Recent advances on two-step and combined multi-step pretreatment of lignocellulosic biomass for cellulose extraction

Lignocellulosic biomass (LB) is a promising renewable resource for sustainable bio-based products, but its complex structure, mainly due to lignin, hinders efficient cellulose extraction. This review highlights recent advances in combined pretreatment strategies that integrate physical, chemical, biological, and physicochemical methods to enhance delignification, reduce crystallinity, and improve enzymatic accessibility. Emphasis is placed on multi-step approaches such as liquid hot water with deep eutectic solvents, steam explosion followed by fungal or ionic liquid treatments, and ammonia fiber expansion coupled with biological catalysis. These combinations have demonstrated superior performance over single-step pretreatments in terms of cellulose recovery, sugar yield, and environmental impact. A comparative analysis explores trade-offs related to scalability, cost, and efficiency, providing practical guidance for selecting pretreatment methods tailored to specific biomass types. This review consolidates emerging synergies in integrated pretreatments to guide future research toward efficient, scalable, and eco-friendly LB valorization. • Enhanced pretreatment methods for cellulose extraction from biomass. • Evaluation of benefits and limitations of diverse pretreatment technologies. • Innovative two or multi-step pretreatment approach to overcome biomass resistance. • Integrating pretreatment reduces the intensity of single-step disadvantages. • The sequence of combined pretreatment impacts the overall effectiveness.