The dynamics of the bacterial community associated with the denitrification process in a fixed bed column reactor (FBCR) were investigated using 454-pyrosequencing methodology. A FBCR filled with elemental sulfur and limestone was operated for about 94 days under autotrophic and mixotrophic (autotrophic + heterotrophic) conditions at 30 °C. Efficient simultaneous bromate and nitrate removal was achieved at feed concentrations of 500 µg/L bromate and 45 mg/L nitrate under autotrophic and mixotrophic conditions. Operational taxonomic units-based analysis (97% similarity cut-off) of bioreactor samples (three periods) revealed that the microbial diversity changed regardless of operational conditions. Sulfurimonas spp. was dominant in the reactor at the adaptation stage. Thiobacillus denitrificans is a chemolithoautotrophic bacterium that is capable of the oxidation of inorganic sulfur compounds. After the adaptation period, the microbial profile changed such that Spirochaetacea spp. and Denitratisoma spp. were major species in the column reactor. After 60 d of operation, Hyphomicrobium vulgare became dominant due to the mixotrophic denitrification conditions.

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