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

Abstract

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.