Gravity-driven ceramic membrane surface electrochemical system with in-situ electrooxidized activated carbon-MnOx layer for enhanced manganese removal and membrane performance in ground water treatment

Manganese contamination in groundwater poses significant challenges for water treatment, necessitating innovative solutions to improve efficiency and sustainability. This study introduced a gravity-driven ceramic membrane surface electrochemical system, which enabled in-situ redox-based membrane cleaning while promoting the formation of electrooxidized activated carbon-manganese oxide (EOAC-MnOx) functional layer. In intermittent electrochemical cleaning, when operated at a 5 V potential, the system effectively mitigated the adverse impacts of microbial mortality on manganese removal, achieving a markedly high removal efficiency (72.8 %) under the optimized configuration. The strong oxidative properties of free chlorine oxidized the high-molecular-weight extracellular polymeric substances (EPS) to medium-molecular-weight fractions (1–4 kDa), while the forward osmosis tended to cause EPS to accumulate on the membrane surface and in the membrane pores, limiting the cleaning effect. Electrochemical backwashing can significantly reduce irreversible membrane contamination and improve water production performance (achieving up to 108.8 % flux recovery after day 70 cleaning). Scanning electron microscopy revealed that the coral-like morphology of the EOAC-MnOx layer provided abundant active sites for manganese adsorption and chemical oxidation. Furthermore, X-ray photoelectron spectroscopy confirmed that the coexistence of mixed-valence states of Mn(IV) and Mn(III) enhanced adsorption capacity and promoted diverse crystal structures, establishing a self-sustaining cycle for manganese removal. This integrated approach offers a promising pathway for addressing manganese pollution in groundwater.