Characteristics Of Simultaneous Carbon And Nitrogen Removal And Electricity Generation In A Two-chamber Biocathode Microbial Fuel Cell

Usually,functional bacterium on the electrode are used as catalyst in a microbial fuel cell, so the organics can be oxidized by the anode in low potential and the electron acceptor can be reduced in high potential. And the electricity is generated by the directional migration of electron and proton.Catalyst such as heavy metals was required to reduce O2on the cathode of traditional chemical cathode MFC and the increasing pH in the cathode chamber caused by the permselectivity defects of the CEM was also a problem, nitrifition is introduced to the cathode chamber to resolve these problems and biocathodic two-chambered MFCs are constructed in this study. Functional bacterium instead of tranditonal catalyst such as heavy metals were used as catalyst by screening and training in the cathode.And based on the fact that proton production from nitrifying need the aerobic environment, O2was reduced in the cathode while NH4+-N were oxided to NO3--N in the cathode, which avoids pH increasing.In order to see the effect of organic carbon on microorganisms in the cathode chamber, the growth rhythm of nitrifying bacteria in solely holophytic (without providing organic carbon) and addition of carbon source by the ratio of COD:N=1.7:1is studied. As a result,the nitrifying ratio of the two ways after cultivation can reach99%except that the tendency is different. And the nitrite bacteria and the nitrate bacteria of the two reactors reach2.5×1064.5×104and2×1067.5×104cfu/mL repectively,almost the same.However.due to the solely carbon source.the MLSS in the first reactor gradually decreased while that in the other it increased gradually. And scanning electron microscope(SEM) result show that there were some bacillus and coccus and so on in the two reactors at the end of the cultivation. The result also showed that on the condition of COD:N=1.7:l,the system is much steadier. In order to decrease the cost of MFCs, electricity generation characteristics of two MFCs using carbon felt and carbon cloth as biocathode materials were investigated. The results show that the start-up periods of the two MFCs were almost the same, about20days, but the voltage of the former one was60mV lower than the latter one. The maximum power density of the two MFCs at10and20days increased from10.24,11.14mW/m2to18.18,30.15mW/m2, while the internal resistance decreased from1000,600Ω to250,200Ω respectively. SEM results show the two materials have different surface characteristics, the sludge is more likely to adhere to carbon felt, which may generate bad effects to DO diffusion and electricity production.Based on the above results, carbon cloth was chosen as cathode material to study simultaneous carbon and nitrogen removal and electricity generation was also investigated in the MFC. The effects of several elements such as different influential COD in the anode chamber, different influential NH4+-N and DO in the cathode chamber on electricity generation and contaminant removal were investigated as well as the function of nitrifying in the cathode. The results showed that when the COD of influent changed from100,400,700to1000mg/L,the steady time of the MFC were10,50,60and90h and the voltage were136.4,145.7,164.9,190.1mV, respectively. Both of them increased gradually. The removal rate of COD changed from74.85%to89.89%,while the coulumbic efficiency decreased from7.15%to5.66%.When the influential COD was700mg/L and cathodic DO was4mg/L, the removal rate of ammonia nitrogens was different with the increasing ammonia nitrogen concentrations,which were27,36.2and51.1mg/(L-d), respectively. There was a small increase in voltage in the steady time,which was165,177and194mV.When the influent COD was700mg/L and NH4+-N was80mg/L, the removal rate of ammonia nitrogen degration in the72hours was almost the same with the cathodic DO increased from2mg/L to4mg/L.But the electricity generation characteristic increased gradually. And the open circuite voltage after12hours was556.8,592.l,597mV respectively,and the corresponding maximum power density were31,52.9,75.2mW/m2and139,161,178mV. In the study of nitrification influence on catalyst,the result showed that when the influential NH4+-N in the cathode was20mg/L, the cathodic pH increased from7.15to7.62in the first2hours and then decreased to6.86gradually in the following time.However,when there was no ammonia nitrogen in the influent,the cathodic pH hastily increased from7.58to8.62in the first2hours and kept no changes in the following time.Finally, the the community structure of the microbe in the carbon cloth of cathode MFC were analyzed after5months by PCR and DGGE technology. The result show that the main microorganisms on the anode were Acinetobacter sp.,Treponema,Pseudomonas saccharophila,uncultured Anaerovorax sp.,while the main microorganisms on the cathode were Sediminibacterium,Treponema,Pedobacter heparinus,uncultured Anaerovorax sp,Bartonella tamiae.And Pseudomonas sp.,Acinetobacter sp.are general electricity generating bacterium in anode.