Insight into the degradation of methomyl in water by peroxymonosulfate

Abstract

Methomyl (MET) is a carbamate pesticide frequently used in agriculture, globally. Its high solubility makes it a potential water pollutant. MET can be removed by peroxymonosulfate (PMS)-based advanced oxidation processes. This study explains MET degradation by PMS-Only, pyrite (PyR)-PMS and zero-valent iron (ZVI)-PMS systems. The degradation by PMS-Only, PyR-PMS and ZVI-PMS systems was 85.4%, 94.9% and 87.0%, respectively. The generation of reactive oxygen species (ROS) and their role in degradation was elucidated by electron paramagnetic resonance (EPR) and free-radical quenching analyses, respectively. EPR analysis indicated the presence of sulfate (SO4•−) and hydroxyl (•OH) radicals. The degradation in PMS-Only and ZVI-PMS systems was not significantly inhibited by tert-butyl alcohol (TBA) and methanol (MeOH), which suggests that the degradation in both systems was not majorly carried out by SO4•− and •OH. However, furfuryl acid (FFA) resulted in reduced degradation by applied systems, which showed that singlet oxygen (1O2) was mainly responsible for degradation in all systems. These results showed that MET was majorly degraded by non-radical PMS oxidation. PMS-Only system resulted in an almost equal degradation, compared with PyR-PMS and ZVI-PMS systems. So, detailed analysis was carried out for PMS-Only system. Hence, experiments were conducted to investigate the effect of PMS concentration, MET concentration, pH and temperature on the degradation by PMS-Only system, which showed that PMS-Only system was efficient from pH 5.0 to pH 9.0, and from 10.0 °C to 40.0 °C. Further, PMS-Only system has a potential for effective degradation in real waters because it resulted in 66.5%, 63.7% and 60.4% degradation in tap water, lake water and sewage water, respectively.