Publication Date

5-2012

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Biology

Department

Biology

Major Advisor

Kevin P. Feris

Second Advisor

Merlin M. White

Third Advisor

Owen M. McDougal

Abstract

Production of lignocellulosic biofuels is one mechanism by which we can reduce our dependence on fossil fuels and enhance the carbon neutrality of transportation fuels. Current biochemical platforms for lignocellulosic biofuel production are not economically viable due to the high costs of hydrolytic enzymes for the conversion of lignocellulose to fermentable sugars. One solution to reducing these costs is the incorporation of on-site enzyme production for consolidated bioprocessing of lignocellulose to fermentable sugars. I have optimized and incorporated a whole-cell encapsulation approach into a novel two-stage fed-batch bioreactor consisting of a nursery reactor and hydrolysis reactor. This design spatially separates enzyme production and lignocellulose hydrolysis, allowing for simultaneous enzyme and sugar production for extended time periods while simplifying enzyme-cell separation. The integrated two-stage design was tested at the bench (250 ml) and pilot (70 L) scales. Encapsulated enzyme production was similar to unencapsulated nursery reactors over four consecutive 72-hour batch runs. Reducing sugar concentrations of hydrolysis reactors containing crude enzymes from encapsulated nursery reactors were similar to, or higher than, reactors containing unencapsulated nursery enzymes. Enzymes from encapsulated treatments produced nearly two times more fermentable sugars during hydrolysis than unencapsulated controls. Pilot scale runs yielded less enzymes in the nursery reactor though hydrolysis performance was only minimally affected. We have established a whole-cell encapsulation approach that enables both high levels of enzyme production and simplified catalyst recovery for extended periods of time. These results serve to illustrate that an integrated on-site enzyme production and hydrolysis reactor system can be self-maintained and operate at high levels of productivity over time. These results also suggest that this system has the potential to be successfully scaled to an industrially relevant size.

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