Different treatments of lignocellulosic biomass for enhanced delignification and enzymatic hydrolysis

Abstract

Lignocellulosic biomass (LCB) valorization is a fundamental step toward circular bioeconomy. The complex structure of lignocellulose must be disrupted to conduct thorough valorization. Conventional methods often lack sustainability, by having high energy requirements, or a harmful impact on the environment. To overcome these impediments, novel tenable methods must be developed. This work compares different green solvent-based treatments of LCB, regarding the delignification rate and the enzymatic hydrolysis efficiency. Due to abundance and high availability, corn residues were used as model substrates. Deep eutectic solvent (DES), microwave-assisted alkaline treatment, combined non-thermal plasma/Fenton, and non-thermal plasma/alkaline treatment were selected as green methods for LCB treatment, having higher selectivity favoring lignin degradation and milder reaction conditions. Treated biomass was analyzed for acetyl bromide soluble lignin content and subjected to enzymatic hydrolysis with Cellic® CTec2, followed by hexose and pentose content determination. The best results regarding lignin content were obtained with DES, when the choline chloride to lactic acid ratio was 1:10, achieving a delignification rate of 86%. Combined plasma/alkaline treatment for 10 minutes decreased lignin content by 77%, while microwave-assisted alkaline treatment decreased it by 74% for only one minute. When combined with the Fenton reagent, a 30-minute-long plasma treatment reduced lignin content by 53%. Moreover, FTIR spectroscopy confirmed partial depolymerization of lignin, making it more suitable for further application. Each treatment intensified LCB decomposition and facilitated enzyme penetration, increasing hexose yield by 2.3-5.6 times, and pentose yield by 1.7-8.0 times compared to the untreated biomass. Methods implemented in this work contributed to feasible biomass delignification. Coupling alkaline hydrogen peroxide with microwave irradiation or non-thermal plasma or applying reusable DES could significantly promote proficient biotechnological exploitation of lignin and carbohydrate fractions in a time-saving and cost-effective way. The possibility of biotechnological production of natural antioxidants and natural aromatic compounds should be particularly underlined.