The vital role of citrate buffer in acetone–butanol–ethanol (ABE) fermentation using corn stover and high-efficient product recovery by vapor stripping–vapor permeation (VSVP) process

Abstract

BackgroundButanol is not only an important solvent and chemical intermediate in food and pharmaceutical industries, but also considered as an advanced biofuel. Recently, there have been resurging interests in producing biobutanol especially using low-cost lignocellulosic biomass, but the process still suffers from low titer and productivity. The challenge for the bioconversion approach is to find an effective way of degrading materials into simple sugars that can then be converted into fuels by microorganisms. The pretreatment of lignocellulosic biomass is the great important process in influencing butanol production and recovery, finally determining its eco-feasibility in commercialization.ResultsThe effects of various strengths of citrate buffer on enzymatic hydrolysis and acetone–butanol–ethanol fermentation using corn stover or glucose as feedstock were investigated. The strengths of citrate buffer in the range of 20–100 mM had no effect on enzymatic hydrolysis, but greatly influenced the performance of ABE fermentation using corn stover hydrolysate. When 30 mM citrate buffer was used for enzymatic hydrolysis, the fermentation broth with the maximum butanol and ABE concentrations of 11.2 and 19.8 g/L were obtained from 30.9 g/L glucose and 9.7 g/L xylose, respectively, which was concentrated to 100.4 g/L butanol and 153.5 g/L ABE by vapor stripping–vapor permeation process. Furthermore, using glucose as sole carbon source, there were no cell growth and ABE production in the P2 medium with 80 or 100 mM citrate buffer, indicating that higher concentrations of citrate buffer had deleterious effect on cell growth and metabolism due to the variation of cells internal pH and cell membrane permeability. To mimic in situ product recovery for ABE fermentation, the VSVP process produced the condensate containing 212.0–232.0 g/L butanol (306.6–356.1 g/L ABE) from fermentation broth containing ~10 g/L butanol (~17 g/L ABE), the performance of which was more effective than pervaporation and gas stripping.ConclusionsAs it has significant impact on butanol fermentation, the strength of citrate buffer is of great importance in lignocellulosic butanol fermentation. Compared with pervaporation and gas stripping, the VSVP process has great potential for efficient butanol recovery in biobutanol production.

Transcriptional analysis of degenerate strain Clostridium beijerinckii DG-8052 reveals a pleiotropic response to CaCO3-associated recovery of solvent production

“…In DG-8052 supplied with CaCO 3 , the increased transport of glucose accompanied with increased production of acetic and butyric acids, while those acids were converted into dissociated form and increased the transmembrane proton gradient. In C. beijercinkii CC101, which derived from NCIMB8052, the addition of citrate could inhibit cell growth by reducing the cells internal pH and proton motive force, and changing cell membrane permeability24. In our research, the supplied CaCO 3 could convert the undissociated acids into dissociated form which reduced the acids stress to cell, while, the produced butyrate and acetate may contribute like citrate did in CC101, which may explain the partial recovery of ABE producing ability in DG-8052.…”

The advanced strategy for enhancing biobutanol production and high-efficient product recovery with reduced wastewater generation

“…Various sugars in JAS hydrolysate were analyzed using the HPLC system (Waters 1525) equipped with the column (Aminex HPX-87H, 300 mm × 7.8 mm) operated at 50 °C, photodiode array detector operated at room temperature and 210 nm, and 0.01 mol/L H 2 SO 4 as the mobile phase with a flow rate of 0.50 mL/min [23]. …”

Comparison of high-titer lactic acid fermentation from NaOH- and NH3-H2O2-pretreated corncob by Bacillus coagulans using simultaneous saccharification and fermentation

“…It also should be noted that several additives can enhance fermentation performance. For example, 30 mM citrate buffer greatly influenced acetone-butanol-ethanol fermentation by Clostridium beijerinckii when corn stover hydrolysate was used as the substrate29. Therefore, useful LA fermentation additives that enhance the yield, titer, and productivity under our pretreatment and fermentation conditions should be identified.…”