Janesville WWTP Upgrade Emphasizes Energy Saving Improvements

Energy efficiency and improved utilization of available energy resources were essential elements of the City of Janesville's Wastewater Treatment Plant (WWTP) upgrade and expansion plan. Using 2008 data prior to the expansion, the WWTP's purchased energy as electricity and natural gas was 285.9 kWh/ML (1082 kWh/MG), placing them well above the 25th percentile of 356.7 kWh/ML (1350 kWh/MG) for WWTPs in efficiency1 In order to maintain or exceed this performance following expansion, energy goals were established early in the design process that included: no net increase in energy purchased, incorporation of at least one renewable energy generation system, LEED or Energy Star certification, and use of solar energy.To date, the project's replacement of two aging biogas generators with microturbines has resulted in a 58 percent average increase in monthly electricity produced for comparable gas production at the WWTP and reduced maintenance costs. Integral heat recovery from the microturbines has thus far completely eliminated the requirement of supplemental natural gasfired boilers to maintain digester temperature. The installation of a 16.65 kW solar photovoltaic system on the WWTP administration building produces additional electricity which is sold back to the utility at a premium rate. Improvements including high efficiency aeration blowers, variable frequency drives, digester and gas storage upgrades, and efficient lighting and HVAC systems continue to improve overall process efficiency as they come online. Upon completion of the project, system and total process optimization will yield additional efficiency improvements