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

The removal of bromate (BrO) as a by-product of ozonation in subsequent managed aquifer recharge (MAR) systems, specifically in anoxic nitrate (NO)-reducing zones, has so far gained little attention. In this study, batch reactors and columns were used to explore the influence of NO and increased assimilable organic carbon (AOC) due to ozonation pre-treatment on BrO removal in MAR systems. 8 m column experiments were carried out for 10 months to investigate BrO behavior in anoxic NO-reducing zones of MAR systems. Anoxic batch experiments showed that an increase of AOC promoted microbial activity and corresponding BrO removal. A drastic increase of BrO biodegradation was observed in the sudden absence of NO in both batch reactors and columns, indicating that BrO and NO competed for biodegradation by denitrifying bacteria and NO was preferred as an electron acceptor under the simultaneous presence of NO and BrO. However, within 75 days' absence of NO in the anoxic column, BrO removal gradually decreased, indicating that the presence of NO is a precondition for denitrifying bacteria to reduce BrO in NO-reducing anoxic zones. In the 8 m anoxic column set-up (retention time 6 days), the BrO removal achieved levels as low as 1.3 μg/L, starting at 60 μg/L (98% removal). Taken together, BrO removal is likely to occur in vicinity of NO-reducing anoxic zones, so MAR systems following ozonation are potentially effective to remove BrO.