Alleviating membrane fouling by enhanced bioelectricity generation via internal reflux of sludge mixed liquor in microbial fuel cell-membrane bioreactor (MFC-MBR) coupling system

The in-situ utilization of sludge mixed liquor was innovatively applied in microbial fuel cell and membrane bioreactor (MFC-MBR) coupling system. MFC-MBR coupling systems with different return flow ratio were designed to investigate the effects of return flow on bioelectricity generation and subsequently membrane fouling mitigation. The results indicated that bioelectricity generation was largely enhanced with the increasing return flow ratio. Furthermore, the slow growth of the transmembrane pressure (TMP) was found in MFC-MBR coupling systems that with return flow ratios of 0.50 and 0.75, respectively (0.66 kPa/d and 0.57 kPa/d). It was evident from the declined absolute value of zeta potential in systems with return flow ratio, which enlarged the flocculation of sludge particles and was in accordance with the particle size distribution. The increase rate of soluble microbial products (SMP) and extracellular polymeric substances (EPS) were also significantly dropped while the ratio of protein to polysaccharide in SMP and EPS rose in MFC-MBR coupling systems with return flow. Importantly, Bacteroidetes and Chlorobiaceae were more abundant in MFC-MBR coupling systems with higher return flow ratios. Thus, MFC-MBR coupling system with internal reflux of sludge mixed liquor was effective in improving bioelectricity generation and minimizing membrane fouling.