The Janesville Wastewater Treatment Plant (WWTP), established in 1970, began operation of its first CHP system in 1985 and is currently on its third iteration of the system. The system initially consisted of two 150 kW reciprocating engines, with heat recovery only from the jacket water, operating on untreated biogas.

In 2002, the 300 kW CHP system was replaced with a new, more efficient 400 kW CHP system that incorporated two reciprocating engines (200 kW each) fueled by biogas. In this system, heat was recovered from the engine jacket as well as from the exhaust gases. The heat recovered from the engines was used in two ways: to preheat the sludge prior to being fed to the digesters and to maintain the desired 98oF in two mesophilic digesters and 130oF in one thermophilic digester.

In 2011, all the engines were replaced with four 65 kW Capstone microturbines for a total CHP capacity of 260 kW and in 2012 a 200 kW Capstone microturbine CHP system was added, increasing the total CHP capacity to 460 kW. All microturbines are fueled with biogas from anaerobic digesters after it has been treated to reduce its moisture, H2S and siloxanes content. The biogas fed to the microturbines is about 25 ppmv of H2S. Heat is recovered from the microturbine exhaust gases for heating the anaerobic digesters.

In 2024, the City of Janesville took advantage of Investment Tax Credit benefits, a Department of Energy grant and local utility incentive to cover 93% of their CHP project costs.