Comparison of the ability of three advanced oxidation processes (AOPs) converting Cl- to active inorganic chlorine species (AICS)

Advanced oxidation processes (AOPs) during wastewater treatment oxidise Cl- to active inorganic chlorine species (AICS). AICS can react with organic compounds in wastewater to form toxic and hazardous chlorinated organic compounds, most of which are carcinogenic, teratogenic, and mutagenic. In this study, the abilities of three AOPs, i.e., electrochemical, ozone, and Fenton, to convert Cl- to AICS were compared. The results showed that at an initial Cl- concentration of 710 mg-Cl/L and a reaction time of 120 min, the conversion efficiencies of electrochemical, ozone, and Fenton processes were 74.1%, 21.0%, and 4.1%, respectively. The respective concentrations were 436.44 mg-Cl/L, 2.23 mg-Cl/L, and below detection limit for free chlorine; and 82.29 mg-Cl/L, 65.11 mg-Cl/L, and 6.30 mg-Cl/L for ClO3- . The abilities of the three AOPs to convert Cl- to AICS were in the order, electrochemical >> ozone >> Fenton. In the present study, the potential reasons for the significant differences in the Cl- oxidising ability of the AOPs were discussed. The effects of temperature and initial pH on the formation of free chlorine in the ozone and electrochemical processes were also investigated. These results are of great significance for the selection of AOPs for treating wastewater containing Cl- in practical applications.