Bioethanol: Production from Lignocellulosic Waste

The growing global demand for renewable energy has sparked interest in second-generation (2G) bioethanol from lignocellulosic biomass. Unlike traditional first-generation food crop-based biofuels, lignocellulosic bioethanol is derived from nonfood crop residues, forestry residues, and industrial waste, thus offering a more sustainable and eco-friendlier alternative. This chapter provides a general overview of the biochemical conversion of lignocellulosic biomass to ethanol, encompassing major processes, such as pretreatment, hydrolysis, fermentation, and product recovery. Various pretreatment processes—physical, chemical, physicochemical, and biological—are analyzed with respect to their capability to deconstruct complex biomass architecture and develop enzymatic accessibility. Successive hydrolysis processes, e.g., acid and enzymatic processes, are compared to yield, energy consumption, and inhibitor generation. Microbial strain engineering for co-fermentation of hexose and pentose sugars, with emphasis on the key role of genetically engineered organisms for maximizing ethanol yield, is also discussed. Advanced fermentation processes such as SSCF and CBP are highlighted for integration feasibility and cost-effectiveness. Recovery processes, e.g., distillation, membrane separation, and CO₂ stripping, are compared on yield efficiency. Valorization of lignin and hemicellulose to high-value products also supports circular biorefinery options. Techno-economic and environmental factors reflect promising factors of sustainability, though with scale-up issues.