A moderate activated sulfite pre-oxidation on ultrafiltration treatment of algae-laden water: Fouling mitigation, organic rejection, cell integrity and cake layer property

[Display omitted] •Moderate pre-oxidation can highly alleviate the membrane fouling.•Algae cell kept integrity in the activated sulfite system.•Moderate oxidation and coagulation synerigistic effect contribute to the performance.•Effluent water quality was improved by the activated sulfite pretreatment. In this study, a moderate oxidation strategy, in-situ pretreatment with ferrous activated sulfite (Fe(II)/S(IV)), was employed to mitigate membrane fouling during the filtration of algae-laden water and to improve the rejection of organic matter. It was worth noting that the moderate oxidant can avoid serious cells breakage and control the release of intracellular organic matter. Besides, sulfite-based pretreatment had an excellent removal effect DBPs, including chloroform (TCM), dichloroacetonirile (DCAN) and trichloronitromethane (TCNM). Fe(II)/S(IV) pretreatment also improved the removal of DOC and UV254 and the proportion of hydrophilic substances was increased to 91.4% which was conductive to membrane fouling alleviation. With the increase in Fe(II) dosage, both the Rr and Rir were declined since the macromolecular organic transforming to micromolecular organic and the coagulation effect by the in-situ generation of Fe(III). Meanwhile, permeable channels formed on the loose and porous cake layer due to the in-situ Fe(III) could enhance the specific flux. When the ratio of Fe(II)/S(IV) was 2:1, the fouling mechanism was inferred to cake filtration which showed a great discrepancy with other condition.