The environmental sustainability of biofuel production is still a debated issue in the world bio-economy development. Therefore, different researches are undergoing to evaluate the sustainability of ethanol production in different countries. This study aimed at analyzing the environmental performance of ethanol production in Ethiopia, considering energy balance and emission reduction using a life cycle assessment approach. It is also intended to identify the environmental hotspots so that possible improvement option can be devised. The life cycle assessment methodology was applied considering three alternative scenarios: 1) Base Case, which is the current situation, 2) Alternative 1, which considers the utilization of biogas from vinasse and bioslurry, and 3) Alternative 2, which includes mechanical harvesting and avoids pre-harvest cane trash burning. The results show that agricultural stage is greatly contributing to the pollutant emissions. The contribution of cane trash burning was significant to all the impact categories considered and avoiding pre-harvest cane trash burning significantly reduced the emissions contributing to global warming, acidification, stratospheric ozone depletion, ozone formation, particulate matter and eutrophication. On the other hand, the introduction of mechanical harvesting to avoid pre-harvest cane trash burning increased ecotoxicity, human toxicity and resource consumption (land, water and mineral) impacts. The net energy balance is positive for all the alternatives considered. In addition to using by-products, proper management of fuel utilization at the agricultural stage can further enhance benefits from the sector. Sensitivity analysis revealed that the price of molasses highly influences both energy ratio and greenhouse gas emissions since it completely shifts the allocation of upstream emissions from sugar to molasses.

Introduction

Crude oil depletion, securing domestic energy supplies, and the increasing global temperatures are considered as major drivers for biofuel development worldwide. In developing countries, a further driver is the promotion of agricultural innovations and rural development (Chapman, 2013). Biofuels could technically substitute all fossil fuels (Gnansounou et al., 2009). However, their production must be constrained to systems ensuring sustainable benefits. There are several environmental concerns associated with bioenergy systems including land use change, deforestation, as well as human and ecological toxicity from chemicals and fertilizer use (von Blottnitz and Curran, 2007). The long-term sustainability should be considered; i.e. the bioenergy sector should at least show positive energy balance and environmental benefits (Farrell et al., 2006), and trade-offs with socio-economic impacts should be investigated. Bioenergy accounts for about 14% of the world energy mix, 10% of which is consumed as traditional firewood (World Energy Council, 2016). Biofuels account for around 4% of global transportation fuels (IEA, 2016). In countries that are highly depending on agriculture, like Thailand, the promotion of bioenergy is a key in development strategies in order to ensure the domestic energy supply (Kulessa et al., 2009). Brazil is a pioneer in producing ethanol from sugarcane juice and molasses covering 25e30% of the world production (OECD/FAO, 2018).