Bioethanol Production Optimization from KOH-Pretreated <em>Bombax ceiba</em> Using <em>Saccharomyces cerevisiae</em> through Response Surface Methodology

The present study was based on the production of bioethanol from alkali-pretreated seed pods of <i>Bombax ceiba.</i> Pretreatment is necessary to properly utilize seed pods for bioethanol production via fermentation. This process assures the accessibility of cellulase to the cellulose found in seedpods by removing lignin. Untreated, KOH-pretreated, and KOH-steam-pretreated substrates were characterized for morphological, thermal, and chemical changes by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Hydrolysis of biomass was performed using both commercial and indigenous cellulase. Two different fermentation approaches were used, i.e., separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF). Findings of the study show that the maximum saccharification (58.6% after 24 h) and highest ethanol titer (57.34 g/L after 96 h) were observed in the KOH-steam-treated substrate in SSF. This SSF using the KOH-steam-treated substrate was further optimized for physical and nutritional parameters by one factor at a time (OFAT) and central composite design (CCD). The optimum fermentation parameters for maximum ethanol production (72.0 g/L) were 0.25 g/L yeast extract, 0.1 g/L K₂HPO₄, 0.25 g/L (NH₄)₂SO₄, 0.09 g/L MgSO₄, 8% substrate, 40 IU/g commercial cellulase, 1% <i>Saccharomyces cerevisiae</i> inoculum, and pH 5.