| Energy for future will continue to be lacking, and the environmental crisis becomes more and more horrible for human being. At the same time, renewable energy has no bad effect for environment, so it has potential to be refill of oli and coal today. As a new renewable energy, microbial fuel cell (MFC) can generate electricity from carbohydrate and mixed organic waste under the catalysis of microbe.. MFC has high conversion efficiency, it can operate normally outside at low temperature and won't release more carbon dioxide than average. Due to its advantages, MFC has great application foreground in alternative energy and waste water treatment. With the increase of attention gained by MFC, however, it has some shortcomings. Power output of MFC is still limited and unstable nowadays, on the other hand, the addition of mediator will cause pollution and increase of MFC cost. Focused on these problems, this article mainly studied on optimization of MFC system, selection of electrode, screening and taming of electricigens. Through these methods, we increased voltage, current and power output of MFC system. Additionally, we created mediator-less MFC based on Saccharomyces cerevisiae 2.39 and Rhodosporidium paludigenum Fell & Tallman. So we finally solved present problems during development of MFC, increase of electrical capability and creation of mediator-less MFC. Concrete results are as follows:1. Construction and optimization of MFC systemThe anode and cathode of this two-chambered MFC were all made from graphite, the model electricigens was Saccharomyces cerevisiae 2.39. We chose open circuit voltage (OCV) as selection parameter. Final area of proton exchange membrane was 25 cm2. The optimized condition were 20 ml glucose solution with concentration of 0.1 g/ml,20 ml Saccharomyces cerevisiae 2.39 with density of 6×1011 cells/ml,0.5 ml methylene blue with concentration of 1%, 3 ml NaH2PO4 solution with concentration of 0.05 g/ml,2 ml K3Fe(CN)6 solution with concentration of 0.05 g/ml. We obtained maximal OCV of (0.534±0.028) V after optimization.2. Selection of electrodes and screening of electricigensAfter optimization, we used different anodes to compare maximal OCV. From results of electricigens 2.39, AS2(434), Y10, Y11(45), Y20, Y17 and 2.67, we can see graphite electrode had the lowest electrochemical activity, but the activity increased with the substitute of copper, aluminum, iron piece and iron loop, so iron loop had highest electrochemical activity.2.39 had maximal OCV of (1.241±0.025) V when iron loop anode. AS2(434) had maximal OCV of (0.985±0.014) V when iron loop anode. Y10 had maximal OCV of (1.103±0.011) V when iron loop anode. Y11(45) had maximal OCV of (1.138±0.016) V when iron loop anode. Y20 had maximal OCV of (1.297±0.031) V when iron loop anode. Y17 had maximal OCV of (1.151±0.029) V when iron piece anode.2.39 and Y20 obtained highest maximal OCV with iron loop among of the electricigens. At the same time, Y10 reached maximal OCV more quick than other electricigens, so it has better stability. So 2.39, Y20 and Y10 would be used for futher taming.3. Taming of electricigensEletricity generated from MFC system while adding certain resistance in a closed circuit under iron loop anode and graphite cathode. Taming of electricigens consisted of re-collection, separation and incubation after MFC electricity generation; and then used these electricigens to generate electricity again, the voltage, current and power output would be collected and compared. Results showed that electrical capability increased greatly after taming.The voltage, current and power output of 2.39 all had great promotion, were 0.392 V,1.1 mA and 0.431 mW respectively.2.39 got maximal point more quickly after taming, in other word, it had better electrical capability and stability.The voltage, current and power output of Y20 all had great promotion, were 0.924 V,0.512 mA and 0.506 mW respectively. So it had better electrical capability.The voltage, current and power output of Y10 all had great promotion, were 0.557 V,1.568 mA and 0.873 mW respectively, comparing to 0.348 V,0.98 mA and 0.341 mW before taming, Y20 got excellent electrical capability and stability after taming.4. Construction of mediator-less MFC systemMediator-less MFC system was based on Y10 (after several time'taming) and Rhodosporidium paludigenum Fell & Tallman (marine yeast), generated electricity under optimized condition without methylene blue using iron loop anode and graphite cathode. Results showed Y10 system got voltage, current and power output of 0.889 V,2.2 mA and 1.99 mW respectively. And Rhodosporidium paludigenum Fell & Tallman system got voltage, current and power output of 0.937 V,1.4 mA and 0.459 mW respectively.In conclusion, the electrical capability of MFC had been greatly improved through optimization of system, screening of electricigens, electrode selection and taming of electricigens. Additionally, we created mediator-less MFC based on Saccharomyces cerevisiae and marine yeast, and this type of MFC can meet requirements for small marine instruments. To some content, our research had solved some problems towards low power output and toxic mediator of MFC. |
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