Perchlorate as a secondary substrate in a denitrifying, hollow-fiber membrane biofilm reactor

In recent years, several oxyanions have emerged as drinking water micropollutants, including arsenate, selenate, bromate, and, most recently, perchlorate (ClO 4 - ).Conventional water treatment processes typically are ineffective in removing these compounds, and advanced treatment processes are expensive. Biological reduction may provide a suitable treatment alternative, since these compounds can serve as electron acceptors. Other acceptors, such as nitrate (NO 3 - ), must act as a primary electron acceptor. We tested our denitrifying, autotrophic, hydrogen-oxidizing hollow-fiber membrane for ClO 4 - reduction. The reactor is highly suited to drinking water treatment, as hydrogen (H 2 ) is inexpensive, nontoxic, and does not leave residuals that can cause regrowth. When 1 to 2 mg/L ClO 4 - was supplied to reactor, which was at steady-state with 5 mgN/L NO 3 - but unacclimated to ClO 4 - , ClO 4 - removals increased from 40 to 99% over three weeks. Removals to 4 μg/L were also achieved in a natural groundwater having 6 to 100 pg/L ClO 4 - , Tests with variable NO 3 - and H2 showed that ClO 4 - reduction requires less than 30 μgN/L NO 3 - and at least 300-μg/L effluent H 2 . Therefore, partial denitrification is probably not consistent with excellent ClO 4 - removal. Mineral medium produced a gradual loss of ClO 4 - -reducing bacteria, but they were re-enriched when tap water replaced minimal medium.