Simultaneously enhancing degradation of refractory organics and achieving nitrogen removal by coupling denitrifying biocathode with MnOx/Ti anode

[Display omitted] •Denitrification biocathode (DB) and MnOx/Ti anode was coupled at 1.3 and 1.5 V.•Coupling of DB increased NO3−-N removal in the cathode chamber.•Coupling of DB increased refractory organic carbon removal in the anode chamber.•Generation of M(∙OH) from MnOx/Ti anode was accelerated after coupling of DB. To simultaneously remove carbon and nitrogen from refractory organic wastewater, this study couples the denitrifying biocathode and MnOx/Ti anode to oxidize refractory organic pollutants in the anode chamber and remove NO3−-N in the cathode chamber (denitrifying biocathode-electrocatalytic reactor, DBECR). After inoculation, DBECR started up at 1.3 and 1.5 V with NO3−-N reduction peak appearing on the cyclic voltammetry curve and increased NO3−-N removal by approximately 90 %. Compared to the electrocatalytic reactor without inoculation (ECR), NO3−-N removal of DBECR significantly increased from 0.09 to 0.45 kg NO3−-N/m3 NCC/d (NCC: net cathodic compartment). NO3−-N removal correlated well with charges/current flowing through the circuit of DBECR, further validating the presence of electrotrophic denitrifiers. Moreover, coupling of denitrifying biocathode significantly enhanced methylene blue (MB) removal in the anode chamber (0.18 ± 0.002 and 2.92 ± 0.02 g COD/m2/d for ECR and DBECR, respectively). This was because the growth of eletrotrophic denitrifiers increased the cathodic potential and thus the potential of MnOx/Ti anode. The higher potential of MnOx/Ti anode promoted the generation of hydroxyl radicals and consequently promoted MB removal. This study demonstrated that DBECR not only realized nitrogen removal in the cathode chamber, but also enhanced refractory organic carbon degradation in the anode chamber.