Startup of the Green, Sustainable Codigestion Project for Johnson County, KS

The recent expansion of the 14.5 million gallons per day Douglas L. Smith Middle Basin Wastewater Treatment Plant (Middle Basin WWTP) in Johnson County, KS included incorporating biological nutrient removal (BNR) to meet new effluent goals for total nitrogen and total phosphorus, addition of a fourth anaerobic digester and enhanced mixing for the other three digesters, and the incorporation of a combined heat and power (CHP) cogeneration system. Another recent upgrade to the Middle Basin WWTP was the construction of a fat, oil, and grease (FOG) waste receiving and processing facility for the treatment of FOG wastes from local restaurants and industrial sources. This waste will be codigested in the mesophilic anaerobic digesters with thickened primary clarifier solids and thickened waste activated sludge from the Middle Basin WWTP and trucked in thickened sludge from the Blue River Main WWTP, another BNR activated sludge plant.The CHP cogeneration system includes two digester/natural gas fired boilers; a membrane digester gas holding facility; gas cleaning equipment for removal of moisture, hydrogen sulfide, and siloxanes; and two 1060 kilowatt combined heat and power cogeneration units. A key driver for installation of the cogeneration system was the additional digester gas anticipated from the FOG waste and the Blue River Main WWTP sludge, which based on computer modeling, is expected to more than double the amount of gas produced in the digesters, thus substantially increasing the amount of electricity produced. When fully operational, the cogeneration system is projected to provide a source of green power for most of the treatment plant's electrical needs with an annual power cost savings of approximately 500,000.This paper presents the experiences and observations during startup of the codigestion system including the digester complex, FOG waste receiving station, and feeding of the industrial and restaurant FOG wastes into the digesters. Acclimation of the digesters to the FOG wastes, especially the high strength material from the industrial food processors will likely continue for several months into 2011.