Bioethanol from Napier grass employing different fermentation strategies to evaluate a suitable operation for batch bioethanol production

Abstract

• Variations in substrate and enzyme additions in SSF of Napier grass were compared. • SHF and SSF resulted in 30.6 g/L and 28.5 g/L ethanol from 15% Napier grass. • Alleviate mixing problem by portioning addition did not improve ethanol production. • Pre-incubating the grass before SSF negatively impacts ethanol production. • Extra loading of substrate during SSF resulted in higher ethanol production. Napier grass has been used as animal feed especially in countries with tropical climates. As interest in alternative feedstocks for fuel bioethanol increases, Napier grass has been considered as a potential feedstock for lignocellulosic bioethanol production. Two main fermentation strategies, including separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF), were investigated with various substrate and enzyme feeding patterns in SSF. Total substrate loading of 15% and enzyme dosage of 40 FPU/g substrate were controlled to compare the performance of each fermentation variation. SHF and SSF resulted in similar ethanol production of 30.6 ± 0.4 g/L and 28.5 ± 2.3 g/L. Preincubation of grass and enzyme resulted in significant lower ethanol at 20.3 ± 1.6 g/L. Portioning the addition of grass and enzyme did not change the ethanol production significantly. Increasing the grass loading to 30% via portioning approach resulted in an increase in ethanol production in batch fermentation, while the addition of extra enzyme did not help with increasing ethanol production.