Masters Theses
Utilization of Organic Co-Solvents to Enhance Bacterial Conversion of Poorly Water-Soluble Compounds
Date of Award
12-2003
Degree Type
Thesis
Degree Name
Master of Science
Major
Life Sciences
Major Professor
Robert N. Moore
Committee Members
Brian H. Davison, Paul D. Frymier
Abstract
Mass transfer of a poorly water-soluble gas in fermentations can reduce the performance of bioreactors. In aerobic fermentations, oxygen often becomes a limiting factor. In the biodegradation of volatile organic contaminants, their poor water solubilities often regulate the process. In fermentations of synthesis gas to fuels and chemicals, the issue of mass transfer is apparent. Since the mass transfer rate of the gaseous substrate to the aqueous phase is often the rate-limiting step in the bacterial conversion, many different reactor configurations have been suggested. An alternative approach could be to incorporate a co-solvent, which has properties that will increase the interfacial mass-transfer area and thereby improve the overall conversion rate. In this thesis work, two bacterial systems were used to illustrate enhancement of the conversion of poorly water-soluble substrates by the addition of co-solvents. The first tested system was anaerobic conversion of synthesis gas by Clostridium ljungdahlii and the second was aerobic conversion of toluene by Pseudomonas putida F1.
Clostridium ljungdahlii (ATCC 55383) converts coal synthesis gas (carbon monoxide, hydrogen, and carbon dioxide) into ethanol and acetic acid. A limiting factor in this process is the low solubility of synthesis gas in aqueous media. Different co-solvent systems were evaluated to increase the effective conversion rate of carbon monoxide. The Ostwald coefficient and the octanol-water partition coefficient values were considered when selecting co-solvent systems, and serum bottle experiments were performed to test solvent systems for biocompatibility. Hexadecane proved to the best solvent tested in terms of both gas conversion rate and biocompatibility. Serum bottles with 10% hexadecane (v/v) converted 100% of the available carbon monoxide to products, while in the control serum bottles, only 30% was converted during the same time.
Pseudomonas putida F1 (ATCC 700007) was used as a model organism to study the conversion enhancement of toluene in stirred tank reactors. Silicone oil was used as a co-solvent with and without rhamnolipids (biosurfactants) to enhance the mass transfer rate. Batch experiments were conducted in two side-by-side fermentation vessels; one with silicone oil and one without it. Silicone oil was tested at three different concentrations: 10%, 30%, and 50% (v/v). Results showed that the presence of 30% silicone oil resulted in a 20% higher conversion of toluene when compared to the control. Rhamnolipids were tested at two different concentrations: 0.025% (no silicone oil) and 0.0025% (with 30% silicone oil) (w/v). No significant enhancement in conversion was observed when rhamnolipids were only added by themselves or when they were added in conjunction with 30% silicone oil. In subsequent experiments, results showed that increasing the silicone oil from 20% to 35% in a continuous stirred tank reactor increased the conversion rate by 10%.
Recommended Citation
Rodríguez, Miguel Jr., "Utilization of Organic Co-Solvents to Enhance Bacterial Conversion of Poorly Water-Soluble Compounds. " Master's Thesis, University of Tennessee, 2003.
https://trace.tennessee.edu/utk_gradthes/2215