Effect of Acid mixtures on the Hydrolysis of Coconut Coir for Recovery of Fermentable Sugars

In this study, coconut coir was hydrolysed to produce fermentable sugars using dilute nitric and acetic acid. The hydrolysis process was carried out according to a four variable Box-Behnken design which was used to develop a statistical model to describe the relationship between the concentration of fermentable sugars produced (dependent variable) and the independent variables (time, temperature, nitric acid concentration and acetic acid concentration). Results of analysis of variance (ANOVA) performed to determine the fit of the statistical model showed that the model was statistically significant (p<0.0001) with a low standard deviation (1.77) and non-significant lack of fit (R²=0.93). The concentrations of nitric and acetic acid as well as the hydrolysis time and temperature all positively influenced the hydrolysis process as evident in the increase in the amount of fermentable sugars produced when the values of these variables were increased. When both acids were combined together, the amount of fermentable sugar produced was increased by as much 54%. Optimisation of the statistical model showed that the maximum sugar concentration was 32.7 g/L and this was obtained for coconut coir catalysed by 0.50 %w/v nitric acid, 0.40 %w/v acetic acid at 160 °C for 30 minutes. Validation of the statistical model showed that there was no significant difference between predicted and observed values.

Keywords
Coconut coir; Lignocellulosic feedstock; Response Surface Methodology; Optimisation