Marine quorum quenching consortium for biofouling control in membrane bioreactor under salinity stress

Quorum quenching (QQ) is a promising biofouling control strategy for membrane bioreactor (MBR), however its application in saline environments (widely present in industrial wastewater and seawater) is still a challenge. It was demonstrated that conventional QQ strategy failed under high-salinity stress (>2 % NaCl) owing to the severe suppression of QQ bacteria. Addressing this problem, present study proposed an innovative approach of cultivating halotolerant QQ consortium from marine environments (e.g. MQQ). Unlike normal sludge-sourced QQ consortium (NQQ), whose AHL-degrading activity was severely inhibited when salinity exceeded 3 % NaCl, the MQQ demonstrated exceptional and broad-spectrum acyl-homoserine lactone (AHL) degradation efficiency (>80 %) across a wide salinity range (1-5 % NaCl). This breakthrough performance stems from a stable and unique salinity-resistant bacterial community, dominated by marine QQ species (e.g. Pseudomonas_aeruginosa, Rhodococcus_hoagii, and Rhodococcus_erythropolis), whose dominance persisted under various salinities, while the dominant QQ species in NQQ (e.g. Acinetobacter_guillouiae, Klebsiella sp., Enterobacter_ludwigii) were gradually eliminated as salinity increased from 2 % to 5 % NaCl. Additionally, to overcome the instability issue of conventional hydrogel QQ beads under saline condition, novel halotolerant polyvinyl alcohol (PVA) hydrogel QQ beads were fabricated via a cyclic freeze-thaw method, which maintained structural integrity and potent QQ activity under salinity up to 5 % NaCl. The MQQ beads were then applied into MBR under high salinity stress (∼3.5 % NaCl) and a remarkable biofouling mitigation was achieved, i.e. the membrane service cycle was extended five-fold (from 3-4 to 17 days), significantly outperforming NQQ-based MBR (only extended to 6-7 days). This work establishes the first halotolerant marine-derived QQ consortium for MBR biofouling control under salinity stress, which could facilitate the wider application of QQ strategy in MBR treating saline wastewaters and be potentially used for biofouling control in seawater desalination or marine instruments.