Production of bioethanol through cofermentation of rice straw hydrolysates by saccharomyces cerevisiae and pachysolen tannophilus

• Main Author: Kang, Jimmie Neil C.
• Format: text
• Language: English
• Published: Animo Repository 2012
• Subjects: Renewable energy sources; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/4129; https://animorepository.dlsu.edu.ph/context/etd_masteral/article/10967/viewcontent/CDTG005132_P.pdf
• Institution: De La Salle University

This study dealt with the cofermentation of rice straw hydrolysates using and Saccharomyces cerevisiae and Pachysolen tannophilus. Rice straw was pretreated with alkali-soaking and alkali-soaking with heat treatment to remove the lignin. Alkali-soaking with heat treatment proved to be more effective in removing lignin yielding 67.86% lignin removal compared to 45.13% removal in alkali-soaked rice straw. Pretreated rice straw was hydrolyzed using dilute acid (1.6%, 2%, and 3% w/v) and concentrated acid (18.032%, 27.048%, and 36.064% w/v). Time was varied at 0.5, 1, and 2 hours in two stages. The most suitable hydrolysate for fermentation was the products of the first stage dilute acid hydrolysis using 3% (w/v) acid concentration and 2 hours residence time, which produced 17.83 g/L of xylose and 7.25 g/L of glucose. Simulated sugar solution containing 20 g/L xylose and 10 g/L glucose was cofermented using the two yeasts at various pH and temperature Highest ethanol yield (0.109 g ethanol/ g glucose) was obtained at 30oC and pH of 4.5, but highest biomass yield (4.9175 g/L) was obtained at 35oC and pH 3.5. The best combination of temperature and pH in terms of ethanol yield was then applied to the actual rice straw hydrolysates which resulted in ethanol yield of 0.0478 g ethanol/ g glucose and a biomass yield of 0.6190 g/L. The fermentation of both simulated sugar solutions and rice straw hydrolysate at 30oC and pH 4.5 followed Monod equation. The kinetic parameters for the simulated sugar solution were: maximum specific growth rate (µm) = 0.31 h-1, saturation constant for glucose (Ks) = 6.41g/L, productivity constant for biomass per substrate consumed (YX/S) = 0.121, and productivity constant for ethanol per substrate consumed (YP/S) = 0.102 with a R2 value of 0.9765 and for the hydrolysates, µm=0.189 h-1, Ks=2.36g/L , YX/S=0.1, and YP/S=0.0427, with a R2 value of 0.8661. Comparison of these kinetic parameters indicate that for the simulated sugar solution, rate is faster and that the Monod equation is applicable to a higher range of substrate concentration.