Formation of Enzymatic Recalcitrance during Bioethanol Production from Pernnisetum Purpureum with Three Pretreatment Methods

Abstract

This research was aimed at observing the inhibiting effects of some substances that are said to be recalcitrant to enzymatic activities during the production of cellulosic ethanol, a source of liquid biofuels. The biomass used for this work was a perennial grass specie (Pernnisetum purpureum S.), which is a lignocellulosic biomass that is predominantly found in the South-South Zone of Niger Delta, Nigeria. The three pretreatment methods; Dilute acid, Sulphite Pretreatment to Overcome the Recalcitrance effects of Lignocellulose(SPORL) and Alkaline Wet Oxidation were used on three different biomass particle sizes. The saccharification reaction was carried out at 10 and 15FPUcellulase/gcellulose of enzyme loading. The fermentation reaction was carried out with Saccharomyces cerevisiae (5.40X10⁸-5.70X10⁸cell/ml) from yeast. Among the three organic inhibitors analyzed for in the cause of the reaction, two were generative as the reaction proceeded while one was deteriorating with time. The difference between the theoretical ethanol yield from the total amount of glucose converted (EY₂) and the theoretical ethanol yield from the initial amount of glucose before fermentation (EY₁) was 23.88% and 8.80% for enzyme loading of 10FPU/g and 15FPU/g respectively, which suggested the formation of side products (potential recalcitrance to enzymatic activities). This was further confirmed by the low values of enzymatic convertibility of cellulose and enzymatic convertibility of glucose; 28.92% and 25.92% respectively. Statistical analysis and optimization of data was done using ANOVA, Pearson correlation, Regression analysis, Duncan’s multiple test, t-test for comparing means and response optimization.

Keywords: Cellulosic ethanol, Hydroxymethylfurfural, Acetic acid, Total Extractable Polyphenolics.