Landfill leachate contains not only high concentrations of refractory organic matter and ammonia nitrogen, but also high concentrations of chloride ions (Cl⁻). The modification of reactive species of the peroxymonosulfate (PMS) oxidation system by Cl⁻ and its priority sequence for the removal of NH₄⁺-N and organic matter from landfill leachate remain unclear. This study investigated the removal characteristics of NH₄⁺-N and organic matter in the microwave (MW)/PMS system with high Cl⁻ content. The results show that increasing Cl⁻ concentration significantly improves the production of hypochlorous acid (HOCl) in the MW/PMS system under acidic conditions, and that the thermal and non-thermal effects of MW irradiation have an important influence on the HOCl produced by PMS activation. The maximum cumulative concentration of HOCl was 748.24 μM after a reaction time of 2 min. The formation paths of HOCl are (i) SO₄^•− formed by the MW/PMS system interacting with Cl⁻ and HO^•, and (ii) the nucleophilic addition reaction of PMS and Cl⁻. Moreover, the high concentration of HOCl produced by the system can not only remove NH₄⁺-N in situ, but also interact with PMS to continuously generate Cl^• as an oxidant to participate in the reaction with pollutants (e.g., NH₄⁺-N and organic matter). Common aqueous substances (e.g., CO₃²⁻, HCO₃⁻, NO₃⁻, and humic acid) in landfill leachate will compete with NH₄⁺-N for reactive species in the system, and will thereby inhibit its removal to a certain extent. It was found that when NH₄⁺-N and leachate DOM co-exist in landfill leachates, they would compete for reactive species, and that humic acid-like matter was preferentially removed, leading to the retention of fulvic acid-like matter. It is hoped that this study will provide theoretical support for the design and optimization of methods for removing NH₄⁺-N and organic matter from landfill leachate with high chloride ion content.

In this study, a microwave-enhanced and iron–carbon (Fe–C)-activated H₂O₂ process (MW/Fe–C/H₂O₂) was applied to the advanced treatment of biologically treated effluent from a semi-aerobic aged refuse biofilter (SAARB). The enhancement achieved by introducing MW radiation into the Fe–C/H₂O₂ process was comprehensively investigated. It was found that the removal effect of the MW/Fe–C/H₂O₂ process on organic matter in the effluent was better than that of other controlled processes. Three-dimensional excitation and emission matrix (3D-EEM) fluorescence spectra showed that the degree of molecular condensation and molecular weight of dissolved organic matter in the effluent were greatly reduced, and humus was largely destroyed and mineralized. When the H₂O₂ dosage was 10 mL L⁻¹, the Fe–C dosage was 1 g L⁻¹, the MW output power was 240 W, the initial pH was 3, and the reaction time was 10 min, the total organic carbon (TOC), absorbance at a wavelength of 254 nm (UV₂₅₄), and color number (CN) removal efficiencies from the effluent were 28.95%, 40.88%, and 75.62%, respectively. By characterizing the iron–carbon materials before and after the reaction, it was found that the iron–carbon materials contained a variety of active substances such as zero-valent iron (Fe⁰) and iron oxides, which can participate in homogeneous and heterogeneous Fenton reactions with H₂O₂, and MW radiation as an external energy source can strengthen the above process to a certain extent. This will accelerate the removal of organic matter from the effluent of a SAARB.