Electro-controlled membrane coupling Fenton (E/M-Fenton) in treating nanofiltration concentrate: Removal performance and membrane fouling behavior

Fenton and membrane filtration are increasingly adopted as treatments to treat nanofiltration (NF) concentrates. However, dosing acid and alkali agents could pose environmental risks for the traditional Fenton. To address this challenge, the performance of traditional Fenton was investigated in NF concentrate treatment. The as-optimized conditions were Fe²⁺ 4 mM, H₂O₂ 10 mM, and pH 3.5. The Fenton effectively degraded fluorescent materials, especially humic-like and fulvic-like substances. Based on these conditions, the traditional Fenton approach improved the specific ultrafiltration (UF) flux above 0.67. An increase in hydraulic shear among 0.4 ∼ 1.6 m/s and a decrease in filtration pressure between 30 ∼ 80 kPa benefited the UF reversible and irreversible fouling, respectively. The electro-controlled membrane coupling Fenton (E/M-Fenton) process was suggested by adding electrolysis, achieving the in situ production of H⁺ cations and OH⁻ anions. Compared with the E/M-Fenton without internal recirculation, the porosity on the surface of the membrane was increased by 15.4% in the system with internal recirculation. Moreover, it averagely removed 66.5% of dissolved organic matter and 78.8% of UV absorbance at 254 nm, limiting the rigidity of the organic molecular structure and further improving the UF permeate. The E/M-Fenton slightly increased transmembrane pressure by 18%, performing stable UF fouling in a week. These results are essential to developing environmental-friendly strategies for Fenton to treat NF concentrate.