Advanced oxidation for optimising biomass-to-biofuel conversion
Easter Chan, Emmanuel I. Epelle
Abstract
The growing global demand for sustainable energy alternatives has spurred significant interest in biofuels derived from renewable lignocellulosic biomass. Advanced oxidation processes (AOPs) have emerged as a promising suite of pretreatment methods to overcome biomass recalcitrance, primarily by targeting lignin degradation while preserving cellulose and hemicellulose for efficient biofuel production. This review evaluates the effectiveness of various AOPs, including photocatalysis, Fenton reaction, wet air oxidation, ozonation, and electrochemical processes, highlighting their mechanisms, operational conditions, and benefits in biological and thermochemical conversion processes. While AOPs have routinely and successfully been applied to facilitate biological conversion processes, their role in thermochemical conversion has been scarcely studied. We compile key findings in this regard herein. The review also examines the independent and synergistic effects between AOPs and conventional pretreatment processes, i.e., acid, alkaline, organosolv, and hydrothermal pretreatments, regarding efficiency, environmental impact, and economic viability. The main findings of our review are that AOPs enhance enzymatic digestibility and reduce inhibitory byproducts in biological conversion processes, while lowering the severity of conversion conditions and reducing char formation in thermochemical conversion processes. The resultant effects of which are improved biomass conversion efficiency. The hybridisation of AOPs and conventional pretreatment shows very good promise in terms of biofuel yield. Additionally, we find that challenges of AOPs' scalability stem from high energy demands, expensive catalysts and complex reactor designs. The review concludes with an analysis of knowledge gaps, particularly in lignin structural understanding, and suggests pathways for optimising AOPs for large-scale applications. By addressing these gaps, AOPs hold potential for optimising biofuel production and contributing to a sustainable circular bioeconomy.