The Construction Of Denitrification Biological Cathode-electrocatalytic Reactor And Its Denitrification And Carbon Removal Characteristics

Anodic oxidation（AO）has recently attracted extensive attention for the treatment of refractory organic wastewater.Current studies mainly focus on pollutants removal by the anode,but reduction reaction on the cathode has still not been utilized to remove pollutants.In this study,denitrifying biocathode-electrocatalytic reactor（DBECR）was developed using graphite felts or activated carbon as the carriers for microorganisms in the cathode chamber and MnO_x/Ti microporous electrode prepared via sol-gel technique as the anode.The anode was used for removal of refractory organic pollutants and the denitrifying biocathode was for denitrification,endowing AO with dual functions of nitrogen and carbon removal.When graphite felts were used as the cathode fillers,after inoculation under 1.3 V and 1.5 V,the current density and cathodic potential of DBECRs exhibited periodical responses to the replacement of nitrate-containing wastewater in the cathode,and the reduction peak of NO₃^-appeared in the cyclic voltammetry curves of cathode.These results indicated that there were electrotrophic denitrifiers growing in the cathode and DBECRs successfully started up.After startup,NO₃^--N and TN removal in the cathode increased from below 5%to above 95%;TOC removal in the anode increased from 5%to about 20%;MB removal was more than 90%.Proteobacteria and bacteroidetes were the dominant denitrifying phyla after DBECR startup.However,when activated carbon was used as the cathode fillers,the DBECR could not well start up under 1.3 V and failed to start up under 1.5 V.Graphite felts were more suitable than activated carbon as the cathode fillers of DBECR.With the increase of the NO₃^--N feed concentration in the cathode,the NO₃^--N removal amount and removal rate in the cathode of DBECR during one cycle increased gradually.When NO₃^--N feed concentration was 700 mg NO₃^--N/L,the NO₃^--N removal amount and NO₃^--N removal rate in the cathode of DBECR reached the maximum,which were 1.72 kg NO₃^--N/m³ NCC and 0.18 kg NO₃^--N/m³ NCC/d,respectively.However,the maximum NO₃^--N removal amount and NO₃^--N removal rate in the cathode of electrocatalytic reactor（ECR）during one cycle were 0.84 kg NO₃^--N/m³ NCC and 0.06 kg NO₃^--N/m³ NCC/d,respectively,which were far lower than those of DBECR.This indicated that the denitrification in the cathode of DBECR was enhanced after coupled with denitrifying biocathode.Further studies indicated that bioelectrochemical denitrification was the dominant process for nitrogen removal in the cathode.There was almost no intermediate product of NO₂^--N accumulation during the reduction of NO₃^--N.With the increase of NO₃^--N feed concentration in the cathode,the COD removal in the anode of DBECR in one cycle increased gradually.When NO₃^--N feed concentration in the cathode was 700 mg NO₃^--N/L,the COD removal amount of DBECR during one cycle reached the maximum,which was 2.89×10^-2 kg COD/m².The maximum COD removal amount in the anode of ECR during one cycle was 0.73×10^-2 kg COD/m²,which was significantly lower than that of DBECR.Compared with ECR,the cathode potential of DBECR was increased after coupled with denitrifying biocathode,and the MnO_x/Ti microporous anode potential was also increased.The higher anode potential was advantageous in promoting the generation of·OH by MnO_x/Ti microporous anode and thus promoted the MB removal in the anode.Hence,DBECR could not only realize denitrification in the cathode,but also promote carbon removal in the anode.