Insight into chloride effect on the UV/peroxymonosulfate process

In this study, we examined chloride impact on UV/peroxyrnonosulfate (UV/PMS) process with benzoate acid (BA) and chloroform (TCM) as target compounds, which react rapidly and slowly with HO' and SO4 center dot-, respectively. The chloride impact on UV/PMS process in simulated real water (mixture of nitrate, carbonates, natural organic matter (NOM) and chloride) was analyzed based on the individual impact of anions and NOM. Pseudo steady-state and dynamic kinetic models were developed to calculate radical concentrations and determine the roles of water matrix in BA and TCM degradation. Radical conversion and radical selectivity were proposed to be quantified by radical termination rate and radical participation ratio (RPR). The latter one indicated the radical participation between target compound and other radical termination species coexisted. Chloride stimulating or inhibiting target compound destruction, due to radical conversion induced by chloride concentration variation, was deduced to depend on the RPR difference of conversion radicals. Nitrate affected target compound destruction rate by two aspects, radical conversion (similar to the role of chloride) and total photoproduction rate of HO center dot and SO4 center dot-. The total photoproduction rate of radicals showed a PMS-concentration involved dependence on nitrate concentration. Nitrate enhanced total photoproduction rate at low PMS concentration and reduced the rate at high PMS concentration. In simulated real water, carbonates played the key role in radical conversion and RPR. The coexistence of carbonates and chloride converted most SO4 center dot- into Cl-2(center dot-) and Cl-center dot, leading to an obvious inhibition of chloride on BA degradation.