Maximizing Resource Recovery from Biosolids: Notes from an Unapologetic Scavenger

Transcription

1 Maximizing Resource Recovery from Biosolids: Notes from an Unapologetic Scavenger Andrew Carpenter Northern Tilth

2 Cleaning our waterbodies should not be the only goal of wastewater treatment With the implementation of the Clean Water Act, wastewater treatment plants were built to collect the solids from the wastewater As a result rivers are cleaner and we can use the captured organic matter and nutrients to build soil fertility, returning us to a natural cycle of using our organic matter based by-products to grow crops

3 Organic Matter Transformations in Soil Organic N Organic C (energy source) C assimilation Microbial attack N Mineralization N assimilation NO 3 - Plant-available nitrogen in a slowrelease form Mature Soil Organic Matter (Soil Humus) Improving soil fertility through the addition of organic matterbased residuals is a primary tenet of sustainable agriculture Healthy soil ecosystem Long-term pool of soil nutrients Reduced erosion Feeding soil not just crops

4 The Value in Biosolids Nutrients Macro-Nutrients Nitrogen (5%) Phosphorus (2%) Calcium Micro-Nutrients Zinc Copper Molybdenum Organic Matter In Soil Food for soil microbes Builds Soil Tilth Erosion Resistance Water-holding capacity Ability to retain nutrients Organic Matter For Energy Recovery Energy in the chemical bonds of organic matter oxidation 22,000 Btu/kg dry solids (undigested) In the ballpark of lower grade coals

5 6.5 Million Dry Metric Tons of Municipal Wastewater Solids Generated Annually in the U.S. Level of Treatment 60% Class B 40% Class A Data excerpted from National Biosolids Regulations, Quality, End Use and Disposal Survey, 2007 (2004 data)

6 Overall Trends in Wastewater Solids Management The amount being recycled to soils versus the amount going to landfills or to incineration appears to have been steady from the mid 1990s through 2004

7 Overall Trends in Wastewater Solids Management There appears to a trend of WWTPs switching to Class A technologies

8 Anecdotal Evidence of Trends with biosolids use/disposal in Maine Recycling Rates approximately the same (85% 82%), but significant shift to Class A processing

9 Class A versus Class B in the Northeastern U.S. Greater Lawrence Sanitary District, Massachusetts Benefits Digester Gas is used as fuel for the dryer Solid market for the biopellets Selling for between $15 - $25 per ton (worth closer to $50 per ton for nitrogen and phosphorus replacement alone) Increased interest from farmers as fertilizer prices have risen General distribution no site-specific permitting

10 Shift from Incineration for Disposal to Energy Recovery ***As a national trend, this represents an important shift from viewing incineration simply as a method for reducing volume of wastewater solids*** Maximizing energy recovery should include Using undigested solids De-watering efficiently, and ensuring that the energy lost in evaporating water from solids is significantly less than the energy provided by oxidizing the organic matter in the solids Greater New Haven Water Pollution Control Authority Installed a heat recovery system on an existing multiple hearth furnace Generating approximately 0.5 MW of electricity from steam turbine run off of the collected heat from incinerating approximately 40 dry tons per day of wastewater solids (26% solids) 5.5 year payback on the project

11 Stabilization Processes for Biosolids Used as Soil Amendments Data excerpted from National Biosolids Regulations, Quality, End Use and Disposal Survey, 2007 (2004 data)

12 Trends in Biosolids Chemical Quality Pretreatment and Regulatory Controls Reduced Cd in PA Biosolids (Stehouwer) Cd concentration (mg kg -1 ) Cadmium Median r 2 = th Percentile Error bars range from 25 th to 75 th percentile PSU data only Slide provided by Dr. Rufus Chaney, USDA Year 0

13 Triclocarban: An example of a personal care product in biosolids Triclocarban in anti-bacterial soap 15,000 ppm Biologically Degraded Compounds CO 2 and H 2 O Effluent Soluble Compounds Wastewater Triclocarban Influent Triclocarban in biosolids 30 ppm (450 X lower concentration than in the soap) Nutrients Organic Matter Insoluble, non-volatile compounds Wastewater Solids

14 Public Perception Fears shifting as the material changes As metal levels decrease, PCPs are a bigger focus Fear of feces (pathogenic concerns) is always there Public resistance to recycling biosolids can have an impact on choice of biosolids management

15 Opportunities in the Future Assumptions 30% of U.S. wastewater solids are landfilled, and half of the 15% of solids incinerated have no associated energy recovery 2.4 million dry Mg/year not utilized All of this would instead go to anaerobic digestion and the anaerobically digested biosolids would be land applied 75% volatile solids on a dry wt. basis 60% volatile solids reduction during anaerobic digestion 75% of nitrogen eventually available for plant uptake gallons of fuel oil used per kg of nitrogen fertilizer produced 40% plant availability of phosphorus in biosolids 650,000,000 m 3 of natural gas use avoided 90,000 Mg/year of nitrogen fertilizer use avoided Additional savings of 44,000,000 gallons of fuel oil 42,000 Mg/year of phosphorus fertilizer (as P 2 O 5 ) use avoided

16 Peak Phosphorus? 90 year supply of economically recoverable phosphorus at current rate of use Population pressures will likely increase demand Geopolitical concentration of phosphate rock deposits Possibility of increased environmental risks with untapped deposits

17 International Trend of Working to Minimize Greenhouse Gas Emissions Hypothetical WWTP GHG Calculations Using the CCME Calculator Utility treating 150 MLD (40 MGD) of wastewater Population of 215,000 people 9000 dry Mg of undigested sludge/year (36,000 Mg at 25% solids) GHG Emissions factors for electricity generation from the mid-atlantic region

18 CO 2 Equivalence (Mg/year) Combined Scenarios (each scenario includes thickening, de-watering and transport) Energy recovery Cold wet climate transport o C 25% solids Digested solids No recovery 900 o C 30% solids undigested Energy recovery Cement replacement Class A using recycled lime source such as CKD 65% heat 30% elect. 1% fugitive Landfill Incineration 1 Incineration 2 Class A Alkaline Land Ap Anaerobic dig. Land ap

19 Spent Gravel Pit No on Site Reclaimed as Topsoil Hay Field Resource Management, Inc. used Topsoil Manufactured a combination of papermill residuals and GLSD biopellets

20 Reclaimed as Hay Field Resource Management, Inc. used Topsoil Manufactured a combination of papermill residuals and GLSD biopellets Increasing trend towards getting the most benefit out of residuals by combining materials for improved overall performance (instead of simply trying to figure out how to get rid of as much as possible without doing damage)

21 Trace Metals/Micro-nutrients added by Biosolids to Topsoil Trace Metal SPF from a deink mill Sub Soil Used for Topsoil Blending Calculated Concentration in Topsoil without Biosolids Massachusetts, USA Soil Average Manufactured Topsoil with SPF and Biosolids mg/kg dry weight Number of Samples 10 6 NA 8 17 Arsenic Copper Lead Zinc

22 Opportunities for Utilization of Incineration By-products Wastewater solids incinerator ash High in phosphorus and micro-nutrients (particularly copper and zinc) Can be used as a feedstock in cement kilns Residuals from gasification and pyrolysis are likely to have some benefit as soil amendments as well

23 Concluding Remarks Use It or Lose It!