Author's School

School of Engineering & Applied Science

Author's Department/Program

Energy, Environmental and Chemical Engineering


English (en)

Date of Award

January 2009

Degree Type


Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Muthanna Al-Dahhan


The removal of water from coproducts in the fuel ethanol process requires a significant energy input. The drying of the coproducts is responsible for as much as 32% of the total utilities cost of the process. In this study, improvements in the energy and water balances of the corn to ethanol process and a decrease in ethanol production costs were achieved. Significant reductions in water-binding capacity of whole stillage were found for two, commercially available, cell wall degrading enzymes, GC220 and MGC. The addition of a protease, GC106, during fermentation was found to significantly enhance ethanol production rates as well as reduce the water binding capacity of the mash. Improvements in fermentation rates were achieved by the addition of GC106 with either GC220 or MGC. To achieve both enhanced dewatering and increased fermentation rates, it was recommended that a plant dose their fermentors using either a MGC/GC106 volume combination of 0.02/0.02 mL or a GC220/GC106 combination of 0.015/0.01 mL. A plant trial was conducted to evaluate the scale-up of enhanced water removal from whole stillage by enzyme addition. Enzymes added during this trial proved to be effective, and an increase in the amount of water being removed during centrifugation was observed during the trial. The firing rate of the drier decreased significantly during enzyme addition, resulting in 12% less natural gas required to produce one gallon of ethanol. DDGS composition was not affected by the enzyme addition. Process simulation results from the enzymatic dewatering model showed a decrease in utility consumption compared to the conventional model. A sensitivity analysis showed a tradeoff between the enzyme cost and the drier's natural gas savings. Because of the non-linear nature of enzyme activity, as the amount of enzyme added was linearly decreased, its resulting effects on the process were non-linear. Even if maximum dewatering effects are not achieved, significant savings in natural gas cost could still be obtained.


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