Clostridium beijerinckii BA101 (mutant strain) and C. beijerinckii 8052 (wild type) were compared for substrate and butanol inhibition. The wild-type strain is more strongly inhibited by added butanol than is the mutant strain. Acetone and butanol were removed from a fed-batch reactor inoculated with C. beijerinckii BA101 by pervaporation using a silicone membrane. In the batch reactor, C. beijerinckii BA101 produced 25.3 g/L of total solvents, whereas in the fermentation-recovery experiment it produced 165.1 g/L of total solvents. Solvent productivity increased from 0.35 (batch reactor) to 0.98 g/L.h (fed-batch reactor). The fed-batch reactor was fed with 500 g/L of glucose-based P2 medium. Acetone selectivities ranged from 2 to 10 whereas butanol selectivities ranged from 7 to 19. Total flux varied from 26 to 31 g/m(2).h.