AWWA WQTC64178

This study investigated perchlorate reduction by autotrophic elemental sulfur oxidizing bacteria. A perchlorate reducing microbial consortium was enriched from a denitrifying wastewater inoculum in medium containing elemental sulfur (S⁰), crushed oyster shell, nutrients and 5 mg/L perchlorate. Perchlorate could be reduced to 0.5 mg/L in approximately 15 days. The enrichment culture was subsequently inoculated into a continuous upflow packed-bed bioreactor containing S⁰ and crushed oyster shell medium. High-level perchlorate concentrations (5-8 mg/L) were reduced to < 0.5 mg/L with an empty bed contact time (EBCT) of 13 hours. Low levels of perchlorate (80-120 µg/L) were treated varying two parameters, recirculation ratio and empty bed contact time (EBCT). Little or no recirculation was required to efficiently reduce perchlorate to less than 4 µg/L. The system also proved somewhat independent of EBCT. Using molecular identification techniques a ß-proteobacterium with 99% 16S rRNA sequence similarity to the known perchlorate reducing bacteria, Dechloromonas sp., was isolated from further batch enrichments. Experiments are ongoing to determine if members of this genus are the sole perchlorate reducers or part of a consortium present in the sulfur containing bioreactors. Includes 17 references, tables, figures.