Reduction in butanol inhibition by perstraction:: Utilization of concentrated lactose/whey permeate by Clostridium acetobutylicum to enhance butanol fermentation economics

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 (98.97 gL(-1)) were produced from lactose (227 gL(-1)) at a yield of 0.44 and productivity of 0.21 gL(-1)h(-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. A membrane with an area of 0.1130 m 2 was used as the perstraction membrane while oleyl alcohol as the perstraction solvent. 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.