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.