AbstractThis thesis investigated the potential of sorghum as a feedstock source for bioethanol production in Nigeria. Sorghum is a cereal with high tolerance for varied environmental and climatic stresses. It can produce starch-rich grains, sweet stalk juice and high lignocellulosic biomass, depending on the crop variety and cultivation location. Nigeria is the third largest sorghum producer worldwide, but less than 10% of sorghum produced has commercial applications. For example, the grains represent a staple food source or can be utilised as a brewing adjunct. The stalk juices are used in syrup production while the green field residues (bagasse) are partly used in forage production and fencing but mostly left in field for burning. This thesis has shown that sorghum crops have alternative uses in liquid biofuel production.
In this study, SSV2, KSV8 and KSV3 sorghum cultivars were cultivated under rain fed conditions without chemical fertilizers in Kano and Kaduna, Nigeria. The climate in Kano is relatively warmer and drier than Kaduna, with Kano favouring higher biomass yields and Kaduna favouring higher sugary stalk juice yield. Total dry bagasse yields in Kano were 29 t/ha, 33 t/ha and 37 t/ha for SSV2, KSV8 and KSV3 crops, respectively. For crops harvested in Kaduna, the yields were 24 t/ha and 31 t/ha for SSV2 and KSV8, respectively. Furthermore, raw stalk juice yields of 25000 L/ha, 23300 L/ha and 22600 L/ha were obtained for SSV2, KSV8 and KSV3 in Kano and 25500 L/ha and 24500 L/ha for SSV2 and KSV8 in Kaduna. Total fermentable sugar (analysed by HPLC) in Kano-grown SSV2, KSV8 and KSV3 sorghum juices were 144 g/L, 66 g/L and 104 g/L, respectively, compared with 162 g/L and 88 g/L for SSV2 and KSV8 juices from Kaduna-grown sorghum. Fermentations of different sorghum juices were performed with Saccharomyces cerevisiae (without exogenous nutrient supplementation) and produced ethanol yields (measured by GC-MS) of 65 g/L, 36 g/L and 62 g/L for SSV2, KSV8 and KSV3 juices in Kano while Kaduna juice fermentations produced 81 g/L and 52 g/L ethanol for SSV2 and KSV8, respectively. Supplementation of sorghum juices with additional nutrients improved fermentation performance. Floured husked grains from different sorghum cultivars were separately mashed with a combination of various enzyme cocktails, followed by fermentations of the mashes with S. cerevisiae. Ethanol yields of 355 L/t, 421 L/t and 379 L/t were obtained for SSV2, KSV8 and KSV3, respectively, and this fermentation performance was also verified by CO2 gas evolution as observed by the ANKOMRF gas monitoring system. Another yeast, Pichia stipitis showed lower corresponding ethanol yields when fermenting sorghum grain mashes. Experiments were also conducted to convert sorghum lignocellulose residues (bagasse) to ethanol. Pre-treatment of the bagasse fractions followed by detoxification of the enzymatic hydrolysates with calcium hydroxide over-liming and charcoal filtration showed ethanol yields of 23 g/L and 20 g/L for SSV2 and KSV3 (Kano) on fermentation with Pachysolen tannophilus (without nutrient supplementation) while S.cerevisiae yielded corresponding ethanol of 21 g/L and 19 g/L respectively Results from this research have shown that whilst sorghum cultivar SSV2 is a very favourable feedstock for bioconversion to ethanol from juice in Kaduna and bagasse in Kano, the KSV8 cultivar is better suited when exploiting husked grain starch as source for bioethanol production in Nigeria.
|Date of Award||Sep 2013|
|Sponsors||Petroleum Technology Development Fund (PTDF)|
|Supervisor||Graeme Walker (Supervisor) & David Blackwood (Supervisor)|