Manure Management Program www.manuremanagement.cornell.edu Anaerobic Digestion at Wagner Farms: Case Study Jennifer Pronto and Curt Gooch, P.E. and Michael Boerman Dept. of Biological and Environmental Engineering, Cornell University Updated April 2014 Contents:  AD overview  Farm overview o Why the digester?  Digester System o System diagram o System and process description o Liquids and solids process description o Heat and electricity generation  Economics o Initial capital costs  Benefits & Considerations  Lessons learned  Contact information Anaerobic digestion overview Digester type Complete mixed Digester designer CH Four Biogas, Inc. (formerly Genesys) Date Commissioned` October 2010 Influent Raw manure Stall bedding material Separated manure solids (switched from sand) Number of cows 390 dairy cows ® Rumensin usage No Dimensions (diameter, height) 52’-5” x 19’-10” Cover material Flexible Design temperature 100°F Estimated total loading rate 6,300 gallons per day Treatment volume 264,200 gallons Estimated hydraulic retention time 28 days Solid-liquid separator Yes; separated manure solids used for bedding Biogas utilization MAN 100-kW engine generator set Carbon credits sold/accumulated Plans to in future Monitoring results to date Currently being monitored using ASERTTI protocol Case Study AD-14 2 Farm overview  Wagner Farms (Poestenkill, NY) is located in Rensselaer County  The farm is owned and operated by Pete and Bobby Wagner  The farm has 390 milking cows  The farm raises forage crops on 1000 acres of land  Digester was commissioned in October 2010 Why the digester? The farm decided to install the digester system for several reasons, one of which was to reduce odor emissions from some fields when manure was land-applied. In addition, the farm feels that dairies are going to transition to anaerobic digestion as a typical manure management strategy. The farm expects to realize savings on bedding and electricity costs, and to position the digester as an income source for the farm. The farm also sells excess electricity, as well as post digested manure solids as compost. Digester System On-site cow manure Influent pit A P Ambient air A Solid liquid to biogas Liquids B Digester head space separator P Long-term storage Heat Solids Biogas Bedding Carbon filter Land base Engine Farm gen-set Grid System and process description A 264,200-gallon, mixed, mesophilic digester with a design hydraulic retention time of approximately 28 days, was designed by CH Four Biogas, Inc. based in Ontario, Canada. Manure from 390 on-farm milking cows is aggregated in the influent pit and heated prior to being pumped to the digester. The digester vessel is a circular above-ground concrete tank 52’- 5” in diameter and 19’-10” in height with the liquid level at 17’. The digester tank has an in-wall heating system and 4” of extruded foam insulation surrounding the tank. One impeller agitator is Updated 4/14 Case Study AD-14 3 inserted through the side of the digester tank, and a second port is available, should the decision be made in the future to install a second mixer. The impeller agitator is a Doda 15-kW (20 Hp) mixer that runs intermittently on a pre-determined schedule. The above-ground concrete effluent storage tank is 80’ in diameter. Compared to other New York State on-farm digesters, one unique feature of the Wagner Farms’ digester is the in-vessel hydrogen sulfide (H2S) reduction system consisting of a series of untreated Hemlock telephone poles laid horizontally on the top of the digester head space, below the cover and provides a medium for biological H2S reduction. Hydrogen sulfide reduction begins by treating biogas with 3%-5% of ambient air pumped into the headspace of the digester to precipitate out the sulfur from H2S. In addition to the ambient air, 1-8 gallons (based on daily H2S levels) of liquid Ferric Chloride is added to the manure influent everyday to help with H2S reduction. Then the gas is condensed in a passive earth-cooling field, then passes through a fine mesh stainless steel particle separator before entering a gas pressure booster/blower prior to the engine. Liquids and solids process description Manure is collected pre-digestion in a digester influent holding pit, and transferred to the digester using a chopper pump located in the influent pit. After digestion, the effluent is separated using a solid-liquid separator (SLS) and liquids are transferred to an above-ground cast-in-place concrete long-term storage and then subsequently land applied; the solids are used for stall bedding and a small amount are sold as compost. The farm formerly used sand bedding, but has switched to post-digested separated solids since the digester has been operating and producing solids. The farm also plans to add substrates in the future as the digester operation stabilizes and a reliable source of organic substrates can be located. Heat and electricity generation The farm has installed a 100-kW MAN engine procured from Martin Machinery that has a base rate of 112-kW. The threshold for the engine is 800 ppm H2S, if the levels are higher, the engine maintenance required increases; this is the reason so many pre-engine H2S removal steps are taken at the farm. The engine receives oil changes about once every 380 hours and a complete engine rebuild once every 23000 hours. The interval for oil changes is increasing as time goes on due to the better control of H2S. The farms utility provider – National Grid – ran 3-phase power to the farm to allow for net metering. Generated power is used on-farm and excess is sold to the grid under the provisions of the New York State net metering law. The digester uses a series of 5/8” Pex tubing to provide in-vessel hydronic heat. Exhaust heat is recovered from the engine and sent through the hydronic heating system to heat the influent pit, and to keep the digester at operating temperature. The farm is explored the possibility of utilizing excess heat to heat the nearby farm house and milking parlor as well, however they found that not enough heat was produced just from the engine during the winter. The farm installed a boiler to supplement digester heating in the winter. Updated 4/14 Case Study AD-14 4 Economics The farm applied and was accepted to participate in the NYSERDA Renewable Portfolio Standard (RPS) program, which provides a performance based incentive of 10 cents per kWh produced by the engine over 3 years. The farm also plans to trade carbon credits and hopes to receive some revenue in doing so. Benefits and Considerations Benefits Considerations  Odor control  Possible high initial capital and/or high  Potential revenue from: operating costs 1) Value-added products  Long and tedious contracts with the local 2) Reduction of purchased energy utility; may require special equipment for 3) Sale of excess energy interconnection 4) Food waste tipping fees  Dedicated management of the digestion 5) Efficient use of biogas production system is required 6) Carbon credit sales  Careful attention to equipment  Nutrient conversion, allowing use by maintenance and safety issues due to the plants as a natural fertilizer, if effluent is characteristics of raw biogas spread at an appropriate time  Increased land base may be required to  Pathogen reduction handle the imported food waste nutrients  Specialized permits may be required to import food waste Lessons Learned  Carefully assess the qualifications of the system designer you choose.  A boiler can be useful in the winter months when more energy is needed for heating the digester.  H2S has been observed to be higher when the digester contents are cooler, so a consistent temperature is desirable.  Dependable flares are important, the farm has replaced the new flares and selected flares made from stainless steel to prevent weathering and corrosion. Who to Contact  Keith Wagner, AD operator for Wagner Farms Phone: 518-852-1257, E-mail: wagnerfarmskw@yahoo.com  CH Four representative contact: Benjamin Strehler, CH-Four Biogas, Inc.  Curt Gooch, Dairy Housing and Waste Treatment Engineer, PRO-DAIRY Program, Cornell University. Phone: 607-255-2088, E-mail: cag26@cornell.edu Updated 4/14 Case Study AD-14 5 Acknowledgements The authors would like to thank the New York State Energy Research and Development Authority (NYSERDA) for funding in support of this work. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of NYSERDA or the State of New York, and reflect the best professional judgment of the authors based on information available as of the publication date. Reference to any specific product, service, process, or method does not constitute an implied or expressed recommendation or endorsement of it. Further, Cornell University, NYSERDA and the State of New York make no warranties or representations, expressed or implied, as to the fitness for particular purpose or merchantability of any product, apparatus, or service, or the usefulness, completeness, or accuracy of any processes, methods, or other information contained, described, disclosed, or referred to in this publication. Cornell University, NYSERDA and the State of New York make no representation that the use of any product, apparatus, process, method, or other information will not infringe privately owned rights and will assume no liability for any loss, injury, or damage resulting from, or occurring in connection with, the use of information contained, described, disclosed, or referred to in this publication. Updated 4/14 Case Study AD-14