Life cycle assessment of ethanol production in a rice-straw-based biorefinery in India

Abstract

This work presents detailed life cycle assessment (LCA) of a novel process to produce ethanol from rice straw in India. The process has been successfully demonstrated and proposed to be scaled-up, and detailed LCA of that process is the key novel contribution of this work. Cradle-to-gate system boundary is considered, which includes rice farming, transportation, and processing at the biorefinery. 1 l of ethanol is used as the functional unit. The process data are based on the demonstration-scale plant as well as the scale-up plant of 100 kilo litres per day being designed based on the same process. The life cycle inventory data are taken from the Ecoinvent® database. OpenLCA 1.6 is used to develop the LCA model, and impact assessment is performed using ILCD 2011 midpoint indicators. The GWP was 2.82 kg of CO2 eq. per liter of ethanol using economic impact allocation. Electricity contributed 86% of the total impact, and use of hydroelectricity reduced the impact to 0.07 kg of CO2 eq. per liter of ethanol. If additional benefits due to this process are considered, the impact reduced to − 0.392 kg of CO2 eq. per liter of ethanol indicating considerable relative reduction in the GWP. Without allocation and implementing system expansion, the impact was 3.35 kg of CO2 eq. per liter of ethanol. The energy return on investment was 1.59, indicating that the process was net energy positive. The lower bound on the life cycle water use was 507.4 l per liter of ethanol. The integrated nature of the process producing various value-added chemicals provided significant benefits from the perspective of environmental impacts.