Development of Alkali-Catalyzed Organosolv Pretreatment and SHF Process for Production of Bio-Succinic Acid from Barley Straw

Abstract

A series of biological processes were developed to extract fermentable sugars from barley straw and produce succinic acid (SA), a microbial metabolite. For selectively removal of lignin with the alkali-catalyzed organosolv, process parameters such as NaOH concentration (w/w, %), ethanol concentration (v/v, %) and reaction temperature ( o C) were investigated using the response surface method. As a result, the cellulose content of pretreated materials was increased about 63% and lignin was removed about 80% compared to the raw materials. For obtaining the high amount of SA, separate hydrolysis and fermentation (SHF) process was performed with high amount (113.9 g/L) of pretreated materials in a 5 L bioreactor. Through employing the fed-batch mode with enzyme feeding, the saccharification could be carried out effectively despite the low concentration (5 FPU cellulase/gglucan) of enzyme, resulting in the fermentable sugars of 58.76 g/L and glucose conversion rate of 63.35%. Actinobacillus succinogenes consumed glucose and xylose simultaneously, the main carbon sources of saccharified solution, at the rates of 0.71 and 0.49 g/L/h, respectively, and the phenomenon of catabolite repression was not observed. SA of 32.58 g/ L was produced with a production yield of 0.56 SA g/total sugars g. Finally, it was turned that the A. succinogenes has metabolic capacities that could effectively utilize the carbohydrates of the lignocellulosic biomass, and the saccharified solution derived from barley straw was suitable as fermentation substrate.