Photocatalytic quorum quenching: A new antifouling and in-situ membrane cleaning strategy for an external membrane bioreactor coupled to UASB

Abstract

Microbial quorum sensing (QS) induces biofilm formation on the membrane surfaces leading to severe biofouling, which remains a major bottleneck for membrane-based systems. Here, we report an effective UV photocatalytic quorum quenching (QQ) strategy in an integrated upflow anaerobic sludge blanket – photocatalytic membrane reactor (UASB-PMR) system, where TiO2 nanoparticles immobilized in porous polymeric beads were kept in suspension as the photocatalysts. The UASB unit reached a methane yield of 0.30 ± 0.05 L CH4/g COD removal while treating the synthetic wastewater, slightly higher than a typical internal anaerobic membrane bioreactor (AnMBR). This novel system showed 7-fold higher efficacy in membrane fouling control than the UV photolytic QQ system (19.1 ± 2.4 d vs. 2.7 ± 1.0 d) under intermittent UV irradiation (17% of total operation time). Continuous UV irradiation, both in photolytic and photocatalytic QQ, significantly alleviated membrane biofouling, while long-term UV exposure exerted some changes in the surface properties of the membranes, which were not observed under intermittent UV irradiation. The reactive oxygen species (ROS) generated by the UV-excited TiO2 not only oxidized the foulants on the membrane surface, but also quenched acyl-homoserine lactones (AHLs), the QS signal molecules, thus retarding membrane fouling to the maximum extent. Additionally, in-situ membrane cleaning, enhanced COD removal, and almost complete disinfection of the effluent were realized in the photocatalytic QQ system. Equipped with these advantages, this innovative photocatalytic QQ can be a readily implementable strategy to prevent fouling in external membrane bioreactors (MBRs) for the pilot- and/or full-scale applications.