Study On Nitrogen Removal By Microbial Fuel Cell In The Micro-aerobic Biological Cathode

In recent years,with the development of China's economy and society,a large amount of nitrogen-containing waste water has been discharged,resulting in serious pollution of surface water and groundwater in many areas by nitrogen,which has caused great harm to people's health.Therefore,removing nitrogen contaminants in water is imminent.The traditional nitrification and denitrification process for treating nitrogenous wastewater has problems such as large area,high aeration energy consumption,need for extra carbon source and alkalinity,etc.,resulting in high treatment costs and low carbon and nitrogen ratios.Oxygen Demand/Total Nitrogen?C/N?wastewater has low denitrification efficiency.Therefore,there is an urgent need for a new nitrogen removal process to solve the current difficulties.Microbial Fuel Cell?MFC?is a bio-electrochemical system that utilizes the catalytic action of microorganisms to convert chemical energy into electrical energy.The MFC is used to treat nitrogen-containing waste water.By controlling the oxygen concentration of the MFC cathode,it reaches a state of micro-oxygen,which is beneficial to the realization of nitrogen removal by short-cut nitrification and denitrification at the cathode.This process can avoid additional carbon sources,save reaction space,reduce excess sludge production,and produce electricity while removing ammonia?NH₄⁺-N?and Chemical Oxygen Demand?COD?.Wastewater denitrification technology with great application prospects.In this experiment,a double-chamber micro-oxygen biological cathode MFC was used to treat nitrogen-containing wastewater.The effects of aeration on the denitrification performance and microbial community structure of micro-oxygen bio-cathode MFC were studied,and the optimal aeration conditions for MFC nitrification and denitrification were investigated.Based on this,the nitrogen removal performance of micro-ammonia bio-cathode MFC in treating high ammonia nitrogen and low C/N wastewater was further explored.In addition,under the optimum aeration conditions,this experiment simulated the changes of water temperature in the four seasons of the sewage plant,and studied the impact of temperature shock on the denitrification efficiency and microbial community structure of microbial fuel cells.The experimental results are as follows:?1?The experimental results show that the aeration ratehas a significant effect on the denitrification of the micro-oxygen biological cathode MFC.When the micro-aerobic bio-cathode MFC was used to simulate municipal wastewater,short-cut nitrification and denitrification was realized under the condition of aeration volume of 1.64 mL?min^-1.The nitrite nitrogen?NO₂^--N?accumulation rate was over 70%in the whole reaction process,with the highest reaching87.79%,and the cathode C/N ratio was 1.57.Under this condition,the removal effect of nitrogen was the best,the total nitrogen?TN?removal rate could reach80.38%,and the TN removal load was 59.99 g/?m³?d?.Its maximum voltage is0.77V,Coulomb efficiency is the highest,43.8%,and its charge utilization rate is the highest.?2?When the micro-aerobic biocathode MFC is used to process simulated municipal wastewater,it is not necessary to add additional alkalinity to maintain a pH environment suitable for the survival of microorganisms.In particular,the aeration rate of 1.64 mL?min^-11 was lower than that of other higher aeration conditions,and the alkalinity produced by the denitrification reaction greatly compensated for the alkalinity previously consumed by nitrification.It is more suitable for the coexistence of nitrifying bacteria and denitrifying bacteria.?3?Under the condition of aeration rate of 1.64 mL?min^-1,when using biocathode MFC to treat high ammonia nitrogen and low C/N wastewater,short-cut nitrification and denitrification can also be achieved and better nitrogen removal effect can be achieved.The removal rate of NH₄⁺-N was up to84.79%,the TN removal rate was 74.41%,and the TN removal load was 239.07g/?m³?d?.?4?The amount of aeration had a significant effect on the distribution of the gates in the microbial communities,and the enrichment of Proteobacteria and?-proteobacteria was beneficial to the aeration volume of 1.64 mL?min^-1.The degrees were 77.81%and 66.16%respectively.At the aeration rate of 1.64mL?min^-1,Nitrosomonas belonging to the ammonia-oxidizing genus accounted for the highest proportion of 1.52%,while Nitrobacter belonging to the genus Nitrobacter was only 0.04%.Thauera,which is beneficial to short-cut nitrification and denitrification,was also effectively enriched with an aeration rate of 1.64mL?min^-1,with an abundance of 51.12%.The Thiobacillus abundance of the autotrophic denitrifying bacteria was higher than that of other aeration conditions at a rate of aeration of mL?min^-1,which was 0.42%.In addition,the amount of aeration under microaerobic conditions had no significant effect on autotrophic denitrifier Afipia.?5?Temperature shock has a great influence on the denitrification effect of microbial fuel cells.Short-cut nitrification was achieved after the temperature was increased from 20? to 25?,and the NO₂^--N accumulation rate was up to89.15%.At 25?,the nitrogen removal effect was the best,the removal rate of NH₄⁺-N was 95.71%,the TN removal rate was 81.13%,and the TN removal load was 64.84 g/?m³?d?.The highest voltage at 25? was 0.57 mV,and the highest Coulomb efficiency was 42.8%with the highest charge utilization.?6?The temperature shock has a great influence on the microbial community structure.At 25?and 20?,the main functional phylums respectively accounted for 98.88%and 96.13%,but only accounted for 63.23%at 15?.At 25?,the growth of Protebacteria and?-proteobacteria was favorable,with the abundances of 78.02%and 65.96%,respectively.At 25?,the abundance of Nitrosomonas is much higher than that of Nitrobacter and Nitrosomonas/Nitrobacter is 53.In addition,Thaurea,which favors short-cut nitrification and denitrification at 25?,has also been effectively enriched at52.14%.At a low temperature of 15?,Nitrobacter is richer than Nitrosomonas,and Nitrobacter is more tolerant of cold shocks than Nitrosomonas.Two typical autotrophic denitrifiers,Afipia and Thiobacillus,were 25? richer than 15? and 20?,0.72%and 0.43%,respectively.