Lignocellulosic biomass is an attractive feedstock for the production of liquid (eg. biofuel) or gaseous (eg. methane) fuels for the transportation sector. The bioethanol production process still produces a large quantity of production waste following the distillation process. Stillage consists mostly of lignin, hemicellulose, extractives, and yeast and therefore does not have any commercial value. The conversion of bioethanol production waste into gaseous biofuels like biogas or biomethane is a promising solution when it comes to transforming stillage into value-added products, enhancing the value of the biomass, and as a strategy for achieving zero-waste societies. This study aims to investigate the potential of bioethanol production waste for biomethane production. The results are compared with samples from different stages of the bioethanol production process. Milled barley straw (Hordeum vulgare) was used as a feedstock to produce energy in the form of methane, and the flue gas pre-treatment method (with and without bubbling) was applied. The results show that the methane production yield of bioethanol production waste, which has been pretreated with flue gas without bubbling is 5% higher than that of untreated substrate, and can achieve 94% of the methane production of fermented samples. Bioethanol production waste from substrates, which have been pretreated with flue gas with bubbling have a methane production level that is 29% higher than that of untreated materials. The results suggest that methane yields are influenced by the bubbling process. It is reasonable to use bioethanol production waste for the production of energy in the form of methane and to increase the energy output from the biomass.