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

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.