Nitrate effects on perchlorate reduction in a H2/CO2-based biofilm

Abstract

The H2/CO2-based membrane biofilm reactor (H2/CO2-MBfR) that effectively combines microporous diffusions of H2 and CO2 is efficient in removing perchlorate (ClO4−). Nitrate (NO3−) is a common oxidized contaminant frequently coexists with ClO4− in water, with the NO3− concentration in most ClO4−-contaminated waters being several orders of magnitude higher than ClO4−. Determining the effect of NO3− on ClO4− reduction is a critical issue in practice. The ClO4− reduction performance, biofilm microbial community and influencing mechanism were investigated under a series of feed NO3− loadings in this work. ClO4− reduction was slightly promoted when NO3−-N levels were <10 mg/L and inhibited at higher NO3−-N levels. Denitrification competed more strongly for H2 than ClO4− reduction, regardless of H2 availability. A higher NO3−-N loading was a strong driving force to change the biofilm microbial community. Betaproteobacteria were the dominant bacteria at all stages, and the biofilm reactor was enriched in Methyloversatilis and Zoogloea (31.9–56.5% and 10.6–25.8%, respectively). Changes in the relative amounts of Methyloversatilis and Zoogloea coincided with changes in the ClO4− fluxes and removal efficiencies and the relative abundances of nitrogen cycle functional genes. These results suggest that Methyloversatilis and Zoogloea likely follow independent reduction mechanisms for ClO4− removal.