Simultaneously enhancing degradation of refractory organics and achieving nitrogen removal by coupling denitrifying...

To simultaneously remove carbon and nitrogen from refractory organic wastewater, this study couples the denitrifying biocathode and MnO_x/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 MnO_x/Ti anode. The higher potential of MnO_x/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.