Integrated process for microbial solvent production from whey permeate. Final report

Acetone and butanol were historically produced through fermentation of carbohydrate raw materials. Conventional feedstocks such as grain and molasses, and the energy required to recover products by distillation, are too costly for traditional batch fermentation to compete with petrochemical synthesis. The authors proposed to evaluate an acetone-butanol-ethanol fermentation of acid whey permeate, a cheap carbohydrate source, using up-to-date bioreactor technology continuous fermentation with cell recycle and in-situ butanol recovery by gas stripping. Clostridium acetobutylicum P262 was the strain chosen, as it assimilates both the lactose and lactic acid in acid whey. Single-stage continuous culture proved unsuitable for butanol production, since productivity is low and cultures degenerated quickly. Two-stage culture improved productivity by a factor of two over batch runs. All continuous cultures showed major oscillations in cell density, substrate concentration and products formed. Under these conditions, cell recycle did not affect productivity in two-stage culture. Gas stripping with fermentor off-gases recovered a clean condensate of butanol and acetone at 70--90% yield and with purification factors of 14 to 35. Stripping maintained solvent concentrations in the range of 2--4 g/l even at the peak of solventogenesis, eliminating product inhibition. Gas stripping produced a 50% improvement in substrate uptake and a 10--20% improvement in solvent productivity