Simultaneous removal of chlorite and coexisting emerging organic contaminants by sulfite: Kinetics and mechanisms

The inevitable formation of chlorite (ClO2–) and the ineffective degradation of some emerging organic contaminants (EOCs) during chlorine dioxide disinfection have aroused increasing concern about their adverse effects on human health. In this study, the kinetics and mechanisms of simultaneous removal of ClO2– and coexisting EOCs by sulfite (S(IV)) were investigated. Under aerobic conditions, ClO2– and coexisting EOCs could be effectively removed by S(IV) at pH 6.5–7.5, and their removal rates decreased as pH increased. ClO3– was generated in this process but its amount decreased with increasing pH. Many lines of evidence verified that the reaction of ClO2– with HSO3– and H+ generated SO3•− and ClO•, and the generated ClO• was rapidly quenched by S(IV) to form OCl– and SO3•−. Subsequently, SO3•− quickly reacted with O2 to form SO5•−, which was further transformed into SO4•−. SO4•− was the dominant reactive oxidant contributing to the degradation of coexisting EOCs and the formation of ClO3–. Using S(IV) to simultaneously control ClO2– and coexisting EOCs in water treatment is a promising approach because its performance was slightly affected by the water matrix.