Fermentative Production of Ethanol from Acid Hydrolyzate of Rice Water Waste Using Saccharomyces cerevisiae: Experimental and Kinetic Studies
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Rice water waste, a starch-bearing effluent waste stream, was utilized as an abundant and low-cost substrate for ethanol production. Prior to the fermentation process, rice water waste was hydrolyzed using dilute H2SO4 solution. To attain the highest concentration of sugars with a minimum amount of inhibitory by-products during the acid hydrolysis, different acid concentrations (2–6 v/v %), hydrolysis temperatures (60–100 °C) and reaction times (0–200 min) were examined. The maximum catalytic efficiency (ηE = 27.36) was obtained using 4% H2SO4 at 80 °C for 100 min; wherein, the concentration of reducing sugars, furfural and 5- hydroxymethylfurfural (HMF) in the hydrolyzate was 43.32, 0.29 and 0.17 g L−1, respectively. This hydrolyzate was utilized as a substrate for ethanol fermentation using Saccharomyces cerevisiae; the maximum ethanol concentration, yield, and cell density were 18.65 g L−1, 0.41 g ethanol g−1 sugar and 3.68 g L−1, respectively. The kinetics of the acid hydrolysis process was studied using “two-fraction” model. The kinetic constants indicated that the rate of release of reducing sugars from starch was high; while, the degradation rate of reducing sugar to furfural and HMF was negligible. Moreover, multi-response nonlinear regression analysis was performed on the experimental data to determine the kinetic parameters regarding cell growth, substrate utilization, and ethanol production.
KeywordsEthanol Rice water waste Kinetics Acid hydrolysis Furfural
The present research was made possible by the sponsorship and financial support of the Ministry of Science of Iran and the Tarbiat Modares University (TMU). The authors wish also to thank Mrs. Haghdoust (Technical Assistant of Environmental Laboratory) of TMU for her cooperation.
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