Study On The Nitrogen-containing Wastewater Treatment By Microbial Fuel Cell

Microbial fuel cell(MFC)is a promising wastewater treatment technology,which converts the chemical energy contained in organic matter to electrical energy using electroactive bacteria,realizing the "win-win" of wastewater treatment and power production.At present,aside from organics,wastewater also contains large amounts of nitrogen,which draws a wide attention of researchers on achieving nitrogen removal by MFC.Among them,the key to promoting the application of MFC in the field of nitrogen removal from wastewater is to construct the MFC system reasonably,which guarantees the high performance of wastewater treatment and electricity generation while reducing the costs.Therefore,it is necessary to select low-cost electrode material with high performance of polluent removal and electricity generation,and develop effective low-cost MFC reactor.Firstly,based on three different unmodified low-cost carbon-based electrode materials,denitrifying MFCs were constructed to evaluate the effect of electrode materials on the performance of MFCs in this research.The electrode material with good pollutant removal effect and high performance of electricity generation was selected.The influence mechanism was explored from three levels including electrochemical characteristics,microbiological characteristics and electrode material properties,which provide the experimental basis and the theoretic support for the selection of electrode materials in the application of nitrogen removal from wastewater by MFC.Then,a novel integrated nitrification-denitrification membrane-less MFC was developed,which used baffles instead of the expensive ion exchange membranes and relied on the reasonable order of reaction chambers.In addition,the electrode material selected in the previous study was used as electrode in the novel MFC.The performance of wastewater treatment and electricity generation was investigated and the energy potential was evaluated.At the same time,the working mechanism was studied,which lays the foundation for pushing forward the practical application of MFC in nitrogen removal from the wastewater.The main conclusions are as follows:1.Effect of electrode materials on the performance of denitrifying microbial fuel cells.Three different unmodified low-cost carbon-based electrode materials of second generation,carbon felt(CF),granular active carbon(GAC)and sugarcane carbon(SC),exerted different effects on the performance of denitrifying MFC,among which the CF were optimal.Under the batch mode operation,the start-up time of MFC equipped with CF electrode was the shortest.During the steady operation,only MFC based on CF electrode achieved efficient removal of COD and nitrate within one cycle(72 h).In terms of the performance of power generation,a maximum power density of 8.516±0.111 W/m3 was achieved in the MFC equipped with CF electrode,which is 15.9 and 1.3 times the maximum power density of MFC equipped with GAC and SC electrodes.The analyses of electrode polarization behavior and microscopic morphology of the biofilm showed that the bacteria attached on the surface of CF grown best and the potential loss of CF electrode was the lowest.2.Study on the influence mechanism of the electrode materials on the performance of denitrifying microbial fuel cells.The charge transfer resistance of CF anode was 89.54%and 75.21%lower than that of GAC and SC,respectively.The exchange current density of it was 4.21 and 2.35 times higher than that of GAC and SC,respectively.Meanwhile,the Rct of CF cathode was 88.85%and 40.36%lower than that of GAC and SC,respectively.The exchange current density of it was 5.39 and 1.49 times higher than that of GAC and SC,respectively.The results showed that the Rct of CF electrode was lower,the kinetic activity was higher and the redox rate was faster.The absolute quantity of the electroactive bacteria in anode(Geobacter,Desulfovibrio,Desuluomonas,etc.)and the autotrophic denitrification bacteria in cathode(Thiobacillus,Geobacter,etc.)was CF>SC>GAC,and the order of cytochrome C content was the same as above,which indicated that the microbial activity of CF electrode was stronger.Based on the analyses of electrochemical characteristics,microbiological characteristics and electrode material properties,it was suggested that the physicochemical properties of electrode materials affected the performance of bacteria,which affected the electrochemical activity of the electrodes,resulting in differences in the performance of MFC.To be specific,the open macroporous three-dimensional structure,the larger surface hydrophobicity,a certain amount of N element and a lower absolute value of zeta potential promoted the attachment of bacteria on the surface of electrode and increasing the biomass.In addition,the high conductivity promoted the interfacial electron transfer between the bacteria and the electrode,which increased the proportion of electroactive bacteria and enhanced the activity of bacteria.The better performance of bacteria reduced the Rct and enhanced the kinetic activity of electrode,which improved the performance of MFC in terms of polluent removal and electricity generation.3.Development and study of a novel integrated nitrification-denitrification membrane-less microbial fuel cell.When treating the synthetic wastewater with the concentration of COD 855±15.03 mg/L,NH4+-N 45.73±2.46 mg/L and TN 46.337±2.583 mg/L under the continuous mode with an external resistance of 750 ?and a hydraulic retention time of 24 h,the novel MFC achieved the removal efficiencies of COD,NH4+-N and TN of 97.07±0.47%,91.76±3.32%,and 87.66±1.59%,respectively.The main monitoring indicators all met Class A standard of the Emission Standard of Pollutants for Municipal Wastewater Treatment Plants(GB 18918-2002).During the nearly 6-month experimental period,the reactor maintained stable operation with the maximum power density of 1.007±0.032 W/m3,which had a promising energy potential.With the reactor running,the proportion of electroactive bacteria in anode(Desulfovibrio,Comamonas)and autotrophic denitrification bacteria in cathode(Thiobacillus)increased by 73.91%,38.17 times and 14.6 times,respectively.The simultaneous carbon and nitrogen removal and electricity generation in this reactor were mainly attributed to the anaerobic hydrolysis and electrochemical reaction in anode,nitrification and heterotrophic denitrification in the nitrifying chamber,and the autotrophic denitrification and heterotrophic denitrification in cathode.