PRODUCTION OF ETHANOL FROM SWEETSTEM SORGHUM AND TROPICAL SUGAR BEET FOR A RURAL COMMUNITY

摘要

Rural communities in the North West Province of South Africa are among the poorest in the worldwith an average income of less than ZAR 8.75 (EU 0.875) per day. The South African government has committeditself to upliftment of these communities through job creation and joining of the first and second economies of thecountry. The Thusanang community project concept was initiated to stimulate job creation and skills development inour local communities through biofuels production. Water is scares in the North West Province with less than 200mm of rain annually. Crops that do not threaten food security and require little water for energy production is thusfavored for use as ethanol feedstock in this area. Sugar beet had been used as a source for sugar production for sometime, but its development as a large scale agricultural crop in South Africa has been limited by the large production ofsugarcane in tropical areas. Recent trials on tropical sugar beet production in the Eastern Cape and North Westernregions of South Africa has shown promise for large scale production of tropical sugar beet for ethanol production.Sweetstem sorghum has attracted the attention of the biofuels world because of the potential of producing both foodand ethanol in a single crop. The picture is not that simple though, since the plants usually contain large amounts offermentable sugar during the flowering period, when the grains for food have not yet been formed, and then the sugarcontent steadily declines towards the time for harvesting of the grain. A trade-off thus needs to be found betweenfood and energy production. The influence of various process parameters such as pH, initial sugar concentration,yeast concentration and nutrient addition on the ethanol yield obtained from sweet stem sorghum juice and tropicalsugar beet juice was studied and the results is reported in this paper. The initial Brix index of the tropical sugar beetused was 21.8 wt% and 40.1wt% for the tropical sugar beet juice and the sweetstem sorghum juice respectively. Alljuice was fermented without prior filtering or sterilization. The highest initial sugar content was observed for theUSA1 sweetstem sorghum cultivar harvested at 3 months (only energy production) and for the Hunni greensweetstem sorghum cultivar harvested at 6 months (food and energy production).