In-situ atomic hydrogen generation: A key to elevating membrane cleaning via citric acid-modified Fenton-like system

Oxidation process has been widely used to clean irreversible membrane fouling, and the development of novel oxidative cleaning process has attracted worldwide attention. In this study, a novel cleaning process with the combination of sodium percarbonate (SPC), citric acid (CA), and ferrous ion (Fe(II)) was introduced to remove organic fouling derived from the complexation of humic acid (HA) and calcium ions (Ca²⁺) for the first time. Remarkably, both flux recovery and resistance removal could reach 99 % within one hour. The efficiency and durability of this novel cleaning system were confirmed through comprehensive characterization and cyclic cleaning test of the ultrafiltration membranes. Furthermore, it effectively removed various natural organic matter-induced fouling and performed well in long-term experiments. This outstanding performance is due to the synergy between oxidative hydroxyl radicals (HO^[rad]) and reductive atomic hydrogen (H*) in SPC/CA/Fe(II). Analysis of intermediate/final products confirmed that H* is generated through the reaction of CA and HO^[rad] and absorbed by HA. Confocal laser scanning microscopy (CLSM) revealed that this absorption makes HA more susceptible to HO^[rad] attack, resulting in enhanced cleaning performance. This mechanism demonstrates the potential of advanced reduction–oxidation systems for membrane cleaning, offering new insights for the development of novel cleaning methods.