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The perchlorate (ClO4(-))-respiring organism, strain perclace, can grow using nitrate (NO3(-)) as a terminal electron acceptor. In resting cell suspensions, NO(-) grown cells reduced ClO4(-), and ClO4(-) grown cells reduced NO3(-). Activity assays showed that nitrate reductase (NR) activity was 1.31 micromol min(-1) (mg protein)-1 in (ClO4)- grown cells, and perchlorate reductase (PR) activity was 4.24 micromol min(-1) (mg protein)(-1) in NO3(-) grown cells. PR activity was detected within the periplasmic space, with activities as high as 14 pmol min(-1) (mg protein)(-1). The NR had a pH optimum of 9.0 while the PR had an optimum of 8.0. This study suggests that separate terminal reductases are present in strain perclace to reduce NO3(-) and ClO4(-).

The bacterium, perc1ace, has been shown to reduce perchlorate to less than the detection limit of 0.004 mg L−1 when grown on acetate under anaerobic conditions. In batch studies, the presence of nitrate does not significantly hinder the reduction of perchlorate. The ability of perclace to remove nitrate and perchlorate from ground water in a flow‐through system is described in this study. Celite‐packed columns of 300 ml were used to demonstrate the removal of perchlorate from ground water. At a flow rate of 1 ml min−1, perchlorate was removed from 0.738 mg L−1 to less than detectable levels and when the flow rate was 2 ml min−1 92 to 95% of the perchlorate was removed. Analysis of bacterial biomass at the completion of the study revealed that most of the bacterial growth was concentrated in the inlet area of the column. A circulating pump was added, with the idea that passing the ground water multiple times through the bacterially active zone might increase the efficiency of the column. In this experiment, perchlorate in ground water was reduced from 0.550 mg L−1 to nondetectable levels at a flow rate of 1 ml min−1. When the flow rate was increased to 2 ml min−1, 98% of perchlorate was removed and when the flow rate was 3 ml min −1 95% of perchlorate was removed. Rapid removal of perchlorate by perc1ace immobilized in a bioreactor may provide an efficient, cost‐effective technology for ground water remediation.

An autotrophic consortium of bacteria, utilizing hydrogen and bicarbonate as electron and carbon sources, respectively, for the reduction of perchlorate has been enriched. The efficiency of this consortium for perchlorate reduction in a packed‐bed bioreactor is described. The use of hydrogen as an electron source for microbial biodegradation of pollutants in a packed‐bed bioreactor is advantageous because hydrogen does not promote vigorous biomass growth, resulting in less clogging of the system, and hydrogen gas reduces the need for post‐reactor water cleanup. The consortium, comprised of four bacteria, was capable of removing nitrate and perchlorate simultaneously from mineral salts medium in a batch culture. A 120‐mL bioreactor was designed to test the capacity of the consortium to remove perchlorate in a flow‐through system. At a flow rate of 1 mL min−1, perchlorate levels naturally occurring in San Gabriel Valley ground water (0.740 mg L−1) were completely removed to less than 0.004 mg L−1, which is the detection limit. However, as the flow rate was increased, the removal efficiency decreased. Factors affecting the rate of perchlorate removal included nonuniform distribution of biomass in the column, unstable pH of the ground water, and limited delivery of hydrogen to the bacteria. This bioreactor also completely removes perchlorate from ground water at a flow rate of 1 mL min−1 without an added carbon source, presumably using the bicarbonate naturally present in the ground water.

The objective of this study was to assess the efficacy of a bench-scale, acetate-fed, packed bed bioreactor (PBR) to treat low concentrations «1 mg L-I) of perchlorate (CI0 4 -) in groundwater collected from an impacted site. The PBR consisted of a cylindrical plexiglass column packed with Celite, a diatomaceous earth product, as a solid support medium. The reactor was inoculated with a CI0 4--reducing bacterial isolate, perc lace. Results showed that with influent CI0 4 -concentrations of approximately 800 ug L-l, nondetectable effluent concentrations «4 u.gL:') were achieved with the PBR/perclace system at residence time as low as 0.3 h. Influent acetate concentrations of less than 500 mg L-1 yielded nondetectable effluent CI0 4 -concentrations, and acetate concentrations generally less than 50 mg L:' were present in the effluent. Nitrate (N0 3 -) was also removed in this system, while sulfate (SO/-) reduction was not observed. The pH remained relatively constant during the process.

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