Mechanistic insights into CO2 pressure regulating microbial competition in a hydrogen-based membrane biofilm reactor for denitrification.

Abstract

CO2 is a proven pH regulator in hydrogen-based membrane biofilm reactor (H2-MBfR) but how its pressure regulates microbial competition in this system remains unclear. This work evaluates the CO2 pressure dependent system performance, CO2 allocation, microbial structure and activity of CO2 source H2-MBfR. The optimum system performance was reached at the CO2 pressure of 0.008MPa, and this pressure enabled 0.18gC/(m2·d) of dissolved inorganic carbon (DIC) allocated to denitrifying bacteria (DNB) for carbon source anabolism and denitrification-related proton compensation, while inducing a bulk liquid pH (pH 7.4) in favor of DNB activity by remaining 0.21gC/(m2·d) of DIC as pH buffer. Increasing CO2 pressure from 0.008 to 0.016MPa caused the markedly changed DNB composition, and the diminished DNB population was accompanied by the enrichment of sulfate-reducing bacteria (SRB). A high CO2 pressure of 0.016MPa was estimated to induce the enhanced SRB activity and weakened DNB activity.