Evaluation of fermentative power of adapted strains in the process of simultaneous hydrolysis and fermentation of rice husks

ARISMENDY, A.M.; SEQUEIRA, M.; AREA M.C.; CHAMORRO, M.

Espoo

Congreso; IX Iberoamerican Conference on Pulp and Paper Research, CIADICYP 2016; 2016

Aalto University, VTT, Åbo Akademi University, RIADICYP, PROVALOR

Due to the depletion of fossil fuels, it has become necessary to find alternative valid renewable sources that do not compete with food production at affordable costs. The production of bioethanol from raw materials such as corn and sugar cane has been worrisome, because it must occupy large areas of crops to supply food production and biofuel, thus generating increased food prices. Bioethanol from lignocellulosic waste is basically obtained through the stages of pretreatment, enzymatic hydrolysis, fermentation and separation.Hydrolysis is generally performed under mild conditions (pH 4.5-5.0 at temperatures between 40°C and 50°C). Following this step, fermentation is performed at temperatures between 25°C and 30°C depending on the fermentative strains used. The process of SSF (Simultaneous hydrolysis and sacharification) has the advantage of being carried out in one step, but has the drawback of the difference in the optimum temperatures of both processes. This work aimed to evaluate fermentative power of adapted strains in the process of simultaneous hydrolysis and fermentation of rice husks Rice husks were subjected to a pretreatment in two stages, an acid pretreatment for hemicelluloses removal followed by an organsolv pretreatment for lignin extraction.  Celullosas enzymes and yeasts were added subsequently to the pretreated material. Applied conditions for SSF were pH 4.8 at 35°C for 72 hours. A cellulases complex from Trichoderma reseei provided by Sigma Aldrich was used for the enzymatic hydrolysis and two types of yeasts (Saccharomyces cerevisiae and Kluyveromyces cerevisiae) were used for fermentation. To overcome the problem mentioned above, the original yeast was adapted for working at high fermentation temperature. The adaptation was carried out taking samples, cultivating, and purifiyng yeast from previous SSF. The comparison of both fermentation yields, the original and the purified one showed that the last one produced better results.The obtained fermentation yields when using the original and the adapted Saccharomyces cerevisiae were 51.69 % and 81.61 %, respectively, whereas yields obtained with the original and the adapted Kluyveromyces cerevisiae were 55.71% and 25.84%, respectively. The determination of ethanol was accomplished by the analytical technique based in titration with sodium thiosulfate.