Effective removal of bromate in nitrate-reducing anoxic zones during managed aquifer recharge for drinking water treatment: Laboratory-scale simulations.

The removal of bromate (BrO3-) as a by-product of ozonation in subsequent managed aquifer recharge (MAR) systems, specifically in anoxic nitrate (NO3-)-reducing zones, has so far gained little attention. In this study, batch reactors and columns were used to explore the influence of NO3- and increased assimilable organic carbon (AOC) due to ozonation pre-treatment on BrO3- removal in MAR systems. 8 m column experiments were carried out for 10 months to investigate BrO3- behavior in anoxic NO3--reducing zones of MAR systems. Anoxic batch experiments showed that an increase of AOC promoted microbial activity and corresponding BrO3- removal. A drastic increase of BrO3- biodegradation was observed in the sudden absence of NO3- in both batch reactors and columns, indicating that BrO3- and NO3- competed for biodegradation by denitrifying bacteria and NO3- was preferred as an electron acceptor under the simultaneous presence of NO3- and BrO3-. However, within 75 days' absence of NO3- in the anoxic column, BrO3- removal gradually decreased, indicating that the presence of NO3- is a precondition for denitrifying bacteria to reduce BrO3- in NO3--reducing anoxic zones. In the 8 m anoxic column set-up (retention time 6 days), the BrO3- removal achieved levels as low as 1.3 μg/L, starting at 60 μg/L (98% removal). Taken together, BrO3- removal is likely to occur in vicinity of NO3--reducing anoxic zones, so MAR systems following ozonation are potentially effective to remove BrO3-.