Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2003
Publication Date: 8/9/2003
Citation: Ezeji, T.C., Qureshi, N., Blaschek, H.P. 2003. Acetone butanol ethanol (ABE) production from concentrated substrate: reduction in substrate inhibition by fed-batch technique and product inhibition by gas stripping. Applied Microbiology and Biotechnology. 63:653-658. Interpretive Summary: Acetone-butanol-ethanol (ABE or solvents) is an excellent liquid fuel that can be produced from agricultural commodities using the microorganism Clostridium beijerinckii. However, its production is hampered because it is toxic to the microorganism. Because of toxicity, only up to 20 g/L ABE (of which butanol is usually 13-16 g/L) can be produced in a batch process. This results in large process streams and uneconomic production of ABE. In order to economize ABE production, solvents should be removed as they are produced. This eliminates the toxicity problem and results in the production of more than 20 g/L ABE, thus benefiting the process economics. Keeping this in view, we designed a system where solvents were removed simultaneously by gas stripping. Employing this process, 232.8 g/L ABE was produced as opposed to less than 20 g/L. The system proved to be superior to the batch reactor. In addition to production of more solvents per L culture volume, a higher production rate (400%) was obtained. In order to economize the process further, a concentrated feed stream was used which reduced the process streams. These results move the ABE process another step closer to commercialization.
Technical Abstract: Acetone-butanol-ethanol (ABE) was produced in an integrated fed-batch fermentation-gas stripping product recovery system using Clostridium beijerinckii BA101 and H2 and CO2 as the carrier gases. This technique was applied in order to eliminate substrate and product inhibition that normally restricts ABE production and sugar utilization to less than 20 and 60 g/L, respectively. In the integrated fed-batch fermentation and product recovery system, solvent productivities were improved 400% of the control batch fermentation productivities. In a control batch reactor, the culture used 45.4 g/L glucose and produced 17.6 g/L total solvents (yield 0.39 g/g, productivity 0.29 g/L/h). Using the integrated fermentation-gas stripping product recovery system and CO2 and H2 as carrier gases, we carried out fed batch fermentation experiments and measured various characteristics of the fermentation including ABE production, selectivity, yield, and productivity. The fed batch reactor was operated for 201 h. At the end of the fermentation, an unusually high concentration of total acids (8.5 g/L) was observed. A total of 500 g of glucose was used to produce 232.8 g solvents (acetone 77.7 g, butanol 151.7 g, and ethanol 3.4 g) in one liter of culture broth. Average solvent yield and productivity were 0.47 g/g and 1.16 g/L/h, respectively.