Role of multivalent iron in enhancing sodium percarbonate oxidation for alleviating membrane distillation fouling caused by shale gas produced water

Membrane distillation (MD) shows significant potential for treating shale gas produced water, yet membrane fouling remains a persistent challenge in conventional MD systems. This study investigates an innovative pretreatment approach using sodium percarbonate (SPC) oxidation combined with various iron-based catalysts, systematically evaluating five distinct treatment processes, including standalone MD and four hybrid systems incorporating iron species. The experimental results demonstrated progressive improvement across all pretreatment methods, with the most effective Fe(VI)/Fe(II)/SPC-MD hybrid process achieving a 27.28% reduction in fluorescent organics, a decrease in hydrophobic fraction from 52.19% to 39.97%, and a notable enhancement in normalized flux from 0.42 to 0.79 compared to untreated shale gas produced water. Comprehensive membrane characterization through advanced analytical techniques, including electron microscopy, infrared spectroscopy, and surface property measurements, conclusively demonstrated the effectiveness of these oxidation pretreatments in mitigating foulant deposition and preserving membrane performance. Statistical analysis highlighted hydrophobic, hydrophilic organic components, and organics along with coagulation effects as primary contributors influencing membrane fouling. The superior performance of the combined Fe(VI)/Fe(II)/SPC oxidation system stems from its multifaceted mechanism that simultaneously leverages oxidative degradation, coagulation, and adsorption processes to reduce both organic concentration and hydrophobicity, thereby significantly alleviating membrane fouling.