From Brown to Green-Reducing Carbon Footprint via Biogas Cogeneration in a Phased Digestion Process Producing Class A Biosolids

Soaring energy costs have made it imperative to reduce consumption of traditional fossil fuels. This has resulted in demand for alternative sources of energy from sustainable localized sources that are considered renewable in nature. Increasingly, the use of biogas from anaerobic digesters to generate process heat and in some case electricity using cogeneration mechanisms have made anaerobic digestion an attractive treatment choice for many small to medium size facilities. Delhi Charter Township Wastewater Treatment Plant (WWTP) located in Ingham County, Michigan has established the states first integrated biomass-to-energy digester system. The plant upgrade included the implementation of a two-phase anaerobic digestion system with a fully integrated state-of-the-art microturbine based cogeneration system. The two-phase anaerobic digestion system is designed to treat primary solids and waste activated sludge to produce Class A biosolids and the microturbine system to capture, treat and utilize biogas to produce heat and electricity. This integrated biomass-to-energy digestion and cogeneration system was designed to help reduce energy consumption in two folds, first, by reducing the volume of sludge to be hauled to the final disposal location by minimizing fuel associated with the transporting of biosolids and second, by minimizing the use of natural gas and electricity usage by locally generating heat for process heating and electricity for electrical operation. At current capacity, the facility is able to reduce electricity consumption by over 40 percent and close to 100 percent of the process heat. This essentially sustains the operation of the solids handing system. The plant demonstrates that wastewater treatment facilities can be designed to significantly reduce consumption of traditional fuels and offset carbon footprint while producing numerous usable bi-products such as Class A biosolids, electricity and process heat. The WWTP is projected to be fully energy independent when the solids treatment facility reaches design capacity.