A comparative assessment and economic implications of physical, chemical, and enzymatic treatments of lignocellulosic waste

A significant portion of the organic waste generated globally comprises garden and agricultural waste, which are primarily lignocellulosic and recalcitrant, making them unsuitable substrates for biorefineries. This investigation focuses on the effect of eight different treatments on grass clippings, providing a comprehensive comparison of mechanical combined with physical, chemical, and biological treatment methods. Additionally, it examines the economic implications of stirring during treatment. The effects of these treatments on grass clippings were assessed using Van Soest Fiber Analysis, Scanning Electron Microscopy (SEM), X-Ray Diffractometry (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). The influence of stirring was explored by repeating the top four treatments, which achieved maximum lignin reduction, with and without stirring. Alkaline treatment with 0.9% NaOH at 37 °C achieved a 58% reduction in lignin content while preserving cellulose and hemicellulose. Subsequent effective treatment methods included ultrasound, hydrothermal, and ammonia treatments. Although acid thermal hydrolysis did not reduce lignin, it significantly removed hemicellulose. Stirring's impact on lignin removal efficiency was found to be minimal with insignificant p-values from Welsch's t-test. Overall, alkaline treatment at 37 °C emerges as a cost-effective and scalable approach for converting lignocellulosic waste into valuable products. This study uniquely contributes to the optimisation of lignocellulosic waste management by providing a comparative analysis of various treatments of lignin-rich grass clippings and evaluating the role of stirring in enhancing treatment efficiency and reducing costs, thereby paving the way towards sustainable waste valorisation.