| With the increasing pollution of nitrogen and the prominent problem of energy shortage,how to carry out nitrogen removal while recovering waste resources is an issue that we urgently need to solve.This project studied the influencing factors of the denitrification process and coupled the microbial fuel cell(MFC)with the anaerobic biofilter(AF)process to make up the inefficient use of carbon source by traditional biological denitrification processes,improving the effective utilization of carbon source and the efficiency of removing nitrogen,the reaction mechanism and microbial community structure were analyzed,and the practical application possibilities and economic efficiency of the microbial fuel cell-anaerobic biofilter(MFC-AF)system were discussed,providing a theoretical basis and reference for the practical application of the MFC.By analyzing the factors that affect denitrification,such as carbon source,pH,and carbon-to-nitrogen ratio in the denitrification process,it was found that denitrification has a high nitrate removal rate of v a=10.1 mg/(L·h)when sodium acetate is used as the carbon source,the nitrite enrichment of sodium lactate was only 5.6%of TN.When the carbon source was sodium acetate,the optimum ratio of carbon to nitrogen was 2:1,and 93.4%of TN was removed at 48 h.The most suitable pH range of denitrification is around 8.At this time,the removal rate of nitrate nitrogen can reach up to 30.08 mg/(L·h),the TN removal rate is 97.36%,and only a small amount of nitrite is accumulated and removed quickly.Denitrification and electricity generation were studied using the constructed MFC-AF reactor and the single AF reactor.Under the condition of sufficient carbon source,the maximum output voltage of the MFC-AF reactor is about 0.47 V,and when the current density is 1.35 A/m~3,the maximum output power is 0.38 W/m~3,and the internal resistance of the reactor is 200Ω.When carbon source is under the condition of 0.6/0.3/0.15 g/L sodium acetate,the average removal efficiency of COD and TN in the MFC-AF reactor were both better than in the single AF reactor.Especially at low carbon concentration of 0.15 g/L,the COD utilization rate of the MFC-AF was as high as 90.10%,the denitrification rate was 75.67%,and the nitrogen removal rate was 16.05%higher than that of the AF reactor,resulting in an output voltage of about 0.10 V.These results indicate that the MFC coupled with the anaerobic biological filter can increase the denitrification efficiency of a single anaerobic biological filter,and can also improve the utilization of the carbon source.To study the optimal power generation efficiency of MFC-AF,the carbon source concentration was optimized.The optimized carbon source concentration was 0.24g/L.The average COD removal rate was 87.60%,and the TN removal rate was86.91%.The voltage is stable at 0.35 V and the Coulomb efficiency is 8.66%,which is similar to the analog value of 8.88%.The microbial community structure of the two reactors was analyzed.It was found that the abundance of the microbial community in the MFC-AF reactor was better than in the AF reactor,and the community structure at different locations was significantly different.The main microorganisms in the coupled reactor were Azospira sp.,Trichococcus sp.,Nitrospira sp.,Dechloromonas sp.,Flavobacterium sp.,Terrimonas sp.,Geobacter sp.,and so on,among which Trichococcus sp.,Geobacter sp.and Flavobacterium sp.have been known to have extracellular electron transfer ability.Azospira sp.,Dechloromonas sp.,Nitrospira sp.and Terrimonas sp.have been demonstrated to have the denitrification ability.RDA/CCA showed a positive correlation between the environmental factors COD and Nitrate,and there was a negative correlation between COD and Nitrate,and the result was same with COD and pH.The two biological reactors had the largest difference in biological community at the bottom of the filter.Five of the eight MFC-AF microorganisms had a positive correlation with Nitrate,while only two microorganisms of AF reactors had a positive correlation with Nitrate,indicating that denitrifying bacteria is more widely distributed and the denitrification capacity is stronger in the MFC-AF.Finally,some preliminary discussions on the practical application of the MFC-AF coupled reaction system were made and economic efficiency analysis was performed.If MFC-AF is applied to a deep nitrogen removal process(using sodium acetate as an additional carbon source),the operating cost is 0.2586 RMB per ton of wastewater.Recycling power is about 357,700 RMB/year(the processing scale is 30 thousand tons/day.The additional carbon source fee is the main component of operating costs. |
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