Discerning realizable advantages of microbial electrochemical system towards raw municipal wastewater treatment: From the analyses of mass and energy flow

Abstract The low-cost biocathode microbial electrochemical system (MES) with microbial separator (MS) is promising for the practical application in wastewater treatment. To evaluate the potential realizable advantages for future full-size MESs, four 2-Liters MES modules with MS are constructed and their energy conversion, biomass metabolism and pollution degradation are systematically investigated. The mass and energy flow for MES with raw domestic wastewater is built under maximum power point (Pmax), maximum current point (Imax), and open circuit (OC) modes. The chemical oxygen demand (COD) removal rates are 0.831 and 0.846 kg m−3 day−1 in Pmax and Imax modes, while that of OC is 0.609 kg m−3 day−1. The effluent COD concentrations at Pmax and Imax are stable at 41 ± 2 and 37 ± 2 mg L−1, while that of OC is up to 101 ± 4 mg L−1. The observed sludge yield is only 23.4% (Pmax) or 19.5% (Imax) of the OC mode with much higher sludge calorific values. For the raw wastewater treatment, the direct electricity harvest and reuse from MES units are unrealistic and uneconomical due to its low energy efficiency. But the high COD removal efficiency and low observed sludge yield are the realizable advantages for practical applicated MESs.