| Microbial fuel cell (MFC) is an emerging process that can generate electricitywith simultaneous organic matter removal from domestic and industrial wastewaters.All such time serried contributions awakened the general interest in MFCs andtriggered a spiral of research achievements that have steadily raised the performancelevels by several orders of magnitude in less a decade.One of the major research topics in the field of MFCs is investigating therelationship between biological factors and abiotic factors both of which areconsidered to limit the output power and overcoming this restriction. These limitingfactors can be measured with internal resistance (Rin) of MFCs or the impedance ofcorresponding electrodes. Rin is composed of three parts: activation internalresistance (also known as the polarization resistance Rp which is related to chargestransfer), ohmic resistance (also known as the solution resistance Rs whichrepresents the total resistance of solution, electron materials and membranematerials) and concentration resistance.This study examined the performances of two double-chamber microbial fuelcells (MFCs) at25oC and15oC. After successful startup, the cell temperature ofMFC A was decreased from25oC to15oC, yielding a sudden breakdown of the entiresystem. Conversely, the MFC B, started up at15oC, delivering higher power densityat25oC than MFC A at the same temperature. The electrochemical analysis revealedthat the MFC B had lower anodic resistance than MFC A. Additionally, a negativetemperature dependence of the polarization resistances of the anodic biofilm wasnoted, a novel phenomenon only reported in this double-chambered study. Microbialanalysis showed that the psychrophilic bacteria were enriched in anodic biofilms ofMFC B, which likely contributed to the robust cell performance of the presentdouble-chambered MFCs.This dissertation focuses on the phenomenon of power overshoot in MFCs. Therelationship between power overshoot and internal reactor mass transfer resistanceis analyzed and we found that internal reactor mass transfer resistance is closelyrelated to reactor configuration, electrode materials, concentration of buffer solution,concentration of substrate (electron donors and electron acceptors), stirring rate andmicrobial catalysts. Under given reactor configuration and electrode material, theeffects of concentration of substrate and stirring rate on over power density havebeen discussed and the causes of power overshoot were also investigated. Besides,the effects of electrode active microbial on the internal MFCs mass transfer havealso been analyzed by establishing reactor with mixed culture and pure culturerespectively. In order to further explore the influence of the mass transfer resistance in themicrobial fuel cell system constructed with pure bacterium, isolated three typicalanode active bacterium, identification through morphology observation,physiological and biochemical, fatty acids,16S rRNA gene identification based onmolecular biology, showed that the three bacteria respectively belong to Citrobactersp., Geobacter sp., Clostridium sp.. Startup double chamber microbial fuel cellsrespectively using three bacteria, are able to stable electricity production. Byalternating current impedance, respectively the full cell, anode and cathode, andmass transfer inside the analysis of microbial fuel cell system change, the resultsshow that the main mass transfer resistance from the anode of the cell.A two-chamber microbial fuel cell was started using iron-reducing strains asinoculum and acetate as carbon sources. The tested microbial fuel cell had anopen-circuit voltage of0.67V, and reached1045mA/m2and a power density of486mW/m2at0.46V before power overshoot occurred. Anodic reactions wereidentified as the rate-determining steps. Stirring the anolyte insignificantly increasedcell performance, suggesting a minimal external mass transfer resistance from theanolyte to the anodic biofilm. Data regression analysis indicates that charge transferresistance at the biofilm-anode junction was negligible. The order of magnitudeestimation of electrical conductance indicates that electron transfer resistance had aninsignificant effect on microbial fuel cell performance. Resistance in electrogens forsubstrate utilization is proposed to induce microbial fuel cell power overshoot. |
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