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Conventional membrane distillation (MD) membranes are hydrophobic and challenged by severe membrane fouling and wetting. Current surface modification strategies for anti-fouling and anti-wetting purposes, usually complex and time-consuming, often compromise the MD flux. Herein, we propose a modified interfacial polymerization (mIP) approach to fabricate Janus membranes with rapid and robust MD performance. In the mIP process, a dry hydrophobic substrate is first immersed in an oil-phase monomer solution and then in contact with an aqueous monomer solution to trigger the mIP reaction. The as-fabricated Janus membrane (e.g., IP2@PTFE) comprised an ultrathin, underwater oleophobic, and defect-free polyamide (PA) layer and a porous polytetrafluoroethylene (PTFE) substrate. Compared with the unmodified PTFE membrane, the vacuum MD flux of the IP2@PTFE membrane held a 177.4 % increase when tackling a NaCl solution (3.5 wt%) at 60 °C. When the NaCl solution contained sodium dodecyl sulfate (SDS) surfactant or/and mineral oil, the IP2@PTFE membrane exhibited fouling and wetting resistance simultaneously; conversely, severe oil fouling and quick SDS-induced wetting occurred on the pristine PTFE membrane. The mIP process does not require any pretreatment of the hydrophobic substrate, so it is facile and scalable. We believe that this study will facilitate the design of robust MD membranes. [Display omitted] • A facile construction strategy via mIP for preparing hydrophilic/hydrophobic Janus membranes • The Janus membranes have obviously higher VMD fluxes than the pristine PTFE membrane. • A two-step mIP process can effectively control the defects of hydrophilic top layer. • The IP2@PTFE membrane has both oil-fouling and SDS-wetting resistance. [ABSTRACT FROM AUTHOR]

• The moderate KMnO 4 /Fe(Ⅱ) pre-oxidation process was quantified. • The KMnO 4 /Fe(Ⅱ) pretreatment delays the formation of cake layer blockage. • In-situ formed MnO 2 has the best effect for organic removal. • In-situ formed Fe(III) has the best effect on algal aggregation. Moderate KMnO 4 /Fe(II) pre-oxidation is a promising technique to mitigate membrane fouling and avoid the environmental risk brought by the breakage of algae cells, which often happens in the practical application of pre-oxidation techniques. Various components, i.e., KMnO 4 , in-situ formed MnO 2 and in-situ formed Fe(III), are involved in this technique, and how they mitigate membrane fouling is still unclear. In this work, we investigated their performances on the mitigation of membrane fouling and their influences on the physiochemical characteristics of the organic foulants and fouling layers individually. It was found that Fe(III) formed in situ showed the best performance in controlling membrane fouling among the various components, and the total fouling resistance was reduced by 87.6%. MnO 2 formed in situ was most effective in enhancing the organic matter removal performance of ultrafiltration, and the removal rate of the dissolved organic matter reached 39.9%. In addition, after the KMnO 4 /Fe(II) pretreatment, the electrostatic repulsion between algal foulants was decreased, facilitating the aggregation of foulants. Based on the physicochemical changes of the characteristics of foulants and fouling layers on the membrane surface, we concluded that KMnO 4 /Fe(II) alleviated the algae-derived membrane fouling mainly in two ways: (1) enhancing the interception effect of ultrafiltration membrane on hydrophobic organic matter, which reduced the blockage of membrane pores; (2) enhancing the sparseness of the cake layer on the membrane surface, which reduced the cake fouling resistance. Our work not only shows that the KMnO 4 /Fe(II) pretreatment technique has considerable applicative potential in alleviating the membrane fouling caused by algae-laden water, but also gives a comprehensive understanding of the fouling mitigation mechanisms. [ABSTRACT FROM AUTHOR]