Long term effects of salinity on pollutants removal, microbial community and membrane fouling in an anoxic membrane bioreactor

This study employed a lab-scale anoxic membrane bioreactor (MBR) to evaluate the treatment performance, microbial community, and membrane fouling at salinities ranging from 2.5 to 15.0 g NaCl/L. Sharply increasing salinity to 5.0 and 15.0 g NaCl/L caused adverse effects on the performance, resulting in loss of active biomass and reduction in organic removal and nitrification capacity. Specifically, the abundance of Proteobacteria declined from 81.5 % at 2.5 g NaCl/L to 56.1 % at 5.0 g NaCl/L and 43.5 % at 15.0 g NaCl/L. Higher salinities (10 – 15 g NaCl/L) promoted irreversible fouling (R_f was 33.5–40.6 %) due to the increased secretion of soluble extracellular polymeric substances (EPS), which adsorbed onto the membrane pores. The presence of Chlorofexi could promote the formation of larger flocs and a decrease in irreversible fouling. Ultimately, the optimal condition for an anoxic MBR treating saline wastewater could be up to 15.0 g NaCl/L, suitable for various industrial applications.