Comprehensive effect of water matrix on catalytic ozonation of chloride contained saline wastewater

Abstract

Chloride ion (Cl−) is one of the most common anions in wastewater and saline wastewater, but its elusive effects on organics degradation are not clear yet in many cases. In this paper, the effect of Cl− on organic compounds degradation is intensively studied in catalytic ozonation of different water matrix. It was found that the effect of Cl− is almost completely reflected by transforming ·OH to reactive chlorine species (RCS), which is simultaneously competitive with organics degradation. The competition between organics and Cl− for ·OH directly determines the ratio of their consumption rate of ·OH, which depends on their concentration and reactivity with ·OH. Especially, the concentration of organics and solution pH may change greatly during organics degradation process, which will correspondingly influence the transformation rate of ·OH to RCS. Therefore, the effect of Cl− on organics degradation is not immutable, and may dynamically change. As the reaction product between Cl− and ·OH, RCS was also expected to affect the degradation of organics. But we found that Cl· had no significant contribution to the degradation of organics in catalytic ozonation, which may due to its reaction with ozone. Catalytic ozonation of a series of benzoic acid (BA) with different substituents in chloride contained wastewater was also investigated, and the results showed that the electron-donating substituents can weaken the inhibition of Cl− on BAs degradation, because they increase the reactivity of organics with ·OH, O3 and RCS.