Research On Simultaneous Nitrification And Denitrification Processes In The Cathode Chamber And Electricity Generation Of A Single-Cathode And Multi-Anodes Microbial Fuel Cell

Denitrification can be achieved in the biocathode of microbial fuel cell?MFC?,but the the rate of autotrophic denitrification was lower.This study utlized a single-cathode and multi-anodes microbial fuel cell?SCMA-MFC?and provided oxygen and organics to the cathode to achieve simultaneous nitrification and denitrification in the cathode which simultaneous heterotrophic denitrification and autotrophic denitrification exsited.Based on the optimization study about the number of anodes and configuration of SCMA-MFC,the removal of contaminants in anodes and cathode,electrical performance of SCMA-MFC were evaluated under different operating parameters?organic concentration in the anodes,dissolved oxygen concentration in the cathode,C/N ratio in the cathode,external resistance value?,different connection modes between anodes and cathode,open or closed circuit.The changes of microbial community structure in the cathode before and after the start-up period of SCMA-MFC and under different C/N ratio in the cathode were analyzed to provide the theoretical basis for the analysis of denitrification pathways and explore the effect of organics on microorganisms in the cathode.The main results were as follows:?1?When the start-up period of MFCs which the number of anodes were 1,3,5respectively were completed,the COD removal rate were above 93.7%in these anodes.When the concentration of CH₃COONa?NaAc?was 0.3 g/L and the DO concentration was 0.7±0.1mg/L in the cathodes,simultaneous nitrification and denitrification was realized successfully in the SCMA-MFCs.When the start-up period of cathodes were completed,the denitrification efficiency of three reactors were stable at 60.9%,61.3%,56.5%respectively.?2?3A-MFC configuration was superior to 1A-MFC and 5A-MFC in terms of electricity production and pollutant removal efficiency.The maximum power density of 3A-MFC was236.7 mW/m³.The removal efficiency of COD in the anodes,NH₄⁺-N,and TN can reached94.0%,84.8%and 71.6%respectively in 3A-MFC.The average removal rate of TN before and after 25 hours can reached 15.7 mg/L·d,4.7 mg/L·d respectively in the 3A-MFC.?3?Take pollutant removal and electricity production performance into account,the optimal operating parameters of 3A-MFC as follows:influent NaAc concentration of anodes was 1.5 g/L,DO concentration of the cathode was 0.7±0.1 mg/L,C/N ratio of the cathode was3.5,the external resistance value was 150?.It can achieved maximum power density of182.9 mW/m³,COD in the anodes,TN and NH₄⁺-N removal of 97.3%,84.1%,and 97.1%respectively.The average removal rate of TN was 13.1 mg/L·d at these operating parameters.Higher current density at low resistance was likely to stimulate the denitrification activity of denitrifying strains.?4?The pollutants removal efficiency in the parallel operation of 3A-MFC were all higher than these in the series operation.The average removal rate of TN was 14.4 mg/L·d in the parallel operation which is 1.9 times to that in series.Stimulation of current promoted denitrifying bacteria and nitrifying bacteria to achieve simultaneous nitrification and denitrification at a higher rate probably.?5?Accompanied by the operation of 3A-MFC,the community diversity and abundance in the system showed a downward trend generally,the denitrification and nitrification functional flora enriched gradually.The main nitrification genuses in the cathode were Nitrosomonas and Nitrospira.Thioalkalispira?Ignavibacterium?Bacillius genuses involved in denitrification in the cathode.Heterotrophic aerobic denitrification and autotrophic denitrifying bacteria existed generally under different C/N ratio in the cathode of 3A-MFC,such as genus Bacillus and genus Comamonas bacteria.When the concentration of organics in the cathode was higher,autotrophic denitrifying bacteria such as Thiobacillus bacteria was inhibited,but hypoxic heterotrophic denitrifying bacteria such as Clostridium sensu stricto bacteria was strengthened.Based on the optimization of the structure of SCMA-MFC,this subject explored the optimal operating parameters of 3A-MFC for simultaneous nitrification and denitrification in the cathode.The operation methods such as parallel connection between multiple anodes and single cathode,the add of organics in the cathode enhanced simultaneous nitrification and denitrification processes in the cathode of 3A-MFC.According to the function of main denitrification microorganisms in the cathode,the denitrification pathways included autotrophic denitrification and heterotrophic denitrification which included aerobic denitrification.