Insight into the degradation of methomyl in water by peroxymonosulfate

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 center dot-) and hydroxyl ((OH)-O-center dot) 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 center dot- and (OH)-O-center dot. However, furfuryl acid (FFA) resulted in reduced degradation by applied systems, which showed that singlet oxygen (O-1(2)) 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 degrees C to 40.0 degrees 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.

Automated summary

Methomyl (MET), a widely used carbamate pesticide, can be effectively degraded using peroxymonosulfate (PMS)-based advanced oxidation processes. Different systems, such as PMS-Only, pyrite (PyR)-PMS and zero-valent iron (ZVI)-PMS, showed varying levels of MET degradation, with singlet oxygen (O-1(2)) playing a major role. The PMS-Only system demonstrated efficient degradation across a wide range of conditions and showed promising results in real water samples.