Ultrafiltration membranes functionalized with lipophilic bismuth dimercaptopropanol nanoparticles: Anti-fouling behavior and mechanisms

- BisBAL NP coating significantly increased filtration fluxes from UF membranes.
- 10% bismuth leaching was detected in MBR suspension but not in permeate after 5-day filtrations.
- Modified surface hydrophilicity and antimicrobial BisBAL NPs determined initial colonizers.
- Heterotrophs were more susceptible to BisBAL NPs than nitrifiers in the MBR with coated membranes.
- Coating reduced enrichment levels of proliferation and oxidative stress response related genes.

The antifouling efficiency and mechanisms of a novel membrane surface modification strategy, namely lipophilic bismuth dimercaptopropanol nanoparticle (BisBAL-NP) coating, were evaluated by using a lab-scale nitrification membrane bioreactor. Filtration performance, bismuth leaching, extracellular polymeric substances (EPS) composition, microbial community structure and function were compared for the control and BisBAL-NP coated ultrafiltration membranes. The coated membrane resulted in up to 17.5% higher flux, 33.0% lower biofilm thickness, and 47.0% less cell volume than the control membrane during 1-, 3-, and 5-day filtration tests operated under constant transmembrane pressure. Bismuth leached into bioreactor suspension after the 5-day filtration was about 10% of the total coated materials, and was not detected in the filtration permeate. High-throughput sequencing revealed that the community composition of suspended sludge differed significantly from the membrane biofilm community. Heterotrophic Xanthomonas spp. were identified as the major surface colonizer on the coated membrane, indicating its low sensitivity to BisBAL NPs. Based on the predicted functional traits of the membrane biofilm communities, antioxidant and DNA repair pathways were among the major molecular targets of BisBAL NPs. Overall, lipophilic BisBAL-NP coating could be a novel, safe, and effective solution to membrane biofouling, offering improved filtration efficiency and extended membrane lifespan.

135