Effects of chemical treatments on the bioethanol yield and composition of Isoberlinia doka waste

Abstract

Isoberlinia doka sawdust; an abundant waste material was pre-treated using FeCl 3 , HCl, NaOH, sequential HCl and NaOH treatments at 121 °C for 15 min to mitigate the challenges of its utilisation as a carbon source for bioethanol production. The effects of these treatments on the biomass were evaluated using Fourier transform infrared (FTIR) spectroscopy and gravimetric methods. The capability of the pre-treated residue to produce fermentable sugars and bioethanol were also assessed. The treated biomass were saccharified using cellulase mix from Aspergillus niger and Trichoderma reesi and fermented using Saccharomyces cerevisiae. The result shows that the chemical treatments significantly (p < 0.05) diminished the lignin contents and improved cellulose content of the treated samples; evident from decreased FTIR spectral intensities related to lignin. The cellulase mixture efficiently digested the treated biomass and resulted in significant (p < 0.05) sugar yield compared to the untreated biomass. Although the sequential HCl and NaOH treatment had the highest reducing sugar yield (280.1 mg/g), its ethanol yield (172.2 mg/g) was low, possibly due to formation of inhibitory bye-products. The alkali treatment reduced the lignin content and resulted in the highest ethanol yield (230.7 mg/g). Isoberlinia doka sawdust demonstrated great potential to be used as a sustainable feedstock for bioethanol production.