Remediation of selenate (SeO4 2−) contamination through microbial reduction is often challenging due to the presence of sulfate (SO4 2−), which can lead to competition for the electron donor and the co-production of toxic H2S. Microbial reduction of SeO4 2− in the presence of SO4 2− was studied in two hydrogen-based membrane biofilm reactors (MBfRs). One MBfR was initiated with SO4 2−-reducing conditions and gradually shifted to SeO4 2− reduction. The second MBfR was developed with a SeO4 2−-reducing biofilm, followed by SO4 2− introduction. Biofilms within both MBfRs achieved greater than 90% SeO4 2− reduction, even though the SeO4 2− concentration ranged from 1,000–11,000 μg/L, more than 20–200 times the maximum contaminant level for drinking water (50 μg/L). Biofilm microbial community composition, assessed by 16S rRNA gene-based amplicon pyrosequencing, was distinct between the two MBfRs and was framed by alterations in SeO4 2− loading. Specifically, high SeO4 2− loading resulted in communities mainly composed of denitrifying bacteria (e.g., Denitratisoma and Dechloromonas). In contrast, low loading led to mostly sulfate-reducing bacteria (i.e., Desulfovibrio) and sulfur-oxidizing bacteria (i.e., Sulfuricurvum and Sulfurovum). SeO4 2− was reduced to elemental selenium (Se°), which was visualized within the biofilm as crystalloid aggregates, with its fate corresponding to that of biofilm solids. In conclusion, microbial biofilm communities initiated under either SeO4 2− or SO4 2−-reducing conditions attained high SeO4 2− removal rates even though their microbial community composition was quite distinct. Biotechnol. Bioeng. 2016;113: 1736–1744.
ASJC Scopus subject areas
- Applied Microbiology and Biotechnology