Recycling of Black Liquor for Treating Sugarcane Bagasse at Low Temperature to Attain High Ethanol Production without Washing Step

Alkaline pretreatment has been commonly used for bioconversion of lignocellulose into fuel ethanol due to its gentle condition. However, the large quantity of water consumption and wastewater generation from the pretreatment and washing steps have been two bottleneck problems for the practical application of alkaline pretreatment. In order to save water consumption and reduce wastewater generation, black liquor (BL) generated in the sodium hydroxide (NaOH) pretreatment process was recycled for pretreating sugarcane bagasse (SCB), and the BL-NaOH-treated SCB without being washed was directly enzymatically hydrolyzed and fermented. After 120-h fed-batch enzymatic hydrolysis with the addition of 20 FPU cellulase/g cellulose and 2.51 mu L Tween80/ mL hydrolytic slurry, the maximum glucose concentration and enzymatic hydrolysis efficiency achieved 99.95 g/L and 71.02%, respectively. After 36-h fermentation with the domesticated Saccharomyces cerevisiae, the ethanol production reached 44.53 g/L, which amounted to 87.35% of theoretical ethanol yield. Compared with other water-saving and wastewater-reducing alkaline pretreatments, this technology saved more than 20% water consumption and reduced over 20% wastewater discharge. It provides a promising applied technology for cellulosic ethanol production