Application of a statistical design to evaluate bioethanol production from Chlorella S4 biomass after acid - Thermal pretreatment

This research evaluates the potential of a native marine isolate, Chlorella S4, for bioethanol production using the Thermo-Tolerant (TT) strain of Saccharomyces cerevisiae. Initially, an acid-thermal pretreatment with different concentrations of microalgal biomass (2, 4, and 6% (w/v)) and H2SO4 (1.5, 3, and 4.5% (v/v)) was investigated to improve the release of glucose (an important substrate of fermentation). The glucose concentration was enhanced 3.7 fold from 0.048 to 0.179% (w/v) using the maximum concentrations of biomass (6% (w/v)) and 3% (v/v) of H2SO4 at 121 °C for 20 min. The I-optimal type of mixture design was applied to select the best combination of two carbon sources (pure glucose and microalga hydrolysate) in the fermentation medium. In the optimum condition, the highest specific growth rate (μmax) of 0.282 h−1 was calculated for the yeast. Subsequently, a maximum ethanol concentration of 8.31 ± 0.18 g/L with a yield of about 0.4 g ethanol/g consumed carbohydrate (about 78.2% of the theoretical yield) was achieved after 48 h of fermentation. These findings indicate that feasible bioethanol production from Chlorella S4 hydrolysate may be applied industrially.