Improving biogas production from wheat plant using alkaline pretreatment

•A mixture of lignocellulosic and starchy biomass was used as a substrate.•Effect of a wide range of temperature (0–100°C) was studied on pretreatment.•Crystallinity as well as surface layer of wheat plant were influenced.•Yield of 404.4ml CH4/g VS by 54.5% enhancement over raw substrate was obtained. Alkaline pretreatment of wheat plant (WP), including its grains and straw, was investigated under different conditions in order to enhance biomethane production at mesophilic temperature. Alkaline pretreatment was performed using 8% (w/v) NaOH solution at different temperatures (0, 25, 50, 75 and 100°C). The best improvement in the yield of methane production was achieved by pretreatment at 75°C for 60min, giving a methane yield of 404mlg−1VS. The highest glucose content was also obtained under this pretreatment. The cumulative methane yield for pretreated WP at 25, 50 and 75°C increased the methane yield around 47.5%, 40.8% and 54.5% higher than that of the untreated WP, respectively, while pretreatment at 0 and 100°C was not effective in improving the biogas production. Qualitative analysis of pretreated WP using Scanning Electron Microscopy and Fourier Transform Infrared showed the reduction of crystallinity as well as the removal of surface layers of lignin and hemicellulose.