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Distillers grain, a byproduct from the dry grind corn ethanol industry, is an industrially available, abundant, preprocessed material comprised primarily of cellulose, hemicellulose, protein, oil, and minerals. This research investigated the utilization of distillers grain as a substrate for solid-state fermentation (SSF). SSF is the growth of microorganisms on a moist, solid substrate in the absence of free water. The substrate acts as both the nutrient source and as a solid support for the microorganisms, typically filamentous fungi. SSF has the unique ability to convert agricultural byproducts into valuable bioproducts such as enzymes and organic acids without hydrolyzing polysaccharides to monomeric sugars prior to fermentation.
This research used the organism Triochoderma reesei with the goal of producing cellulase enzymes used in the production of lignocellulosic biofuels. Research investigated the effects of temperature and moisture on fungal activity, cellulase production, and substrate weight loss. The residual distillers grain substrate after SSF was evaluated as an animal feed product. Reductions in cellulose and hemicellulose content of the substrate with an increase in protein content, makes SSF an attractive method for simultaneously producing value added bioproducts while increasing the feed value of byproducts. The effect of mechanical mixing on fungal growth and product formation was also investigated to determine if bioreactor designs incorporating mechanical agitation were feasible. The results showed mechanical agitation at frequencies of up to 6 d-1 resulted in minimal effects on product formation. Data from labscale experiments were used to develop a kinetic model for fungal activity and product formation as a function of temperature, moisture, and fermentation time. The kinetic model was based on easily measurable CO2 concentration, which can be incorporated into online monitoring of bioreactors. The kinetic model was combined with material and energy balances to evaluate the design and scale-up of SSF bioreactors.
Acid and base catalyzed soluble fiber extraction from distillers grain was also investigated as a method of reducing hemicellulose content while simultaneously producing monomeric sugars.
Adviser: Hossein Noureddini