Alkali Pretreatment of Lignocellulose Feedstock Improves Morphological Structure and Biomethane Yield

This study investigates the effects of NaOH pretreatment on the microstructural distribution and biomethane released from Xyris capensis. Xyris capensis was pretreated with NaOH using 1, 2, 3, 4, and 5% w/w concentrations for 60, 45, 30, 20, and 15 min of exposure time, respectively, at a 90 °C autoclave temperature. The impacts of the pretreatment technique on microstructural arrangement, crystallinity, and functional groups were examined with a scanning electron microscope (SEM), X-ray diffraction, and Fourier transform infrared (FTIR), respectively. NaOH-pretreated and untreated feedstocks were digested at the laboratory scale at a mesophilic temperature (37 ± 2 °C) for 35 days for their biomethane potential. It was discovered from the SEM analysis that NaOH pretreatment affects the microstructural arrangement of Xyris capensis, and the sample with the longer exposure time is the most affected. The results of XRD and FTIR also indicated that NaOH pretreatment lowered the crystallinity of the feedstock and significantly influenced the functional groups at varying degrees. Biomethane yield was recorded to be 258.68, 287.80, 304.02, 328.20, 310.20, and 135.06 mL CH₄/gVS_added, representing 91.53, 113.09, 125.10, 143.00, and 129.68% more increases than the untreated feedstock. It was discovered that the optimum biomethane generation was achieved when 4% w/w of NaOH concentration was utilized for 20 min. This study shows that a higher NaOH concentration with a shorter retention time is more suitable for Xyris capensis. This pretreatment method can improve the biomethane yield of Xyris capensis and can be investigated for industrial applications and its use on other lignocellulose feedstocks, especially energy grasses.