Enzymatic hydrolysate of water hyacinth with NaOH pretreatment for biobutanol production via ABE fermentation by Clostridium beijerinckii JCM 8026

Abstract

Water hyacinth (WH; Eichhornia crassipes) is an invasive and free-floating aquatic plant that is rapidly spreading over the world causing various environmental problems. The utilization of WH as a feedstock for biofuel production is a challenging solution to overcome the environmental problem as well as address the energy shortage. Due to the complex structure of lignocellulosic materials, pretreatment is an inevitable step to maximize the sugar yield before being used as a substrate in fermentation. The aim of this study was to investigate the utilization of WH for biobutanol production via acetone-butanol-ethanol fermentation by Clostridium beijerinckii JCM 8026. The WH was pretreated with sodium hydroxide (NaOH) at various concentrations [0, 2, and 4% (w/v)], reaction times (30, 60, and 90 min), and temperatures (80, 100, and 120 °C). The pretreatment results were optimized using response surface methodology with a Box-Behnken design and Minitab software analysis. The maximum total sugar concentration (21.05 g/L) following cellulose digestion was obtained after a 2% (w/v) NaOH for 90 min at 100 °C. This hydrolysate slurry gave a subsequent butanol concentration, yield, and productivity of 2.09 g/L, 0.15 g/g, and 0.012 g/L/h, respectively, following C. beijerinckii JCM 8026 fermentation. To help understand the effect of the pretreatments, changes in the pretreated samples were observed by surface area analyses, scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis.