Fuel ethanol production from sweet sorghum bagasse using microwave irradiation

Sweet sorghum is a hardy crop that can be grown on marginal land and can provide both food and energy in an integrated food and energy system. Lignocellulose rich sweet sorghum bagasse (solid left over after starch and juice extraction) can be converted to bioethanol using a variety of technologies. The largest barrier to commercial production of fuel ethanol from lignocellulosic material remains the high processing costs associated with enzymatic hydrolysis and the use of acids and bases in the pretreatment step. In this paper, sweet sorghum bagasse was pretreated and hydrolysed in a single step using microwave irradiation. A total sugar yield of 820 g kg−1 was obtained in a 50 g kg−1 sulphuric acid solution in water, with a power input of 43.2 kJ g−1 of dry biomass (i.e. 20 min at 180 W power setting). An ethanol yield based on total sugar of 480 g kg−1 was obtained after 24 h of fermentation using a mixed culture of organisms. These results show the potential for producing as much as 0.252 m3 tonne−1 or 33 m3 ha−1 ethanol using only the lignocellulose part of the stalks, which is high enough to make the process economically attractive.