Multi-objective optimization of lignocellulosic feedstock selection for ethanol production in India

Abstract

Indian biofuel policy targets large scale utilization of lignocellulosic feedstock. Efficient utilization of the available feedstocks without increasing the pressure on the agricultural land, water and other inputs is essential for overall sustainability. This work focuses on recommending the optimal selection of lignocellulosic feedstock for the Indian biofuel sector considering several sustainability indicators. Six different feedstocks, namely, cotton stalk, rice husk, wheat stalk, sorghum stalk, sugarcane bagasse, and sugarcane molasses, are considered for the production of ethanol using a standardized process. The criteria for selection include life cycle greenhouse gas (GHG) emissions, energy return on investment (EROI), life cycle water use, and land use for ethanol production. Since the decision making criteria show trade-offs, multi-objective linear programming problem was formulated. The model targeted a specific amount of ethanol production without exceeding the feedstock availability, and was solved for different ethanol blending targets. The results recommended complete utilization of sugarcane molasses followed by use of feedstocks such as sugarcane bagasse and sorghum stalk. A strong trade-off was observed between GHG footprint and the other two objectives for EROI 5.08 for base case of 20% blending. Optimal feedstock combination included sugarcane molasses (26.8%), sugarcane bagasse (67%), and sorghum stalk (6.2%) for lowest EROI of 5.08. But for highest EROI of 5.6 the optimal feedstock combination included sugarcane molasses (10.2%), sugarcane bagasse (68.3%), sorghum stalk (6.2%) and cotton stalk (15.3%). The scenarios such as reduced availability of sugarcane bagasse, increase in gasoline demand, effect of data variation gives the additional insights for optimal selection of feedstocks for different blending percentages. The work concluded that sugarcane based feedstock were very critical. Moreover, the proposed approach needs to be systematically used by the decision makers for sustainable biofuel development in India.