Novel Advanced Oxidation Processes (AOPs) as Lignocellulosic Biomass Pretreatment Approaches and Their Sustainability Assessment: A Review

Lignocellulosic biomass, as a green and sustainable resource, can be used in biorefineries to produce bio-based products. The complex and resistant structure of lignocellulose prevents microorganisms access to carbohydrates in the biorefinery’s main processes, necessitating pretreatment. Different conventional pretreatment methods (physical, physico-chemical, chemical, and biological methods) and also novel advanced oxidation processes (AOPs) and their sustainability, environmental impact, economic viability, energy efficiency and, commercialization state are investigated in this review. Due to various reviews and studies on conventional pretreatment methods, they are briefly described with proper data. As the mechanisms and principle of operation of AOPs were investigated, during the AOPs pretreatment methods, hydroxyl radicals (·OH) are generated sufficiently to decompose lignocellulosic structure through oxidation. In this paper, we review the different AOPs, i.e., Fenton process, ozonation, photochemical, wet air oxidation, ultrasound, and electrochemical, which are recently used in the pretreatment of lignocellulose. Also, the achievement of different AOPs pretreatment research studies and general trends governing the process operating conditions are presented briefly in tables. Moreover, lignocellulosic biomass pretreatment sustainability assessment approaches such as life cycle assessment (LCA) and economic value and environmental impact (EVEI) are discussed. Although no study compared the sustainability aspects of different AOPs with conventional methods, this review generally addresses them. Further, environmental, energetic, and economic aspects of AOPs methods have been compared as important criteria in selecting a pretreatment method. This review provides a thorough insight into the biorefinery’s bottleneck, pretreatment, and comprehensively investigated mechanisms, principle of operation, sustainability, environmental, economic, energy, and commercialization state of AOPs methods.