Submitted to: Institution of Chemical Engineers Transactions
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/13/2004
Publication Date: 3/1/2005
Citation: Qureshi, N., Maddox, I.S. 2005. Reduction in butanol inhibition by perstraction: utilization of concentrated lactose/whey permeate by Clostridium acetobutylicum to enhance butanol fermentation economics. Transactions of the Institution of Chemical Engineers. 83(C1):43-52. Interpretive Summary: Butanol is a superior fuel to ethanol and can be produced from agricultural wastes and residues using the microorganism Clostridium acetobutylicum. Butanol can be used in internal combustion engines. Whey permeate, a dairy industry by product, can be converted to butanol. However, C. acetobutylicum cannot accumulate more than 2% butanol (or acetone butanol ethanol also called ABE) in batch reactors due to toxicity (butanol) resulting in use of dilute whey permeate medium (6% whey permeate containing 5% lactose). Use of dilute sugar solutions is not economical because of large process streams this requires. In order to make it economically attractive, concentrated whey permeate medium (lactose >22%) was used in combination with a butanol recovery technique called "perstraction." Perstraction is a technique that allows continuous removal of butanol as it is produced in the reactor, thus alleviating the inhibition problem. This resulted in the production of 9.9% ABE. The perstraction assisted butanol fermentation is superior to traditional batch fermentation and is anticipated to be economical. Dairy industries that produce whey permeate would be able to benefit from this investigation.
Technical Abstract: Acetone-butanol-ethanol (ABE) were produced from whey permeate medium, supplemented with lactose, in a batch reactor using Clostridium acetobutylicum P262, coupled with ABE removal by perstraction. ABE (136.6 g, reaction mixture volume 1.38 L) were produced from lactose (313.3 g) at a yield of 0.44 and productivity of 0.21 gL**-1h**-1. It should be noted that the ratio of acids to solvents was significantly lower in the perstraction experiment compared to the control batch process, suggesting that acids were converted to solvents. The perstraction experiment results are superior to the control batch fermentation where 9.34 gL**-1 ABE was produced. It was determined that lactose at 250 gL**-1 was a strong inhibitor to the cell growth of C. acetobutylicum and fermentation. Removal of ABE by perstraction was faster than their production in the reactor, and the maximum concentration of ABE in the oleyl alcohol was 9.75 gL**-1. It is viewed that recovery of ABE from oleyl alcohol (at this concentration) would be more economical than recovery from the fermentation broth. It is suggested that a new membrane be developed, which can offer a higher ABE flux. Alternately, silicalite membranes that were successfully developed for pervaporation could be used for perstraction. Using such an integrated system would reduce process streams and save significant processing costs. It is also viewed that the process of concentrated lactose-whey permeate fermentation to butanol can be adapted in the existing solvent fermentation industries without making significant changes.