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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.

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Fats, Oils, and Grease (FOG) wastes and high-strength wastes (HSW) are frequently received at municipal water resource recovery facilities (WRRFs) as trucked-in wastes. These wastes offer significant benefits in terms of revenue from tipping fees and feedstock for co-digestion in anaerobic digesters that produce biogas, which can be beneficially used as fuel. The number of treatment plants receiving and beneficially using trucked-in wastes currently in operation or under investigation is increasing rapidly across the North America as utilities strive to remove this material from normal wastewater to avoid sewer system clogging, maintenance and backups, avoid the oxygen demand of these wastes in secondary treatment systems, and to capture and beneficially reuse the energy that is contained within the material. Historically, trucked-in wastes have been discharged to the head end of treatment plants or to an upstream manhole in the incoming interceptor sewer to enable the material to be mixed with raw wastewater prior to treatment through the liquid stream of the WRRF. However, this approach results in loss of material and degradation of the energy value of the FOG wastes and HSW and also creates collection and maintenance issues in the preliminary and primary treatment systems. To prevent degradation of the material and retain maximum energy for the CHP system, receiving stations are being constructed for direct off-loading of the wastes to processing and storage facilities prior to their transfer to anaerobic digesters at a relatively uniform rate to minimize the potential for digester upsets while at the same time to increase biogas production. This paper presents the key components and considerations in the design and operation of modern FOG waste receiving and processing facilities.