In recent years, several oxyanions have emerged as drinking water micropollutants, including arsenate, selenate, bromate, and, most recently, perchlorate (ClO4-). 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 (NO3-), must act as a primary electron acceptor. We tested our denitrifying, autotrophic, hydrogen-oxidizing hollow-fiber membrane for ClO4- reduction. The reactor is highly suited to drinking water treatment, as hydrogen (H2) is inexpensive, non-toxic, and does not leave residuals that can cause regrowth. When 1 to 2 mg/L ClO4- was supplied to reactor, which was at steady-state with 5 mgN/L NO3- but unacclimated to ClO4-, ClO4- 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 μg/L ClO4-. Tests with variable NO3- and H2 showed that ClO4- reduction requires less than 30 μgN/L NO3- and at least 300-μg/L effluent H2. Therefore, partial denitrification is probably not consistent with excellent ClO4- removal. Mineral medium produced a gradual loss of ClO4--reducing bacteria, but they were re-enriched when tap water replaced minimal medium.

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