Effect of current density on denitrification performance and microbial community spectra in a pyrite-oxidizing bioelectrochemical system (PBES)

Abstract

A lab-scale system (PBES) combined electrolysis hydrogenotrophic denitrification and pyrite-oxidizing denitrification was established to evaluate the effect of current density on nitrate removal performance and community dynamics. Results indicated that the optimal NO3−-N removal efficiency with lowest NO2−-N accumulation was obtained when current density was 0.10 mA/cm2, a higher current density did not promote NO3−-N removal. The activities of nitrate reductase and nitrite reductase in both the cathode biofilm and pyrite biofilm showed similar variation trend with that of NO3−-N removal. The estimated contribution of hydrogenotrophic denitrification (23.77 %–43.53 %) was lower than that of pyrite-oxidizing denitrification (58.19 %–76.23 %) in the PBES. Illumina MiSeq sequencing indicated that microbial diversity of cathode biofilm increased with current density increased from 0.05 to 0.10 mA/cm2, then ceased to increase at a higher current density, whereas the microbial diversity of pyrite biofilm continuously increased along with increased current density. Azoarcus may be the key player for nitrate removal in both cathode and pyrite biofilms. Our results can provide useful information to improve PBES designs for the future applications.