Effect of low- and medium-pressure Hg UV irradiation on bromate removal in advanced reduction process

Advanced Reduction Processes (ARP) have been developed by combining UV irradiation with reducing reagents, which produces reactive reducing free radicals that degrade contaminants (e.g. vinyl chloride, 1,2-dichloroethane, perchlorate, and bromate). This study investigates bromate destruction by ARPs using medium-pressure mercury UV light lamp (UV-M) and low-pressure mercury UV light lamp (UV-L). Effects of experimental parameters including initial bromate concentration, reducing reagent (sulfite) dose, and pH on bromate removal kinetics and quantum yield were evaluated. The pseudo-first-order rate constant (kobs) by UV-M ARP was greater by 3 times than that by UV-L ARP. UV-M and UV-L achieved a complete bromate removal of an initial concentration at 500 ppb with fluences of 10.5 J cm−2 and 73.5 J cm−2, respectively. It was found that direct photolysis is a dominant mechanism with the UV-M ARP showing that the effect of sulfite dose had no apparent influence on the bromate removal, whereas kobs was dependent on the sulfite doses in UV-L/sulfite ARP. In the presence of sulfite, kobs was affected by the solution pH in both the UV-M and UV-L ARPs. The pH effect on UV-L ARP or UV-M ARP was explained by the effect of pH on the sulfite species distribution between sulfite and bisulfite or the hydrated electrons concentrations. Also it was found that dominant reaction mechanism of bromate removal was changed by initial bromate concentrations, and its behavior was varied dependent on the UV light sources.