Abstract
Alternative fuels from renewable sources are receiving public and scientific attention due to continuous depletion of petroleum fuel-reserves and environmental problem such as global warming and climate change. Transportation fuel from biofuel is extensively encouraged as it is known to be both renewable and environmentally friendly source of energy. Isobutanol is one of the suitable candidates in replacing gasoline as transportation fuel. This fuel is superior compared to the biofuel that have been commercialised, bioethanol, as it possesses several advantages including high energy content, low solubility, and has lower vapour pressure. Yeast Saccharomyces cerevisiae is able to produce small amount of isobutanol naturally as the end product of amino acid degradation. In order to increase the isobutanol production, experiments based on response surface methodology (RSM) with central composite design (CCD) were conducted to study the effects of operating conditions by Saccharomyces cerevisiae towards isobutanol yield. The independent variables studied were temperature (28-40 °C), pH (4-7), agitation speed (50-200 rpm), and inoculum size (3-10% v/v). From the experimental results, maximum isobutanol concentration of 200 mg/L was obtained at the optimum condition of temperature (28 °C), pH (7), agitation speed (179 rpm), and inoculum size (10 % v/v). The experimental value (200 mg/L) agreed well with the predicted value from mathematical model (220 mg/L), indicates the suitability of the model and the success of response surface methodology in optimising the operating conditions of isobutanol production. Throughout the study, it can be concluded that the isobutanol yield can be increased by manipulating several factors.
