Exploring the feasibility of novel double-skinned forward osmosis membranes with higher flux and superior anti-fouling properties for sludge thickening

Sludge thickening from sewage treatment plants is an essential step in reducing the sludge volume and processing cost of the subsequent treatment. Forward osmosis (FO) technology is one of the research endeavors used in the field of membrane separation and feed solution concentration. However, the traditional used single-skinned FO membranes encounter the problems of serious internal concentration polarization (ICP) and fouling phenomenon within porous substrates. A novel double-skinned FO membrane was proposed in this study in order to enhance the anti-fouling performance and mitigate the ICP phenomenon. Single-skinned FO membrane using the same substrate was also fabricated. Results demonstrated that the double-skinned FO membrane significantly reduced ICP and exhibited higher flux when using draw solutions with high concentrations as compared to the single-skinned FO membrane. Furthermore, the double-skinned FO membrane demonstrated reasonably high-water flux (11.6 LMH), whereas zero flux was recorded from the single-skinned FO membrane when using the feed solution that contained 15.0 g/L organic foulants in the fouling tests. At last, the double-skinned FO membrane exhibited superior anti-fouling properties and much higher flux than that of single-skinned FO membrane operated under both modes during the long-term sludge thickening process, indicating the great potential of the double-skinned FO membrane to deal with the high-water-content sewage sludge in the water treatment process.