Bromate reduction by iron(II) during managed aquifer recharge: A laboratory-scale study

The removal of bromate (BrO₃ ^-) as a byproduct of ozonation in subsequent managed aquifer recharge (MAR) systems has so far gained little attention. This preliminary study with anoxic batch experiments was executed to explore the feasibility of chemical BrO₃ ^- reduction in Fe-reducing zones of MAR systems and to estimate potential inhibition by NO₃ ^-. Results show that the reaction rate was affected by initial Fe²⁺/BrO₃ ^- ratios and by pH. The pH dropped significantly due to the hydrolysis of Fe3+ to hydrous ferric oxide (HFO) flocs. These HFO flocs were found to adsorb Fe²⁺, especially at high Fe²⁺/BrO₃ ^- ratios, whereas at low Fe²⁺/BrO₃ ^- ratios, the mass sum loss of BrO₃ ^- and Br^- indicated intermediate species formation. Under MAR conditions with relatively low BrO₃ ^- and Fe²⁺ concentrations, BrO₃ ^- can be reduced by naturally occurring Fe²⁺, as the extensive retention time in MAR systems will compensate for the slow reaction kinetics of low BrO₃ ^- and Fe²⁺ concentrations. Under specific flow conditions, Fe²⁺ and NO₃ ^- may co-occur during MAR, but NO₃ ^- hardly competes with BrO₃ ^-, since Fe²⁺ prefers BrO₃ ^- over NO₃ ^-. However, it was found that when NO₃ ^- concentration exceeds BrO₃ ^- concentration by multiple orders of magnitude, NO₃ ^- may slightly inhibit BrO₃ ^- reduction by Fe²⁺.