Antifouling characteristics and mechanisms in visible-light photocatalytic membrane bioreactor based on g-CN modified membrane.

A novel visible-light photocatalytic membrane bioreactor (R3) was constructed for membrane fouling control and effluent quality improvement. Specially, g-CN modified membrane was evaluated for the performance of synergistic separation and photocatalysis. Another two parallel reactors, MBRs with ceramic membrane (R1) and g-CN membrane in dark condition (R2), were operated synchronously for comparison. A satisfactory effluent quality was obtained in R3 with COD and NH-N around 22.0 mg/L and 1.02 mg/L during 60-day operation, which was superior to R1 (27.8, 1.42 mg/L) and R2 (29.9, 2.26 mg/L). The thickness of cake layer on membranes in R3 (2.46 μm) was thinner than R1 (3.52 μm) and R2 (4.97 μm) after operation, indicating the introduction of visible light could effectively mitigate membranes fouling. Moreover, microorganism community analysis revealed that visible light increased the relative abundance of Bacteroidetes and Chryseolinea, which not only enhanced the activity of microorganisms in metabolizing organic nutrients, but also improved the transfer and utilization of photogenerated electrons on the semiconductor-microorganism interface. The active aromatic protein metabolism and the upregulated related enzymes further demonstrated the synergistic effect of photocatalysis and microbial communities on the membrane fouling mitigation. This work provides a novel application of photocatalysis into antibiofouling effect in MBRs, and opens a strategy for bacteria inactivation and foulants removal with eco-friendly solar energy.