A comparative study of the degradation of refractory organic matter in MBR effluent from landfill leachate treatment by the microwave-enhanced iron-activated hydrogen peroxide and peroxydisulfate processes

Abstract

This study applied two advanced oxidation processes dominated by different reactive oxygen species (ROS), microwave-iron-hydrogen peroxide (Microwave/ZVI/H2O2) and microwave-iron-peroxydisulfate (MW Microwave/ZVI/PDS), to the degradation of refractory organic matter in the membrane bioreactor (MBR) effluent from landfill leachate treatment. The two processes were systematically compared according to their degradation efficiencies and transformation mechanisms toward refractory organic matter in MBR effluent. Controlled experiments and an influential factor analysis showed that the total organic carbon (TOC) removal efficiencies of the Microwave/ZVI/H2O2 and Microwave/ZVI/PDS processes were 74.48% and 64.40%, respectively. After treatment by the two processes, fulvic-like substances with a low molecular weight and high fluorescence frequency, and humic-like substances with a large molecular weight, stable chemical structure, and high aromaticity were substantially degraded. In addition, the Microwave/ZVI/H2O2 process had a better TOC removal efficiency than the Microwave/ZVI/PDS process over a wider pH range (3−11), which was mainly attributed to the different dominant ROS in the two processes. Both Fe3O4 and FeOOH were found in the reacted ZVI of the two processes, and the reaction mechanisms included Fenton-like reactions and adsorption-precipitation by iron (hydro)oxides, which were promoted by microwave irradiation. This study provided a theoretical reference for the efficient treatment of MBR effluent.