A gravity-driven membrane bioreactor in treating the real decentralized domestic wastewater: Flux stability and membrane fouling

Domestic wastewater in decentralized sites is capturing increasing attention. However, conventional treatment technology is not sufficiently cost-effective. In this study, real domestic wastewater was treated directly using a gravity-driven membrane bioreactor (GDMBR) at 45 mbar without backwashing or chemical cleaning, and the effects of different membrane pore sizes (0.22 μm, 0.45 μm, and 150 kDa) on flux development and contaminants removal were examined. The results showed that the flux initially decreased and then stabilized throughout long-term filtration and that the stabilized flux level of the GDMBR equipped the membranes with the pore size of 150 kDa and 0.22 μm was higher than that of 0.45 μm membrane and was in the range of 3–4 L m−2h−1. The flux stability was related to spongelike and permeable biofilm generation on the membrane surface in the GDMBR system. The presence of aeration shear on the membrane surface would cause the slough off of biofilm from the membrane surface, especially in the scenarios of GDMBR with the membrane pore size of 150 kDa and 0.22 μm, contributing to lower accumulation of extracellular polymeric substance (EPS) and smaller biofilm thickness compared to that of 0.45 μm membrane. Furthermore, the GDMBR system achieved efficient removals of chemical oxygen demand (COD), and ammonia, with average removal efficiencies of 60–80% and 70%. The high biological activity and microbial community diversity within the biofilm would improve its biodegradation and should be responsible for the efficient removal performance of contaminants. Interestingly, the membrane effluent could effectively retain total nitrogen (TN) and total phosphorus (TP). Therefore, it's feasible to adopt the GDMBR process to treat the actual domestic wastewater in the decentralized locations, and these findings could be expected to develop some simple and environmentally friendly strategies for decentralized wastewater treatment with fewer inputs. [Display omitted] •GDMBR can be operated without backwashing in treating domestic wastewater.•Effects of different membrane pore sizes on flux development and contaminants removal were examined.•GDMBR process exhibited efficient removals of organic contaminants and ammonia.•Nitrogen and phosphorus in domestic wastewater can be effectively retained.