Applying S(IV)-Fe(II) binary activation of permanganate as ultrafiltration pretreatment for fouling mitigation: Performance, influencing factors, and mechanism

The widespread implementation of ultrafiltration (UF) technology, which has gained popularity for drinking water treatment, has been impeded by rising operational costs and shortened membrane lifespans resulting from membrane fouling. Here, an integrated pretreatment technique combining oxidation, adsorption, and coagulation was developed using the S(IV)-Fe(II) binary activated permanganate (PM) system, S(IV)-Fe(II)/PM. The efficacy of S(IV)-Fe(II)/PM pretreatment in mitigating UF membrane fouling was investigated for various raw water sources, including lakes, rivers, and seawater. The operational parameters of S(IV)-Fe(II)/PM pretreatment were optimized, and the underlying mechanisms for fouling alleviation were explored. Relative to conventional pretreatment methods, S(IV)-Fe(II)/PM pretreatment reduced reversible fouling-induced resistance by 13%-92% and irreversible fouling-induced resistance by 11%-86%. The S(IV)-Fe(II)/PM system exhibited optimal mitigation of membrane fouling at a PM:S(IV):Fe(II) dosage ratio of 2:3:3, with Grapid x Trapid = 45948, Gslow x Tslow = 12480, and a settling time of 30 min (where G is the velocity gradient and T is contact time). The effectiveness of S(IV)-Fe(II)/PM pretreatment in controlling UF membrane fouling can be attributed to the following mechanisms: 1) modification of feed water quality in terms of organic compound characteristics and concentration, colloidal particle quantity and size distribution, and microbial activity and quantity; and 2) adjustment of the membrane surface deposition environment, resulting in reduced polysaccharide and protein content, particle size distribution range, and biomass, as well as alterations in physicochemical properties such as hydrophilicity and interfacial free energy. This study highlights the efficacy of S(IV)-Fe(II)/PM pretreatment in ensuring highquality UF effluent while effectively reducing membrane fouling, especially its potential for alleviating irreversible membrane fouling.