Comparison of the energy efficiency of methane and ethanol production from sweet sorghum (Sorghum bicolor (L.) Moench) with a variety of feedstock management technologies

Abstract

This study investigated the energy outputs from methane and ethanol production from sweet sorghum (Sorghum bicolor (L.) Moench). Different methods of sorghum biomass management were compared. The effect of bio-based waste products – sewage sludge and digestate replacing urea – on the energy output of biofuels produced from two different hybrids of sweet sorghum was evaluated. Conversion of fresh sorghum biomass into methane generated 76.6–179.5 GJ ha−1, while the gross energy output from ethanol was only 22.6–70.5 GJ ha−1. Application of digestate allowed the highest energy efficiency ratio to be obtained in terms of ethanol production for both tested hybrids and in terms of methane for Rona 1. Sorghum should be used as biogas feedstock in the temperate climate of Central Europe. The application of waste – sewage sludge and digestate – in feedstock management increased the energy efficiency of biofuel production.