Changed carbon fixing affects denitrification in a hydrogen-based membrane biofilm reactor under high salinity conditions

Abstract

The use of hydrogen (H2)-based membrane biofilm reactor (MBfR) has proven to be a promising method for treating nitrate and salt enriched ion-exchange spent brine. However, the influencing mechanisms of salinity in MBfRs are rarely deeply discussed from a microbiological perspective. In this study, the dynamics of the microbial community and functional genes in response to salt stress in an MBfR system were comprehensively evaluated. As salinity increased, the MBfR achieved a NO3−-N effluent concentration of 0.0 mg L−1 and a NO2−-N effluent concentration of 18.0 mg L−1 at 5 % salinity from an influent with 50 mg L−1 NO3−-N. Significantly higher salinity (7 %) led to complete inhibition of nitrate reduction. Community analysis indicated that Thauera was the dominant genus at 0 % and 1 % salinity, and Azoarcus showed high salinity tolerance from 3 to 7 % salinity. Pearson analysis proved the significant negative correlation between salinity and the expression of cbbM instead of cbbL. Thus, high salinity changed inorganic carbon fixing and the denitrification process in the MBfR. This work provides a foundation for the practical application of MBfRs with nitrate and salt-enriched wastewater treatment.