Monday, April 30, 2007

Bioethanol production from steam exploded barley straw

María del Prado García-Aparicio1, José M. Oliva1, Paloma Manzanares1, Mercedes Ballesteros2, Felicia Sáez1, and María J. Negro2. (1) Renewable Energies, CIEMAT, Avda. Complutense, MADRID, Spain, (2) Renewable Energies Department, CIEMAT, Avda. Complutense 22., Madrid, 28040, Spain

Barley straw is a very attractive lignocellulosic substrate for bioconversion to ethanol because it has high carbohydrate content, and is present in large quantities in Europe.
One of the most promising process  to perform enzymatic hydrolysis and fermentation is the Simultaneous Saccharification and Fermentation (SSF). This SSF configuration process minimizes the end-product inhibition of the enzymes used to hydrolyze the cellulose-enriched solid residue after pretreatment. Economic analysis has indicated that high-solid SSF process will significantly reduce the operating cost of ethanol production. Since the optimum saccharification temperature is close to 45-50º C, the use of thermotolerant microorganisms is desirable when applying the coupled SSF process for cellulose conversion to ethanol.

 In this work, the thermotolerant yeast Kluyveromyces marxianus CECT 10875 was used for SSF experiments on pretreated barley straw. The steam explosion pretreatment conditions, selected in a previous work, were 210ºC and 5 minutes. SSF was performed at 42ºC on steam-exploded barley straw at two different concentration of water insoluble solid (WIS) (5 and 10% w/v) and at an enzyme loading of 10 FPU/ g cellulose of cellulase sumplemented with β-glucosidase. It has been shown that endo-xylanase addition improves cellulose conversion of this pretreated material and hence, it could enhance ethanol production. The effect of endo-xylanases on SSF was also studied
Results show that adding endo-xylanases at SSF of steam exploded barley straw at 5% and 10% (WIS, w/v), increased the ethanol yield from 46% to 71% and 49.5 to 62% respectively based on the theoretical yield.