Modelling and optimization of xylose and glucose production from napier grass using hybrid pre-treatment techniques

Siphelele Mafuleka, E.B. Gueguim Kana

University of KwaZulu-Natal, School of Life Sciences, Pietermaritzburg, South Africa.

Abstract

This work models and optimizes four hybrid techniques of Napier grass pre-treatment for xylose and glucose production, namely HCl and moist heat (HH), HCl and microwave (HM), NaOH and moist heat (NH) and NaOH and microwave (NM) using the Response Surface Methodology (RSM). The coefficients of determination (R²) of 0.83 and 0.97 were obtained for xylose and glucose production respectively using HH hybrid pre-treatment, and 0.90 and 0.80 were obtained for xylose and glucose respectively using HM hybrid pre-treatment. The optimized pre-treatment conditions of HH gave 12.83 gL^-1 xylose and 2.28 gL^-1 glucose, and optimized HM pre-treatment gave 15.06 g L^-1 and 2.44 gL^-1 xylose and glucose respectively. A xylose to glucose concentration ratio of 5.6:1 was obtained for the optimized HH pre-treatment compared to 6.1:1 for the optimized HM pre-treatment. For NH and NM hybrid pre-treatments, low concentrations of fermentable sugars were observed (<0.5 gL^-1). The findings indicate that xylose and glucose production from Napier grass can be enhanced by an optimal combination of pre-treatments of HCl and moist heat at a volume fraction of 4.39% HCl, 93.07°C for 180 min, or using a combination of microwave and HCl at a volume fraction of 5% HCl, 500 W for 30 min.

Keywords: Biohydrogen production; Bioprocess modelling and optimization; Lignocellulosic biomass pre-treatment; Pennisetum purpureum.