Operation Performance And Microbial Community Analysis Of Simultaneous Treatment Of Sulfur-and Nitrogen-containing Wastewater By MFC

With the development of industrialization,a large amount of organic wastewater containing sulfur and nitrogen is produced.Therefore,there are more and more researches on the simultaneous use of chemical and physical methods to desulfurize and remove nitrogen from wastewater,but its cost is high.Microbial fuel cell（MFC）has received widespread attention due to its low energy consumption,environmental protection,and convenient operation.It can simultaneously achieve desulfurization,nitrogen removal,and electricity generation under the action of microorganisms.However,the pollutant degradation of MFC and the process of electricity generation are susceptible to the influ-ence of operating parameters and microbial communities,and further research is still needed.In this paper,a two-chamber microbial fuel cell is constructed,the anode solution is sulfide simulated wastewater,and the cathode solution is simulated nitrate wastewater.The anode and cathode are respectively inoculated with sludge flora,and the desulfuriza-tion and nitrogen removal MFC is successfully constructed.The effects of different sul-fur-nitrogen ratios（5:2、5:5、5:8）,pH（5、7、9）,and open and closed circuits on the performance of MFC denitrification and desulfurization and electricity generation by the cathode and anode flora were studied,and the environmental response of the microbial community structure during the process of pollutant degradation and electricity genera-tion was further studied.The specific conclusions are as follows:（1）Using continuous culture method,first domesticate the anode microorganisms,then domesticate the cathode microorganisms,and use the blank carbon brush as a refer-ence after the end of the operation,observe the surface morphology of the anode and cathode carbon brushes with SEM,and explore the use of MFC for desulfurization and denitrification Feasibility.The experimental results show that the most suitable sulfide mass concentration for this MFC anode is 100.00 mg/L.At this time,the sulfide conver-sion rate is 97.08%,and the COD removal rate is 82.16%.While the MFC anode removes sulfide,it also has high organic matter removal efficiency;the maximum voltage can sta-bly reach about 700.00 m V,and the maximum power density is 2.92 W/m³;after several cycles of cathode exchange operation,the mass concentration of NO₃^--N from 40.00 mg/L to 6.07 mg/L,the operating cycle is 72 h,and the conversion rate is 84.83%.Observing SEM,it was found that sulfur particles were deposited on the anode carbon brushes,and the cathode microorganisms adhered to the surface of the carbon brushes,and formed a community through themselves and their secretions.（2）The effects of different sulfur-to-nitrogen ratios,pH,and open and closed circuits on the operating performance of the MFC simultaneous desulfurization and denitrifica-tion process were studied.The influence of operating parameters on the degradation of pollutants and the process of electricity generation is discussed.The experimental results show that the sulfur-nitrogen ratio has little effect on the removal of S^2-in the anode chamber,and the conversion rate is above 94%.S^2-is converted to SO₄^2--S The conver-sion rate is 73.34%.The sulfur-nitrogen ratio has a greater impact on the nitrate removal rate and the total nitrogen degradation rate in the cathode compartment of the MFC.When the sulfur-nitrogen ratio is 5:5,the denitrification performance in the system is the best,the mass concentration of the nitrate outlet liquid of the cathode chamber is reduced from100.00 mg/L to 8.68 mg/L,the conversion rate is 91.32%,and the operation period is 90h,The average conversion rate is 24.35 mg/（L·d）;the removal rate of TN is also the highest,61.20%;when the influent sulfur-nitrogen ratio is 5:5,the current density and power density both reach the maximum value,respectively,16875.00 m A/m³,1560.56m W/m³;according to the slope of the polarization curve,the sulfur-nitrogen ratio is 5:5,and the internal resistance of the reactor is the smallest and the average voltage output is the highest,which represents the best actual power generation performance.When the pH is 5,7,and 9,the conversion rate of sulfide is 84.17%,98.63%,74.10%,the removal rate of COD is 69.93%,83.54%,52.79%,and the average conversion rate of NO₃^--N is 0.47,,1.06,0.68 mg/（L·h）respectively.If the pH value is too small or too much,it will affect the growth and metabolism of microorganisms.When the pH is 7,MFC has the best desulfurization and denitrification performance.The removal rate of nitrate in the closed circuit is 2.07 times that of the open circuit,and the removal rate of sulfide in the closed circuit is 1.73 times that of the open circuit.The micro-voltage generated by MFC has a stimulating effect on the cathode and anode microorganisms,and enhances the removal of nitrate and sulfide（3）The effects of different sulfur-nitrogen ratios,pH,and open and closed circuits on the MFC simultaneous desulfurization and denitrification microbial community were studied.The study and analysis of the response of the microbial community structure in the process of pollutant degradation and electricity generation has a guiding role in the expansion of the application range of MFC.The sulfur-nitrogen ratio affects the abun-dance of the dominant bacteria.The dominant bacteria in the MFC that are related to the degradation of sulfide are Chlorobaculum,Desulfobacterium,and Longilinea,which are composed of a variety of electricity-producing bacteria and sulfur-oxidizing bacteria;cathode bacteria The population abundance changes with the continuous increase of the sulfur-nitrogen ratio.The dominant bacteria genus changed from Acidovorax（relative abundance 4.27%）to Azonexus（relative abundance 5.18%）and finally became Longi-linea（relative abundance 6.03%）;pH will have an impact on the comprehensive effect of the metabolic activity of the positive and negative microbes.With the increase of pH,the abundance of the dominant bacteria of the anode such as Desulfobacterium,Longi-linea,and the dominant bacteria of the cathode such as Azospira,Nitrosopira,Thermomo-nas,etc.would firstly increase and then decrease.Liquid neutral conditions are more suitable for bacterial growth,which is conducive to the removal of sulfides and nitrates,and improves the power generation performance of the battery;Geobacter,Longilinea and Azospira have higher levels in closed-circuit MFC biofilms.It shows that closed cir-cuit conditions are beneficial to the enrichment of MFC electricity-producing microor-ganisms.