Ethanol Production from Cotton Gin Waste by Simultaneous Saccharification and Fermentation Jiacheng Shen and Foster A. Agblevor Department of Biological Systems Engineering Virginia Polytechnic Institute and State University Blacksburg, VA 24061 USA Sept. 25, 2007 Abstract Cotton cultivation is of growing importance in southeastern Virginia. Over the past decade, the cotton cultivation has grown greatly. The cotton gin waste generated from cotton gins must be disposed to meet EPA regulations. However, due to the small scale of all the cotton gins in the area, it is becoming difficult for them to meet EPA clean air rules using combustion technology to dispose of the wastes. We have developed a simultaneous saccharification and fermentation (SSF) process to convert the cotton gin waste to bio-ethanol, while simultaneously solving cotton gin waste disposal problem. Compared to the traditional separate hydrolysis and fermentation (SHF) process, the SSF has the following advantages: (1) the sugar monomers can be utilized directly to form ethanol after they are depolymerized by the enzymatic action. Hence, the SSF process can reduce the inhibitory effect of glucose and cellobiose on the enzymatic activities, which results in a more effective hydrolysis than SHF; (2) the capital costs in SSF are expected to be less than in SHF because only one process unit is required; (3) the higher productivity (product per time per volume) can be reached than SHF, resulting from SSF shorter operating time. In our process, the mixtures of cotton gin waste (75 wt%) and recycled paper sludge (25 wt%) was first pretreated by steam explosion at the Severity factor 3.83. The recycled paper sludge was used to inhibit the production of toxic chemicals to fermentable microorganisms during the steam explosion, and omitted the overliming step for elimination of these chemicals. The steamed mixture was hydrolyzed and fermented simultaneously in a reactor with yeast, Saccharomyces cerevisiae, at pH 4.8 and temperature 36oC. Two enzyme loadings (Novozyme NS50052) of 10 and 20 FPU/g substrate were used. The experiments showed that the maximum yield (g ethanol/g substrate), and theoretical yield (g ethanol/g glucose), and productivity (g ethanol/g substrate/hour) were 0.15, 0.62, and 0.0031, respectively, after 48-hour SSF at enzyme loading 10 FPU/g substrate. When the enzyme loading was increased to 20 FPU/g substrate, the concentrations of glucose, ethanol, and cellobiose were obviously higher that those at 10 FPU/g substrate in the early period, resulting from faster catalytic reaction due to more enzyme, but the final ethanol concentrations at the two enzyme loadings were almost the same, which reflects the catalytic reaction characteristic: the catalyst can enhance reaction rate, and cannot change chemical equilibrium (final concentration). Keywords: Simultaneous Sacharification and Fermentation; Cotton Gin Waste; Ethanol; Saccharomyces cerevisiae. 1