By Dale Gabel, CH2M HILL Vice President and Regional Wastewater Practice Lead
Gabel and Johnson County Wastewater’s Doug Nolkemper will be presenting the paper, “Startup of the Green, Sustainable Codigestion Project for Johnson County, KS,” at the Water Environment Federation Residuals and Biosolids 2011 conference on Tuesday, May 24, at 2:00 pm in room 309-310.
Sustainability, energy efficiency, and greenhouse gas reductions are becoming increasingly important to governmental agencies as they upgrade and expand their infrastructure. An example is the Board of County Commissioners for Johnson County, KS, which passed a resolution adopting goals to reduce the amount of greenhouse gases (GHGs) associated with energy use to zero by the year 2030 and develop and implement a plan to reduce GHG emissions by 80 percent by the year 2050, consistent with the National Association of Counties’ initiative. To support these goals, Johnson County Wastewater (JCW) seized the opportunity to utilize biosolids and trucked-in high-energy wastes as a renewable energy source while improving solids handling and expanding services to its customers.
JCW began their efforts by expanding the Douglas L. Smith Middle Basin Wastewater Treatment Plant (Middle Basin WWTP) to increase the hydraulic capacity to 14.5 million gallons per day and incorporate biological nutrient removal (BNR) to meet new effluent goals for total nitrogen and total phosphorus. Additionally, JCW will haul thickened sludge from the Blue River Main WWTP, another BNR activated sludge plant, to the Middle Basin WWTP for processing. The next 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 which will be codigested with the various WWTP solids streams. The recent upgrades also included the addition of digester gas utilization systems including 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 the cogeneration system was production of 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, with GHGs emissions reduced by 9,700 metric tons in CO2 equivalent emissions annually. In addition, the new facility will reduce the average miles traveled by FOG waste haulers by at least 40,000 miles annually, resulting in an estimated savings of 8,000 gallons/yr of fuel and a reduction of 80 metric tons CO2e/yr emissions.
The project is one of the largest wastewater cogeneration projects in the state’s history, and proper start-up of the various systems is critical. In my Water Environment Federation Residuals and Biosolids 2011 presentation, I will discuss the experiences and observations during startup of the codigestion system, which began in 2010, including the digester complex, FOG waste receiving station, and feeding of the industrial and restaurant FOG wastes into the digesters. One observation that I’ll share now is that major operation and maintenance activities not related to the digester operation can significantly impact digester startup activities, as experienced during the startup of Middle Basin WWTP codigestion system, and should be analyzed and coordinated prior to execution. It is anticipated that normal operation of all new systems added to the Middle Basin WWTP will require several months into 2011.
Dale Gabel has more than 34 years of experience in the planning, design, and construction of water and wastewater treatment facilities around the world, including the US, Australia, Egypt and Hungary. His recent focus includes integrating sustainable solutions into wastewater infrastructure projects including wastewater reuse, biological nutrient removal, digester gas utilization, and management of fats, oils, and grease waste streams. He has interfaced extensively with local, state, and federal regulatory agencies, and has participated in public meetings as a technical expert.