Bioethanol Production from Ziziphus abyssinica Agroresidues: a Comparison of Effect of Different Pretreatment Approaches on Amount of Glucose

The aim of this research was to optimize bioethanol production from Ziziphus abyssinica agroresidues (inner stone). Proximate composition of the agroresidues was determined. Seven pretreatment approaches comprising of single-step (Aspergillus niger, sodium hydroxide, sulphuric acid) and multi-step (sodium hydroxide + A. niger, sulphuric acid + A. niger, sulphuric acid + sodium hydroxide, sulphuric acid + sodium hydroxide + A. niger) were carried out. Fermentation was carried out for three (3) days using Saccharomyces cerevisiae. Proximate analysis of these agroresidues revealed that it contain high amount of crude fibre (35.59 %) and non-fibrous carbohydrates (36.60 %) making it potential feedstock for bioethanol production. Pretreatment with dilute sulphuric acid produced the highest amount of glucose (286.80 mg/g biomass) while the unpretreated biomass yielded the lowest amount of glucose (10.87 mg/g biomass). Fermentation under optimized condition yielded bioethanol of concentration 4.5133 % (v/v).