Removal of kathon by UV-C activated hydrogen peroxide: Kinetics, mechanisms, and enhanced biodegradability assessment

Abstract

Kathon (CMI-MI), a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one (CMI) and 2-methyl-4-isothiazolin-3-one (MI), was extensively used in industry as a nonoxidizing biocide or disinfectant. However, it would show adverse effects on aquatic life when it is discharged into surface water.In this study, the removal performance, parameter influence, degradation products and enhancement of subsequent biodegradation of CMI-MI in UV/H2O2 system were systematically investigated. The degradation rate of CMI-MI could reach 90% under UV irradiation for 20 min when the dosage of H2O2 was 0.3 mmol·L–1. The DOC (dissolved organic carbon) mineralization rate of CMI-MI could reach 35% under certain conditions ([H2O2] = 0.3 mmol·L–1, UV irradiation for 40 min). kobs was inversely proportional to the concentration of CMI-MI and proportional to the concentration of H2O2. The degradation rate of CMI-MI was almost unchanged in the pH range from 4 to 10. Except the presence of CO32- inhibited the removal rate of CMI-MI, SO42-, Cl−, NO3-, and NH4+ did not interfere with the degradation of CMI-MI in the system. It was found that UV/H2O2 system had lower energy consumption and more economic advantage compared with UV/PS system by comparing the EEO (electric energy per order) values under the same conditions. Two main organic products were identified, namely HCOOH and CH3NH2. There’s also the formation of Cl− and SO42-. After UV and UV/H2O2 photolysis, the biochemical properties of CMI-MI solution were obviously improved, especially the UV/H2O2 treatment effect was better, indicating that UV/H2O2 technology is expected to combine with biotechnology to remove CMI-MI effectively and environmentally friendly from wastewater.