A review on the removal of Cl(-I) with high concentration from industrial wastewater: Approaches and mechanisms

Large quantities of wastewaters containing high concentrations of Cl(-I) can be generated in several industries when chloride-containing materials and additive agents are employed. Because Cl(-I) is unavailable to microorganisms, physicochemical methods are generally used for the removal of Cl(-I); however, as the most stable form of chlorine under aqueous conditions, Cl(-I) in wastewaters is difficult to remove to achieve low residual concentrations through common physicochemical methods. This paper provides new insights into traditional precipitation, oxidation, ion exchange and physical separation methods, as well as newly developed approaches, for Cl(-I) removal from various industrial wastewaters through analysis of the mechanisms, applicable conditions, optimum parameters, and method advantages and disadvantages. Moreover, the developmental trends and potential improvements to these approaches are also presented. Currently, precipitation is the most common and efficient Cl(-I) removal method, for which ultraviolet (UV) light is regarded as an effective means of improvement. Additionally, advanced oxidation processes (AOPs), where Cl(-I) can be oxidized to generate Cl radicals, Cl2− radicals, Cl2 gas, etc., show great promise for Cl(-I) removal. This review provides a theoretical foundation for the effective treatment and for the secondary utilization of industrial wastewaters containing Cl(-I). [Display omitted] •Precipitation is still the most common and efficient method for Cl(-I) removal.•UV light is the effective improvement means for precipitation methods.•AOPs show great promise for Cl(-I) removal.•Leakage of Cl2 during Cl(-I) removal is the big issue in AOPs.