Reduction of bromate in a biological activated carbon filter under high bulk dissolved oxygen conditions and characterization of bromate-reducing isolates

Abstract

A biological activated carbon (BAC) filter was constructed using BAC from a pilot system that exhibited the ability to reduce bromate (BrO3−) and two BrO3−-reducing bacteria were isolated and characterized. The BAC filter could almost completely reduce BrO3− (60μgBr/L) to bromide (Br−) at an influent dissolved oxygen (DO) level of approximately 8.0mg/L and an empty bed contact time of 30±2min using acetate as the electron donor shortly after the start-up. Phylogenetic analysis of the 16S rRNA gene sequences of a biological sample from the BAC filter showed that among the six detected orders, Rhodocyclales- and Burkholderiales-related microorganisms were dominant and Rhodocyclaceae- and Comamonadaceae-related microorganisms may play a role in BrO3− reduction. Two isolated pure cultures, i.e. Sphingomonas sp. 4721 and Deinococcus sp. 4710, exhibited the ability to reduce BrO3− in the presence of NO3−. The result of this study clearly indicated that DO was a competitor of BrO3− as an electron acceptor while NO3− was not. Construction of a BAC filter which could restrict oxygen transfer within a biofilm still remains to be a challenge.