Abstract
Background, Aim, and Scope. In most sugarcane-producing countries bound by the limitations of arable land, bioethanol is derived from the molasses obtained from sugar production by adding ethanol production processes. Two problems are associated with this approach: the inferior productivity of ethanol and the consumption of fossil fuel for the additional energy demand required for the extended processes. A novel sugar-ethanol combined production process using modified sugarcane, known as “monstercane,” has been developed by the authors, which allows for a significant enhancement of ethanol production from molasses after only one extraction of raw sugar instead of the three extractions in the conventional process. Furthermore, due to the enhancement of bagasse productivity, the use of fossil fuel for producing ethanol is eliminated. This study aims to evaluate the greenhouse gas (GHG) emissions induced by the introduction of the conventional and novel processes in Japan, thereby demonstrating the advantages of our approach in applying both process retrofitting and raw material modification to the production of multiple bioproducts.
Methods. Agricultural and process inventories were established by reviewing the literature and primary data from pilot experiments conducted on Ie island of Okinawa, Japan. LCI was conducted for the production processes of sugar (Case 1), conventional sugar and ethanol (Case 2), and the novel combined sugar-ethanol from the modified sugarcane (Case 3). The impact on global warming was assessed, and comparisons were made of the three cases. The sensitivity of the results to 84 parameters in the inventory model was examined.
Results. Cases 2 and 3 resulted in -0.7 and -40.2 ton-CO2 equivalent of GHG emissions per hectare compared to Case 1, respectively. In addition, greater contribution of the modification of sugarcane among other improvements made by retrofitting the processes on the GHG emission reduction was revealed. Several parameters were identified as important in our model, thus those parameters were more closely analyzed, and useful information was obtained for further improvement of process and material.
Discussion. The advantage of the combined sugar ethanol production over a mere recycling of the residue (i.e. third molasses) was elucidated. The results provided directions in further optimization that could make the most of the land available for production of renewable resources to satisfy multiple needs. Some of the other impact categories, including consumption of fossil fuel and water resources, will also reveal improvements in case 3 because resources for cultivation remain equivalent, process resource input (fossil fuel) was reduced, and products increased. However, other important impacts, such as emission of pollutants into the air and water, should be further evaluated.
Conclusions. The combined bioproduct (e.g., food and fuel) production concept demonstrated in this study would be applicable to exploring a system whose raw material is a crop with emerging applications in addition to conventional applications. The effectiveness of individual applications using the proposed concept can be confirmed with a lifecycle assessment.
Recommendations and Perspectives. Application of the proposed concept to other biomass utilization systems is recommended. More cases should be explored in sugar-ethanol combined production, for example by changing the production ratio of sugar and ethanol and investigation of how the choice of sugarcane line and the reduction in GHG emissions would be affected. Crops such as sugarcane have a multiple-year cropping cycle; therefore, yields and process inventories should reflect the entire cropping cycle in any successive study.
