Assessing the performance and microbial structure of biofilms adhering on aerated membranes for domestic saline sewage treatment

The presence of high salt concentration has always been considered as a common inhibitor that hampers effective municipal wastewater treatment. In this study, a bench-scale membrane-aerated biofilm reactor (MABR) was first introduced to degrade and remove the carbon and nitrogen pollutants under saline conditions. At influent concentrations of 220 mg CODCr per L and 32 mg NH4-N per L with an HRT of 24 h and salinity level of 3%, the reactor demonstrated excellent CODCr, NH4-N and TN removal efficiencies of 92.8%, 98.5% and 70.6%, respectively. Alphaproteobacteria, Anaerolineae, Gammaproteobacteria, Betaproteobacteria and Flavobacteria were the major functional classes in bacterial community. Candidatus Nitrososphaera exhibited stronger salt resistance compared with Nitrosomonas, and was probably the dominant nitrifier. Although the microbial diversity (Shannon-Wiener index) changed slightly along with the increasing salinity from 0.4% to 3%, the community composition substantially altered mainly through a fluctuant process via the growth of halophilic bacteria and the reduction of halotolerant bacteria. The halotolerant bacteria was mainly affiliated with Anaerolineae and Ignavibacteria while the halophilic bacteria mainly belonged to Alphaproteobacteria and Anaerolineae. The succession ensured a stable performance of the system under salty environments. This research suggests that MABR has the potential to effectively treat domestic saline sewage.