Sustainable Cellulose Production From Livestock Waste: A Comparative Study of Alkaline Hydrolysis and Green Deep Eutectic Solvent

Abstract

India's massive cow dung waste can be turned from an environmental burden into a renewable resource, opening up a sustainable path for soil enrichment, rural electricity, and climate mitigation. This would make a persistent waste management issue a key component of the country's circular bioeconomy. Cow dung, often considered agricultural waste, poses a significant environmental disposal challenge despite being a rich source of lignocellulosic biomass containing cellulose, hemicellulose, lignin, and other valuable compounds. Conventional methods of cellulose extraction from such biomass often involve harsh chemicals and energy-intensive processes, raising sustainability concerns. This study addresses the issue by exploring the more eco-friendly and energy-efficient valorization protocols of cow dung through a comparative analysis of two extraction techniques: deep eutectic solvents (DES), a green and environmentally benign alternative, and traditional alkaline hydrolysis. The goal is to evaluate and optimize cellulose fiber recovery using these methods, promoting the sustainable use of an underutilized biomass resource. The impact of deep eutectic solvent and alkaline hydrolysis treatments was assessed based on yield, lignocellulosic composition analysis, and functional and structural properties. In a comparative study, washed cow dung and cellulose fibers obtained were analyzed using various physicochemical characterization techniques, including compositional analysis, ultimate analysis, Fourier-transform infrared, x-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. Among both methods, the deep eutectic solvent method proved to be the most effective, yielding a 74.4% crude solid fraction with 34.1% cellulose content at 100°C. In comparison, the alkaline hydrolysis method resulted in a 25% crude solid fraction with 32% cellulose content. The cellulose extracted using the deep eutectic solvent (DES) method has a 49% crystallinity index and a thermal decomposition temperature of 390°C. In contrast, cellulose obtained through alkaline hydrolysis has a crystallinity index of 47% and decomposes at 380°C. Life cycle analysis depicted the impacts of cellulose production methods on various environmental impact categories, exhibiting significantly reduced impacts in critical categories such as global warming (18 vs. 47 kg CO2 eq), photochemical oxidation, eutrophication, and toxicity indicators. These findings highlight deep eutectic solvent extraction as the superior method for cellulose extraction compared to alkaline hydrolysis, highlighting the potential of deep eutectic solvents as a green and efficient substitute for conventional chemical methods.