Production of Ethanol From Cassava (MANNIHOT ESCULENTA) Waste Water Using Saccharomyces Cerevisiae and Escherichia Coli

Abstract

The ethanol producing capabilities of axenic cultures of Saccharomyces cerevisiae and Escherichia coli from cassava waste water was investigated. Analysis of the initial composition of the substrate showed that it contained 71.97%, 1.2%, 0.5% and 23% (w/v) of starch, protein, fat and cyanide respectively. The cassava waste water pre-treatment approach for converting starch into reducing sugar involved inoculation of a consortium of indigenous amylolytic fungi (which include Geotrichum candidum, Aspergillus fumigatus and Aspergillus niger) and heating at 80oC for 30minutes which yielded 41.67% and 11.62% (w/v) glucose respectively. The glucose values decreased progressively with increasing duration of fermentation. At the end of fermentation period (7days), glucose levels recorded were 5.03% and 7.3% in amylolytic fungi pre-treated set-ups containing S. cerevisiae and E. coli respectively. In heat treated set-ups containing S. cerevisiae and E. coli, glucose levels at the end of fermentation were 1.01% and 1.82% (w/v) respectively. Also, the pH dropped with increasing duration of incubation such that pH values decreased from 4.48 to 4.1. A decrease in pH from 5.2 to 4.7 and 4.0 were observed in heat pre-treated set-ups containing S. cerevisiae and E. coli respectively while control pH dropped from 5.2 to 4.9. However, ethanol produced seemed to be limited by fermentation duration. Highest yield were obtained after 72h of fermentation. Further increases in fermentation duration did not result in any significant yield in ethanol production. Also, fungal hydrolysis method resulted in higher yield in ethanol production than heat hydrolysis of cassava waste water. Maximum ethanol produced were 13.33% and 5.6% (w/v) by S. cerevisiae and E. coli inoculated into cassava waste water hydrolyzed by amylolytic fungi. Control flask yielded 0.03% w/v ethanol. Heat pre-treatment of cassava waste water resulted in the production of 2.61% and 0.72% (w/v) ethanol by S. cerevisiae and E. coli respectively. The study revealed that the isolates had the ability of ethanol production from cassava waste water. Also, it demonstrates that cassava waste water is a suitable substrate which can be harnessed for ethanol production, thus curbing the pollution nuisance it poses in cassava processing areas.