Feiyan Fang, Weiming Chen
Fenton oxidation is increasingly used to remove refractory dissolved organic matter from biologically treated landfill leachate effluent (BTLE). However, in this chloride-rich matrix, the oxidation process inevitably generates toxic chlorinated oxidation by-products (Cl-OBPs), compromising the safety of the treated effluent. Herein, we investigated the role of polymeric ferric sulfate (PFS) flocculation pretreatment in the control of Cl‑OBP formation during Fenton oxidation of BTLE. Under the optimized Fenton conditions (pH = 3, [Fe2+]:[H2O2]=1:10, [H2O2]:[TOC]0 = 5), the standalone Fenton system achieved a total organic carbon (TOC) removal of 51.82 %, but concurrently generated a high concentration of Cl-OBPs (1576.56 μg/L), with haloacetic acids (HAAs) being the predominant species. Compared with the standalone Fenton system, the Flocculation-Fenton system (at the same [H2O2]:[TOC]0 ratio of 5) enhanced TOC removal efficiency to 59.83 % and reduced total Cl-OBP concentration by 41.55 %. This suppression effect was most pronounced for polychlorinated HAAs, with the concentrations of dichloroacetic acid and trichloroacetic acid reduced by 76.00 % and 78.55 %, respectively. Flocculation pretreatment selectively removed highly aromatic, highly unsaturated, high-molecular-weight organic compounds, particularly those with electron-rich functional groups (e.g., -OH), from BTLE, which are key precursors for HAA formation. Removal of these organic compounds suppressed the two primary HAA formation pathways: direct chlorination by reactive chlorine species (Cl•, Cl2•-, and free chlorine) and chlorination following hydroxyl radical oxidation. After treatment with the Flocculation-Fenton system, both the Cl-OBP-associated cytotoxicity and the phytotoxicity of the effluent were reduced. These findings provide mechanistic insight and practical guidance for advanced treatment and by-product control in high-chloride landfill leachate systems.