Applying permanganate/bisulfite (PM/BS) pre-oxidation enhanced coagulation to control fouling of ultrafiltration membrane in drinking waterworks

Abstract

Coagulation is an effective pre-treatment step for ultrafiltration (UF) drinking water treatment but is limited by the inability to regulate membrane fouling, particularly organic and biological fouling. Herein, we propose a permanganate/bisulfite (PM/BS) pre-oxidation enhanced coagulation process (PM/BS + coagulation) as UF pre-treatment and apply it to treat samples of natural surface waters. The results indicate that PM/BS + coagulation demonstrated superior performance in mitigating membrane fouling. For the four different types of real water, the specific membrane flux decline of UF following PM/BS + coagulation was 4.2 %–22 % less than that of UF following coagulation, and PM/BS + coagulation decreased the total filtration resistance by 21.7 %–74.9 % compared to coagulation alone. To achieve the best membrane fouling alleviation, PM/BS was suggested for use with aluminum polychloride-coagulation under optimized oxidation CoxTox, coagulant dosage, GT value, and sedimentation time. PM/BS + coagulation pre-treatment controlled UF membrane fouling by: 1) directly changing the UF feed water quality (e.g., composition and properties of organic matter, amount and properties of particulate matter, quantity, and metabolic activity of microorganisms) and affecting the foulant characteristics; and (2) indirectly adjusting the foulants' depositional environment (e.g., zeta potential, roughness, hydrophobicity, and interfacial free energy). These two factors influenced the subsequent fouling development. This work highlights the potential of PM/BS + coagulation to assist UF in producing high-quality drinking water while preserving a low membrane fouling propensity.