Switchgrass as an alternative biomass for ethanol production in a biorefinery: Perspectives on technology, economics and environmental sustainability

The production of biofuels from lignocellulosic biomass is not economically viable unless it is co-produced with other marketable high value bio-based compounds using a biorefinery strategy. Advanced cellulosic biofuels derived from agricultural and forestry residues, non-food/feed energy crops or organic waste, could overcome concerns associated with conventional biofuels (impact on food prices, use of land for agricultural and forest products) and achieve large greenhouse gases emissions savings. The main obstacles to the use of advanced biofuels are availability and price of feedstocks, efficiency in conversion, reliability of the technology involved, stability of national polices, level of subsidy and mixing requirements. Switchgrass is a dedicated lignocellulosic energy crop that has great potential for bioethanol production due to its ease of adaptation to the soil in different geographical regions (use of marginal soils), its high yields, poor soil erosion, low incidence of pests and diseases, and low water and nutrient requirements. This review discusses several switchgrass-to-ethanol conversion pathways, considering different aspects of the feedstock, research on the cultivar, yield, and characteristics that have driven research to develop the perennial crop for biofuel. A comprehensive gathering of literature on alternative pretreatment methods, fermentation processes and microorganisms, co-products synthesized when fractionating multiple sugars, and biorefinery economics are presented. Meta-data about pretreatment and fermentation experimental work and how these studies have informed techno-economic analysis of bio-ethanol conversion are reported. Environmental life cycle assessment studies and to a lesser extent, socio-economic and social aspects of biofuels and dedicated energy crops like switchgrass are also reviewed.