Pilot study on bromate reduction from drinking water by UV/sulfite systems: Economic cost comparisons, effects of environmental parameters and mechanisms

The degradation of bromate (BrO3−) with UV/sulfite processes attracts much attention because of its high removal rate and easier combination with ultraviolet (UV) disinfection. This pilot study demonstrated the effectiveness of UV/sulfite systems and further investigated influences of typical environmental parameters such as UV fluence, pH, concentrations of sulfite ([S(IV)T]), humic acid (HA), bicarbonate (HCO3−), and nitrate (NO3−) on BrO3− degradation. Results showed that the decomposition was increased with the enhanced UV irradiance and [S(IV)T], whereas a considerable improvement was observed with enhancing pH only over pH 4.5-8.0 ranges probably due to the variation of sulfite species with pH in UV/sulfite systems. In contrast, the dosing of 2-5 mg/L HA proportionally suppressed BrO3− removal in UV/sulfite systems. The obvious inhibitory effect on removal kinetics suggests that HA acted primarily as a scavenger for active species. 2-8 mM HCO3− addition slightly depressed BrO3− degradation, indicating a weak inhibitor of HCO3− in photochemical processes. Moreover, scavenging experiments with NO3− demonstrated that the aqueous electron was responsible for decomposition of BrO3− by UV/sulfite systems in pilot studies. All the bromine atoms in BrO3− were reduced to Br−. Principal component analysis further substantiated that high NO3− and HA levels in authentic water inhibited the removal of BrO3− in a lower extent in pilot studies than that in laboratory experiments. The cost evaluation proved UV/sulfite processes to be economical, indicating its full-scale potential in BrO3− removal from drinking water.