Significance of integrated therapy of biological and physical cleaning for biofouling control and energy saving in AnMBRs

To avoid the limitations of single biofouling control methods, this study proposed the synergistic therapy of quorum quenching (QQ) and traditional but essential physical cleanings (i.e., backwashing and gas sparging) to cost-effectively manage membrane biofouling of anaerobic membrane bioreactors (AnMBRs). QQ reduced content of proteins in the extracellular polymeric substances (EPS) of suspended biomass (solid fraction of mixed liquor) and retarded colloidal organics in supernatant (liquid fraction of mixed liquor), which inevitably resulted in the mitigated membrane biofouling. The biocommunities of planktons in supernatant were similar to those of cake layers, while biocommunities of suspended biomass were significantly different from those of cake layers, as reflected by nonmetric multidimensional scaling and analysis of similarities. It suggested the significance of planktons of the supernatant in membrane biofouling formation in AnMBRs, and QQ could decrease membrane biofouling in AnMBRs by reducing content of planktons in supernatant. Of note, both backwashing and QQ were not effective in improving filtration performance at a low gas sparging rate of 0.6 m³/m²/h. In addition to high energy consumption, a high gas sparing rate of 1.2 m³/m²/h could lead to a high content of aromatic proteins in the EPS and total content of protein in soluble microbial products of mixed liquor, which would counterbalance the benefits of QQ. At a middle gas sparging rate of 0.9 m³/m²/h with consumption of comparatively low energy, QQ improved filtration efficiency by 247 %, and filtration performance was further improved by 58 % via backwashing due to the simultaneous reduction of cake layer and pore blocking. The results highlight the considerable improvement of cost-effectiveness for biofouling control in AnMBRs via synergistic manipulation of QQ, gas sparging and backwashing.