Ethanolic Fermentation of Saccharified Common Thatch Grass Hydrolysate by Candida shehatae AND Saccharomyces cerevisiae Species

Abstract

Fossil fuels, such as oil, coal and natural gases, still remain the prime sources of energy worldwide. These resources are likely to be depleted within the next few decades. Current environmental issues like global warming, acid rain and urban smog have led to a shift of focus to utilizing renewable energy sources, such as solar, wind,and biofuels, which are less environmentally harmful and are sustainable. Ethanol is one of the most promising alternative biofuel in this respect. A number of biomass feedstock have been considered for bioethanol production among which grasses have been suggested. In this study, bioethanol was produced by the fermentation of a hydrolysate obtained from the saccharification of pre-treated common-thatch grass (Hyparrhenia spp.). The grass is abundant in Southern Africa and can be used as feed during its early stages of development. Older grasses have low nutritional value due to lignification and is thus used for thatching, fences or is burnt to clear the veld. Size reduction was done to the grass after-which it was pre-treated with either alkali or acid to remove lignin which is a barrier to saccharification. The grass was enzymatically saccharified using a mixture of cellulases namely Celluclast™ and Aspergillus niger cellulase mixture to produce glucose and other fermentable sugars. Candida shehatae CSIR -Y 0492 and Saccharomyces cerevisiae WBSA 1386 were utilised to convert the glucose in the hydrolysate to ethanol. The effect of adding a nutrient supplement on the production of ethanol was also investigated. The pre treatment method and addition of nutrients had no significant effect on the amount of bioethanol produced from the grass hydrolysate. Both S. cerevisiae WBSA 1386 and C. shehatae CSIR-Y 0142 were able to produce ethanol above the theoretical expected value of 0.5 g/L, indicating the use of sugars other than glucose in the production of ethanol. Ethanol production was at an average of 8.3 g/L for both organisms. The results obtained indicate that pre-treated thatch grass, when saccharified by cellulases and xylanases, can potentially be utilized for production of bioethanol.