Electricity from complex biomass using microbial fuel cells

I examined the effect of three different chitin particle sizes on microbial fuel cells (MFC) power generation and longevity. The results demonstrated that an increase in particle diameter from the smallest (0.28 mm) to largest (0.78 mm) size tested resulted in an increase in longevity from 9 to 35 days. Coulombic efficiency based on removal of chitin was also increased from 18% for the smallest particles to 56% for the largest ones. However, the maximum power generation was lower for large particles (201 mW/m2) as compared to the small and medium size (0.46 mm) (301 and 285 mW/m 2). Measured MFC longevity was explained by the fractal particle degradation model a mass transfer equation.;Cellulases are used to achieve rapid conversion of cellulose to sugar for ethanol production, but these enzymes have not been previously tested for their effectiveness in MFCs. It was not known if cellulases would remain active in an MFC in the presence of exoelectrogenic bacteria or if enzymes might hinder power production by adversely affecting the bacteria. Electricity generation from cellulose was therefore examined in two-chamber MFCs in the presence and absence of cellulases. The maximum power density with enzymes and cellulose was 100 +/- 7 mW/m2 (0.6 +/- 0.04 W/m 3), compared to only 12 +/- 0.6 mW/m2 (0.06 +/- 0.003 W/m3) in the absence of the enzymes. This power density was comparable to that achieved in the same system using glucose (102 +/- 7 mW/m2, 0.56 +/- 0.038 W/m3) suggesting that the enzyme successfully hydrolyzed cellulose and did not otherwise inhibit electricity production by the bacteria. The addition of the enzyme doubled the Coulombic efficiency (CE) to CE=51% and increased COD removal to 73%, likely as a result of rapid hydrolysis of cellulose in the reactor and biodegradation of the enzyme. These results demonstrate that cellulases do not adversely affect exoelectrogenic bacteria that produce power in an MFC, and that the use of these enzymes can increase power densities and reactor performance.;When cellulose is used as the substrate, electricity generation requires a microbial community with both cellulolytic and exoelectrogenic activity. This was not previously demonstrated in pure culture without the provision of an exogenous mediator. Using a specially designed U-tube MFC, I enriched a consortium of exoelectrogenic bacteria capable of using cellulose as the sole electron donor. After 19 dilution-to-extinction serial transfers of the consortium, 16S rRNA gene-based community analysis using denaturing gradient gel electrophoresis and band sequencing revealed that the dominant bacterium was Enterobacter cloacae. An isolate designated E. cloacae FR from this enrichment was found to be 100% identical to the type strain Enterobacter cloacae 13047 based on partial 16S rRNA sequence. In polarization tests using the U-tube MFC and cellulose as a substrate, strain FR produced 4.9 0.01 mW/m2 compared to 5.4 +/- 0.3 mW/m2 for strain 13047. These results demonstrate for the first time that it is possible to generate electricity from cellulose using a single bacterial strain without the need for exogenous mediators.;In order to use cellulosic feedstocks like switchgrass that will be annually harvested, there needs to be a low-cost method for their storage year round. Ensilage was previously shown to have potential as a low-cost method for corn stover storage as well as simple pretreatment prior to ethanol production. Before using ensiled feedstock for ethanol fermentation with pH neutral microorganisms, the organic acids that were generated during ensilage will need to be removed or neutralized. Production of organic acid during ensilage was previously modeled for different crops. In this research, the model was used to predict the organic acid generation during ensilage of switchgrass. Observed data was highly correlated with predicted values (r>0.85). While these organic acids are problematic for fermentation, they are a potentially valuable byproduct. Conversion of these acids to electricity in a microbial fuel cell was analyzed as one such alternative. (Abstract shortened by UMI.)...