A Comparative Study on the Effects of Chemical and Hydrothermal Pretreatment Methods on the Valorization of Lignocellulose Agricultural Waste (Sugarcane Bagasse)

To effectively valorize agricultural waste (sugarcane bagasse) through biorefinery process, pretreatment which can be carried out in several ways is inevitable. This study explored the effects of chemical (acid and alkaline) and hydrothermal (steaming and autoclave) pretreatment methods on reducible sugar and ethanol yield from sugarcane bagasse. Acid pretreatment chemicals which include hydrogen peroxide and acetic acid were mixed together with sugarcane residue and heated at 85 oC for one hour. In alkaline pretreatment sodium hydroxide was mixed with the sugarcane waste and allow to incubate at 50 oC for one hour. The steaming approach involved using a steam distillation equipment. The sugarcane bagasse was first placed in a steam bag and then into a steam distillation unit which was steamed over a heating mantle for an hour. Autoclave pretreatment method used a stove type autoclave to disintegrate the processed sugarcane residue at 121oC. Each of these pretreated samples underwent independent hydrolysis and simultaneous saccharification and fermentation operations. Sugar yield was determined by the 3,5-dinitrosalicylic acid method, whereas the bioethanol yield was determined from refractometer readings. Sugarcane bagasse pretreated with acids gave a sugar yield of 995.567 mg/l and ethanol concentrations of 1.7303% in both enzymatic and acid hydrolysis, and 2.0758% ethanol concentration in simultaneous saccharification and fermentation process. Alkaline-pretreated sample gave a fermentable sugar yield of 441.2591 mg/l with 0.8655%, 0.6938%, and 1.73033% ethanol concentrations from enzymatic hydrolysis, acid hydrolysis and simultaneous saccharification and fermentation processes respectively. Steaming yielded 913.4849 mg/l of fermentable sugar, whereas the ethanol concentrations in the enzymatic hydrolysis, acid hydrolysis and simultaneous saccharification and fermentation methods were 1.2121%, 0.6938%, and 0.8666% respectively. Autoclave pretreatment resulted in a fermentable sugar yield of 800.9 mg/l with ethanol concentration of 1.3848% in both the enzymatic and acid hydrolysis, while that of simultaneous saccharification and fermentation was 1.0393%.