Simultaneous flux recovery and trade-off breakthrough: New insights into repeated radical-based membrane cleaning

Radical-based cleaning technology is regarded as an efficient solution for fouled membranes. Nevertheless, limited studies have investigated the inevitable residual fouling and its effects on membrane filtration under prolonged use of these methods. To explore, the peroxymonosulfate/hydroxylamine/ferrous (PMS/NH₂OH/Fe(II)) system, known for generating abundant radicals, was employed in this study. With the help of hydroxyl radical (HO^·), PMS/NH₂OH/Fe(II) effectively restored the flux of membranes fouled by humic acid (HA), bovine serum albumin (BSA), and sodium alginate (SA) in dead-end filtration to 96 %, 97 %, and 103 % of their original values, respectively. Over cyclic radical cleanings, the membrane flux increased to 181 %∼219 % of the original flux. However, the retention performance remained nearly unchanged, suggesting a breakthrough in the selectivity-permeability trade-off. Comprehensive characterization of the membranes indicated that the maintenance of retention performance relied on the reduced porosity due to residual fouling, while the increased flux was attributed to the carboxylation modification of residual fouling. Supported by this mechanism, PMS/NH₂OH/Fe(II) maintained satisfactory cleaning efficiency during practical cleaning of East Lake-fouled membranes. Overall, this study uncovers how repeated radical-based cleaning affects membrane performance, offering foundational insights for the application of this technology.