Assessing resource intensity and renewability of cellulosic ethanol technologies using eco-LCA.

Recognizing the contributions of ecosystem services and the lack of their comprehensive accounting in life cycle assessment (LCA), an in-depth analysis of their contribution in the life cycle of cellulosic ethanol derived from five different feedstocks was conducted, with gasoline and corn ethanol as reference fuels. The relative use intensity of natural resources encompassing land and ecosystem goods and services by cellulosic ethanol was estimated using the Eco-LCA framework. Despite being resource intensive compared to gasoline, cellulosic ethanol offers the possibility of a reduction in crude oil consumption by as much as 96%. Soil erosion and land area requirements can be sources of concern for cellulosic ethanol derived directly from managed agriculture. The analysis of two broad types of thermodynamic metrics, namely: various types of physical return on investment and a renewability index, which indicate competitiveness and sustainability of cellulosic ethanol, respectively, show that only ethanol from waste resources combines a favorable thermodynamic return on investment with a higher renewability index. However, the production potential of ethanol from waste resources is limited. This finding conveys a possible dilemma of biofuels: combining high renewability, high thermodynamic return on investment, and large production capacity may remain elusive. A plot of renewability versus energy return on investment is suggested as one of the options for providing guidance on future biofuel selection.