| Microbial fuel cells(MFCs) are devices that removal pollutant and generate electricity with microorganisms as the catalysts simultaneously. It provides a new technology for biological nitrogen removal from wastewater. In this study, dual chamber MFCs were constructed for simultaneous bioelectricity generation and removal of organic matter and three nitrogen substance(e.g., NH4+-N, NO3--N or NO2--N) as cathode substrate respectively from synthetic wastewater. The influences of operating parameters(e.g., the concentration of nitrogen substance, flow rate, and external resistance and so on) on the performance of denitrifying microbial fuel cell were investigated. Denaturing gradient gel electrophoresis was used to identify the functional characteristics of the cathode denitrifying bacteria. The working mechanisms were investigated to achieve biological denitrification and electricity generation. The main results are as follows:(1)The influences of different operation modes on the performance of denitrifying microbial fuel cell were investigated when simultaneous nitrification and denitrification taken place in the cathode of MFC over ammonia nitrogen.(1) The experimental results demonstrated that maximum ammonia nitrogen removal rate was 95.17 % under the condition of open circuit, which indicated that the open circuit is beneficial to nitrification while the closed circuit is more advantageous to COD and nitrogen removal, the total nitrogen removal rate reached 0.064 g/(L·d).(2) The aeration-unaeration process was an effective way to remove nitrogen, produce electricity and reduce the energy input to maintain high DO concentration, which the total nitrogen removal rate reached 0.46 g/(L·d).(2)The influences of operating parameters on the performance of denitrifying microbial fuel cell were investigated when nitrate and nitrite were used as the cathode substrate, respectively.(1) The performance of denitrifying and generating electricity microbial fuel cell could be promoted with increasing substrate concentration in a certain range. The variation tendency betweent the current density and the influent nitrate concentration was modeled.For the nitrite as the substrate of MFC, operation mode with a low flow and high influent nitrite concentration could reduce nitrite nitrification and enhance denitrification efficiency.(2) It would be rather desirable for the TN removal and electricity generation of MFC at lower external resistance. For No. 3, MFC, the maximum TN removal rate of 66.86 g/(m3·d) and the highest current density of 14.25 A/m3 were obtained at 25 Ω.(3) Appropriate hydraulic retention time(HRT) can shorten wastewater treatment time and improve the processing efficiency of the reactor. For No. 3, MFC, the TN removal rate of 93.23 % was obtained with HRT of 59 h.(4) PH has a great influence on the activity of denitrifying bacteria and the TN removal in MFC. Weak acidic environment is benefit to the improvement of the performance of the MFC. For No. 2, MFC, the maximum TN removal rate of 54.82 g/(m3·d) was obtained at p H of 6.85.(5) Increasing the temperature contributed to improve the performance of MFC, for nitrite as electron acceptor in the cathode, the maximum TN removal rate of 55.27±0.84 g/(m3·d) at 32℃,but an over-high temperature could inhibit the activity of denitrifying microorganism.(6) The method of intermittent aeration to the anode of long-running MFC process was an effective way to inhibit the growth of methanogens and improve the performance of the anode.(3) It compared the characteristics of the microbial communities at bio-cathodes when nitrate and the nitrite as the cathode substrate,and then speculated for possible reactions in the cathode, respectively.(1) MFC1 with nitrate as the substrate was the best effect according to the performance of reactors; From the point analysis of microbial communities, two microbial communities similarity coefficient was 52.2 %; In MFC1 with nitrate as substrate, Ignavibacteriae was the predominant genus, and Thiobacillus was subdominant groups; In MFC2 with nitrite as substrate, Truepera was the predominant genus. In two MFCs, Alphaproteobacteria and Betaproteobacteria might contribute to electricity generation, Thiobacillus sp.、Ignavibacterium sp.、Afipia sp. and Aquamicrobium sp. mainly benefit to autotrophic denitrification in MFC.(2) It speculated for possible reactions in the cathode with nitrate as electron acceptor that were autotrophic denitrification, heterotrophic denitrification, oxygen reduction and other electrochemical reactions. Similarly, autotrophic denitrification, heterotrophic denitrification, autotrophic nitrification, oxygen reduction and other electrochemical reactions existed in the cathode with nitrite as electron acceptor. |
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