Research On Electricity Generation And Bacterial Communities Phylogeny Of Circulating Microbial Fuel Cell

The research and development on new and sustainable energy have been considered as an important approach to solve the environmental pollutions and energy crisis in the world. Microbial fuel cells (MFCs) as a type of new clear energy with the advantages of high energy translate efficiency and non-pollution have received great attentions from different countries. However, most of MFCs in previous studies employed non-bacterial cathode and proton exchange membrane to separate the cathodic and anodic chambers, which lead to high cost, low stability and invalid catalyst. As a result, those limitations have effected the development of MFCs and their scale-up for application.This research was supported by China Scholarship Council with the cooperation between Huazhong University of Science and Technology and University of California, Ivine (UCI). The writer focused on the project of the Circulating Microbial Fuel Cell (CMFC) in Sunny C. Jiang’s lab in UCI, aiming to develop a low costing advanced MFC that combined with the practical wastewater treatment process and improve the possibility for the further scale-up application. The CMFC was designed and built, and its electricity generation performance, development of bacterial communities in anode and cathode and the electrons transmission mechanism also have been studied in this dissertation. The main results are summarized as following:CMFC was designed and built which has the different construction compared with the conventional MFC. In CMFC, a porous separator was used to replace the proton exchange membrane that was usually used in conventional MFC, and microorganism was employed in both of the cathode and anode. With this construction, the polar pH problem was avoided, the transport of proton from andod to cathode and the electricity generation performance were improved. The condition of a separator with4.5cm diameter and fuel flow rate of1L/d ensured the anaerobic anode. Under continual feeding regime that was benefit to the bacteria growth and the transport of proton, the voltage creased to200mV after short adaptation and to500mV after7days’ operation, and then the voltage keep in the range of500-610mV. Maximum power density of30.1mW/m2and coulomb efficiency of58.1%were achieved when the acetate of12mM as the substrate was fed into CMFC at the flow rate of1L/d.Three samples under different stages (the initially inoculated sludge samples (Al), the bacteria sample after1month of CMFC operation (A2) and after4months of CMFC operation (A3)) from the anode of CMFC were collected for16S rDNA pyrosequencing analysis. The bacterial communities in all of samples had the high species diversity in phylum, class, order and genus levels. The change of growth condition and the effect of polar chemotaxis led to the obvious change of species in anode. Some species were suppressed when others were developed. Sequencing analysis of the microbial consortia showed the dominance of Firmicutes, Proteobacteria and Thermotogae in A1while the dominance of Firmicutes, Bacteroidetes and Proteobacteria in A2and A3. Sequencing analysis of the archaea consortia showed the high archaea density but low diversity with a decreasing density and dominance and increasing diversity and evenness during the operation. The dominant species changed from Methanosaeta thermophila to Methanosarcina vacuolata and Methanoregula formicicum. The main species to affect the electricity output of CMFC in anode were Bacteroides spp., Bacillus spp.and Clostridium spp.Three samples under different stages (the initially inoculated sludge samples (Cl), the bacteria sample after1month of CMFC operation (C2) and after4months of CMFC operation (C3)) from the cathode of CMFC were collected for16S rDNA pyrosequencing analysis. The bacterial communities in all of samples had the high species diversity, density and Shannon-Weiner indexs in phylum, class, order and genus levels. Sequencing analysis of the microbial consortia showed the dominance of proteobacteria and Bacteroidetes. The predominance had no obvious change when some of others were declined or developed during the operation of CMFC. Overall, the species diversity changed from decrease to increase and the evenness changed from increase to decrease. The main species in the cathode to effect the electricity generation were Dokdonella spp. and Rhodanobacter spp. in both of start and stable stages and Cytophaga spp. and Pseudomonas spp. in the stable stage.The observation of SEM and FM showed the abundant valid biofilm were covered on the surface of both cathode and anode. The electron transmission tests and the study of anodic species suggested the direct electron transmission by biofilm has the main effect on the electricity generation and the indirect ones by primary and secondary metabolites that generated by bacteria also existed in anode. The primary metabolite for indirect electron transmission were generated by the Desulfovibrio spp. and Hydrogenobacter spp. while the secondary one was pyocyanine that generated by Pseudomonas spp. Then an electron transmission mechanism was included based on the study in the CMFC.