How membrane aeration and organic carbon enhanced the performance of algal-bacterial biofilm systems for acid mine drainage treatment?

Acid mine drainage (AMD), characterized by low pH, high sulfate concentrations, and toxic heavy metals, poses severe ecological and human health risks. This study compared the performance of a conventional aerated algal-bacterial biofilm reactor (CAABR) and a membrane-aerated algal-bacterial biofilm reactor (MAABR) for AMD treatment. Six reactors with different influent COD concentrations (400 ± 11.41, 1400 ± 19.07, and 2800 ± 18.37 mg/L) were operated for 80 days, and pollutant removal, biofilm properties, and microbial community dynamics were systematically analyzed. Results showed that the MAABRs and CAABRs exhibited broadly comparable sulfate-removal performance, whereas the MAABRs maintained greater aqueous DIC availability and more stable heavy-metal removal under shock loading. Kinetic analysis revealed a transition from algal assimilation (first-order) to SRB-mediated reduction (zero-order) as COD increased, confirming that COD/SO42- ratios regulate pathway dominance. Multiscale biofilm characterization and EPS fluorescence analysis demonstrated that membrane aeration improved CO2/O2 mass transfer, enhanced algal biomass, and maintained higher EPS secretion under stress. High-throughput sequencing revealed the simultaneous enrichment of Pseudomonas and the sulfate-reducing genus Desulfosporosinus, indicating that the MAABR supported the coexistence of functionally distinct microbial populations. Overall, this study demonstrates that membrane aeration enhances algal-bacterial symbiosis, improves pollutant removal efficiency, and strengthens system resilience, providing a promising and sustainable approach for AMD remediation.