Ethanol from Indian agro-industrial lignocellulosic biomass—a life cycle evaluation of energy, greenhouse gases, land and water

Abstract

Purpose: India is one of the fastest growing economies in the world. Energy is a critical input for socio-economic development, and its strategy aims at efficiency and security. To provide access to environmentally friendly energy resources, the national biofuel policy targets cellulosic feedstocks which necessitates analysing feedstocks using holistic approaches. This paper studies the life cycle impact of ethanol production from cellulosic agricultural feedstocks. Methods: The difficulty of finding appropriate life cycle inventory data for the analysed biofuels in the Indian context is overcome by combining data from diverse sources such as journal articles, government reports and personal contact with farmers. Variation in these numbers across studies is captured by means of error bars. These data are used to calculate environmental sustainability metrics such as energy return on investment, life cycle greenhouse gas emissions and life cycle water use for each fuel. Biomass sources considered in this work include cellulose from wheat stalk, rice husk, sorghum stalk, sugarcane bagasse and cotton stalk. These results are compared with ethanol from molasses and sugarcane juice, which are the conventional approaches. Results and Discussion: Results of the analysis indicate that sorghum stalk is most attractive due to its high energy return on investment, low greenhouse gas emissions, and low water and land use. Ethanol from rice husk has relatively high water use and greenhouse gas emissions, but these are within the margin of variability of other fuels. Despite the attractiveness of sorghum stalk from the current analysis, it is not likely that this will become a major feedstock for cellulosic ethanol in India. This is because farmers value sorghum as an animal feed and may not be willing to convert it into ethanol. Conclusions: This is the first life cycle study of Indian cellulosic biofuel pathways. The inventory data collected in this work is a novel contribution that should be useful for other studies. Findings from the analysis can help guide the decision-making process in the biofuel sector for India.