Ultraviolet-enhanced Fe0-activated H2O2 process for the removal of refractory organic matter from landfill leachate: Performance and mechanism.

The Fenton-like process, utilizing zero-valent iron (Fe0) and hydrogen peroxide (H2O2), is employed to degrade refractory organic matter in membrane bioreactor (MBR) effluent derived from landfill leachate. However, the rate-limiting Fe2+/Fe3+ redox step diminishes treatment efficacy and generates substantial iron sludge. This study elucidates the mechanism by which ultraviolet (UV) irradiation augments the Fe0/H2O2 process for the removal of refractory organic matter in MBR effluent. The results show that the UV- enhanced H2O2 process effectively disrupts the aromatic structure of organic compounds, reducing molecular weight, degree of polymerization, and humification. Compared with the Fe0/H2O2 process, the removal efficiency of UV254, color number, and total organic carbon in the effluent treated by the UV/Fe0/H2O2 process increased by 24.16%, 14.62%, and 57.46%, respectively. Concurrently, the generation of iron sludge was reduced by 21.6%. This enhancement is primarily attributed to UV's ability to intensify the Fe2+/Fe3+ redox cycle and expedite the surface corrosion of Fe0, yielding more iron oxides. This accelerates the decomposition of H2O2, generating a higher quantity of •OH through both homogeneous and heterogeneous Fenton-like reactions. The refractory organic matter is removed through the oxidation by •OH, as well as the adsorption and precipitation facilitated by iron-based colloids. PRACTITIONER POINTS: UV promotes Fe0/H2O2 process to degrade refractory organic matter in MBR effluent. UV promotes Fe0 to dissolve more Fe2+ and the redox cycle of Fe2+ and Fe3+. The dosage of H2O2 or Fe0 influences the treatment effect of the process.