biogas utilization on a normal basis, the plant will typically need to maintain a boiler system as a backup heating method, so that digestion heating is assured even if mechanical breakdown or other problems arise in the biogas utilization system Biogas Flares Biogas flares (sometimes referred to as waste gas burners or emergency flares) are required at digestion plants as a safety and air emission control measure. If biogas use in boilers, cogeneration, or other methods is not able to handle the quantities of biogas being produced, the flares must be used to combust excess biogas. Flare design in the last couple of decades has achieved improved combustion of the biogas to minimize products of incomplete combustion and NOx emissions. Typically, flares are sized to handle the peak potential biogas production from the facility, to account for the emergency situation whereby the biogas may not be able to be sent to any other combustion device Hydrogen Sulfide Removal Reduction of hydrogen sulfide gas concentrations within the biogas is becoming very common because of air emission regulatory controls. For wastewater agencies in California, the most common approach has been to add iron salts so that the ferric or ferrous ion precipitates the sulfide within the liquid phase sludge. Agencies in California using this approach can often reduce hydrogen sulfide concentrations from 1000 ppm or greater down to 100 ppm or less. However, air districts sometimes require hydrogen sulfide levels less than 100 ppm. In this case, agencies have used iron oxide/hydroxide technology (iron sponge). Other technologies occasionally used include water or hydroxide scrubbing, or activated carbon treatment Moisture Removal Biogas is saturated with water vapor. At mesophilic temperature (37 C, or 99 F), water vapor is about 6 percent by volume. However, at thermophilic temperature (55 C, or 131 F), water vapor is about 15 percent by volume. Moisture must be removed prior to combustion and is also removed to minimize condensation within gas piping (potential pipe blockages), to protect instruments, and limit corrosion from low ph liquid conditions. Moisture is removed by cooling the biogas. Condensers are common technology for this purpose. A slight re-heating of the biogas after condensation limits chances for moisture problems downstream Siloxane Removal Organo-siloxanes and silicones are present in typical municipal wastewater sludge, and these compounds are also contained in the biogas. These compounds cause tough, whitish-colored deposits to form on biogas combustion surfaces in boilers, engines, and other devices. Increasingly, these siloxane-caused deposits cause maintenance problems and equipment downtime, and, therefore, there is a need to minimize the siloxane content in the biogas. Condensation of biogas for moisture removal (cooling to about 4 C DRAFT - September 14,

81 temperature) removes a small portion of the siloxanes from the biogas, but greater removal is often required. The most common current method to bring siloxane levels down to < 1 ppm, is through the use of granular activated carbon. Another method for siloxane removal is to cool the biogas down to very low temperature (-30 C or colder); however, this approach has not met with high success rate to date. Other removal methods are undergoing research work Carbon Dioxide Removal Several technologies are available for carbon dioxide removal from biogas. However, water scrubbing/absorption has been used more frequently than other methods in the US because, for wastewater treatment plants, there is an abundance of water available to carry off the carbon dioxide. Hydrogen sulfide is also largely removed in this absorption process. The driver for CO2 removal is normally to create pipeline-quality gas or vehicular fuel. These CO2 removal technologies can be complicated, and, therefore, wastewater plants are less inclined to pursue this approach without clear economic advantage. Besides water scrubbing, other methods for CO2 removal include polyethylene glycol absorption, carbon molecular sieves (pressure swing adsorption), and membrane separation Biogas Storage A small amount of biogas storage is normally used at sludge digestion plants as a means of equalizing the gas pressure in the system, and providing consistent feed of biogas to engines, boilers, and other gas use systems. The storage volume provided is often one hour or less of biogas production; however, sometimes several hours of storage time are constructed. Beyond this quantity of storage, the cost typically becomes hard to justify. Most biogas storage at wastewater plants is within low pressure units such as variable volume bladder tanks or within digester covers that can store biogas directly. Compressing the biogas for medium or high pressure storage is more costly and is usually done only when the biogas use system requires increased pressure. 7.7 Screening Criteria The technologies described above are screened here to ascertain their suitability for implementation in San Francisco. The screening criteria are described below Technology maturity Biosolids and sludge treatment technologies typically require time to develop into viable options. The USEPA has developed three categories to assess technology maturity (USEPA, September 2006), and others have used similar descriptions of technology development: Embryonic Technologies in the development stage and/or tested at laboratory or bench scale. New technologies that have reached the demonstration stage overseas, DRAFT - September 14,

82 but cannot yet be considered to be established there, are also considered to be embryonic with respect to North American applications. Innovative Technologies meeting one of the following qualifications: (1) have been tested at a full-scale demonstration site in this country; (2) have been available and implemented in the United States (U.S). for less than 5 years; (3) have some degree of initial use (i.e., implemented in less than 25 utilities in the U.S.; and (4) are established technologies overseas with some degree of initial use in the U.S. Established Technologies widely used (i.e., generally more than 25 facilities throughout the U.S.) are considered well-established. Established technologies generally represent the lowest risk for investment of substantial amounts of public funds. Substantial investment in innovative technologies carries greater risk for the public agency involved. Embryonic technologies are not suitable for full-scale application using public funds Experience at similar-size facilities Biosolids and sludge processes often present significant materials handling challenges for equipment manufacturers. Experience has shown that design and operational problems are often encountered when equipment size is scaled-up to meet the needs of larger wastewater treatment plants. For these reasons it is prudent for wastewater agencies to carefully consider whether technologies have proven success at similar-sized facilities prior to investment of significant quantities of public funds Area Requirements Some technologies require significantly more land area than others. Area requirements are a significant issue for highly-developed San Francisco Odor Risk Processing technologies produce varying degrees and types of odors, depending on the physical and chemical nature of the reactions involved. The likelihood/extent of odor produced and the complexity of the odor control systems that will be required to mitigate odor risks are significant issues for San Francisco Operations and Maintenance Complexity Some technologies require higher skill levels to operate and maintain than others. The operations and maintenance complexity of technologies must be considered because qualified staff must be hired, trained, and retained throughout the life of a project Worker Health and Safety Some technologies present greater worker health and safety challenges than others due to chemical handling needs, high pressures, high temperatures, radiation, or equipment DRAFT - September 14,

83 inertia. The complexity of maintaining a safe and healthy work environment must be considered Product Marketability Market considerations were discussed in detail in a previous section of this report. The marketability of the products produced by technologies must be carefully considered, including regulatory compliance, product aesthetics, and market diversification potential Implementation Risks Some technologies present greater implementation risks (such as permitting, overcoming negative public perceptions, etc.) than others. 7.8 Screening to Identify Viable Technologies Table 29 presents the result of the technology screening. Each technology was considered with respect to the screening criteria described above. The determination was then made whether: The technology has good potential for near-term application at San Francisco. These technologies were carried forward for more-detailed evaluation. The technology, with development and refinement has potential for future use at San Francisco. The SFPUC should continue to monitor the development of these technologies, but they are not carried forward for more-detailed evaluation at this time. The technology is not suitable for San Francisco, and is eliminated from further consideration. 7.9 Recommendations on Viable Technologies Table 30 provides a summary of the viable technologies based on the screening review in Table Solids Processing Approach In evaluating the Technology Recommendations Summary in Table 30, it is obvious that there are many processes not well suited to San Francisco s situation. The reasons for this are presented previously in Section 5. It is also obvious that there are many processes that should be tracked over time to determine if they develop into systems that could be considered for the future. DRAFT - September 14,

84 Table 29 Technology Screening 2030 Sewer System Master Plan City and County of San Francisco Further Evaluation Warranted? Category Technology Screening Evaluation and Assessment Thickening Thicken PS in clarifier Better methods are available. No Gravity belt thickener Dissolved air flotation In common use in North America. Good performance, and use for co-thickening service. In common use in North America. Good performance, and can use for cothickening service. Yes Yes Centrifuge Costly operation, and thickening performance not as good as other options. No Gravity thickening Odorous process. Performance not as good as other options. No Rotary drum thickening Use for smaller WWTPs. Not as good a process for co-thickening. No Membrane thickening Not in common use. No MBR facilities at San Francisco, at this time. Future Digestion Stabilization Anaerobic digestion - mesophilic Pasteurization/mesophilic anaerobic digestion Most common sludge stabilization technology in North America. Used in Europe historically. Now used at a few plants in North America. Class A product. Yes Yes Anaerobic digestion thermophilic Temperature phased anaerobic digestion Increasing use in North America, including at some large plants in California. Increasing experience in North America benefit of additional volatile solids reduction. Can be Class A process with proper configuration. Yes Yes Acid/gas phased digestion (including 3-phase digestion) Increasing experience in North America. Can be Class A with proper configuration. Yes DRAFT - September 14,

85 Table 29 Technology Screening 2030 Sewer System Master Plan City and County of San Francisco Category Technology Screening Evaluation and Assessment Class A Thermophilic Includes several advanced digestion process options to produce pathogen-free Digestion using batch or biosolids within the digestion process. Working at large plants in North America. multiple stages. Further Evaluation Warranted? Yes Thermal hydrolysis/anaerobic digestion Aerobic digestion Experience in Europe is increasing. Pilot tested at San Francisco in Class A process and high-solids cake. Common for small plants and plants with only waste-activated sludge. High energy costs and only Class B pathogen reduction. Yes No Auto-thermal thermophilic aerobic digestion (ATAD) Used at small plants and has had significant odor problems/concerns. Class A process. Vertad process is similar to ATAD. No Dual digestion Consider with high purity oxygen plants. Can be Class A. City of Tacoma has had success. Odor concerns. Yes Non- Digestion Stabilization Anaerobic/aerobic digestion Alkaline stabilization (PSRP) Very limited experience new research being conducted at Virginia Tech. Rarely used at larger plants. Product use perceived as minimal in Bay Area and Northern California. Odor concerns. Creates larger mass of biosolids for transport and disposition, due to addition of alkaline amendments. Future No Alkaline treatment (Class A) Involves high ph, high temperature, and drying. Significant odor issues. Consider as Class A option for rapid implementation if situation warrants. Yes Composting unconfined Inadequate space within San Francisco, and odors would be too high, even with digested feedstock. Unconfined composting considered infeasible. No DRAFT - September 14,

86 Table 29 Technology Screening 2030 Sewer System Master Plan City and County of San Francisco Category Technology Screening Evaluation and Assessment Composting confined Space/footprint is major issue; therefore, only small-scale operation is considered feasible. Extensive odor control would be required. Digested biosolids required as feedstock. Further Evaluation Warranted? Yes Vermiculture Lack of experience at required scale. Space requirements are significant. No Slurry-Carb process Pyrolysis Gasification First facility may be built in Rialto, CA by Pressurized and heated reactions allows high-solids dewatering for energy value. Rialto facility product to be used in nearby cement kiln. High-temperature processes to create char product and combustible off-gas for energy value. Public perception may be difficult to overcome. Limited experience and odor concerns. Testing work at Philadelphia has been troubling over the years. Future Future Future Sludge-to-oil technology Very limited experience. Process has been in development for at least 20 years. No Thermal depolymerization and thermal conversion process Thermal processing with energy recovery First plant at Carthage, MO working on turkey waste no facilities using biosolids. Odor problems at Carthage facility. Destruction of organics and pathogens. Concerns from air quality perspective, and major investment required. Ash is the final product, usually disposed. Continues to be a successful process at approximately 50 US WWTPs. Public perception may be difficult to overcome. Future Yes DRAFT - September 14,

87 Table 29 Technology Screening 2030 Sewer System Master Plan City and County of San Francisco Category Technology Screening Evaluation and Assessment Thermal conditioning and Significant odor problems at these plants over time. Existing plants with this heat treatment technology have been, and continue to be, phased out. Further Evaluation Warranted? No Wet air oxidation in deep well Small footprint is advantage. Very little experience. Possible advancements in future, but also risks from deep wells. Essentially, an ash is produced from the process. Odor may be crucial concern. Future Irradiation Pathogen reduction process, which can produce Class A. Not a stabilization process. No High temperature melting and vitrification Limited experience and odor potential. Perceived as high cost approach. Destruction of organics and pathogens. Future Bio-brick production Lack of experience at required scale. Involves high temperature processes. Advancements in technology are possible as costs for biosolids management increase. Future Dewatering and Drying Belt filter press Very common dewatering process at scale required. Low-shear process. However, the technology has not achieved high solids content cake material, even with newer advancements. Yes Centrifuge Very common dewatering process at scale required. Achieves good cake solids content, but can be high-shear process with odor regrowth potential. Yes DRAFT - September 14,

88 Table 29 Technology Screening 2030 Sewer System Master Plan City and County of San Francisco Category Technology Screening Evaluation and Assessment Screw press Relatively new process for biosolids, used at smaller plants to date. Low-speed machine with low-shear. Space requirements may be excessive for San Francisco. A version of this process adds steam to produce Class A cake. Further Evaluation Warranted? Yes Rotary press Plate and frame pressure filter Air/solar drying open systems Air/solar drying within structure Used at smaller plants space requirements for San Francisco would be excessive. Low-shear dewatering conducted in batches. Sludge/biosolids industry has had few installations, and most have been phased out. Newer technology using vacuum and heat provides Class A, but only used at smaller-scale plants to date. Inadequate space in San Francisco. Even with excellent upstream stabilization, there would be odor concerns. New, mechanical greenhouse-type systems. Odor must be highly controlled. Not yet proven at scale required. Might be implemented for portion of City s biosolids production, if space is available. No Future (for newer form of these filters) No Yes Heat drying graded pellet product Heat drying ungraded product Digested feedstock required. Very high degree of odor control needed. Experience is increasing in North America, and considerable experience in Europe at required scale. Safety is an issue particularly fire/explosion. Class A product. Digested feedstock required. With highly controlled systems and advances in dust control and safety, this type of heat drying may be feasible at San Francisco. Yes Yes DRAFT - September 14,

89 Table 29 Technology Screening 2030 Sewer System Master Plan City and County of San Francisco Category Technology Screening Evaluation and Assessment Innovative Biosolids Use of waste-heat hot water stream from cogeneration at San Francisco needs Drying to be explored for possible use with other innovative drying techniques using Combined Centrifuge/Drying solar energy, belt drying or other technology. Implemented in Europe, primarily as pre-processing before incineration. Not a Class A product. Further Evaluation Warranted? Yes Future Other Solids Processing Technologies Disintegration processes Applied to TWAS, normally, to achieve greater volatile solids reduction in digestion. Processes being researched and tested in North America. Several facilities built in Europe and overseas in last 5 years. Future Nutrient removal processes Purposeful crystallization to remove phosphorus and perhaps ammonia from sludge streams. Crystals used as fertilizer material. Implemented overseas primarily. Future Cannibal process Process to minimize sludge production. Not very conducive if plants have primary clarifiers and fairly low MCRT biological process. Has been implemented at small plants to date. Future Biogas Processing and Use Technologies On-Site Power/Cogeneration On-Site Direct Engine Drives Most common form of biogas utilization at WWTPs after boiler use. Produces electrical power (and heat from cogeneration) for use in the WWTP. Already in use at San Francisco. Not cost-effective, currently, to make changes to this approach in San Francisco plants due to distributed nature of sources that could use direct drive engines. Yes Future Sell Biogas to Local User No identified user or power plant located near the San Francisco wastewater plants. No DRAFT - September 14,

90 Table 29 Technology Screening 2030 Sewer System Master Plan City and County of San Francisco Category Technology Screening Evaluation and Assessment Clean Biogas and Sell to Rarely done in North America, but interest is increasing. The historical example Utility is at the King County South Plant in Renton, Washington. Complex technologies required. Further Evaluation Warranted? Future Clean Biogas for Vehicle Fuel Use to Heat-Dry Biosolids Boiler Use for Heating Rarely conducted in North America, but there have been some examples, and interest is increasing due to increased fuel prices. Complex technologies required, and CNG user fleet must be organized. This is being done in a few North American plants. Must be continuous, reliable heat drying system for continuous use of biogas. Most common use for biogas produced at wastewater plants. Boilers are almost mandatory as a backup system, if other gas utilization methods are normally used. No Future Yes Biogas Flares Required for safety and air pollution control. Yes Hydrogen Sulfide Removal Moisture Removal Siloxane Removal Carbon Dioxide Removal Required for almost all biogas utilization methods. Reliable systems are available. Required for almost all biogas utilization methods. Reliable systems are available. Very likely to be required for biogas utilization. Reliable systems are available, and research for new technologies is underway. Few carbon dioxide removal systems have been implemented in North America at wastewater treatment plants. These technologies would be typically used for options to sell the gas to the natural gas utility or to use the gas for vehicle fuel. Yes Yes Yes Future DRAFT - September 14,

91 Table 29 Technology Screening 2030 Sewer System Master Plan City and County of San Francisco Category Technology Screening Evaluation and Assessment Biogas Storage Biogas storage is required for safety and operating reasons, however, storage quantity is usually limited. Reliable systems are available and used at WWTPs. Further Evaluation Warranted? Yes DRAFT - September 14,

92 Table 30 Technology Recommendations Summary 2030 Sewer System Master Plan City and County of San Francisco Technologies to Carry Forward for Category More-Detailed Evaluation Thickening Gravity belt thickener Dissolved air flotation Digestion Stabilization Anaerobic digestion mesophilic Pasteurization/mesophilic anaerobi digestion Anaerobic digestion thermophilic Temperature phased anaerobic digestion Acid/gas phased digestion Class A Thermophilic Digestion options Thermal hydrolysis/anaerobic digestion Dual digestion Technologies with Potential for Future Application. SFPUC Should Continue to Monitor the Development of These Technologies. Technologies not Suitable for San Francisco Membrane thickening Thicken PS in Clarifier Centrifuge Gravity Thickening Rotary Drum Thickenin Anaerobic/aerobic digestion Aerobic digestion Auto-thermal thermophilic aerobic digestion DRAFT - September 14,

93 Table 30 Category Non-Digestion Stabilization Dewatering and Drying Other Solids Processing Technologies Technology Recommendations Summary 2030 Sewer System Master Plan City and County of San Francisco Technologies to Carry Forward for More-Detailed Evaluation Alkaline treatment (Class A) Composting confined Thermal processing with energy recovery Technologies with Potential for Future Application. SFPUC Should Continue to Monitor the Development of These Technologies. Slurry-Carb Process Pyrolysis Gasification Thermal depolymerization and thermal conversion process High temperature melting and vitrification Bio-brick production Belt filter press Plate and frame pressure filter Centrifuge Combined centrifuge/dryer Screw press Air/solar drying within structure Heat drying graded pellet product Heat drying ungraded product Innovative biosolids drying Disintegration processes Nutrient removal processes Cannibal process Technologies not Suitable for San Francisco Alkaline stabilization (PSRP) Composting Unconfined Vermiculture Sludge-to-oil technolog Thermal conditioning and heat treatment Irradiation Lagooning Air/solar drying open systems DRAFT - September 14,

94 Table 30 Category Biogas Processing and Use Technologies Technology Recommendations Summary 2030 Sewer System Master Plan City and County of San Francisco Technologies to Carry Forward for More-Detailed Evaluation On-Site Power/Cogeneration Boilers for Heating Flares Hydrogen sulfide removal Moisture removal Siloxane removal Biogas storage Technologies with Potential for Future Application. SFPUC Should Continue to Monitor the Development of These Technologies. On-site direct engine drives Use to heat-dry biosolids Clean biogas and sell to utility Carbon dioxide removal Technologies not Suitable for San Francisco Sell biogas to local use Clean biogas for vehicl fuel DRAFT - September 14,

95 The stabilization processes that are available for continued planning and development at this time in San Francisco are dominated by the anaerobic digestion category (see Table 30). Based on work in Section 5, the only non-digestion processes to be evaluated further are as follows: Alkaline treatment (Class A). This is on the list primarily as a fast-track method to produce a Class A biosolids product if that were required. In the long-term, alkaline treatment is not considered a good candidate. Composting Confined. This is on the list to process a portion of the City s biosolids, however, the site for this is undetermined, and, therefore, substantial development of this concept would be required. Thermal processing with energy recovery. This approach is longer-term, and needs further study and development before it could be considered ready for implementation. Heat drying. Thermal or heat drying of biosolids is an important category for follow on evaluation by the City. However, heat drying should be evaluated only for biosolids which has already received digestion stabilization. Therefore, heat drying is an additional process to be considered following anaerobic digestion and dewatering. Solar and innovative drying. Potential exists to dry, or partially dry, biosolids with newer solar and methods using waste heat available from cogeneration facilities. Therefore, the City should proceed with anaerobic digestion as its base or core stabilization and processing approach for wastewater solids processing and biosolids management. This will necessarily involve rebuilding the digestion and related facilities on the Bayside. For Oceanside, this approach involves the continued use of digestion and related facilities. Proceeding with anaerobic digestion as a base program provides a sound stabilization method that fits well with essentially all potential add-on, advanced, Class A, and thermallyoriented biosolids alternatives that could be considered for San Francisco Solids Facilities for Bayside The solids facilities that need to be rebuilt are primarily the anaerobic digestion facilities and associated biogas handling and processing equipment. Many of these facilities, as identified in other SSMP tasks, are structurally deficient, have outlived their service lives, and are the cause of odor problems. Also, the thickening facilities need to be modified because thicker feed to digestion has proven more cost-effective (work at the OSWPCP over the last decade has shown this). Implementing co-thickening of sludge can produce six percent solids on a reliable basis to feed digestion, and is, therefore more cost-efficient. Thickening facilities will need to be rebuilt to make this change; however the City has already invested in two large GBT machines at the SEWPCP which could be transferred to DRAFT - September 14,

96 a new co-thickening facility. Dewatering equipment also should be changed out to newer, more efficient machines. For biogas processing, review of options in Section 5 indicates that on-site power or cogeneration is the preferred approach and is already being used at the City s two solids processing plants. An expansion of this approach to produce even more electrical power and heat is recommended. Therefore, a rebuilt and mitigated Bayside solids processing system is needed as a base program for Bayside biosolids. This rebuilt facility would have the following major elements: Co-thickening of sludges for digester feed. Anaerobic digestion, using mesophilic, Class B digestion for the base program Biogas utilization using an on-site cogeneration system Mechanical dewatering of biosolids and truck loadout facility All associated facilities and equipment including odor and aesthetic control and mitigation to assure a neighbor-friendly facility. The construction cost estimate for this base program for Bayside biosolids facilities is estimated to be about $500 million. This major facility will need to be well planned, designed, and implemented and must be sited properly. Section 6 describes siting options for this facility which is termed the Bayside Biosolids Center, or, if it is located on the Oceanside, it is termed toe Oceanside Biosolids Center Solids Facilities for Oceanside Mesophilic (Class B) anaerobic digestion facilities were built at the OSWPCP within the last two decades and can provide good service for several more decades. Co-thickening of sludge using GBTs was implemented at the Oceanside plant in the 1990s. Biogas processing includes cogeneration, and dewatering uses belt filter presses. There will be need for upgrades to these solids facilities over time, but the major processing elements exist, with generally adequate capacity for the planning period References Brown and Caldwell, San Francisco Wastewater Solids Facilities Project. For the City and County of San Francisco. August 1982 Brown and Caldwell, SEWPCP Anaerobic Digestion Upgrade Project Facilities Planning Report. For the San Francisco Public Utilities Commission, August Brown and Caldwell, Screening of Feasible Technologies. For the San Francisco Public Utilities Commission. July DRAFT - September 14,

97 Carollo, Long-Term Biosolids Management Plan. For the City and County of San Francisco. December CH2M-Hill, Bay Area Regional Biosolids Management Program Initial Market Assessment. Prepared for the Bay Area Clean Water Agencies. April City and County of San Francisco, Preliminary Design Report Solids Handling Upgrade Project Southeast Water Pollution Control Plant, December USEPA, Process Design Manual for Sludge Treatment and Disposal. EPA 625/ USEPA, Environmental Regulations and Technology, Control of Pathogens and Vector Attraction in Sewage Sludge. EPA/625/R-92/013. Revised July USEPA, Emerging Technologies for Biosolids Management. EPA 832-R September Water Environment Federation, Design of Municipal Wastewater Treatment Plants. WEF Manual of Practice no. 8. Water Environment Research Foundation, Biosolids Management: Assessment of Innovative Processes. Project 96-REM SOLIDS PROCESSING SITES This section considers alternative sites for wastewater solids processing. Minimum land area requirements for solids processing have been determined within other SSMP work, and that work is summarized here. Several different sites for solids processing have been considered over the last decade in San Francisco, and these were reviewed, along with new potential sites that came to the attention of the planning team. Screening and evaluation of the sites is followed by site recommendations. 8.1 Dispersed Versus Centralized Solids Processing The options of implementing decentralized liquid treatment and distributed liquid treatment for water reuse are the subjects of two separate project memoranda within the SSMP. Decentralization of wastewater treatment facilities has been considered for San Francisco for environmental justice reasons. Facility dispersion could potentially spread the wastewater treatment site burdens for the City among several, rather than just a few, neighborhoods. Similarly, solids processing facilities could potentially be dispersed throughout the City, rather than become centralized. However, centralization of solids processing at San Francisco is preferred for the following reasons: Significant economies of scale can be realized by implementing centralized solids processing systems, particularly when solids processing moves to higher levels of DRAFT - September 14,

98 treatment. Over the last 25 years, several wastewater agencies in the US have centralized their solids processing by piping or otherwise transporting solids/sludges to central or regional processing centers. Larger, centralized solids processing systems are less prone to upset conditions than smaller, decentralized systems, where adequate monitoring and control are difficult and costly. Larger, centralized solids processing systems offer significantly greater opportunities for renewable energy production than smaller, decentralized facilities. Greater odor risk is presented to the community by having several solids processing facilities, each with its own set of odor issues, control measures, and need for proper maintenance and attention. Truck traffic associated with solids processing can be channeled to more appropriate routes with centralized facilities that are properly sited. Therefore, the remainder of the siting evaluation assumes that all Bayside wastewater solids are treated at a centralized location, and solids generated at the OSWPCP continue to be processed at the OSWPCP. 8.2 Land Area Needs for Centralized Processing An evaluation was undertaken to determine the minimum land area or footprint requirements for a centralized solids processing facility. This work is contained within the SSMP Project Memorandum titled: Criteria/Footprint Requirements and Costs for the Bayside Biosolids Center and the Oceanside Biosolids Center, dated February 18, For SSMP Alternatives 1, 2, and 4, this centralized facility is located in the Bayside portion of the City and is called the Bayside Biosolids Center (BBC). For SSMP Alternative 3, this centralized facility is located at the OSWPCP site and is called the Oceanside Biosolids Center (OBC). The centralized facility is the same size and contains the same solids processing systems whether it is located on the Bayside or the Oceanside. Sizing assumptions included the following for this centralized facility: Wastewater solids projections from Section 2 of this document are used, which cover the Bayside portion of the City for the SSMP planning period, including estimated trucked brown grease quantities. Solids processing facilities are summarized in Section 5.10 of this report for a core biosolids program which includes: co-thickening, anaerobic digestion (Class B), biogas utilization, dewatering, and truck loadout. Additional facilities area is estimated to upgrade the digestion to a Class A anaerobic digestion facility. DRAFT - September 14,

99 Design and operating criteria for the facilities are defined in the Project Memorandum reference above. These criteria are used to size the facilities. Area for a future advanced biosolids processing facility is included. The area is estimated at 2.0 acres, but the specific technology is undetermined at this time. Area is included for all associated facilities such as chemical systems, odor control, electrical, instrumentation, and process control. A key assumption is that process buildings have three levels, either (1) a basement plus two levels above grade; or (2) no basement and three levels above grade. Based on these assumptions and criteria, the minimum land area required for a centralized processing facility would be 8.6 acres. A minimal area evaluation was also completed for the option whereby combined thickening/digestion/biogas utilization was conducted at one site, and dewatering/advanced processing/loadout was conducted at a second site nearby. In this case the two sites would require minimums of 5.5 and 4.2 acres, respectively, for a total of 9.6 acres. In all cases, these minimum areas or footprints do not include requirements for site or facility screening or mitigation in terms of buffer needs, perimeter landscaping, berming, or other concepts. There could also be the need for internal mitigation, depending on the specific site. Also, these areas do not include potential area for San Francisco s organic waste processing. There could be advantages to a joint processing facility for wastewater solids and food waste. Anaerobic digestion of both of these waste materials produces valuable biogas. Combining the biogas production from digestion of both these waste materials would allow a much larger electric power production or cogeneration facility to be implemented, resulting in greater renewable energy production and other benefits. Further evaluation of organic waste processing in San Francisco is underway. 8.3 Bayside Solids Site Alternatives Siting evaluations for Bayside solids processing have been underway since the mid-1990s, when it was determined that the anaerobic digestion facilities at the SEWPCP needed replacement. Site options in the late 1990s focused on parcels either part of, or adjacent to, the SEWPCP and included several variations at the existing solids processing site, as well as options across Jerrold Avenue at the Central Plants site and at the Caltrans site to the north of the plant. Site options were also examined to the north of Islais Creek near the Bay, at the Hunter s Point Shipyard area, and on a portion of the large Tuntex site in Brisbane to the south of San Francisco. A preliminary design of new solids processing facilities was developed in 2001 for the 6 ½ acre Caltrans site on the south side of Islais Creek, adjacent to I-210 and Evans Ave. This preliminary design included egg-shaped digesters. Public review of this option resulted in further discussion of facility requirements, sites, and community needs. DRAFT - September 14,

100 Sites for the Bayside Biosolids Center evaluated for the SSMP in 2006/2007 included primarily the sites shown on Figures 12 and 13. Within the SEWPCP boundary, the existing solids property south of Jerrold Avenue totals about 9.5 acres. The Central Shops portion of the site contains about 5.3 acres. These are the two portions of the SEWPCP site that could be potentially available for solids processing. In the event that the current solids area south of Jerrold Avenue is considered for the BBC, there may be an option of acquiring the private property to the southeast of that site and converting it to a buffer area. The sites evaluated for the BBC are listed in Table 31 along with their areas and other important information. It is recognized that the existing solids site at the SEWPCP (9.5 acres) may be large enough for the BBC, however, the Central Shops portion of the site is only adequate for a portion of the solids facilities, such as the thickening/digestion/gas utilization. Therefore, there is a severe limitation for the Central Shops site. Table 31 Sites Considered for BBC 2030 Sewer System Master Plan City and County of San Francisco Site Designation Gross Area (acres) Zoning (1) Building Height Limit (feet) Current Ownership Existing SEWPCP + Buffer 14.8 (2) P/M-2/R 65 CCSF (3) /Private Properties Selby Wedge 6.6 M-1 80 Private CALTRANS + Parcels A, B, 17.4 M-2 80/65 State/Private C, and D Circosta Metals 3.0 M-2 80 Private Pier 92/94 Backlands 35 M-2 40 Port of San Francisco Griffith Pump Station 8.8 P/M-1 40 CCSF/Private Notes: (1) P = Public Use; M-1 = Light Industrial; M-2 = Heavy Industrial (2) Existing solids treatment portion = 9.5 acres Central Shops portion = 5.3 acres (3) CCSF = City and County of San Francisco 8.4 Oceanside Solids Siting The existing OSWPCP is located on 12 acres of a 42.7 acre site. The site is zoned for Public Use, and is owned by the City and County of San Francisco. The solids processing facilities for the plant are located integral to the treatment plant, and include thickening, digestion, biogas utilization, and dewatering and truck loadout. It is assumed that this solids processing facility remains intact to handle the Oceanside solids production, although these solids processing facilities may need modification over time. The National Guard Armory has a long-term lease on 27.7 acres of the remaining portion of the site. DRAFT - September 14,

101 Figure 12 Sites Considered for Bayside Biosolids Center (1) (see separate pdf file) DRAFT - September 14,

102 Figure 13 Sites Considered for Bayside Biosolids Center (2) (see separate pdf file) DRAFT - September 14,

103 For SSMP Alternative 3, solids processing for Bayside production would be located adjacent to the OSWPCP. The area/footprint required for this would be the same as described above for the BBC. The only site identified for this solids processing on the Oceanside is adjacent to the OSWPCP. Other sites are not available on the Oceanside due to relatively complete urbanization. 8.5 Evaluation of Bayside Site Options The Bayside sites listed and described above are evaluated and screened here to eliminate infeasible or unsuitable properties Siting Criteria Table 32 summarizes criteria considered when screening the alternative BBC sites. Table 32 BBC Siting Criteria 2030 Sewer System Master Plan City and County of San Francisco Criteria Considerations Zoning Planned uses for property and adjacent land uses. Allowable building height. Proximity to residences. Acquisition time Shortest to longest acquisition time: Property currently owned by City and County of San Francisco Surplus property owned by another public agency Private property, willing seller Private property, use of eminent domain required Constructability Site features that would make project more or less difficult to construct. Geotechnical issues Presence of site soil or other conditions that would make structures significantly more expensive to construct. Contamination Presence of hazardous wastes or contaminated soils that require remediation. Terrain Natural hills can provide visual screening. Area - footprint Sufficient area is required for facility, including set-backs, buffers, visual mitigation, etc. Wind conditions Locations are preferred where downwind odor impacts are limited. Access Acceptable truck routes to/from the site. Other planned uses Redevelopment or recreational opportunities or needs at or Distance from liquid treatment facilities adjacent to the site Sludge pipelines and pumping costs Bayside Site Screening Evaluation The sites listed in Table 29 were screened using the criteria listed in Table 30 to determine suitability for the BBC. Table 33 presents the screening results. DRAFT - September 14,

104 Table 33 BBC Site Screening Evaluation 2030 Sewer System Master Plan City and County of San Francisco Sufficient Site Designation Area? Other Considerations Existing SEWPCP + Yes (for the Construction phasing would be Buffer Properties existing solids difficult. Close to residential site). properties. Buffer properties are No (for the privately owned. The Central Plants Central Plants portion of the site can only portion of site) accommodate a portion of the BBC facilities - a serious drawback. Selby Wedge No Railroad right-of-way separates this property from the SEWPCP, raising major access issues. Private ownership of site. Inadequate area for BBC. CALTRANS + Parcels A, B, C, and D Yes Parcels A, B, C, and D are privately owned. Railroad right-of-way intersects through the site. Site is adjacent to Islais Creek, with future recreation potential. Difficult geotechnical conditions. Circosta Metals No Site remediation is likely to be required. Private ownership. Inadequate footprint/area for entire BBC. Pier 92/94 Backlands Griffith Pump Station Yes Possibly difficult soil conditions. 40- foot allowable building height would increase footprint needs. Increased pipeline lengths to reach the site from SEWPCP. No Inadequate area for BBC considering setback and buffer/mitigation needs for the site. Truck access is poor through residential area. Significant distance from SEWPCP. Potentially Suitable? Yes (for the existing solids site) No Yes No Yes No Suitable Bayside Sites Only three of the Bayside sites are shown to be potentially feasible and adequate. Advantages and disadvantages associated with each of the three sites are presented in Table 34. The final site selection will be made after the environmental and public review process of the SSMP. If City organic waste processing/digestion/biogas utilization was to be considered in addition to wastewater solids processing, the footprint/area requirements for the joint site would need to be increased by several acres at a minimum. In this case, the existing solids site at the SEWPCP (south of Jerrold Ave) would almost certainly not have DRAFT - September 14,

105 sufficient acreage, and this site option, therefore, would probably be eliminated. However, the other two site options in Table 34 would likely have sufficient area for this enlarged operation. Truck access is also good at these two sites for the increased truck traffic expected from an organic waste processing operation Oceanside Site The existing OSWPCP site appears to be a suitable location for a centralized biosolids processing facility on the oceanside of the city References Brown and Caldwell, SEWPCP Anaerobic Digestion Upgrade Project Facilities Planning Report. Prepared for the San Francisco Public Utilities Commission, August Brown and Caldwell, Criteria/Footprint Requirements and Costs for the Bayside Biosolids Center and the Oceanside Biosolids Center. February 18, 2007 City and County of San Francisco, Preliminary Design Report Solids Handling Upgrade Project - Southeast Water Pollution Control Plant, December (Preliminary Design at the CALTRANS site) City and County of San Francisco, Site and parcel information for various potential solids processing sites. EA Engineering, Science and Technology, Alternatives Analysis Study Southeast Water Pollution Control Plant (Draft Report). Prepared for the San Francisco Public Utilities Commission. May EVALUATION OF BIOSOLIDS MANAGEMENT ALTERNATIVES This section develops and evaluates several biosolids management alternatives for San Francisco. These are developed as categories of alternatives (i.e., categorical alternatives) rather than alternatives having specifically defined processes with tankage and equipment sizing. Costing and economic analysis is completed on each categorical alternative by selecting example processes and facilities within each category that have relatively well-known costs both capital costs and annual operating costs (and revenues, if applicable). This approach can be useful in comparing the economics as well as the pros and cons of each categorical alternative. DRAFT - September 14,

106 Table 34 Suitable Bayside Sites - Advantages and Disadvantages 2030 Sewer System Master Plan City and County of San Francisco Site Designation Advantages Disadvantages Existing SEWPCP + Buffer Properties (existing solids processing site south of Jerrold Avenue) CALTRANS + Parcels A, B, C, and D Closest site to liquid treatment processes of SEWPCP. Heavy industrial and public use zoning for the process parcels. Process parcels are already owned by the City and County of San Francisco. Reasonable truck access. Heavy industrial zoning. Highest building height limit. CALTRANS parcel is owned by a public agency. Good truck and rail access. Pier 92/94 Backlands Site located in port/industrial area. Public (Port of San Francisco) ownership reduces acquisition time. Heavy industrial zoning. Large site offers construction advantages and better opportunities for site mitigation. Good truck and rail access. 1. Closest site to residential properties. 2. May require purchase of residential properties for odor/site buffer time for property purchase. 3. History of odors at the existing site may make implementation difficult. 4. Difficult to phase construction on this site due to space limitations. Existing warehouse and other commercial/industrial uses would require relocation. Privately-owned parcels increase acquisition time. Site adjacent to Islais Creek may require more mitigation or buffer. Forty-foot building height limit. Possibly difficult soil conditions. Greater pipeline length connections to/from liquid treatment plant. DRAFT - September 14,

107 Five categorical alternatives have been developed and are outlined in Table 35. All of the alternatives include, as a minimum, the mitigation/upgrading of the Bayside biosolids processing system as described in Section 5 of this document. And, for reasons explained in Section 5, anaerobic digestion is retained as the base stabilization process for wastewater solids in San Francisco. The alternatives are termed B-1, B-2, etc. to stand for Biosolids-1, Biosolids-2, etc, so they are differentiated from the SSMP s overall wastewater Alternatives 1 through 4, which are defined and evaluated in other SSMP documents. Each alternative is defined and developed within a separate section below. Table 35 Alt. # Outline of Five Categorical Biosolids Alternatives 2030 Sewer System Master Plan City and County of San Francisco Title and Key Features B-1 Retain/Upgrade Existing Class B Program - Rebuild and mitigate the Bayside biosolids processing system and continue City s Class B dewatered Cake program. B-2 Upgrade to Class A Program and Expand Uses - Rebuild/mitigate/upgrade to Class A digestion and expand uses for Class-A cake-based product program. B-3 Create Marketable Products for ~Half of Production - Rebuild/mitigate/upgrade to Class A digestion and produce marketable Class A biosolids products for horticulture/silviculture and agricultural markets with about half of City s biosolids production. B-4 Create Marketable Products for Entire Production - Rebuild/mitigate/upgrade to Class A digestion and produce marketable Class A biosolids products for horticulture/silviculture and agricultural markets for entire City biosolids production. B-5 Utilize Thermal Processing - Rebuild/mitigate Bayside biosolids System to Class B digestion, and use new/evolving thermal technologies to destroy pollutants, minimize residuals, and create products or provide other benefits. 9.1 Alternative B-1 - Retain/Upgrade Existing Class B Program The approach for Alternative B-1 is outlined by the following summary statements: DRAFT - September 14,

108 Rebuild/mitigate the Bayside biosolids processing system (currently located at the SEWPCP) as discussed previously in this report. Provide anaerobic digestion stabilization of solids to the Class B pathogen level. Continue the current City program of contracting with private companies to transport and use/dispose of the Class B dewatered cake material. Over the past 10+ years, this has included mostly land application in Northern and Central California counties, as well as Alternative Daily Cover (ADC) at landfills and occasional landfill disposal for the City s biosolids. Backup arrangements for this alternative, in case of failure of primary use outlets, would be landfilling. Such landfilling is likely to be at increasingly distant landfills over time Solids Facilities Required for Alternative B-1 For Alternative B-1 (as for all biosolids management alternatives), the Bayside solids processing facilities would be reconstructed. This includes the thickening, anaerobic digestion, biogas utilization, dewatering and cake loadout facilities. Anaerobic digestion would be provided to produce Class B biosolids for this alternative. Possible sites for these rebuilt and mitigated solids facilities are discussed in Section 6. The rebuilt facilities are referred to as the Bayside Biosolids Center (BBC) if constructed on the Bayside of the City (as part of SSMP Alternatives 1, 2, and 4) and are referred to as the Oceanside Biosolids Center (OBC) if constructed on the Oceanside portion of the City (as part of SSMP Alternative 3). In this document, this replacement facility is often referenced as being the BBC/OBC facility, depending on the SSMP alternative selected. No significant facility changes or modifications are anticipated for Alternative B-1 at the Oceanside Plant (OSWPCP) Disposition of Biosolids Materials/Residuals in Alternative B-1 There are two materials/residuals created from Alternative B-1: (1) dewatered cake biosolids material; and (2) biogas. The use of biogas would be maximized through various possible alternative systems including engines, turbines, fuel cells or other technology that is developed to convert methane gas to electrical energy, heat, or both. Anaerobic digestion reduces the quantity of raw sludge solids material by almost 50 percent (in terms of dry weight of solids). The remaining digested solids would be dewatered to a consistency of between 15 and 30 percent solids content (probably about 15 percent for belt press dewatering and about 25 percent solids for centrifuge dewatering). For Alternative B-1, it is envisioned that the City would continue to contract with private companies specializing in this business to transport the dewatered cake material from both Bayside and Oceanside to beneficial use (or disposal) locations. The availability of DRAFT - September 14,

109 traditional land application sites is becoming more restrictive over time, and contractors will need to find new areas/sites at further distances from San Francisco, such that these costs are likely to increase over time. Likewise, availability of nearby landfills for using the biosolids as ADC or availability of landfills for disposal is also becoming more limited with time. Recent evaluation by City staff shows that there are fewer landfills in Northern California that are willing or allowed to take biosolids materials today than there were several years ago, and prices for such landfill disposal at remaining landfills have risen. Figure 14 shows historical prices for truck transport and use/disposal in California for Class B dewatered cake materials. This figure shows that prices have risen dramatically in recent years. Prices have risen higher in Southern California than in Northern California, but the trend is clear within the State. Recent contracts (2006 and 2007) in Southern California have reached price levels of $60 to $70 per wet ton. The figure also shows estimates of the likely range for prices in the future based on trends in California and in other portions of the country. Figure 14 Price Range for Biosolids Cake Disposition in California As prices rise, there are greater potential areas that could be considered for land application and landfill use/disposal. Transporting the biosolids materials 200 miles or more is often economical at prices of about $50 per wet ton. Biosolids in Southern California are DRAFT - September 14,

110 sometimes transported over 300 miles to sites in Arizona or Nevada. Therefore, if/when prices rise to the range of $50 to $60 per wet ton in Northern California, additional potential sites and use areas could become available. Transporting Class B cake by rail to Nevada or even Utah has been suggested as potentially feasible if prices rise to levels of about $70 per wet ton. However, use/disposal at out-of-state locations is not considered to be politically acceptable in the long-term. If Northern California hauling and use/disposal prices rise to the range of say $60 to $80 per wet ton and higher in coming years, contractors may develop biosolids processing centers. Sometimes these operations are called Merchant Facilities, to identify them as private company facilities, whereby the company has contracted with one or more municipalities to have their biosolids materials brought to these sites for processing and final disposition. These facilities could include composting operations or could involve other types of processing to produce marketable biosolids products for Northern California. These types of facilities and contractor operations have risks for agencies contracting with them, but there are also potential advantages. At this time, it is unknown if these types of private processing centers (Merchant Facilities) would be developed, whether the products or materials produced would be acceptable to users long-term, and whether the operations would be profitable at competitive price ranges. Clearly, there are significant risks and issues for Alternative B Alternative B-2 - Upgrade To Class A Program and Expand Uses The approach for Alternative B-2 is outlined here: Upgrade the solids processing systems at both Bayside and Oceanside to Class A, advanced digestion processing for the entire solids production of the City. Improve the characteristics of the dewatered cake material to minimize objections by the public, users, and regulatory agencies. Continue the practice of contracting for hauling and final use/disposition of the Class A cake biosolids materials. By creating Class A biosolids, there are reduced risks and greater acceptance of the material by the public and users. New product uses and users are likely with Class A biosolids (over Class B), and opportunities may exist for contractors to create marketable products from the Class A cake Solids Facilities Required for Alternative B-2 A key objective of Alternative B-2 would be to improve the characteristics of the digested, dewatered cake material as indicated here: DRAFT - September 14,

111 Increase the stability of the biosolids material, so that it has reduced odor and has very little attraction to vectors. Create a pathogen-free, or Class A, biosolids material/product. Improve the visual characteristics of the material/product by removing plastics, other debris, and extraneous materials. Dewater the biosolids to a higher degree to improve the cake appearance, enhance handleability as a bulk solid material, and improve the potential for creation of more marketable materials. For Alternative B-2, the BBC/OBC would be reconstructed and an advanced digestion process would be used to produce Class A biosolids. As discussed in Section 5, several potential digestion (and perhaps pre-digestion) processes are available for this purpose. Such advanced digestion processes also typically destroy a somewhat larger amount of volatile solids, thus reducing the final dry weight of biosolids, usually by about 5 to 10 percent. Increased gas production and energy recovery are also achieved by destroying more solids in the digestion process. For some processes, significant improvement in dewatered solids content is realized. These benefits can offset much of the additional incremental cost of an advanced, Class A digestion process. Additional upgrades to solids processing would probably include screening for debris removal, so that the final Class A cake material has the best chance of acceptability. At the OSWPCP, the digestion process would be upgraded to Class A by the addition of a supplemental process several such processes are available as described in Section 5. Screening to remove debris would also be a logical addition at the OSWPCP. Energy recovery facilities would be used at both Bayside and Oceanside to make maximum use of the digester gas, probably producing both electrical power and heat Disposition of Biosolids/Residuals for Alternative B-2 As with Alternative B-1, there are two types of products/residuals created from Alternative B-2 facilities: (1) dewatered cake biosolids material; and (2) biogas. Since about 10 to 20 percent greater gas production is likely with the advanced digestion systems of Alternative B-2, energy recovery would be commensurately increased over Alternative B-1 (electrical power, heat, or both). The dewatered cake material in Alternative B-2 has significantly improved characteristics over that produced in Alternative B-1, with the primary feature involving Class A or pathogen-free biosolids in Alternative B-2. This feature, along with the other improved biosolids characteristics discussed, would be strong reasons for improved long-term acceptability by the public, product users, and regulatory agencies responsible for safe biosolids beneficial use practices. Some California counties have implemented ordinances DRAFT - September 14,

112 requiring that only Class A biosolids materials be used in agricultural land application or related practices within those counties. In response to these ordinances, several California wastewater agencies have proceeded to upgrade/modify their solids processing system so that they produce Class A materials. California county biosolids ordinances are continuing to be modified over time, with some counties implementing or attempting to implement a complete ban on biosolids land application. In addition to Class A requirements, some ordinances require additional monitoring of the biosolids, or place other requirements and restrictions on the land spreading operations and on the agencies or private companies involved. By producing Class A dewatered cake materials, the City would provide opportunities for development of further processing arrangements to create more marketable products. One example of this is the system developed by the City of Tacoma, Washington. At Tacoma, the wastewater department staff has developed its own set of products under the trade name of Tagro. The digestion system at Tacoma s Central Wastewater Plant produces Class A biosolids, and following dewatering, the staff mix the cake with sand and sawdust in varying percentages to produce bulk Class A products used for landscaping and related uses in the Tacoma area. The products are sold directly by Tacoma. Other communities are evaluating Tacoma s success with this approach. City of San Francisco staff could evaluate similar post-dewatering processing and product marketing/distribution, and determine if this has potential. The major point here is that once Class A dewatered cake is produced, there are likely opportunities for product development and use. The costs (and potential revenues) for such an approach need further research and evaluation. It is unlikely that Class A dewatered products would become revenue-generators, but producing such Class A material could make uses available within shorter distances of San Francisco, thus reducing the costs of final transportation. 9.3 Alternative B-3 - Create Marketable Products for ~Half of the Production The approach for Alternative B-3 is outlined here: Rebuild/mitigate/upgrade the solids processing system at Bayside and Oceanside to Class A, advanced digestion. Implement advanced biosolids processing to create one or more marketable biosolids products i.e., Class A products having much improved characteristics over dewatered cake material. The capacity envisioned for these products is about half of the City s biosolids production. DRAFT - September 14,

113 The remainder of the City s biosolids production would be produced as a Class A dewatered cake material, and it is envisioned that private contractors would continue to transport and use the cake material in Northern and/or Central California. Backup arrangements for this alternative, in case of failure of primary use outlets, would be landfilling of biosolids. In this case, either dewatered cake or marketable product material could be landfilled in emergency, however, due to the value of the marketable products, there are likely to be outlets other than landfill Solids Facilities Required for Alternative B-3 For Alternative B-3, reconstruction of the Bayside solids processing facilities is required, similar to previous alternatives (i.e., thickening, digestion, biogas utilization, dewatering and cake loadout). The digestion process would provide Class A biosolids at both the BBC/OBC and at the OSWPCP. A major requirement for Alternative B-3 is to provide advanced biosolids processing facilities that would create marketable biosolids products. We define marketable products as biosolids products that: Are bought and sold in an organized system, Have characteristics that are significantly or greatly improved over a dewatered cake material, and Meet Class A or pathogen-free requirements, as well as chemical or other pollutant limitations for use by the public. Examples of such marketable products are a compost product and a heat-dried and granulated/pelletized product. Such products could also include nutrient-fortified Class A materials, or partially dried and blended Class A materials. A major issue in providing this further processing system within San Francisco is that the process would need to be conducted within a relatively small footprint site. Composting is a process that is not feasible on small sites (of a few acres) because considerable area is required for the long detention times required for the process, as well as areas for bulking agent storage and transfer, and land for curing piles, stockpiling, and product loadout. Even a small capacity composting system would be difficult to site in San Francisco unless areas of say 20 to 50 acres could be made available at the Presidio, Golden Gate Park or another location. Even if sites this large were located, there may be considerable concern about odor emissions and odor impacts that would be difficult to overcome. Therefore, at this time, it does not seem reasonable to consider a composting operation unless it was operating on a limited capacity and was fully contained with very reliable and highperformance odor control systems. DRAFT - September 14,

114 Heat drying of biosolids (producing a granulated/pelletized product) is an example of a Class A biosolids process that has been implemented successfully on small footprint sites in urban areas. Area requirements for drying half of the City s biosolids production (about 30 to 40 dry tons/day) could be as low as about 1.5 acres. Adequate odor control might be challenging for a small-footprint heat drying operation in San Francisco, however, there are odor control systems available that should be able to meet even the stringent odor control requirements needed for the SSMP. For this size range of facility anticipated, a single equipment train would be a logical approach for maximum cost-efficiency. This approach provides for planned shutdowns of the advanced processing facility. When the advanced processing facility is not operating, then the only product is dewatered cake material, so that during these periods, the City would need to provide for disposition of the entire cake production. To evaluate Alternative B-3 and be able to compare it with other alternatives, the assumption is made here that marketable products such as a heat-dried and granulated/pelletized product could be produced, and such a facility could be sited as part of the BBC/OBC. This assumption allows costing work and economic analysis to proceed on this alternative. Innovations are occurring in low-temperature biosolids drying, solar drying, and related fields that could offer advantages to San Francisco if a few acres of land were available. There is likely to be considerable excess waste heat in the form of hot water available from the cogeneration facilities. The hot water might be used to advantage in an innovative drying operation for a portion of the Class A cake, to achieve say 50 or 60 percent solids (i.e., partial drying). This is an option to heat drying, or as supplemental to heat drying, to significantly reduce the need for outside fuel usage for drying. This option needs further research and development to determine its feasibility and to determine the type of product(s) that could be created and their potential use or marketability Disposition of Biosolids/Residuals for Alternative B-3 For Alternative B-3, there are three types of products/residuals that are created from the biosolids processing system: (1) dewatered cake biosolids material; (2) biogas; and (3) one or more marketable biosolids products. Biogas would be used for its energy value either within a cogeneration arrangement, or as a fuel for the advanced biosolids processing system (as a fuel for a heat drying operation, as an example). The marketable product that is developed using about half of the City s biosolids production would be distributed and sold within San Francisco, the San Francisco Bay Area, and perhaps wider distribution depending on the type of product and its market situation. Recent biosolids product marketing work by BACWA for a good-quality heat-dried product showed that there is sufficient demand in the Bay Area and Northern California for even larger quantities than discussed for Alternative B-3. There are several options concerning how DRAFT - September 14,

115 such a product is actually marketed and distributed, and often a specialized company is used to handle this aspect of the program. For agencies with small production quantities in rural areas, the marketing and distribution is handled more casually, but for production quantities at San Francisco, a well-organized system is required to insure that product is moved out of the production site on a regular basis, and any further processing for bulk or bagged sales is probably handled at another location by the distribution and marketing firm. For the other half of the City s biosolids production, the City would continue to contract for dewatered cake hauling and use/disposal at locations in Northern California. The dewatered cake from the plants would be Class A biosolids. 9.4 Alternative B-4 - Create Marketable Products for Entire Production The approach for Alternative B-4 is outlined here: Rebuild/mitigate/upgrade the solids processing system at the BBC/OBC to provide Class A, advanced digestion. Upgrade the OSWPCP solids processing system to Class A digested material. Implement advanced biosolids processing to create one or more marketable products i.e., Class A products similar to that described in Alternative B-3. The capacity envisioned for these products is the entire City s biosolids production, or as nearly close to 100 percent as possible. The production of such Class A products could be located at each of the two plants, or a centralized facility could be implemented Under this alternative, dewatered cake material would typically not be hauled out of the City unless this cake material would become a biosolids product elsewhere. Backup arrangements for this alternative, in case of failure of primary use outlets, would be landfilling of biosolids, use as ADC or other outlet. Either dewatered cake or marketable product material could be landfilled in emergency Solids Facilities Required for Alternative B-4 The major requirement for Alternative B-4 is to provide advanced biosolids processing facilities that would create marketable biosolids products. These products would be the same as defined previously under Alternative B-3. The difference for Alternative B-4 is that 100 percent of the City s biosolids production would be processed in this advanced system to produce marketable products. Therefore, to be reliable for 100 percent of the production, the advanced processing system would need to be sized to handle the peaks in production and also have a degree of backup and reliability that would be subject to further assessment. Advanced biosolids processing could be located at both the OSWPCP and at the BBC/OBC, or a centralized facility would be an option. DRAFT - September 14,

116 A major issue in providing this further processing system within San Francisco is that the process would probably need to be conducted within a small footprint site as discussed above for Alternative B-3. As discussed in that section, composting does not seem feasible to be operated with San Francisco except perhaps at small scale in a highly-odor-controlled situation. Heat drying facilities (producing a granulated/pelletized product) represent an example of a Class A biosolids process that has been implemented successfully on small footprint sites in urban areas. Area requirements for drying all of the City s biosolids production (about 80 to 90 dry tons/day) could be as low as about 2 acres on a centralized facility, and somewhat less than this for smaller capacities. To evaluate Alternative B-4 and be able to compare it with other alternatives, the assumption is made here that marketable products such as a heat-dried and granulated/pelletized product could be produced, and such a facility would be sited as part of the BBC/OBC and at the OSWPCP. This assumption allows costing work and economic analysis to proceed on this alternative As discussed for Alternative B-3, various innovative drying concepts might be explored to reduce the extreme energy requirements for thermal drying. The disadvantage of this option is that almost certainly more land would be required likely several acres as a minimum Disposition of Biosolids/Residuals for Alternative B-4 For Alternative B-4, there are several types of products/residuals that could be created from the biosolids processing system on a normal basis: (1) biogas; and (2) one or more marketable biosolids products. Biogas would be used for its energy value either within a cogeneration arrangement, or as a fuel for the advanced biosolids processing system (as a fuel for a heat drying operation, as an example). The marketable product(s) that are developed using the entire City s biosolids production would be distributed and sold within San Francisco, the San Francisco Bay Area, and perhaps wider distribution depending on the type of product and its market situation, similar to Alternative B-3. Recent biosolids product marketing work by BACWA for a good-quality heat-dried product showed that there is sufficient demand in the Bay Area and Northern California for the quantities required under this alternative. There is the opportunity to create different marketable products at each of the two treatment plants. At the BBC/OBC, for instance, a heat-dried product could be produced for horticulture, silviculture and even agriculture. At the OSWPCP, a different type of process could be utilized to create a different product, thus providing more diversity to the City s biosolids program. Or, if the innovative drying option proved feasible, that approach may create another different product. On a normal basis for Alternative B-4, there would probably be little dewatered cake material removed from the City for use or disposal, since most material would be processed into marketable products locally. However, if the advanced biosolids processing systems DRAFT - September 14,

117 were not working properly, or there was excessive equipment down for maintenance or repair, dewatered cake material would need to be removed from the treatment plants for a period of time. This material could be transported to landfill if there were no beneficial use outlets for the material. Over time, however, landfilling is expected to become more restrictive in Northern California, such that transport distances to acceptable landfills would be longer. 9.5 Alternative B-5 - Utilize Thermal Processing The approach for Alternative B-5 is outlined here: Rebuild/mitigate/upgrade the solids processing system at the BBC/OBC to Class B digestion. Continue to dewater the Class B biosolids to cake form at the OSWPCP and Bayside. Utilize thermal processing systems to minimize the final end use/disposal of the biosolids on land or as products for soil conditioning. These thermal processes destroy or modify the organic material within biosolids such that fuels, construction products, or other materials are created. Backup arrangements for this alternative, in case of failure of the thermal processing systems, or in those instances when equipment is down for maintenance and repair, would be landfilling of dewatered cake biosolids. As indicated, landfilling over time is likely to be at increasingly distant locations Solids Facilities Required for Alternative B-5 For Alternative B-5, reconstruction of the Bayside solids processing facility is required, similar to previous biosolids alternatives. The digestion process would provide Class B biosolids. Little, if any, changes would be required at the OSWPCP for the digestion process. This alternative would provide final biosolids processing within one or more thermal processing systems. By the term, thermal processing systems, we mean one of several potential types of system that exist or are being developed to destroy volatile solids and create fuel or other types of final products. Examples are: Pyrolytic processes are conducted at various pressures and temperatures, and create a fuel char having high solids content, typically. These chars can be used as fuel in cement kilns and biomass to energy facilities. Gasification processes are driven by partial pyrolysis, normally to create a combustible gas along with solid residues of tar or char. The gas would be combusted to create energy that is recovered through heat-recovery systems (i.e., steam from a heat recovery boiler). DRAFT - September 14,

118 Vitrification is the melting of biosolids at high temperatures with oxygen. The organics are burned off and the inorganics melt to form an aggregate or similar construction product. Wet oxidation in various forms. Historically, the Zimpro process (and similar processes) were used, but oxidation in higher temperature/pressure processes can fully oxidize organic material, resulting in ash residues. Ash residues can have beneficial uses in construction. Some or many of these thermal processing systems are still in the developmental stage, although some full-scale installations are operating in North America and overseas Disposition of Residuals for Alternative B-5 The residuals from these thermal processing systems would be used for other-than-land application or other-than-soil fertilization approaches. The residuals would be solid fuel or construction materials, pyrolytic gases for combustion, or other types of residuals. If a fuel char is used in cement manufacturing, these biosolids residuals end up as part of the cement product. If the fuel char, tar, or oil is used as part of a biomass to energy facility, the ash material from combustion would be the final residual. Vitrification would result in aggregate material used in construction. And, ash residuals could become part of construction as roadway base or other use. These methods of final residuals disposition are attractive in the long-term because the organic material and organic pollutants would be largely or completely destroyed (i.e., oxidized) by the thermal processing system. And, the residual inorganic materials become part of a product matrix i.e., within fuels, road base, concrete, or other product. If fuel materials are created, the final combustion product that results is often ash, which can be a useful material, not necessarily disposed to landfill. However, if final ash residues are disposed to landfill, they represent only a fraction of the original biosolids quantity. 9.6 Economic Comparisons The operating and overall annual costs for the five biosolids management alternatives are developed here and compared. Costs for each alternative are developed from costs known for similar facilities in other locations, taking into account the differential price levels between locations. Costs for these categorical alternatives are shown within ranges, since these alternatives are not highly defined at this point Basis for Costs For all five biosolids management alternatives, the current Bayside solids facilities need to be replaced and mitigated and this represents a base program applicable to all options. Therefore, the costs of constructing the BBC/OBC as a Class B digestion system along with thickening, dewatering and gas utilization are not used in the alternative cost comparisons. DRAFT - September 14,

119 All costs for facilities beyond mesophilic, Class B digestion and dewatering, are included in this economic comparison. The major cost factors for the biosolids alternatives are summarized here: Hauling and Use/Disposition. The most significant operating cost factor for many years (and at least for the near-term future as well), is truck hauling and use/disposal/disposition of the dewatered cake material. A wide range of future costs for this factor is used in this analysis to attempt to provide cost sensitivity on this issue. For estimating near the midpoint of the planning period (2018), this becomes speculative; however, various information used to develop Figure 14 would indicate that for Class B cake, a range of $55 to $110 per wet ton is not unreasonable. For Class A cake, we estimate that a 10 percent cost reduction (over Class B cake) may be supportable in the future, to account for likely advantages in use/disposition of Class A biosolids cake. Therefore, a range of $50 to $100 per wet ton is used for Class A cake hauling and use/disposition. Class A Digestion. Incremental costs to implement Class A digestion (over Class B digestion) have been determined for both the BBC/OBC and for the OSWPCP. There are several Class A digestion and pre-digestion processes that could be used for this purpose (see Section 5), and we have selected representative processes for costing purposes. For the BBC/OBC, we used thermophilic digestion in batch tanks as a basis for costs, and for OSWPCP, we used thermal hydrolysis (prior to mesophilic digestion) for the cost basis. Operating cost increases for Class A digestion (over Class B digestion) are largely (and perhaps entirely) offset by increased gas production and value of additional electrical power. The impact is too small to affect overall alternative economics, and, therefore, is not considered. Reduced Cake Quantities With Class A Advanced Digestion. Several different advanced Class A digestion processes are available. Besides producing Class A biosolids, these processes either destroy more volatile solids during digestion or result in improved cake solids content, or both. As a general rule, these processes typically provide about 10 percent less final weight of dewatered cake material than a comparative Class B mesophilic digestion process. Some processes would provide more than 10 percent, and some less than this. For the economic comparisons here, we have chosen to use a 10 percent reduction as an average situation. Advanced Biosolids Processes. As indicated, the advanced biosolids process that might be used for Alternative B-3 and B-4 is unknown at this time. However, for economic evaluation, we have assumed this is a thermal drying facility that would create a Class A marketable product that is different from biosolids cake products and is acceptable to many users. Capital and O&M costs (and potential revenues) for this type of facility are known from other projects. Large quantities of energy are used in such drying facilities and, typically, natural gas has been the fuel used. This use of non-renewable fuel is a major disadvantage. Biogas from anaerobic digestion might DRAFT - September 14,

120 be used in drying if the drying operation was conducted full-time (24 hrs/day, 7 days/week) and had the reliability of using the biogas on a continuous basis. In reality, however, this has proven difficult at other plants and few facilities attempt this. Furthermore, if the biogas is used for thermal drying, it would not be available for use in cogeneration and power production. Thermal Processing. The thermal processing category includes technologies which are still evolving and being developed, and, therefore, this category is the most difficult one for estimating costs. We have chosen to use costs for incineration and similar processing at this time. Again, as for advanced biosolids processing technologies, fuel usage from non-renewable fuels could be an issue Cost Development Table 36 presents the costs that have been developed based on the previous discussion of these categorical biosolids management alternatives. In the table, costs are presented in $millions or in $millions/year and the size of the range is an indication of the uncertainty associated with each major cost factor. A factor of 30 percent has been added onto construction costs to account for soft costs such as engineering, administration, legal, construction management, and similar costs. All capital costs are brought to an annual cost basis using 30 years at 5 percent interest. Table 36 Alternative Costs for Biosolids Management Alternatives 2030 Sewer System Master Plan City and County of San Francisco Capital Cost Range Annual O&M Cost Range B-1 Retain/Upgrade Existing Class B Program B-2 Upgrade to Class A Program and Expand Uses None required beyond Class B rebuild at BBC/OBC. Class A Digest BBC/OBC = $50 to 55 mil Class A Digest OSWPCP = $25 to 30 mil Total Construction = $75 to 85 mil + 30 % Soft = $22 to 25 mil Total Capital Cost = $97 to 110 mil Annualized Capital = $6 to $7 mil/yr Hauling + use/disposalrange of $55 to $110/wet ton - $6 to 12 mil/yr O&M of Class A digestion offset by gas production. Hauling + use/disposal range of $50 to $100/wet ton = $5 to $10 mil/yr. DRAFT - September 14,

121 Table 36 Alternative Costs for Biosolids Management Alternatives 2030 Sewer System Master Plan City and County of San Francisco Capital Cost Range Annual O&M Cost Range B-3 Create Marketable Products for about Half of Production B-4 Create Marketable Products for Entire Production B-5 Utilize Thermal Processing Class A Digest BBC/OBC = $50 to 55 mil Class A Digest OSWPCP = $25 to 30 mil Adv. Process = $30 to 40 mil Total Construction = $105 to 125 mil + 30 % Soft = $31 to 38 mil Total Capital Cost = $136 to 163 mil Annualized Capital = $9 to $11 mil/yr Class A Digest BBC/OBC = $50 to 55 mil Class A Digest OSWPCP = $25 to 30 mil Adv. Process = $70 to 100 mil Total Construction = $145 to 185 mil + 30 % Soft = $44 to 55 mil Total Capital Cost = $189 to 240 mil Annualized Capital = $12 to $16 mil/yr Thermal Processing = $180 to 220 mil +30% Soft = $54 to 66 mil Total Capital = $234 to 286 mil Annualized Capital = $15 to 19 mil/yr O&M of Class A digestion offset by gas production hauling + use/disposal for 50,000 tons/yr = $3 to $5 mil/yr. Drying O&M at $90 to $110/wet ton for 45,000 wet tons/yr = $4 to $5 mil/yr Drying O&M at $90 to $110/wet ton for 95,000 wet tons/yr = $9 to 11 mil/yr. Hauling and use/disposal of cake material is small at ~ 3,000 tons/yr for <$0.3 mil/yr, so this is not used in the calculations. O&M for thermal processing at $120 to $150 per wet ton = $13 to 18 mil/yr. Annual costs are based on quantities estimated to occur at the mid-point of the planning period about For instance, dewatered cake quantities for Class B cake are estimated to total 106,000 wet tons/year at this midpoint. Dewatered cake quantities for Class A cake are estimated to be 10 percent less (95,000 wet tons/year) at the midpoint. Figure 15 compares the total annual costs for the five biosolids management alternatives. DRAFT - September 14,

122 Figure 15 Biosolids Management Alternatives 9.7 Evaluation of the Alternatives The comparison or evaluation criteria are presented and discussed here. The evaluation and comparison is then conducted on the biosolids management alternatives Evaluation Criteria Table 37 presents the evaluation criteria. The criteria are defined within five categories as follows: Technical and Risk Criteria Customer Service and Local Criteria Environmental Criteria Recycling and Sustainability Criteria Economic Criteria DRAFT - September 14,