Recent Advances in Pre-treatment Strategies for Anaerobic Digestion of Lignocellulosic Biomass: A Review

Abstract

This review critically examines recent advancements in the anaerobic digestion (AD) of lignocellulosic biomass for biogas production, highlighting its promise as a sustainable alternative to fossil fuels. Lignocellulosic residues from agriculture and forestry, generated at an estimated 180–200 billion tonnes annually, represent a vast and renewable energy resource. Under optimal conditions, these substrates can yield 0.35–0.40 m³ of methane per kilogram of volatile solids. However, their complex matrix of cellulose, hemicellulose, and lignin poses significant barriers to microbial degradation. The review categorizes and evaluates a wide array of pretreatment strategies—physical, chemical, hydrothermal, biological, and hybrid—based on their mechanisms, effectiveness, energy demands, and impact on methane yield. Additionally, the synergistic role of co-digestion, feedstock variability, and microbial dynamics is explored to identify process optimization opportunities. Despite technological progress, key challenges persist, including feedstock heterogeneity, process inefficiencies, and economic constraints. The review concludes by identifying critical research gaps, such as the need for integrated pretreatment systems and robust microbial consortia, to enhance the scalability and economic feasibility of lignocellulosic biogas systems.