Biological Perchlorate Reduction in Packed Bed Reactors Using Elemental Sulfur

Sulfur-utilizing perchlorate (ClO4-)-reducing bacteria were enriched from a denitrifying wastewater seed with elemental sulfur (SO) as an electron donor. The enrichment was composed of a diverse microbial community, with the majority identified as members of the phylum Proteobacteria. Cultures were inoculated into bench-scale packed bed reactors (PBR) with SO and crushed oyster shell packing media. High ClO4- concentrations (5-8 mg/L) were reduced to <0.5 mg/L at an empty bed contact time (EBCT) of 13 h. Low ClO4- concentrations (60-120 mu g/L), more typical of contaminated groundwater sites, were reduced to <4 mu g/L at an EBCT of 7.5 h. PBR performance decreased when effluent recirculation was applied or when smaller SO particle sizes were used, indicating that mass transfer of ClO4- to the attached biofilm was not the limiting mechanism in this process, and that biofilm acclimation and growth were key factors in overall reactor performance. The presence of nitrate (6.5 mg N/L) inhibited ClO4- reduction. The microbial community composition was found to change with ClO4- availability from a majority of Beta-Proteobacteria near the influent end of the reactor to primarily sulfur-oxidizing bacteria near the effluent end of the reactor.