Bromate removal during transition from new granular activated carbon (GAC) to biological activated carbon (BAC)

Abstract

Bromate removal by activated carbon after ozonation is a subject of concern, since bromate is commonly found in the ozonation of bromide-containing water. Though new GAC (granular activated carbon) shows the capacity to reduce bromate to bromide, in the long-term use of GAC following ozonation, its bromate removal rate apparently decreases during transition from new GAC to BAC (biological activated carbon) after 3 months. Batch bromate reduction experiments using new GAC and BAC confirmed new GAC's ability and BAC's inability to reduce bromate to bromide. Our experiment also indicated that ion exchangeable bromate adsorption on new GAC was very limited. Based on the results of our long-term experiment, the bromate removal rate during the transition from new GAC to BAC was calculated; 1.5 mg BrO 3/g carbon when bromate concentration was 50 μg/l. BAC's inability to reduce bromate makes it necessary to optimize ozonation conditions to minimize the formation of bromate and other by-products while maintaining target levels of organic matter decomposition.