Energy recovery from municipal wastewater: impacts of temperature and collection systems

Municipal wastewater contains valuable organic contents that can be recovered as energy through anaerobic digestion. The operating temperature impacts the design and performance of anaerobic digestion systems and can be selected to accommodate different geographical zones, from tropical to frigid. Here the biological methane potential (BMP) and the effect of temperature on methane production are compared for municipal wastewater collected from different collection systems, including source-diverted toilet wastewater (i.e. blackwater) and conventionally collected sewage. The sewage and blackwater collections were performed in Canada. BMP tests were conducted at 20 and 35°C. The BMPs of municipal sewage and water-wasting toilet (6–9 l per toilet flush) blackwater were comparable at 20 and 35°C. Water-conserving toilet (1 l per toilet flush) blackwater had lower BMP than municipal sewage and water-wasting toilet blackwater at 35°C, due to FA inhibition. Under the lower-temperature condition (20°C), although no apparent inhibition in the methanogenic process was observed for water-conserving toilet blackwater, a much lower hydrolysis rate was observed.