Biofuel production via fermentation is produced primarily by fermentation of simple sugars. Besides the sugar fermentation route, there exists a promising alternative process that uses syngas (CO, H2, CO2) produced from biomass as building blocks for biofuels. Although syngas fermentation has many benefits, there are several challenges that still need to be addressed in order for syngas fermentation to become a viable process for producing biofuels on a large scale. One challenge is mass transfer limitations due to low solubilities of syngas species. The hollow fiber reactor (HFR) is one type of reactor that has the potential for achieving high mass transfer rates for biofuels production. However, a better understanding of mass transfer limitations in HFRs is still needed. In addition there have been relatively few studies performing actual fermentations in an HFR to assess whether high mass transfer rates equate to better fermentation results. Besides mass transfer, one other difficulty with syngas fermentation is understanding the role that CO and H2 play as electron donors and how different CO and H2 ratios effect syngas fermentation. In addition to electrons from CO and H2, electrodes can also be used to augment the supply of electrons or provide the only source of electrons for syngas fermentation. This work performed an in depth reactor comparison that compared mass transfer rates and fermentation abilities. The HFR achieved the highest oxygen mass transfer coefficient (1062 h-1) compared to other reactors. In fermentations, the HFR showed very high production rates (5.3 mMc/hr) and ethanol to acetic acid ratios (13) compared to other common reactors. This work also analyzed the use of electrons from H2 and CO by C. ragsdalei and to study the effects of these two different electron sources on product formation and cell growth. This study showed that cell growth is not largely effected by CO composition although there must be at least some minimum amount of CO present (between 5-20%). Interestingly, H2 composition has no effect on cell growth. Also, more electron equivalents will lead to higher product formation rates. Following Acetyl-CoA formation, H2 is only used for product formation but not cell growth. In addition to these studies on electrons from H2 and CO, this work also assessed the redox states of methyl viologen (MV) for use as an artificial electron carrier in applications such as syngas fermentation. A validated thermodynamic model was presented in order to illustrate the most likely redox state of MV depending on the system setup. Variable MV extinction coefficients and standard redox potentials reported in literature were assessed to provide recommended values for modeling and analysis. Model results showed that there are narrow potential ranges in which MV can change from one redox state to another, thus affecting the potential use as an artificial electron carrier.

The cell is the basic unit of all living organisms. It is an amazing machine capable of self-replicating, growing, and synthesizing and shuttling thousands of compounds. To perform all of these activities the cell needs energy. The original source of energy for all living beings is the Sun. The energy of the sun is collected by the autotrophs (mostly plants) through photosynthesis and stored in the chemical bonds of carbohydrates and lipids through carboxylic acid intermediates; animals use these compounds to obtain the energy for their cells. Most of the energy extracted by the cell comes from the citric acid cycle. Therefore, two crucial energy transfer checkpoints are photosynthesis and citric acid cycle. With growing need for energy, the limited supply of fossil fuel, and the search for a cleaner environment, scientists have turned to the Sun (directly or indirectly through wind, tides, biomass, etc.) to satisfy the needs of modern society trying to reach the dual Holy Grail of energy: harvesting energy through Artificial Photosynthesis and Low Temperature Biomass Oxidation. This work represents one more step toward reaching these Holy Grails. The core reagent used in our technique is ferritin. Ferritin recapitulates some of the essential features of a plant cell: it contains a semiconductor capable of charge separation, like chlorophyll, acts as a membrane to isolate compartments, and has an enzymatic activity that prevents charge build up and oxidative damage. The energy absorbed by ferritin from the artificial “solar” radiation is used to extract reducing equivalents from stable and partially oxidized compounds, mainly carboxylic acids. The energized electrons produced are then used for a number of technical applications, from synthesis of catalytically active nanoparticles, to reductive precipitation of contaminant heavy metals (i.e.: mercury), to hydrogen evolution.