Batch fermentation of bioethanol from the residues of elaeis guineensis: Optimisation using response surface methodology

Abstract

In oil palm industry, large quantity of oil palm trunk (OPT) and palm oil mill effluent (POME) are generated. These residues are not fully utilised. They are served as wastes, which lead to serious environmental pollution. Realising that OPT sap contains high glucose concentration while POME contains essential nutrients required by microorganisms for growth, in this study, bioethanol was produced from OPT sap and POME by Saccharomyces cerevisiae in shake flasks culture. OPT sap was used as carbon source, and POME was utilised as nutrient supplier for the fermentation process. To obtain the optimum ratio of OPT sap to POME, inoculum size, initial pH, and incubation time for maximum bioethanol yield, response surface methodology (RSM) via face centred central composite design (FCCCD) was employed. The experimental data for glucose consumption, bioethanol yield, and biomass growth were fitted to polynomial equations and analysed. The quadratic models were employed to fit the data. The optimum bioethanol fermentation conditions were as follows: OPT sap to POME ratio of 63 : 37, inoculum size of 4.3 vol%, initial pH of 8.0, and incubation time of 118 h. Under these conditions, the expected bioethanol yield is 0.453 g/g. To evaluate the accuracy and validate the results, five additional runs were carried out at the optimum point. It was found that the range of bioethanol yield within 95 % confidence level was 0.448 - 0.457. It can be concluded that there is no difference between the experimental values and the predicted data within 95 % confidence level since the predicted data were within the range.