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

摘要

AbstractThe 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−.Graphical abstractDisplay OmittedHighlights•This study focused on BrO3−removal in NO3−-reducing anoxic zones of MAR systems.•NO3−presence is a precondition for BrO3−reduction in NO3−-reducing anoxic zones.•The ozonation pre-treatment promotes microbial activity and therefore BrO3−removal.•BrO3−biodegradation by denitrifying bacteria can happen in anoxic NO3−-reducing zones.•The effective BrO3−removal in MAR systems broadens the applicability of ozonation.