Efficiency and mechanism of dichlorvos removal by ozonation

The efficiency and mechanism of ozonation of dichlorvos (DDV) had been studied, and experimental result showed that ozone could effectively decompose DDV in the water, and the removal efficiency of DDV could be increased under basic condition. More than 90% of the DDV was removed within the initial 5 min. During the DDV ozonation degradation process, organic chlorine was almost completely converted into chloride. In the initial reaction stage, most of the TOC decomposition was finished during the first 5 min. The TOC removal rate increased with the increasing of ozone concentration. The analysis of GSMS showed that the main intermediate products were trimethyl phosphate, dichloroacetic acid (DCAA) and dichloro acetaldehyde. The quantitative analysis of DCAA showed that pH and reaction time had no obvious influence on the formation of DCAA. During the DDV ozonation process, there were three reaction modes: hydrolysis, direct ozone molecular oxidation and free radical reaction. The double bond of ethylene in the DDV molecule was first attacked by hydroxyl radical (·OH) to form dimethyl phosphate and dichloroethylene radical, which were further oxidized to other kinds of product or mineralized to phosphoric acid, carbondioxide and chloride.