BIOCONVERSION OF VARIOUS AGRO-INDUSTRIAL BYPRODUCTS INTO BIOETHANOL BY TWO LOCAL YEAST STRAINS USING STATIC CULTURE TECHNIQUE

Abstract

Some agro-industrial byproducts [sugar cane molasses (SM), corncobs waste (CW), sugar cane bagasse (SB), sawdust (SD), sugar beet pulp (SBP) and fruit juice waste (FJW)] were used as substrates for bioethanol production by Clavispora lusitaniae Gr45 and Saccharomyces cerevisiae B1 after 3 days incubation at 30°C in static batch culture. Different treatments of these materials as a sole carbon source were applied with or without nitrogen sources (yeast extract or ammonium sulfate). The highest bioethanol concentration when SM is used (13.05 gl-1) was obtained by Sacch. cerevisiae at the treatments: [yeast fermentation medium (YFM) -glucose + 4 % SM], (yeast extract + 6 % SM) and (10% SM), which represent about 10.6 % increase comparing to YFM medium (control). The addition of acid CW hydrolyzate as the sole carbon source to YFM medium was the best of the CW treatments by Cl. lusitaniae Gr45 which recorded the highest bioethanol concentration, productivity, yield and conversion coefficient being, 13.32 gl-1, 0.18 gl-1h-1, 26.64 % and 26.65 %; respectively. These figures were increased to 15.8 gl-1, 0.22 gl-1h-1, 31.6 % and 35.9 %, respectively, on YFM medium containing acid SB hydrolyzate as the sole carbon source. All acid SD hydrolyzate treatments increased bioethanol production by Cl. lusitaniae Gr45 and decreased it by Sacch. cerevisiae B1. The highest bioethanol production obtained on SD was on SD hydrolyzate containing yeast extract followed by SD hydrolyzate only and SD hydrolyzate containing ammonium sulfate being 16.5, 13.76 and 13.54 gl-1; respectively. Using SBP as sole carbon source added to YFM medium decreased significantly the growth and bioethanol production by both strains. Generally, FJW was the best carbon source in YFM medium which increased bioethanol production to about 68 % and 38 % by Sacch. cerevisiae B1 and Cl. lusitaniae Gr45; respectively using static culture technique.