Pervaporative butanol removal from PBE fermentation broths for the bioconversion of glycerol by Clostridium pasteurianum

Effectiveness of Low-Cost Bioreactors Integrated with a Gas Stripping System for Butanol Fermentation from Sugarcane Molasses by Clostridium beijerinckii

The effectiveness of column bioreactors for butanol fermentation from sugarcane molasses by Clostridium beijerinckii TISTR 1461 was investigated. This fermentation was operated at an initial pH of 6.5 and temperature of 37 °C under anaerobic conditions. A 1-L bubble column bioreactor was used with various gas circulation rates ranging from 0.2 to 1.0 L/min. The highest butanol concentration (PB, 8.72 g/L), productivity (QB, 0.24 g/L∙h) and yield (YB/S, 0.21 g/g) were obtained with a gas circulation of 0.2 L/min. To improve butanol production efficiency, gas-lift column bioreactors with internal and external loops at 0.2 L/min of circulating gas were used. Higher PB (10.50–10.58 g/L), QB (0.29 g/L∙h) and YB/S (0.22–0.23 g/g) values were obtained in gas-lift column bioreactors. These values were similar to those using a more complex 2-L stirred-tank bioreactor (PB, 10.10 g/L; QB, 0.28 g/L h and YB/S, 0.22 g/g). Hence, gas-lift column bioreactors have potential for use as low-cost fermenters instead of stirred-tank bioreactors for butanol fermentation. When the gas-lift column bioreactor with an internal loop was coupled with a gas stripping system, it yielded an enhanced PB and sugar consumption of approximately 9% and 7%, respectively, compared to a system with no gas stripping.

Increased Butanol Yields through Cosubstrate Fermentation of Jerusalem Artichoke Tubers and Crude Glycerol by Clostridium pasteurianum DSM 525

Clostridium pasteurianum DSM 525 can produce butanol, 1,3-propanediol, and ethanol from glycerol. The product distribution can be tilted toward butanol when adding butyric acid. The strain predominantly produces acetic and butyric acids when grown on saccharides. Hence, butyrate formed from saccharide conversion can be used to stimulate butanol production from glycerol under cosubstrate cultivation. The optimal cosubstrate ratio was determined, and under optimal conditions, a butanol yield and a productivity of 0.27 ± 0.01 g_butanol g^-1 _{(glycerol + sugar)} ^-1 and 0.74 ± 0.02 g L^-1 h^-1 were obtained. On the basis of these results, batch fermentation in a 5 L bioreactor was performed using Jerusalem artichoke hydrolysate (carbohydrate source) and crude glycerol (residue from biodiesel production) at the previously determined optimal condition. A butanol yield and a productivity of 0.28 ± 0.007 g_butanol g_{(glycerol+sugar)} ^-1 and 0.55 ± 0.008 g L^-1 h^-1 were achieved after 27 h fermentation, indicating the suitability of those low-cost carbon sources as cosubstrates for butanol production via C. pasteurianum.

Clostridial conversion of corn syrup to Acetone-Butanol-Ethanol (ABE) via batch and fed-batch fermentation

Corn syrup - a commercial product derived from saccharification of corn starch - was used to produce acetone-butanol-ethanol (ABE) by Clostridium spp. Screening of commercial Clostridium spp., substrate inhibition tests and fed-batch experiments were carried out to improve ABE production using corn syrup as only carbon source. The screening tests carried out in batch mode using a production media containing 50 g/L corn syrup revealed that C. saccharobutylicum was the best performer in terms of total solvent concentration (12.46 g/L), yield (0.30 g/g) and productivity (0.19 g/L/h) and it was selected for successive experiments. Concentration of corn syrup higher than 50 g/L resulted in no solvents production. Fed-batch fermentation improved ABE production with respect to batch fermentation: the butanol and solvent concentration increased up to 8.70 and 16.68 g/L, respectively. The study demonstrated the feasibility of producing solvents via ABE fermentation using corn syrup as a model substrate of concentrated sugar mixtures.