Delignification of Oil Palm Frond via particle size reduction and chemical pretreatment for enhanced biogas production potential

Oil palm frond (OPF) is an abundant lignocellulosic biomass with significant potential as a renewable energy source. However, its high lignin content limits its biodegradability and efficiency in biogas production. This study examined the effects of particle size reduction and chemical pretreatment (using NaOH/HCl mixtures) on lignin removal and structural modification of OPF. Particle sizes of 0–250 µm, 251–500 µm, and 501–750 µm were pretreated at 150–190°C for 4–12 minutes, with NaOH/HCl ratios between 0.001 and 0.1. The pretreatment reduced lignin content from 22.6%, 24.7%, and 25.5% in raw OPF to 9%, 12%, and 13%, respectively. Fourier Transform Infrared (FTIR) analysis indicated the reduction of amine-hydroxy ketone bands (from 1636 to 1625 cm⁻¹), while Scanning Electron Microscope (SEM) images revealed surface stripping and disorganization of lignocellulosic fibres, improving cellulose accessibility. The proximate composition and volatile solids showed minimal change, confirming substrate suitability for biogas conversion. These findings demonstrate that combined particle size reduction and alkaline-acid pretreatment effectively enhance delignification and bioconversion potential of OPF for sustainable bioenergy production.