Life cycle assessment of bioethanol production from three feedstocks and two fermentation waste reutilization schemes

Abstract

More than 95% of energy supplies for Taiwan are imported. Conversely, approximately 150,000 ha half-fallow and 50,000 ha fallow paddy fields exist because of increasing labor costs and competition from rice imports. The potential for energy crop production from such underutilized paddy fields merits significant attention. However, selecting crops for optimal environmental performance when producing bioethanol is equally important. The life cycle assessments (LCAs) of rice straw (agricultural waste), Napier grass (energy crop), and Eucalyptus spp. (short rotation coppice) as bioethanol feedstocks in such fallow paddy fields were investigated in this study. The LCAs of two schemes for on-site fermentation waste utilization were also investigated as pellet fuel and molded pulp feedstocks. Experimental and field survey data were used in this study. Due to higher biomass yields, Napier grass and Eucalyptus spp. resulted in 47% and 28%, respectively, less weight-based negative impacts compared to rice. Pursuing high bioethanol production requires consideration of the overall environmental loading. Conversely, the rankings of the three crops based on acreage and bioethanol yield differed due to extensive farming practices and bioethanol conversion yields. On-site production of pellet fuel using fermentation waste was 7% and 31% higher than that of Eucalyptus biomass pellets and imported coal, respectively, for Taiwan. On-site production of molded pulp products using fermentation waste was 5% and 49% higher than that of recycled newspaper and virgin chemical pulp, respectively, for Taiwan. Thus, fermentation waste utilization schemes could provide a broader evaluation for planning alternative crops for bioethanol production.