| Nowadays, microbial fuel cell (MFC) has attracted great interests for its potential in recovering energy and resource. MFC has been developed into a cross-platform for studies of microbiology, chemistry, physics, materialogy and engineering. Hence, in-depth investigations into microbial extracellular electron transfer (EET) under various conditions are needed to manipulate the EET, microbial electron transfer is of great significance to the MFC development.In this thesis, the mechnism of microbial electron transfer in the presence of uncouplers and different Fe(Ⅲ) species as electron acceptors was investigated to find out the feasibility of manipulating the microbialEET. We also tried to introduce the microbial EET into current wastewater treatment systems. The main results of this work are as follows:1. The microbial EET in the absence and presence of 3,3’,4’, 5-tetrachlorosalicylanilide (TCS) and 2,4-dinitrophenol (DNP) was evaluated using MFC method and WO3-electrochromic probe. Six pure strains including Shewanella oneidensis MR-1 and mixed cultures were examined. Results showed that the microbial EET could be facilitated by uncoulers at appropriate concentrations. The coulombic efficiency of the MR-1-seeded MFC increased by about 10% after the dose of TCS or DNP (50 μg/L). The microbial physiological properties related to EET were also examined with S. oneidensis MR-1as the model strain. The mechnism behind the enhanced EET by uncouling was proposed on the basis of the results.2. Alpha-ferric oxide, hydrous ferric oxide, ferric EDTA sodium salt and ferric citrate were classitied into two types of electron acceptors by examining the growth yield of S. oneidensis MR-1 in the absence and presence of the electron acceptors. The growth yield of S. oneidensis MR-1 was considerably increased in the presence of ferric EDTA sodium salt and ferric citrate, which were classitied as active electron acceptors, while the yield remained nearly unchanged in the presence of alp ha-ferric oxide and hydrous ferric oxide, which were classitied as electron sink. S. oneidensis MR-1 obtained energy through substrate level phosphorylation when electron sink existed and through oxidative phosphorylation when electron acceptors existed. This result was consistent with the results of respiration inhibition test by copper ion and dicoumarol, which was also evidenced by the results of the nitrate co-existing test. It was found that S. oneidensis MR-1 could use different electron pathways for Fe(Ⅲ) reduction.3. An MFC was tactfully integrated into an MBR through a simple modification of MBR construction, forming a cost-effective wastewater treatment system. For future practical application, the raw materials for constructing the MFC and MBR module were all low-cost and easily available. The coupled system showed good performance in terms of wastewater treatment and current generation. The results demonstrate a great potential of the coupled system for practical application.4. The response of different modules/parameters under different substrate concentrations and hydraulic retention times was investigated in the built MFC-SBR (sequencing batch reactor) coupled systems. Results showed that the oxygen reduction at the cathode was the main restrict of system current generation, which was linked closely to the anode substrate consumption through the "food chain" of the system The cathode-respiring bacteria co-existed with common heterotrophs in SBR, competing for oxygen. This competition could be alleviated by enhancing the substrate interception by MFC module and the system performance on wastewater treatment and electrochemistry could be improved. |
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