Microbubble Plasma-Assisted Pretreatment of Lignocellulosic Biomass for Biogas Generation

The utilisation of lignocellulosic biomass for energy production has gained significant attention in recent years as a strategy to reduce carbon emissions and achieve renewable energy and net-zero targets. However, the recalcitrance of lignin in biomass hinders the effectiveness of biomethane production from anaerobic digestion, necessitating pretreatment. This study investigates the impact of a novel microbubble plasma-assisted pretreatment on structural changes in lignocellulosic biomass (maize, wheat, and rice husk) with subsequent biomethane generation. Pretreatment conditions, including durations of 1 h and 3 h under neutral, acidic (pH 3), and alkaline (pH 9) environments, were systematically investigated. Comprehensive material characterisation of untreated and pretreated material using ATR-FTIR, TGA, SEM, and XRD indicated physicochemical changes in the biomass structure, where ATR-FTIR detected lignin disruption, SEM revealed surface morphology changes, and XRD revealed minor crystallinity changes. The potential of pretreated material to generate biogas was tested using the standard BMP test. Maize pretreated in tap water for 1 h resulted in the highest biomethane yield improvement of 18% among the tested conditions. Conversely, for longer pretreatment durations of 3 h, the formation of inhibitory compounds resulted in reduced yields. Wheat and rice husk pretreated in tap water for 1 h also increased yields, but only slightly, by 5% and 7%, respectively. This study emphasises the need to optimise pretreatment duration and conditions to balance lignin breakdown and inhibitor formation and illustrates the potential of microbubble plasma-assisted pretreatment for improving Anaerobic Digestion (AD) efficiency.