Effectiveness of combined UV-C and bacteriophage approach over repeated cleaning cycles to alleviate membrane fouling of anaerobic bioreactors

• UV-C combined with phage is evaluated over repeated membrane cleaning cycles • Efficacy was sustained over 3 cleaning cycles • Decrease in performance at the 4 th cycle due to loss in protein and bacteria removal • Certain core bacteria populations exhibit adaptive response against treatment A combined ultraviolet C (UV-C) and bacteriophage treatment has been previously identified as an effective and environmentally sustainable approach to mitigating biofouling in anaerobic membrane bioreactors (AnMBRs) treating municipal wastewater. This study investigated the efficacy of this treatment across multiple cleaning cycles to assess its long-term applicability. The results demonstrated that the combined treatment effectively delayed transmembrane pressure (TMP) regrowth and maintained stable reactor performance over three cleaning cycles. Polysaccharide removal remained consistent throughout, while the efficiency of protein and bacterial cell removal declined progressively with repeated cycles. Transcriptional analysis revealed an adaptive response among key biofilm-forming bacteria, including Geobacter spp, characterized by increased expression of genes associated with biofilm formation, particularly flagellar proteins. These findings suggest that repeated treatment may induce bacterial resistance, diminishing long-term efficacy. Despite this limitation, the UV-C and bacteriophage treatment presents a promising alternative to chemical cleaning, with the potential to minimize environmental impact and membrane degradation leading to a potential broader adoption of biologically-based cleaning approaches in membrane-based systems.