The Basis Of The Microbial Fuel Cell Research

In this thesis, the research interest was focused on the direct conversion of chemical energy stored in abandoned organic matter to electricity in designed MFC systems in which natural freshwater sediment was used as the source of functional microorganism. Simultaneously, the performances and characters exhibited by these MFC systems were discussed under some given conditions, and some significant results were obtained as following:1. Fresh sediment MFCs were constructed with freshwater sediment as functional microorganism under different conditions simulating natual environment. The performance of the sediement MFCs presented in this thesis was close to that of marine sediment MFCs reported in recent years. When different organic compounds were added into the sediments, both the chemical properties of the organic matter and the mode by which the compounds were applied enable the induced MFC systems to exhibit characteristics different from that of the MFC systems without addition of exogenous organic compounds.2. Good results could be obtained in double-chamber MFCs when potassium ferricyanide and air-oxygen were combined as oxidant in cathodic chamber, and the natural fresh sediment as innoculum in anodic chamber, and two types of excellent MFC systems, which utilized glucose and acetate as substrates respectively, had been constructed in this model double-chamber MFC setting, without addition of artificial electron mediators. For MFCs with acetate feeding, the current output and electron recovery achieved were 0.41 mA and 80% respectively, whereas current and electron recovery were 0.35 mA and 60% respectively for glucose-feeding MFCs.It also showed that the power output of MFC can be enhanced by connecting individual MFC into MFC stack. Moreover, in MFC systems which were constructed with the same organic matter as substrate, feeding different organic compounds gave rise to the variation of MFC performance in terms of substrate conversion. Additional study demonstrated that the performance of MFCs in which sediment that had been incubated for several weeks or months by simply adding organic contaminants were use as innoculum was also different.3. Systematic experiments demonstrated that working electrode in double-chamber MFC systems with glucose-feeding exhibited selective function for electricity-generating microorganism and these functional bacteria were found to enrich on the surface of graphite cloth electrode. The MFC systems were found to have maximal output power at temperature 35℃, however, 30℃was selected as experimental temperature in our experiments, in order to compare the results with most reported previously in literture. A wide range of factors that may affect the performance of the MFC systems were investigated intensitively, and the results indicated that increase in the effective reaction surface of anode enhanced the power output due to lowering the current density through the electrode; the position of anode in anodic chamber had little effect on the power generation by the MFC systems; current output and coulombic efficiency decreased with increasing external resistance. It was found that the mode by which the organic substrate was fed into the systmes also affected the electricity generation. For example, substrate concentration was showed to be the primary factors to control the power output and charge anount when the MFCs were operated in fed-batch mode, however, when the substrate was accumulatively added into the anodic chamber without redrawl of the medium, the performace of the MFCs was significantly decreased with final effectiveness due to the production of intermediate metablic products (i.e. proton and low mass organic acids). In further experiments, cyclic voltammogram method with anode of MFC as working electrode was used to characterize the production of compounds with electrochemical activity and to moniter the variation of amount of these metablic products. The measuement was performed in two different modes for the same MFC system, with one determing the medium sampled at different phase within an electricity-generating cycle, and the other continously following the whole process by the MFC. The results indicated a presence of redox peak at approximate -0.4 V (versus saturated calomel electrode), and the height of peak in voltammogram was found to change with the electricity-generationg process in MFCs.4. The air-cathode glucose-fed MFCs in continous mode, with excellent output performance, were constructed successfully through simple manufacture method of cathode (Graphite powder, the kleit, the iron sulfate and nickel sulfate were mixed according to stated proportion (60:36:3:1), which was made into the cathode material after calcining.). Brushing a layer of kleit on the surface of the cathode, it was used for the cation exchange membrane, graphite pellet (diameter 3mm) as the anode, for reducing the cost. The changing of output performance of the MFCs due to the influence of flow speed in anodic chamber was investigated, and the results showed that the maximal current output was 0.75 mA when the flow speed was 0.2 ml/min. The output performance due to the influence of phenol was also investigated, and the results indicated that the current output fall stpwise with the phenol cocentration ingcreasing when the phenol as only substacte. However, the current output was gradually stable (0.30 mA) when the concentration of phenol more than 10 mM. And when both phenol and glucose were used as substrate, glucose was remarkably degenerated though the concentration of phenol only has a little change. Simultaneously, the output performance was also stable with gradually ingcreasing phenol. And the current output was still maintaining high (0.70mA) when the concentration of phenol was 20 mM.