Synergistic Effects of Torrefaction and Alkaline Pretreatment on Sugar and Bioethanol Production from Wood Waste

Abundant availability of lignocellulosic biomass (LCB) coupled with diverse pretreatment methods have made it a promising option for energy production. However, it faces several challenges, some of which can be overcome by integrating pretreatment processes. The present study aims to optimize the integration of two different pretreatment methods—torrefaction (to reduce moisture content and fractionate biomass) and alkaline pretreatment of wood waste (to delignify biomass)—and utilize it for bioethanol production. Pretreatment performance was evaluated based on delignification, biomass hydrolysis, and bioethanol production. Initially, torrefaction was performed in a continuous reactor at a temperature range of 225–300 °C, followed by optimization of the critical parameters of alkaline pretreatment of torrefied wood waste (TWW), that is, the temperature, reaction time, solid–liquid ratio, and alkali concentration. Subsequently, the chemical and carbohydrate compositions of raw wood waste (RWW) and TWW were studied, followed by enzymatic hydrolysis and bioethanol fermentation. Integrated pretreatment positively impacted the cellulose and glucose contents of raw and torrefied biomass at lower temperatures. The enzymatic hydrolysis of TWW treated with alkali produced higher levels of glucose and bioethanol than (stand-alone) TWW. These results can be used as a basis for choosing the most suitable pretreatment for enhanced biomass conversion.