In situ integration of microbial electrochemical systems into anaerobic digestion to improve methane fermentation at different substrate concentrations

Abstract

Microbial electrochemical system (MES) was integrated into anaerobic digestion (AD) to improve the overall process efficiency by enhancing methane (CH4) production. CH4 fermentation at various glucose concentrations (2, 4, 8 and 10 g/l) was evaluated along with corresponding control (without electrodes) operations. The maximum CH4 yield of 0.34 l- CH4/g COD was obtained with both 2 and 4 g/l glucose concentrations (MES), which was about 1.4 and 2.4 times, respectively, higher than the values obtained with corresponding control operations. However, at 10 g/l, similar performance (∼0.07 l- CH4/g COD) was observed with both control and MES operations, which might be due to pH drop occurred by volatile fatty acids (VFAs) buildup in the process. Substrate removal was amplified in the presence of MES with faster degradation of VFAs at all substrate concentrations except 10 g/l. This enhanced utilization of VFAs in the MES process is an important aspect to recover from initial pH drops, especially at higher substrate concentration to maintain the optimum pH for methane fermentation. The current generation and cyclic voltammetric profiles suggest that the enhanced CH4 production in MES was attributed to the bioelectrochemical reactions on the electrodes.