Simultanious Carbon Removal, Nitrification And Denitrification Using Microbial Fuel Cell Technology

The microbial fuel cell(MFC) technology has been demonstrated to be a promising method for nitrogen removal with simultaneous po wer generation. However, most of the previous studies concerned simultaneous nitrification and denitrification(SND) in the aerated cathode chamber of an MFC, whereas the enrichment of cathodic denitrifying bacteria in the presence of aeration was difficult. Here, we show the concept of SND that occurs in separate anode and cathode chambers, rather than in the same cathode chamber. Cathode nitrification coupled to anode denitrification for nitrogen removal was achieved in an MFC with the help of an anion-exchange membrane(AEM) which enabled nitrate and nitrite as a result of cathode nitrification to transfer from the aerobic cathode chamber to the anaerobic anode chamber. When the ammonium with a concentration of 200 NH4+-N mg/L was fed to the cathode chamber, the AEM-MFC allowed complete nitrogen removal within 66 hrs, significantly lower than the time of 26 days required for the MFC with a cation-exchange membrane(CEM-MFC) that was operated under the identical conditions. Moreover, the AEM-MFC was stably run over a seven- month period with successive feedings of ammonium with different concentrations(e.g., from 50 to 500 NH4+-N mg/L), exhibiting insignificant variations in performance of nitrogen removal and power generation. The results showed that the AEM-MFC offers the pronounced advantages including no requirement of adding acids or alkalis for p H adjustment, less COD demand for denitrification and energy production as compared to the traditional biological method for nitrogen removal.Further experiments were performed with the AEM-MFC to demonstrate the concept of simultaneous phenol removal, nitrification and denitrification. A series of experiments were performed with ammonium(230 NH4+-N mg/L) and phenol(with concentrations varying from 0 to 1400 mg/L) fed to the aerobic cathode chamber of the MFC. Experimental results demonstrated that no apparent inhibitory effect of phenol on the nitrifying reaction was noted even at the phenol concentration up to 600 mg/L For all the experiments, simultaneous nitrification and denitrification was achieved in the MFC. In comparison to the traditional aerobic bioreactor(ABR) and the same MFC running under the open-circuit condition, the MFC reactor allowed less inhibition of nitrification to phenol exposure and higher rate of nitrogen removal. The data of bacterial analysis revealed that electrochemically active bacteria and denitrifiers in the anaerobic chamber play a significant role in electricity generation and anaerobic denitrification, respectively. However phenol-degrading bacteria, nitrifiers, and denitrifiers in the aerobic cathode chamber are responsible for phenol oxidation, aerobic nitrification and aerobic denitrification, respectively. These results imp lied that the MFC holds potential for simultaneous removal of phenolic compounds and nitrogen contained in some particular industrial wastewaters.On the basis of the above experimental results, we investigated the feasibility of using the AEM-MFC to achieve simultaneous carbon and nitrogen removal with the real coking wastewater. The preliminary results indicated that the removal efficiencies of COD and NH4+-N were 88.6% and 99.0%, respectively after 120 h-operation, when the diluated coking wastewater(dilution ratio was 2 times) was directly fed to the AEM-MFC. Moreover, less than 10 mg/L NO3--N was detected after the same period, suggesting that simultaneous nitrification and denitrification can proceed with the real coking wastewater. Moreover, no acids or alkalis were added to the system, indicating the significant reduction in chemical costs.