Chlorate reduction by dithionite/UV advanced reduction process

Chlorate is one of the disinfection byproducts that are formed when chlorine/chlorine dioxide is used as a primary disinfectant. This study investigated the removal of chlorate by photochemical degradation using an advanced reduction process, which is a treatment method that combines a reducing agent with an activating method to generate reducing radicals. The effectiveness of combinations of reducing agents and three UV light sources having a peak output at 254, 365, and 312 nm were evaluated for chlorate removal. Dithionite irradiated by broad-band UVB lamp having the peak energy at 312 nm showed the highest chlorate removal. In pursuit of finding the optimum advanced reduction process conditions, the environmental process variables including pH, reducing agent dose, and light intensity were investigated. Dithionite/UV-B advanced reduction process was effective in weakly acidic conditions (pH < 5), and chlorate removal occurred in two steps. The first was an initial rapid decrease in chlorate concentration that occurred before initiating UV irradiation and was attributed to reaction with dithionite decomposition products. The second step was a slow decrease during UV irradiation that is caused by radicals produced by photolysis of the products of dithionite decomposition. The major product of chlorate destruction was chloride, with negligible amounts of chlorite produced.