Overlooked heavy metal-induced natural organic matter property transformation and its positively resultant interaction with membrane surface

Heavy metals (HMs), which pose significant ecological and human health risks, spontaneously interact with ubiquitous natural organic matter (NOM) in aquatic environments, forming aggregates with distinct physicochemical properties from their precursors. However, the implications of these altered properties on membrane-based advanced water treatment have been largely overlooked. Herein, the HMs-NOM complexation mode and their interaction mechanisms with ultrafiltration membranes were explored. The results demonstrated that HMs primarily modified both the dipole moment and electron-donating capacity of NOM, thereby affecting its hydrophilicity and interfacial filtration performance. Moreover, electrostatic complexation and bridging between HMs and NOM facilitated partial HMs retention and NOM removal. The extended Derjaguin-Landau-Verwey-Overbeek theory revealed that HMs elevated interfacial energy barriers between membranes and humic acid/sodium alginate, as well as among NOM aggregates, promoting looser fouling layer formation and mitigating irreversible fouling. For HMs and protein co-contamination systems, membrane flux improvement principally originated from protein secondary structures disorder rather than interfacial interactions. The filtration performance of Songhua River water further verified the potential exploration value of this study for membrane-based HMs contaminated water treatment.