Effect Of Phosphorus Concentration On Nitrate Removal And Electricity Generation Of Bio-cathode MFC

Nitrogen pollution is a serious environmental problem faced by all mankind.It is imperative to remove nitrate and nitrite(oxidized pollutants)from water.Microbial fuel cell(MFC)uses microorganisms as catalyst to directly convert the chemical energy contained in wastewater pollutants into electrical energy,which can achieve simultaneous pollution control and power generation,especially the biological cathode can directly provide electrons to make up for the lack of carbon source in the denitrification process of nitrate.However,nitrogen and phosphorus coexist in water.MFC research focuses on the removal of a single pollution source.It is of practical significance to investigate the effect of phosphorus concentration in water on the removal of nitrogen and electricity by MFC biocathode.In this paper,the denitrification microbial fuel cell with potassium nitrate as electron acceptor was constructed.The denitrification performance,influencing factors and working mechanism of MFC with four mass concentrations of potassium phosphate were studied.The main results are as follows:(1)To explore the electricity production efficiency of MFC with different mass concentration ratio of phosphorus and nitrogen.When the ratio of P / N concentration is 1:8,the electricity production efficiency of mfc1 is the highest.The maximum output voltage,maximum circuit density and maximum power density of MFC-0,MFC-1,MFC-2,MFC-3 are 0.41,0.42,0.30,0.25 V,4.08,4.49,4.18,2.51 A.m-3,0.79,0.83,0.40,0.11 W.m-3,respectively.It is found that the change range of cathode potential is larger than that of anode.The MFC values of anode potential and cathode potential were kept at-0.12 V and 0.09-0.30 V respectively.(2)To study the denitrification efficiency of MFC with different mass concentration ratio of phosphorus and nitrogen.When the ratio of P to n is 0,the degradation rate of nitrate is the highest.With the increase of the concentration of potassium phosphate,the removal rate of nitrate was negatively correlated with the concentration of cathode potassium phosphate.The COD removal rates of MFC-0,MFC-1,MFC-2,MFC-3 were 88.73%,84.18%,80.70% and 72.35% respectively,and the nitrate removal rates were 91.85%,87.86%,79.76% and 72.44% respectively.The results show that different mass concentration ratio of phosphorus and nitrogen has some influence on the removal of nitrate,and the larger the mass concentration ratio of phosphorus and nitrogen is,the more unfavorable it is to the removal of nitrate.Through the comparative experiment of open circuit and closed circuit conditions,the removal rate of salt in closed circuit is 2.3 times of that in open circuit conditions,which shows that MFC micro voltage can stimulate the cathode microorganism and strengthen the removal of nitrate.The accumulation of nitrite in the whole process is very small,which shows that it has little effect on the activity of MFC cathode microorganism.(3)Analyze the diversity value of the cathode bacterial group MFC in the original sludge,start-up period,stable period,decay period,and cathode microbial community in the microbial stable period.The results of biodiversity analysis showed that the microorganisms had the highest species richness in the stable period.The dominant bacterial species of MFC in the stable period of operation are Proteobacteria(Proteobacteria).And in the stable period of reaction,the dominant genus of MFC is Azonexus,Zoogloea and Ignavibacterium,Comamonas and Acidovorax,but the distribution ratio of each dominant genus is different,and the above several microbial genus have the degradation of nitrate enhancement.