Microbial production of a biofuel (acetone-butanol-ethanol) in a continuous bioreactor: impact of bleed and simultaneous product removal

Authors: EZEJI, THADDEUS - The Ohio State University; Qureshi, Nasib; BLASCHEK, HANS - University Of Illinois

Submitted to: Bioprocess and Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/2012
Publication Date: 6/29/2012
Citation: Ezeji, T.C., Qureshi, N., Blaschek, H.P. 2013. Microbial production of a biofuel (acetone-butanol-ethanol) in a continuous bioreactor: Impact of bleed and simultaneous product removal. Bioprocess and Biosystems Engineering. 36(1):109-116.

Interpretive Summary: Butanol [a major product of acetone butanol ethanol (ABE) fermentation; ratio 3:6:1] is a superior liquid fuel to ethanol and can be produced from agricultural crops such as corn. Currently, 2.6 billion pounds of butanol are produced from petrochemical sources in the United States. Traditionally, ABE production is achieved in batch process where their total concentration rarely exceeds 20 g/L (ABE) due to its toxicity to the fermentation microorganism. Recovery of such a low level of butanol by distillation is not economic. Hence, butanol should be produced and recovered from the fermentation broth simultaneously (as it is produced) using alternative product removal techniques. In the present studies, butanol was produced and recovered simultaneously from the fermentation broth. By applying this technique (continuous production and simultaneous recovery), over 460 g/L ABE was produced as compared to 20 g/L in a batch process. This investigation would benefit the fermentation industry and farmers.

Technical Abstract: Acetone butanol ethanol (ABE) was produced in an integrated continuous fermentation and product recovery system using a microbial strain Clostridium beijerinckii BA101 for ABE production and fermentation gases (CO2 and H2) for product removal by gas stripping. This represents a continuation of our previous work involving an integrated fed-batch fermentation product recovery system employing gas stripping. In the prior work, fermentation ceased after 201 h due to accumulation of unknown inhibitory chemicals and macromolecules in the broth in the absence of bleed. The present study describes the operation of a bioreactor in an integrated mode where continuous fermentation and product recovery were combined. In this system, the bioreactor was fed with a concentrated sugar solution (250-500 gl**-1 glucose). The bioreactor was bled continuously to avoid accumulation of inhibitory chemicals and products. The continuous system was operated for 504 h (21 days) after which the fermentation was intentionally terminated. The bioreactor produced 461.3 g ABE from 1125.0 g total sugar in 1 l culture volume, resulting in productivity and yield of 0.92 gl**-1h**-1, and 0.41, respectively. These results are superior to results obtained from a control batch fermentation and demonstrated that ABE fermentation can be operated for a long period of time if butanol and inhibitory substances in the bioreactor are kept below threshold of toxicity.