Impact of preformed composite coagulants on alleviating colloids and organics-based ultrafiltration membrane fouling: Role of polymer composition and permeate quality

Abstract

In situ formed inorganic-organic polymer composite coagulant (IPCC) is being increasingly applied in modern drinking water purification, although the impact of cationic polymers on the ultrafiltration (UF) process is controversial. This study evaluates the impact of preformed IPCC in coagulation-ultrafiltration treatment of humic acid (HA) and bovine serum albumin (BSA) rich water by using a cationic poly(diallyldimethylammonium) chloride (pDADMAC) of various molecular weight (MW) range. The effect of feed water components, and composition (2%, 5%, 10%) of polymers (large, L-pDADMAC and small, S-pDADMAC) on UF permeate water quality and membrane fouling were systematically investigated. Results show that IPCC effectively mitigated membrane fouling and improved permeate quality depending on polymer composition. Consistent with AFM and SEM fouling analysis, the membrane contact angle (fouling) under all pretreated BSA feed filtration was higher (82.0°–90.3°) than HA. It was very low (49.1°) particularly under 10% L-pDADMAC pretreated HA media than that of 10% S-pDADMAC (51.9°), but interestingly, the permeate flux in S-pDADMAC was high owing to its cake layer permeability. Consequently, BSA demonstrated more permeate flux decline (0.32–0.54) than HA (0.53–0.9), but highest DOC removal (~90%) was achieved, attributed to the propensity of the cake layer for BSA, thereafter aggravating fouling.