A submerged membrane bioreactor under unprecedentedly short hydraulic retention time enabled by non-woven fabric pre-filtration and electrochemical membrane cleaning

This study reports that electrochemical oxidation (EO) coupled with non-woven fabric (NWF) filter synergistically mitigated fouling in a submerged membrane bioreactor (MBR) under hydraulic retention time (HRT) of 1 h. Our NWF-EO-MBR was equipped with NWF prefilter cage surrounding microfiltration (MF) membrane with IrO2 anodes in vicinity. Continuous operation showed a retarded increase of transmembrane pressure at intermittent current density (5 mA cm(-2)) to prolong operation duration by 40% under constant flux (13.75 Lm(-2) h(-1)). Primary separation of bio-flocs by NWF not only reduced physically removable fouling on MF, but also allowed augmented concentration of electrolytic free chlorine (FC) near 4.0 mgCl(2) L-1 inside the NWF cage. The FC degraded dissolved foulants to reduce physically irremovable hydraulic resistance of MF. A limited nitrification under the short HRT was assisted by electrochemical breakpoint chlorination, resulting 72% total nitrogen removal efficiency on average. Terminal restriction fragment length polymorphism fingerprinting indicated that the microbial community in mixed liquor was less influenced by FC than that in bio-cake on MF. The energy consumption of EO was approximated to 28 Wh per m(3) of permeate.