Fouling studies of a pervaporation membrane (area based on internal tube diameter 0.08 m(2)) were carried out in batch mode using model butanol solution in distilled water, commercial fermentation media (P2 and corn steep liquor, CSL), and P2 and CSL fermentation broth. Butanol fermentations were conducted using semidefined P2 medium, CSL medium (a low cost commercial nutrient medium), and the Clostridium beijerinckii BA101 hyper-butanol-producing mutant strain. The rates of removal of butanol from the commercial fermentation media (P2 and CSL) were similar to the rates of butanol removal from butanol solution in water. The rates of removal of butanol from the CSL fermentation broth were higher than the rates of butanol removal from butanol solution in water and fermentation media. Butanol removal experiments were run from 14 to 240 hours using different media and fermentation broth, and it was concluded that the pervaporation membrane did not foul under the conditions employed. The selectivities of butanol ranged from 20 to 55 when feed butanol ranged from 33.0 to 3.33 g/L. The total flux was 25-45 g/m(2).h using air as the sweep gas. In the permeate, the butanol concentration ranged from 122.9 to 458 g/L.