Comparison of acid-, alkaline-, and ionic liquid–treated Napier grass as an immobilization carrier for butanol production by Clostridium beijerinckii JCM 8026

Abstract

Immobilization is a simple technique in which microorganisms adhere and agglomerate onto the porous material’s surface, resulting in a higher cell density, cell tolerance, and productivity. Acetone-butanol-ethanol (ABE) fermentation using immobilized Clostridium beijerinckii JCM 8026 on Napier grass (Pennisetum purpureum) chemically pretreated with H2SO4, NaOH, and 1-ethyl-3-methylimidazolium acetate (EMIM-OAc) was compared in order to investigate the effect of the treatment on butanol production. X-ray diffraction, Fourier-transform infrared spectroscopy, and surface area measurement analyses indicated that the alkaline-pretreated Napier grass sample had the highest crystalline level with the lowest lignin content (lignin/cellulose) and a high surface area compared with other pretreated samples, suggesting its potential as an immobilized material. The fermentation was operated in a batch system for 5 days with an initial glucose level of 60 g/L. Clostridium beijerinckii JCM 8026 immobilized on the NaOH-treated Napier grass gave the highest butanol concentration (8.99 g/L), which corresponded to a 24.7% and 25.6% higher concentration than that when the cells were immobilized on untreated Napier grass and free cell culture, respectively. It is likely that immobilization on NaOH-treated Napier grass increased the cells’ protection from environmental stresses and prevented their washing out due to its swollen structure within an enlarged surface area.