Thermochemical pretreatment enhanced bioconversion of elephant grass (Pennisetum purpureum): insight on the production of sugars and lignin

Abstract

Pennisetum purpureum, commonly known as elephant grass, possesses an immense ability to be recognized as bioenergy crop due to its high carbohydrate content and ample availability in the northeastern states of India. In the present study, an alkaline treatment was conducted using NaOH of different concentrations (1%, 2% and 3% (w/v)) at varying reaction periods of 30, 60 and 90 min with an aspiration of maximum delignification and an enhanced recovery of carbohydrates from biomass. A maximum delignification of 81.0% (w/w) was obtained when the biomass was pretreated with 2% (w/v) of NaOH for 60 min while in the presence of 3% (w/v) of NaOH, the highest cellulose recovery of 72.3% (w/w) was accounted at 90 min of reaction time. During saccharification of biomass, a maximum 18.4 g/L of glucose was produced using 20 filter paper unit of commercial cellulase after 48 h of enzymatic reaction with a cellulose conversion of more than 46%. Furthermore, product inhibition study showed the significant inhibitory effect on enzymatic production of sugars even in the presence of 2 g/L glucose and xylose in the reaction system. The severity of alkaline treatment of the untreated and treated biomass was evaluated using different physiochemical analyses. Moreover, the extracted lignin obtained after acid precipitation of alkaline filtrate was characterised using UV-Visible spectrophotometer. Finally, two-way ANOVA revealed a significant variation in the production of glucose and xylose from biomass even when glucose was added at a fixed concentration (P value = 0.00044 << 0.05) into the reaction system. On the other hand, xylose shows significant inhibition in glucose and xylose production from biomass at both of a particular (P value = 9.05 × 10−7 << 0.05) and different (P value = 0.0078 << 0.05) concentrations of extraneous addition.