Comparison of peroxodisulfate and peroxymonosulfate activated by microwave for degradation of chlorpyrifos in soil: Effects of microwaves, reaction mechanisms and degradation products

Abstract

The combination of microwave (MW) and persulfate (PS, including peroxodisulfate (PDS) and peroxymonosulfate (PMS)) has been proved to be a potential method for degradation of organic pollutant. In this study, the degradation of chlorpyrifos (CPF) in soil by MW/PDS and MW/PMS was investigated. As a result, a synergistic effect was created between MW and PS. Compared with conventional heating (CH) providing thermal effect, MW also played a special non-thermal effect for PDS activation, causing superior CPF degradation by MW/PDS. However, the similar degradation efficiency of CPF in MW/PMS system and CH/PMS system indicated mainly a thermal effect was played by MW in MW/PMS system. The generation of reactive oxygen species (ROS) was explored in detail, SO4•− and •OH, generated in water, was the main ROS in MW/PDS system, and 1O2, generated in soil/water interface, was the main ROS in MW/PMS system. 100:1 of PS to CPF molar ratio, 1:1 of water and soil mass ratio were selected as appropriate reaction conditions. Environmental factors including pH and humic acid showed different effects on CPF degradation in MW/PDS system and MW/PMS system. Moreover, the degradation products were different due to different selectivity of ROS, reaction pathways were predicted based on Gaussian calculation and detected products. In addition, toxicity prediction, energy estimation and the applicability in different types of soils were investigated for practical significance of CPF degradation by MW/PS. Therefore, MW/PS provides a promising approach for remediation of CPF-contaminated soils.