Regulating biofiltration and predation to trigger gravity-driven membrane System: Biofilm transformation and membrane efficiency

The gravity-driven membrane (GDM) system provides decentralized water treatment by utilizing the formation of a biofilm to sustain stable flux. Our study systematically investigated the individual and combined effects of biofiltration (powdered activated carbon, PAC) and predation (oligochaete T. Tubifex) in GDM systems through four groups: PES, PES@TT, PES/PAC and combined PES/PAC@TT, revealing novel insights into biofilm system optimization. Compared with the pristine PES group (UV₂₅₄: 3.87%; TOC: 32.37%), T. Tubifex alone increased stable flux by 20.35% and improved removal efficacy (UV₂₅₄: 33.04%; TOC: 42.26%), marking the first demonstration of its viability as a bio-tool in GDM systems. Its unique “upward mover” behavior (tail-up, head-down) enhanced biofilm porosity and eukaryotic predation through bio-irrigation and bioturbation, effectively balancing flux stability with water quality. Similarly, PAC pre-deposition alone enhanced flux by 45.93% and achieved superior pollutant removal (UV₂₅₄: 89.94%; TOC: 60.86%) by fostering microbial enrichment and biofilm heterogeneity. By pre-depositing PAC to establish a mature biofouling layer and subsequently introducing T. Tubifex, we demonstrated that sequential application maintained high pollutant removal (UV₂₅₄: 84.13%; TOC: 50.16%). However, the physical presence of the PAC restricted predator movement and predation, causing late-stage mortality and biofilm densification, which reduced stable flux by 10%. Our findings demonstrate that adsorbents and non-native predators can regulate biofouling layer composition and structure, enhancing both flux and water treatment efficiency. By linking biofiltration and predation to biofilm dynamics, optimization of predator-absorber pairing and operational sequence to take advantage of ecological synergies, offers actionable insights for scalable water treatment solutions.