Methanotrophic denitrification in wastewater treatment: microbial aspects and engineering strategies

Management of biofilm by an innovative layer-structured membrane for membrane biofilm reactor (MBfR) to efficient methane oxidation coupled to denitrification (AME-D)

Aerobic methane oxidation coupled with denitrification (AME-D) has garnered significant attention as a promising technology for nitrogen removal from water. Effective biofilm management on the membrane surface is essential to enhance the efficiency of nitrate removal in AME-D systems. In this study, we introduce a novel and scalable layer-structured membrane (LSM) developed using a meticulously designed polyurethane sponge. The application of the LSM in advanced biofilm management for AME-D resulted in a substantial enhancement of denitrification performance. Our experimental results demonstrated remarkable improvements in nitrate-removal flux (92.8 mmol-N m-2 d-1) and methane-oxidation rate (325.6 mmol m-2 d-1) when using an LSM in a membrane biofilm reactor (L-MBfR) compared with a conventional membrane reactor (C-MBfR). The l-MBfR exhibited 12.4-, 6.8- and 3.4-fold increases in nitrate-removal rate, biomass-retention capacity, and methane-oxidation rate, respectively, relative to the control C-MBfR. Notably, the l-MBfR demonstrated a 3.5-fold higher abundance of denitrifying bacteria, including Xanthomonadaceae, Rhodocyclaceae, and Methylophilaceae. In addition, the denitrification-related enzyme activity was twice as high in the l-MBfR than in the C-MBfR. These findings underscore the LSM's ability to create anoxic/anaerobic microenvironments conducive to biofilm formation and denitrification. Furthermore, the LSM exhibited a unique advantage in shaping microbial community structures and facilitating cross-feeding interactions between denitrifying bacteria and aerobic methanotrophs. The results of this study hold great promise for advancing the application of MBfRs in achieving efficient and reliable nitrate removal through the AME-D pathway, facilitated by effective biofilm management.