COMPARATIVE SUSTAINABILITY STUDY OF FUEL-GRADE BIOETHANOL
PRODUCTION FROM CORN COB AND RICE STRAW

Comparative sustainability study of corn cob and rice straw as feedstocks for fuel-grade bioethanol production was conducted using superPro® Designer and OpenLCA sustainability software. The model comprises the different bioethanol production technology pathways: pretreatment (steam explosion), hydrolysis, fermentation and purification. The paper is targeted towards addressing the economic, environmental and energy challenges faced with the use of fossil fuel. The paper ensures the production and consumption of corn cob and rice straw derived fuel-grade bioethanol with the established economic minimum bioethanol plant capacity of 75 000 m ³/annum. Based on the estimated economic indices, the plant utilising corn cob had a higher return on investment (ROI) of 75.98% compared to that using rice straw which recorded 49.86%. This ROI values fell relatively close (recording 65.46 and 64.83% for corn cob and rice straw respectively) after adjusting the annual operating costs to incorporate pollutants emission and discharge costs. The environmental assessment conducted on the two feedstocks using life cycle assessment approach in OpenLCA sustainability software showed that the process utilising rice straw posed lesser environmental burden with generated carbon credit of $9 770 177 and better net energy balance (NEB) of 4.3. The lost work analyses conducted showed that distillation columns were the least energy efficient units in both processing plants recording about 61% of the net lost work in the two process plants. However, based on the trade-offs among the three sustainability indicators assessed (economic, environmental and energy indices), corn cob is a more sustainable feedstock for fuel-grade bioethanol production than rice straw.