Research On CW-MFC For Bio-Refractory Organics Removal And Electricity Production

In this study,a single-chamber air-cathode microbial fuel cell was constructed on the basis of vertical-flow constructed wetland,forming microbial fuel cell coupled with constructed wetland(CW-MFC).Reactive brilliant red X-3B,a kind of azo dye,was selected as the target pollutant,and the dye wastewater wastewater was configured as the substrate to run CW-MFC constantly.The effects of CW-MFC on the removal of refractory organic matter and synchronous electricity production was investigated from three aspects:cathode area,double-anode structure and external resistance.The main research contents and results were as follows:The effects on electricity production,removal efficiency of X-3B and microbial community of CW-MFC were investigated in five groups of CW-MFC with different cathode areas.The results showed that increasing cathode area in a certain range were benefit to improving the cathodic polarization phenomenon and the growth environment of anodic microbes,so the performance of electricity production and the removal efficiency of X-3B were enhanced.However,when the cathode area was further increased,the anodic polarization phenomenon became more serious,and the electronic supply and demand became imbalance in the anode layer,resulting in the maximum power density and X-3B decolorization rate gradually reduced.With the increase of cathode area,the density of bacteria was increased both in the cathode and anode layer,in which the density of electrogens increased and the density of methanogens reduced.The single-anode CW-MFC and double-anode CW-MFC were constructed and operated under different X-3B concentration and different HRT.The operation condition of single-anode CW-MFC and double-anode CW-MFC were studied comparatively,combining the degradation intermediate product of X-3B and microbial community in double-anode CW-MFC,to analyze the effect of double-anode structure on electricity production,removal efficiency of X-3B and microbial community of CW-MFC.It was found that the electricity production performance and X-3B removal efficiency decreased with the increase of the X-3B concentration,and the performance of double-anode CW-MFC were much better than that of single-anode CW-MFC,showing a good stability.in dealing with the increase of organic load.When the HRT was reduced,the electricity production performance and X-3B removal efficiency also decreased,and the performance of double-anode CW-MFC were much better than that of single-anode CW-MFC,showing a good stability.in dealing with the increase of impact load.When X-3B was degraded in the double-anode CW-MFC,a large number of conjugated system n-? bonds was destroyed at the bottom matrix layer and lower-anode layer,and a small amount of conjugate system n-? bonds was destroyed in the upper-anode layer.After that some intermediate product were produced,which contained some functional groups,such as benzene ring,triazinyl and naphthalene ring.Due to the co-substrate was consumed layer-by-layer in the double-anode CW-MFC,the proportion of methanogens was dominant in the upper-anode layer while the electrogens was predominant in the lower-anode layer,and the total bacterial density of the upper-anode layer was lower than that of the lower-anode layer.To investigate the effects of external resistances on electricity production,the removal of X-3B and microbial community,three close circuit CW-MFC with external resistances of 200,600 and 1000 Ohm and an open circuit CW-MFC were constructed.The result showed that the external resistance was the only way to transfer electrons from the anode to the cathode,which hindered the electron transfer process.When the external resistance increased,the current decreased and the internal resistance increased.Under the catalysis of the electrode,the decolorization efficiency of X-3B in the close circuit CW-MFC was better than that in the open circuit CW-MFC,and the decolorization efficiency decreased with the increase of the external resistance.When the external resistance increased,the density of bacteria in anode layer was decreased,in which the density of electrogens decreased and the density of methanogens increased.