Perchlorate reduction by the sulfite/ultraviolet light advanced reduction process

•Perchlorate removal by sulfite/UV-L advanced reduction process documented.•Perchlorate removal efficiency increases with increasing pH and temperature.•Increasing pH results in decreasing quantum yield for sulfite loss.•An optimal sulfite concentration exists for maximum perchlorate degradation.•Satisfactory chlorine recovery was obtained with chlorate and chloride the major products.•Oxygen abstraction mechanism to reduce perchlorate proposed. Advanced reduction processes (ARPs) are a new class of water treatment processes that combine activation methods and reducing agents to form highly reactive reducing radicals that degrade oxidized contaminants. The combination of sulfite with low-pressure ultraviolet light (UV-L) is the most effective ARP tested to date. In this study, batch kinetic experiments were conducted to characterize the kinetics of perchlorate destruction by the sulfite/UV-L ARP. Experimental variables were pH, sulfite concentration, temperature and UV-L irradiance. The rate of perchlorate degradation by sulfite/UV-L increases with increasing pH and temperature and increases with increasing sulfite concentration to a maximum and then decreases due to lack of mixing within the reactor system used. Efficiency of perchlorate degradation was measured as a quantum yield and was observed to decrease with increasing sulfite concentration. The ultimate product of perchlorate degradation by the sulfite/UV-L ARP is chloride, but chlorate was detected as an intermediate.