In this study, persulphate and nanoscale zero-valent iron were activated by ultraviolet irradiation (PS/nZVI/UV), followed by formation of dynamic flocs with AlCl3-TiCl4 coagulant directly injected into a gravity-driven membrane (GDM) tank. Membrane fouling caused by typical organic matter fractions including humic acid (HA), HA together with bovine serum albumin (HA-BSA), HA combined with polysaccharide (HA-SA) and the HA-BSA-SA mixture at pH of 6.0, 7.5 and 9.0 were evaluated by specific flux and fouling resistance distribution. The results showed that GDM pre-layered with AlCl3-TiCl4 flocs exhibited the maximum specific flux, followed by AlCl3 and TiCl4. Pre-oxidation with 0.5 mM PS and 0.1 g nZVI under UV radiation for 20 min was beneficial to degrade HA and SA fraction with molecular weight >100 kDa and <30 kDa, and BSA fraction with <30 kDa. The presence of BSA attributed mostly to irreversible fouling, SA together with BAS could exacerbate irreversible fouling, while HA caused the least fouling. The irreversible resistance of a PS/nZVI/UV-GDM system was 62.79%, 27.27%, 58.03% and 49.68% lower than that of control GDM in the treatment of HA, HA-BSA, HA-SA and HA-BSA-SA, respectively. The PS/nZVI/UV-GDM system could achieve the highest foulants removal efficiency at pH of 6.0. Morphological observations confirmed the differences in biofouling layers in different water types. Over 30-day operation, the bacterial genera on the biofouling layer could affect the organic removals, while the type of organic matter that was present influenced the relative abundance of bacterial genera.
Keywords: Gravity-driven membrane; NOM fractions; biofouling layer; flocs layer; persulphate/nanoscale zero-valent iron/ultraviolet (PS/nZVI/UV).