Delignification of Halophyte Atriplex crassifolia by Green Recyclable Deep Eutectic Solvents for Enhanced Production of Biogas

Abstract

Deep eutectic solvents (DESs) have upgraded the practices of valorizing lignocellulosic feedstock by lessening biomass recalcitrance through delignification in precise and economical manner. In this study, the influence of a series of deep eutectic mixtures was evaluated on the halophyte Atriplex crassifolia for achieving elevated biogas production. Initially, the biomass was pretreated via several DESs with varying hydrogen bond donors (HBDs) including carboxylic acids, amine/amide, and polyols/glycols. DES composed of choline chloride (ChCl) and lactic acid (LA) evidenced as the most effective solvent in achieving high lignin removal rates and was further optimized by evaluating the parameters of molar ratio of DES components, solid-to-liquid ratio, and solvent addition. A maximum delignification value of 89.5% was achieved by 15% diluted ChCl: LA (1:2) DES at a biomass loading of 1:15. The solubilization rate of diluted ChCl: LA was also raised up to 38%. FT-IR analysis revealed significant lignin elimination from ChCl: LA pretreated substrates. Moreover, ≥88% of ChCl: LA DES was recovered after up to three pretreatment cycles, retaining ≥85% delignification efficiency. Fresh DES-pretreated Atriplex crassifolia recorded 32.2 mL/g of biogas production yield due to increased cellulosic content. The findings validated Atriplex crassifolia as an efficient feedstock for biogas production and confirmed the affectivity of ChCl: LA pretreatment in eliminating the lignin barrier, ultimately making cellulosic sugars readily biodegradable and highly accessible for anaerobic microorganisms.