Enhancing bio-cathodic nitrate removal through anode-cathode polarity inversion together with regulating the anode electroactivity.

Bio-cathodic nitrate removal uses autotrophic nitrate-reducing bacteria as catalysts to realize the nitrate removal process and has been considered as a cost-effective way to remove nitrate contamination. However, the present bio-cathodic nitrate removal process has problems with long start-up time and low performance, which are urgently required to improve for its application. In this study, we investigated an anode-cathode polarity inversion method for rapidly cultivating high-performance nitrate-reducing bio-cathode by regulating bio-anodic bio-oxidation electroactivities under different external resistances and explored at the first time the correlation between the oxidation performance and the reduction performance of one mixed-bacteria bioelectrode. A high bio-electrochemical nitrate removal rate of 2.74 ± 0.03 gNO 3 −-N m−2 d−1 was obtained at the bioelectrode with high bio-anodic bio-oxidation electroactivity, which was 4.0 times that of 0.69 ± 0.03 gNO 3 −-N m−2 d−1 at the bioelectrode with low bio-oxidation electroactivity, and which was 1.3–7.9 times that of reported (0.35–2.04 gNO 3 −-N m−2 d−1). 16S rRNA gene sequences and bacterial biomass analysis showed higher bio-cathodic nitrate removal came from higher bacterial biomass of electrogenic bacteria and nitrate-reducing bacteria. A good linear correlation between the bio-cathodic nitrate removal performance and the reversed bio-anodic bio-oxidation electroactivity was presented and likely implied that electrogenic biofilm had either action as autotrophic nitrate reduction or promotion to the development of autotrophic nitrate removal system. This study provided a novel strategy not only to rapidly cultivate high-performance bio-cathode but also to possibly develop the bio-cathode with specific functions for substance synthesis and pollutant detection. Unlabelled Image • Biocathode prepared by reversing bioanode cultured under different external resistances. • Biocathodic denitrification rate increased by over 3.0 times. • Cathodic denitrification activity correlated to electroactivity of anode reversed for biocathode. • Electrogenic bacteria could participate in or promote biocathodic denitrification. [ABSTRACT FROM AUTHOR]