PRELIMINARY STUDIES OF CELLULOSIC BIOETHANOL PRODUCTION FOR SIMULTANEOUS HYDROLYSIS AND FERMENTATION TESTING

ARISMENDY, A. M.; FELISSIA, F. E.; AREA, M. C.; CHAMORRO, E. R.

Concepción

Congreso; 4º Congreso Latinoamericano sobre Biorrefinerías; 2015

Universidad de Concepción

To cope with the exhaustion of fossilfuels, it has become necessary to find valid renewable sources that do notcompete with food production at affordable costs and alternatives. Cellulosic biomass can be chemically orenzymatically hydrolyzed, and the obtained sugars can be fermented with yeaststo produce ethanol. The possibility of performing simultaneous hydrolysis andfermentation prevents enzymes inhibition, pollution risks and decreasesproduction costs. The drawback is that the optimum temperature for the enzymetreatment is about 50°C, whereas the corresponding fermentation is close to 32°C.Rice husks (i.e. lignocellulosic waste of riceproduction), is an abundant resource in the NEA region of Argentina, and it is anexcellent raw material for the bioethanol production because it has a highcellulose content. As preliminary tests for the application of simultaneous enzymatichydrolysis and fermentation to rice husks, enzymatic hydrolysis on Whatmanfilter paper N°1 at temperatures below the optimum (32°C), and subsequentfermentation with four different yeast, Saccharomyces cerevisiae, Candidatropycalis, Candida guilliermondiiand Candida kefir, were performed at the same temperature. Yeast selectionwas based upon specific criteria. Candida kefir can withstand temperaturesup to 37°C, so it was taken as a feasible alternative for the simultaneousprocess at high temperatures. Candidas and Saccharomyces work at 32°C,but they also have affinity for 5-carbon sugars such as xylose, present insmall amounts if the material has been pretreated with acid to remove hemicelluloses.The filter paper was characterized through moisture and ash amounts. The enzymatichydrolysis with celullases of Trichoderma reseei and celobiassesof Aspergillusníger was accomplished during 72 hours at 32ºC in a rotary shaker.The supernatants of the hydrolysis were supplementedwith nutrients, and were subjected to subsequent fermentation with the fouryeasts listed above, stirring for 24 hours at 32°C. The amount of glucoseobtained by the hydrolysis was determinate by High Performance Liquid Chromatography(HPLC) with refractive index (IR) detector. Inthe hydrolysis at 32°C the cellulose conversion to glucose was 81%. The ethanolgenerated by each fermentation was determined by HPLC. Ethanol yields obtainedwere 66.2% for Saccharomyces cerevisiae, 50.1% for Candida kéfyr, 45.0% for Candidaguilliermondii and 61.5% for Candida tropycalis. Results showed that all yeasts generated ethanol, evenwhen the fermentation time was only 24 hours. Encouraging results were obtainedin the hydrolysis at 32°C, as in the fermentation for 24 hours at the sametemperature. Based on these results, the simultaneous processing of rice hulks wasaccomplished with temperatures between 35 and 37°C for 48 hours.