Impacts of nitrate and electron donor on perchlorate reduction and microbial community composition in a biologically activated carbon reactor

• 5 mg/L ClO4− can be completely reduced with ≥21.95 mg C/L of acetate supply.
• NO3− can promote ClO4− reduction with the ratio of NO3−/ClO4− less than 1.
• NO3− can inhibit ClO4− reduction with the ratio of NO3−/ClO4− higher than 2.
• The inhibition of NO3− could be mitigated by supplying excess acetate.
• The presence of NO3− did not alter microbial structure significantly.

The sensitivity of perchlorate reduction and microbial composition to varied nitrate and acetate loadings was studied in a biologically activated carbon reactor with perchlorate loading and empty bed contact time fixed at 5 mg/L and 226 min, respectively. In stage 1, the sole electron acceptor ClO4− realized complete removal with ≥21.95 mg C/L of acetate supply. As nitrate loading gradually increased to 5 mg/L (stage 2), perchlorate reduction was slightly promoted and both ClO4− and NO3− were completely removed at an acetate loading of 29.7 mg C/L. When nitrate loading continued increasing to 10–60 mg/L (stage 3), perchlorate reduction converted to be inhibited, along with nondetectable NO3− and approximately exhausted DOC in effluent. When acetate loading increased to 43.9 mg C/L in stage 4, both ClO4− and NO3− were again removed, though lags still existed in perchlorate reduction. β-Proteobacteria accounted for about 60%, 55%, 58%, 61% and 12% in samples from the base and top of the filter in stage 1 and those from the base, middle and top in stage 4, respectively. These findings implied that ratio of NO3− to ClO4− loadings and acetate loading were two key factors impacting ClO4− reduction and microbial structure along the filter.

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