The effects of dilution rate and glucose concentration on continuous acetone-butanol-ethanol fermentation by Clostridium acetobutylicum immobilized on bricks

BACKGROUND: Owing to the rapid depletion of petroleum fuel, the production of butanol through biological routes has attracted increasing attention. However, low butanol productivity severely impedes its potential industrial production. It is known that the immobilization of whole cells can enhance productivity in the acetone-butanol-ethanol (ABE) continuous fermentation process. Therefore, the objective of this study was to develop a low-cost continuous operation for butanol production. RESULTS: Bricks were chosen as cell support because of their low cost and ease of use for immobilization. The solvent productivity for the bricks with immobilized cells was 0.7 g L-1 h(-1), 1.89 times that of free cells (0.37 g L-1 h(-1)) at a dilution rate of 0.054 h(-1). The productivity improvement can contribute to greater retention of biomass inside the reactor due to immobilization. The increase in glucose feed concentration raised total solvent production. However, it resulted in a decrease in yield (grams of solvents produced per gram of glucose introduced). Continuous operation with immobilized cells at a dilution rate of 0.107 h(-1) resulted in a solvent productivity of 1.21 g L-1 h(-1), 2.1 times that of the operation at 0.027 h(-1). However, the yield (butanol produced per glucose consumed) was decreased to 0.19 from 0.29 under the same glucose feeding condition of 60 g L-1. CONCLUSION: The increase in dilution rate and feed glucose concentration enhanced productivity, but decreased the utilization of substrates and the final solvent concentration. Therefore, a balance between productivity and glucose utilization is required to ensure continuous process operation. (C) 2011 Society of Chemical Industry