Submitted to: Journal of Food and Bioproducts Processing
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/21/2003
Publication Date: 6/1/2004
Citation: Qureshi, N., Lai, L.L., Blaschek, H.P. 2004. Scale-up of a high productivity continuous biofilm reactor to produce butanol by adsorbed cells of Clostridium beijerinckii. Journal of Food and Bioproducts Processing. 82(C2):164-173. Interpretive Summary: Butanol is an important fuel and chemical that can be produced from agricultural crops or agricultural biomass. Currently, 2.5 billion lbs. of butanol is produced annually (worldwide) from petrochemical resources of which approximately one half is produced in the United States. Butanol has a calorific value (heating value) higher than ethanol, which makes it a superior fuel. Production of 1.25 billion lbs. of butanol/year would result in the utilization of 3.79 billion lbs. of corn/year. If butanol is produced from corn, this would benefit our farmers and make us partially independent of foreign oil. Butanol is produced by the microorganism Clostridium beijerinckii BA101 in batch reactors. It was determined that continuous, high productivity reactors for butanol production be used in combination with product recovery for the process to be economically competitive to the petrochemical route. For this reason, butanol production was scaled up from a reactor size of 25 mL to a reactor size of 312 mL. The rate of production of butanol, in these continuous reactors, was approximately 45 times higher than in the traditional batch reactors, making it attractive for further scale up. The scaled up reactor was operated for a period of 2,302 hours as compared to the small reactor's operation of approximately 550-650 hours. Furthermore, various scenarios were attempted to make the process of butanol production more economic.
Technical Abstract: An immobilized cell reactor for producing acetone butanol ethanol (ABE or solvents) when using Clostridium beijerinckii BA101 demonstrated reactor productivities of 3.49, 5.99, and 16.13 gL**-1h**-1 at dilution rates of 0.29, 1.00, and 2.00 h**-1, respectively. These dilution rates are based on the total volume of the reactor. The reactor was scaled up successfully as these productivities are close to those achieved in a small reactor. Dilution rate, based on the void volume, increased reactor productivity from 16.13 gL**-1h**-1 to 34.76 gL**-1h**-1. The packed bed reactor blocked after a period of 2302 h of continuous operation due to excessive cell growth. Nutrient limitation was applied as a means to reduce cell growth while keeping the reactor productive, however, this approach was not successful. It was found that most of the cell growth in adsorbed cell bioreactors occurs on the surface of the cell support. The free cell continuous reactor demonstrated much lower reactor productivity. In the immobilized cell reactor only a fraction of the biomass was in the solventogenic state. A significant amount of biomass was present as inactive biomass (spores). It is suggested that sporulation be blocked in C. beijerinckii BA101 in order for reactors to be more productive. It is postulated that once such a culture is developed, nutrient limitation be attempted to avoid reactor blockage due to excessive cell growth.