Online chemical cleaning-triggered microbial responses and membrane fouling: Peroxymonosulfate versus ferrous-activated peroxymonosulfate

Journal article, 2026

Online chemical cleaning has been widely employed as an effective strategy to alleviate membrane fouling while maintaining continuous operation of membrane bioreactor (MBR). Recently, peroxymonosulfate (PMS) has been demonstrated as a new online cleaning agent in place of sodium hypochlorite (NaClO). However, little is known about PMS-triggered microbial responses and the consequent impact on membrane refouling. Therefore, this study investigated the effect of online cleaning with PMS and ferrous-activated PMS (PMS/Fe(II)) on sludge properties, microbial physiology and membrane refouling potential. Results show that PMS/Fe(II) treatment (e.g., 30 mg/L PMS with 2 mg/L Fe(II)) significantly enhanced sludge flocculation, increasing the mean particle size from 66.22 μm to 77.44 μm, which was likely due to the formation of in-situ Fe(III) through the oxidation of Fe(II) by PMS. Besides, the live cell fraction of treated sludge reduced to 77.2% while the reactive oxygen substance (ROS) increased to 641% after treatment by 30 mg/L Fe(II)-activated PMS against non-treated sludge, which were 15% higher and 26% less than non-activated PMS, indicating a weaker cell damage caused by activated PMS against non-activated PMS. This implies that in the presence of PMS, Fe(II) could be quickly oxidized to Fe(III), which led to bridging of extracellular substances (EPS) and floc aggregation, thus decreasing cell lysis by reducing direct contact of bacteria with oxidants. Due to the enhanced sludge aggregation and weaker cell lysis, activated PMS-triggered membrane refouling propensity was only 50% to that of same concentration of non-activated PMS. Consequently, this study demonstrated that PMS/Fe(II) could offer a promising solution for online chemical cleaning of MBR, with less adverse effects on microorganisms and reduced membrane refouling potential.