An investigation of refractory organics in membrane bioreactor effluent following the treatment of landfill leachate by the O3/H2O2 and MW/PS processes

Abstract

In this study, refractory organics in a membrane bioreactor (MBR) effluent were investigated following the treatment of landfill leachate by the ozone combined hydrogen peroxide (O₃/H₂O₂) and microwave-activated persulfate (MW/PS) processes. The treatment efficiency and the transformation characteristics of refractory organics and reactive oxygen species were determined. It was found that an acidic environment and an increase in the O₃ dosage improved the organic removal efficiency in the O₃/H₂O₂ process, and the use of H₂O₂ improved the treatment efficiency, while excessive H₂O₂ inhibited it. In the MW/PS process, an increase in the PS dosage and MW power greatly improved the treatment efficiency, while an alkaline environment inhibited it. Under the optimized reaction parameters, the O₃/H₂O₂ and MW/PS processes effectively degraded refractory organics (i.e., humic acid and fulvic acid) into components with a smaller molecular weight and simpler structure. The humification, aromaticity, and conjugation of organics in wastewater were greatly reduced. Compared to the O₃/H₂O₂ process, the MW/PS process had a better treatment effect on refractory organics, and there were more low molecular weight organics (<1 kDa) in the treated wastewater. Because O₃ is the main selective oxidant in the O₃/H₂O₂ process, a large amount of organic acids were accumulated. A large amount of hydroxyl radicals and sulfate radicals with strong oxidation ability were produced in the MW/PS process, and therefore the combined action of hydroxyl and sulfate radicals can efficiently decompose humus and intermediate organics. Overall, the MW/PS process was more effective in treating the MBR effluent than the O₃/H₂O₂ process. The results of this study provide a reference for the selection of an advanced oxidation process to eliminate refractory organics in landfill leachate.

Keywords: Landfill leachate; Membrane bioreactor; Ozone combined hydrogen peroxide process (O(3)/H(2)O(2)); Persulfate.