6.2. SR 09-15-2008 - Laserfiche WebLink

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Memorandum Date: September 9, 2008 To: Terry Maurer, P.E. .~-~ BDM CONSULTIIVG ENGINEERS AND SURVEYORS, PLC 60 Plato Boulevard East; Suite 140 St. Paul, MN 55107 763-786-4570, Fax 763-786-4574 From: Bill Chang, P.E. RE: Feasibility Study on WWTP Biosolids Incineration at Great River Energy A. The City's Needs for Long Term Biosolids Disposal The City of Elk River Wastewater Treatment Plant (WWTP) generates approximately 900,000 gallons a year (or 0.3 dry tons a day) of biosolids (sewage sludge} from its wastewater treatment operation. The biosolids were treated at the existing anaerobic digesters for pathogen reduction and land applied to the City owned farmland in liquid form. In the past, the City pays approximately $25,000 a year to retain a contractor for liquid biosolids hauling and land application. So far this year, the City has already paid $16,000 to haul 400,000 gallons of biosolids as a result of the digester mixing problems. The total biosolids hauling this year is expected to cost the City $35,000. In addition, the City budgeted $50,000 this year for natural gas used at the WWTP, mostly to heat the anaerobic digesters. With the rising fuel prices, these operating costs may continue to increase. B. Potential Opportunities at Great River Enemy Incinerate Sewage Sludge at Great River Energy Great River Energy (GRE} operates an incinerator adjacent to the City's WWTP. Each day, the incinerator consumes 1500 tons of municipal waste to generate 35 to 42 megawatts of .electricity. The amount of sewage biosolids from the WWTP is insignificant as compared to the mass of municipal waste burned at the incinerators. On May 29, 2008, we met with GRE representatives and Gary Leirmoe to discuss the concept of incinerating municipal sewage biosolids. GRE was interested in incinerating the sewage biosolids as a service to the City. GRE would be interested in working with the city to advance this proposal. 2. Anaerobic Digestion of Municipal Solid Waste at GRE GRE is currently exploring an innovative anaerobic digestion process which has successfully been used by several European countries to convert municipal solid wastes into fuel. This technology requires dilution water in the digestion process. GRE would like to evaluate the feasibility of using the raw sewage sludge from the City's wastewater treatment plant, which is mostly water, as the dilution water. If this innovative technology is feasible, the City may eliminate the need for sludge disposal and the need for sludge treatment at its plant.