SEPTAGE BIOREACTOR LANDFILL PROJECT SMITHS CREEK LANDFILL COUNTY OF ST. CLAIR, MICHIGAN, USA

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1 SEPTAGE BIOREACTOR LANDFILL PROJECT SMITHS CREEK LANDFILL COUNTY OF ST. CLAIR, MICHIGAN, USA Prepared by Xianda Zhao, Ph.D., P.E., Te-Yang Soong, Ph.D., P.E., Morgan Subbarayan, P.E. CTI and Associates, Inc., Wixom, Michigan Matthew Williams, Environmental Services Director County of St. Clair, St. Clair, Michigan This paper is prepared to summarize the findings to date for the Bioreactor Landfill project at the Smiths Creek Landfill, owned and operated by St. Clair County, Michigan. The purpose of the project is to demonstrate the impact to landfill operations and waste degradation as a result of subsurface injection of residential septage into municipal solid waste. While research is ongoing, several important findings have been made and the potential benefits to the management of solid waste are numerous. Important legislative changes are needed in order to secure the future of this technology so it may be utilized by other landfills across the U.S. 1.0 BACKGROUND In 2005, the County of St. Clair, Michigan (the County) was looking for ways to extend the life of the existing County-owned landfill (Smiths Creek Landfill, SCL) while addressing concerns associated with run-off from the land application of septage in the predominately rural County. Hence, the concept for a septage bioreactor landfill project was born. Essentially, by injecting septage into the landfill, Michigan s important water resources could be protected, with the added benefit of increasing the rate of waste degradation in the landfill and helping to extend its useful life. At the time, the State of Michigan prohibited the introduction of liquids other than leachate in to landfills. Therefore, the County worked with local legislators and the Michigan Department of 2005 Project inception 2006 Regulatory changes allow for RDDP 2007 Permit issued 2008 injection begins; project underway Figure 1. Project Timeline Page 1 of 10

2 Environmental Quality (MDEQ) to amend Michigan s 1994 Public Act 451 to allow for the injection of septage under a Research, Development, and Demonstration Project (RDDP) permit. In 2007, the County was issued a permit to construct the RDDP and in 2008, septage injection began (see Figure 1 for more project timeline information). 2.0 SYSTEM LAYOUT Bioreactor Landfill Cells The RDDP consists of one landfill cell divided into two sections, designated as Cells 3A ( Bioreactor Cell) and 3B (Leachate Bioreactor Cell). During construction, liquid injection and gas extraction lines (as well as a variety of other monitoring devices) were installed in each cell as filling progressed. generated by residential sources (septic tanks) was delivered to the site and introduced into Cell 3A ( Bioreactor Cell), while leachate generated on-site was introduced into Cell 3B (Leachate Bioreactor Cell). Extensive monitoring of a variety of parameters was conducted in order to provide a comparison of the performance of each cell. Receiving Station The septage receiving station (Figure 3) constructed at the project site includes a drive-through unloading area, a septage processing unit, an odor control system (bio-filter) and an underground lift station. received is first processed to remove larger solid objects before being temporarily held in underground lift station tanks and then transmitted through a forcemain to the septage holding and sludge separation system. The system was designed and constructed to process and maximum of 23,000 gallons per day of incoming septage. Odor controlling (Bio-filter) Leachate Bioreactor (Cell 3B) Bioreactor (Cell 3A) Underground lift station Storage Unloading Receiving Figure 2. Site Aerial Photo Solid Figure 3. Receiving Facility Leachate Storage Leachate Pretreatment GTE Plant Processing Unit Liquid Page 2 of 10

3 Holding and Sludge Separation System Two 50,000-gallon collapsible tanks (Figure 4) were deployed to allow for sludge separation and volume accumulation. The sludge accumulates in the bottom of the first tank and the supernatant flows into the second tank. The sludge that accumulates in the first tank is removed and disposed periodically in the landfill. Figure 4. Sludge and Liquid Holding Tanks (Liquid) Injection System After the sludge separation process, the liquid is injected into the liquid injection lines embedded in the solid waste mass (Figure 5). The injection lines were constructed using perforated pipes and embedded in stone mounds to improve the liquid distribution into the waste. The injection lines were installed at strategically arranged, pre-determined locations during the waste filling process. Both vertical and lateral distances between Figure 5. Subsurface Liquid Injection Line the injection lines were designed to optimize the moisture distribution. An injection manifold (Figure 6) was used to selectively control the flow of liquid into predetermined injection lines. During the septage injection event, liquid accumulated in the second tank is directed to the preselected injection Figure 6. Injection Manifold line(s) in the Bioreactor Cell. A flow meter, actuated valves and a batch processor are used to control the injection volume to each line. Leachate accumulated in the on-site leachate storage tank (receiving leachate from entire site) is injected into the Leachate Bioreactor Cell. Landfill Gas Extraction As a byproduct of waste degradation, landfill gas (typically 50% methane and 50% carbon dioxide), is generated. In order to capture and quantify landfill gas generated by the septage bioreactor, landfill gas extraction lines were constructed. These extraction lines were constructed similarly to the liquid injection lines. Each LFG extraction line consists of a perforated pipe placed within a stone mound (Figure 7). To minimize the potential of liquid migration into the LFG extraction system, the LFG Page 3 of 10

4 extraction lines were constructed directly above liquid injection lines. Additionally, gas extraction lines and liquid injection lines were constructed on alternating waste lifts to further limit the potential of liquid intrusion into the LFG extraction lines. Photographs of the constructed LFG extraction lines are shown in Figure 7. The gas extraction lines were connected to an active gas extraction Figure 7. Installed LFG Extraction Line system through an extraction manifold (Figure 8). Gas composition, gas temperature, applied vacuum and flow rate on each LFG extraction line were monitored on a weekly basis. The applied vacuum is adjusted, as appropriate, based on the gas composition. In 2011, operation of a LFG-to-electricity plant began, allowing the site to generate renewable energy with LFG collected from the project. Monitoring Figure 8. LFG Extraction Manifold To provide a better understanding Table 1. Monitoring Parameters of bioreactor performance, SCL Weather Solid Waste Liquid LFG implemented a comprehensive Air temperature Daily tonnage Injection volume CH4 concentration monitoring plan. The monitoring Soil temperature Temperature Leachate volume CO2 concentration parameters were divided into four Precipitation Moisture content Temperature O2 concentration categories including: weather Humidity In-placed density ph-value Temperature conditions, solid waste, liquid, and landfill gas (LFG). The parameters Wind speed Wind direction Settlement Conductivity Alkalinity Flowrate are listed in Table 1. Waste Solar radiation COD / BOD temperature was measured with 148 thermistor embedded in the Total phosphorous Phosphate Ammonia waste. Liquid samples were Oil / grease collected and analyzed from TDS leachate sumps, incoming septage TSS / VSS and leachate storage tank (source Total iron for leachate recirculation) on a monthly basis. LFG measurements were conducted at each gas extraction line. 3.0 TECHNICAL SUMMARY In operation for four years, substantial monitoring data has been collected and is presented in the following sections. Page 4 of 10

5 Waste Filling As of the end of 2011, waste filling processes were completed in both bioreactor cells. Table 2 summarizes filling activities for both Cells. Total of 245,028 tons and 139,207 tons of MSW were filled in Cell 3A ( Bioreactor Cell) and 3B (Leachate Bioreactor Cell), respectively. Liquid Injection Volumes Table 2. Waste Filling Periods Cell 3A Cell 3B 10/5/06-4/17/08 3/19/2008-2/27/09 1/26/09-4/7/09 3/11/09-11/13/09 11/16/09-3/9/10 3/10/10-3/31/10 4/2/10-12/27/10 12/28/10-1/31/11 As of the end of 2011, 3,238,214 gallons of septage and 454,480 gallons of leachate have been injected into the subsurface of Cell 3A ( Bioreactor Cell) through embedded lines and sludge disposal, while 1,003,451 gallons of leachate were injected into Cell 3B (Leachate Bioreactor Cell). Leachate injection in Cell 3B was carefully controlled as to maintain a similar trend of moisture content as Cell 3A since waste filling began. Temperature and Moisture Content in Solid Waste In order to compare the performance between Cells 3A and 3B, the waste temperature and moisture content in the two Cells should be maintained to follow a similar trend. The waste temperature was affected by the weather conditions during the waste placement and the waste filling progress. As showed in Figure 9, the average waste temperature in Cell 3A was slightly lower than the values in Cell 3B. Given the 60 40% meteorological conditions Cell 3A ALL Lifts 50 during waste filling and Cell 3B ALL Lifts 35% 40 other outside variables, the 30 30% moisture content vary in 20 Cell 3A both bioreactor cells. To 25% 10 Cell 3B maintain a similar trend in 0 Cell 3B_Prediction both bioreactor cells, 20% leachate was only injected Elapsed Days (from start of waste filling) Elapsed Time for Waste Filling (Day) into Cell 3B to mimic Figure 9. Average Waste Temperature Figure 10. Moisture Content moisture content in Cell 3A since waste filling began (Figure 10). Temperature (C) Leachate Quality from Bioreactors Based on the chemical analysis results, the leachate quality from both bioreactor cells is comparable with other cells at this site. The high BOD, TSS, VSS, oil and grease, and phosphorus concentration in the septage did not have significant impacts on the leachate quality in Cell 3A ( Bioreactor Cell). Moisture Content (%) Page 5 of 10

6 Remaining LFG in Waste Gas Production LFG extraction operations were started 3.0E and 22 months after the waste filling started in Cell 3A ( Bioreactor Cell 3A Flowrate Cell 3B Flowrate E-03 Cell 3A Volume Cell) and 3B (Leachate Bioreactor Cell), Cell 3B Volume 70 respectively. The applied vacuum levels 2.0E were adjusted regularly at each E-03 extraction line based on the gas composition. The unit LFG collection 40 rates and cumulative volumes 1.0E (normalized by in-placed waste tonnage) E-04 are showed in Figure 11. Using a first 10 order decay model (similar to EPA LandGEM model), the decay rate 0.0E Time (year) coefficients were determined as and per year for Cell 3A ( Figure 11. Unit LFG Collection Rate and Volume Bioreactor Cell) and 3B (Leachate Bioreactor Cell), respectively. This indicated that the methane generation rate in the septage bioreactor is four times faster than in the leachate bioreactor under the similar conditions. 4.0 BENEFITS The benefits for operating the septage landfill bioreactor are both environmental and economical in nature. The primary benefits are detailed below. 100% 1. Accelerated waste stabilization: LFG generation rates were significantly higher in the septage bioreactor cell, indicating accelerated waste decomposition (stabilization). As shown in Figure 12, the time for waste stabilization can be decreased from several decades to approximately ten years. After waste is stabilized, there are less potential impacts to the environment. Unit LFG collection rate (cfm/ton) 90% 80% 70% 60% 50% 40% 30% 20% 10% Leachate Bioreactor Bioreactor 0% Year Figure 12. Theoretical Remaining LFG in Waste Unit LFG Acc. (cu. yd/ton) Page 6 of 10

7 2. Reducing pollution to surface water: Using septage to accelerate solid waste decomposition will reduce the need to dispose septage using land application and therefore reduce the potential for non-point source pollution to surface water. Through protection of surface waters, beach closures and other detrimental impacts can be avoided. 3. Reducing nutrient loading to wastewater treatment systems: The beneficial use of septage in landfills also reduces the need for disposal of septage at wastewater treatment facilities. Due to high phosphorous concentrations in the septage, the treatment of septage in typical wastewater treatment facilities may result in uncontrolled nutrient discharges from the plant. 4. Recover and reuse airspace in landfill: As waste decomposition occurs, the in-place waste volume will be reduced. As this process can take many decades to be completed in a conventional landfill, the reduction of the in-place waste volume may not be recognizable within the site life. In the septage bioreactor landfill, the reduction of in-place waste volume will occur at a much faster pace making it possible to reuse the recovered airspace before the landfill closing and expand the service life of landfill Gas Flowrate (SCFM normalized to 50% Methane) 1,400 1,300 1,200 1,100 1, Total SCL Gas Collection Bioreactor Cell Gas Collection 41% of total in 2011 Figure 13. LFG Collection Rate at SCL 5. Generate green electricity: Prior to the collection of LFG from the bioreactors, SCL collected approximately 700 standard cubic feet per minute (scfm) of LFG (Figure 13). As the LFG generation rate increased in the septage bioreactor landfill, the LFG collection rate on-site continually increased to a current rate exceeding 1,300 scfm. Due to the additional landfill gas from the bioreactor cell, SCL s overall gas quantity and quality is sufficient to support two electric generators generating up to 3.2 megawatts (MW) of electricity. Operational beginning in 2011, the on-site LFG-to-electricity plant (Figure 15) is currently producing enough energy to power 3000 homes. By burning this gas for power, St. Clair County is turning methane, a powerful greenhouse gas, into useful power while reducing the community s Figure 15. Inside of Gas to Electric Plant Page 7 of 10

8 dependence on outside sources of fuel. If the bioreactor landfill operation continues, SCL is capable of providing LFG to operate both generators for several decades (Figure 14). 6. Capital Reinvestment in the Community: Savings in landfill operations (i.e., airspace recovery) and the revenue from the operation of a gas-to-electric power generation facility has made it possible for reinvestment of these funds for other county initiatives, such as regular contributions to the County Economic Development Fund, used to assist local communities in attracting private investment. The County will also be using these funds to help with the expected operational costs of a new exhibition and conference center scheduled to be completed in late 2013 and the continued funding of the County Road Commission and Airport who maintain vital transportation assets in the County. Without the flexibility in funds afforded by septage bioreactor research and the gas-to-electric facility operation, it is unlikely that these endeavors could be fulfilled. 5.0 IMPACT OF CURRENT 12-YEAR TIME LIMITATION ON RDDP Collected LFG Flowrate (cfm) Operate all future cells as septage bioreactors No bioreactor demo cell only Two Engines (total 3.2 MW) One Engines (total 1.6 MW) Figure 14. LFG Collection Rate Predictions Interal Rate of Return (IRR) 24% 21% 18% 15% 12% 9% 6% 3% 0% Daily Waste Tonnage Figure 16. Comparison of Internal Rate of Return on Bioreactor Landfill Project The current RDDP rule sets a maximum duration of 12 years for any RDDP permit and fails to provide an avenue to take a research and development project forward for future development following successful demonstration. Data generated in the SCL septage bioreactor landfill project has demonstrated the benefits of adding septage to municipal solid waste including the acceleration of waste decomposition. However, there is no clear regulatory path for SCL to apply this technology to other areas of landfill. Operating a bioreactor landfill requires a long-term commitment due to the scale of the project. If the project is limited to a maximum of 12 years, the septage bioreactor landfill operation (and the associated benefits) may extend only to a limited area. As shown in Figure 14, if the operation is not Page 8 of 10

9 extended to other areas of the landfill, continued LFG and green energy production will be significantly reduced, adversely impacting the effectiveness of this technology. In order to determine whether a project is economically viable, the rate of return for the investment must be evaluated. For this technology, there are significant initial costs involved (e.g., construction of the bioreactor landfill cells, liquid management system, and LFG-to-electricity facility). In addition, due to the nature of the waste filling and decomposition process, the project may not be able to produce enough LFG for energy production during the initial stage of the project. Investors interested in this technology must examine the long-term return on investment. By limiting the project to a maximum of 12 years, the internal rate of return (IRR) of investment will be significantly lower than a 20 year project (Figure 16). With the 12-year limitation, an investor who is interested in projects with an IRR of 18% or higher would seek a landfill that receives more 2,000 tons per day of MSW as indicated in Figure 16. By removing the 12-year limitation and allowing the typical 20-year project timeframe, any landfill that receives more than 800 tons of MSW per day will become a possible candidate for renewable energy development. 6.0 CONCLUSIONS Residential septage is an on-going wastewater challenge for municipalities. Conventional methods of septage disposal land application and waste water treatment plants can result in surface water pollution, overloading treatment plants, and increased energy consumption. Additionally, landfill space is limited and maximizing the use of existing landfills helps to eliminate the need to site new facilities. bioreactor landfill technology improves the management of both septage and municipal solid waste (MSW) to avoid these problems. Mixing septage with MSW can be a win-win combination residential septage is safely treated and waste decomposition and methane generation are accelerated in the landfill. The County s septage bioreactor landfill project included the construction and operation of a full-scale, 7-acre demonstration bioreactor landfill cell to demonstrate the feasibility of this concept.. After four years of operation, results show that septage addition has dramatically increased the methane generation rate in the septage bioreactor landfill, making it possible for the owning municipality to construct a landfill-gas-to-electricity facility. The electricity generated from this facility is sold to a local utility, generating revenue for the County. Monitoring performed to date has shown no adverse environmental impact, demonstrating that this technology is a viable option for the safe and effective treatment of both septage and municipal solid waste. The current 12 year limitation on permitting for RDDP projects is restrictive. The investment involved in many potential projects requires a 20 year return on investment to be economically viable, which is not possible given the current structure of the RDDP rule. The results of this project in conjunction with other EPA bioreactor research indicate that bioreactor technology has advanced beyond innovation and is now a demonstrated technology. The RDDP rule needs to be amended to allow for full scale Page 9 of 10

10 permitting so this innovative technology can be utilized at other facilities where the benefits of waste stabilization, increased site life, and revenue from LFG to electricity can be realized. 7.0 ADDITIONAL LITERATURE Reports 2008 Smiths Creek Landfill Bioreactor Annual Report 2009 Smiths Creek Landfill Bioreactor Annual Report 2010 Smiths Creek Landfill Bioreactor Annual Report 2011 Smiths Creek Landfill Bioreactor Annual Report Presentations Paper Zhao, X., Soong, T.Y., Qian, X., and O Keefe, L., (2005), Enhanced Waste Decomposition in Bioreactor Landfill with Additions, Proc. GRI-18 Conference, Austin, TX Soong, T.Y., Zhao, X., Liu, W.L., Subbarayan, M., and Williams, M., (2009). Full size septage bioreactor landfill a RD&D project update, Proc. WASTECON 46th Solid Waste Exposition, SWANA, Long Beach, CA Zhao, X., Soong, T.Y., Subbarayan, M., Williams, M., Larsen, K. and Ridgway, J. (2011). Using septage to accelerate energy generation in a bioreactor landfill, Proc. Energy and Water 2011, WEF, Chicago, IL Zhao, X., Soong, T.Y., Subbarayan, and M., Williams, M., (2012). Jump start methane production in a bioreactor landfill using septage, 22 nd Annual Solid Waste Technical Conference, Engineering Society of Detroit/Michigan Waste Industries Association, East Lansing, MI Zhao, X., Soong, T.Y., Subbarayan, M., and Williams, M., (2012). Full Scale Field Research and Demonstration of Bioreactor Landfill Technology, Journal of Hazardous, Toxic and Radioactive Waste, in review. Page 10 of 10