Control of ultrafiltration membrane fouling caused by algal extracellular organic matter (EOM) using enhanced Al coagulation with permanganate

This work was aimed to investigate the mechanism for the control of ultrafiltration (UF) membrane fouling caused by algal extracellular organic matter (EOM) using permanganate enhanced aluminum (Al) coagulation. Impacts of Al coagulation, permanganate (KMnO₄)-aided Al coagulation and in-situ formed manganese oxide (MnO₂)-aided coagulation on EOM fouling evolution were compared with respect to EOM characteristics and fouling indexes. The Al coagulation using polymeric aluminum (0.4 mg Al mg⁻¹ DOC) alone substantially alleviated the flux decline caused by EOM via reducing organic amounts by 18% and preferentially removing the high-molecular-weight (MW) (>100 kDa) components of EOM. The KMnO₄-aided Al coagulation obtained even better organic removal than the Al coagulation, especially for the fluorescent components of EOM, due to oxidative degradation and adsorption provided by manganese oxide, and thus resulted in the improved performance in fouling control. The best membrane permeability and fouling reversibility were achieved by the MnO₂-aided Al coagulation, probably attributed to adsorption of the hydrophilic fractions of EOM on in-situ formed MnO₂ particles. In terms of fouling mechanisms, EOM fouling was governed by multiple mechanisms with standard blocking and cake filtration dominating the fouling formation. The enhanced Al coagulation with KMnO₄ or in situ formed MnO₂ particles decreased the role of cake filtration but boosted the impact of standard blocking by preferentially removing the high-MW biopolymers.