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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