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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]

A novel electrochemical oxidation-methanogenesis (EO-M) system was proposed for the first time to simultaneously achieve antibiotic degradation and a bioelectrochemical conversion of CO 2 to CH 4 with low energy costs. A dual-chamber system was installed with an antimony-doped tin oxide anode (Ti/SnO 2 -Sb) for the electrocatalytic generation of hydroxyl radicals to degrade ciprofloxacin (CIP), and a CO 2 -reducing methanogenic biocathode was enriched based on a three-dimensional (3D) graphitized granular activated carbon (GGAC) for microbial electromethanogenesis. The anode achieved removal efficiencies as high as 99.99% and 90.53% for CIP (14 mL, 50 mg L−1) and the chemical oxygen demand (COD, 89 mg L−1), respectively. The biocathode was rapidly enriched within 15 days and exhibited a methane production rate that stabilized at 15.12 ± 1.82 m3 m−3 d−1; additionally, the cathodic coulombic efficiency reached 71.76 ± 17.24%. The energy consumption of CIP degradation was reduced by 3.03 Wh L−1 compared to that of a single electrochemical oxidation system due to the lower cathodic overpotential of CO 2 bioelectrochemical reduction in the EO-M system. A detailed analysis of the biofilm evolution in the 3D biocathode during the start-up process demonstrated that the enhanced absorption of extracellular polymeric substances by the GGAC cathode accelerated the enrichment of methanogens and induced the formation of methanogens with a large number of flagella. An analysis of the microbial community showed that a high relative abundance of Methanobacterium movens could promote a flagella-mediated direct electron transfer of the biocathode, eventually reducing the cathodic overpotential and energy costs of the EO-M system. Unlabelled Image • Anodic oxidation of antibiotics and bio-cathodic reducing CO 2 to CH 4 was realized. • 99% of ciprofloxacin (CIP) was removed with CH 4 production rate of 15 m3 m−3 d−1. • System saved energy cost of 3.03 Wh L−1 to treat CIP comparing with traditional EO. • Graphitized granular activated carbon promoted the start-up of biocathode. [ABSTRACT FROM AUTHOR]