(546d) High Cumulative Amount of Ethanol Fermentation in Continuous and Closed-Circulating Fermentation Process with Pervaporation Membrane Bioreactor

During traditional ethanol batch fermentation processes, the cumulative production amount is low, due to the inhibition of ethanol to the microorganism. Coupling pervaporation with ethanol fermentation, ethanol is in situ removed from the broth by the pervaporation membrane and the inhibition is released or eliminated. Therefore high cumulative production with long fermentation period would be achieved. A continuous and closed-circulating fermentation (CCCF) process with a pervaporation membrane bioreactor had been proposed for ethanol fermentation. When the pervaporation had been intermittently coupled with fermentation, the fermentation process had been lasting for 500 h and the cumulative ethanol production was about 670 gL^-1, with the average ethanol productivity being in the range of 1.3 gL^-1h^-1and 1.5gL^-1h^-1. The fermentation process could be improved when the pervaporation was continuously coupled with fermentation. An experiment in the CCCF process lasting for 264 h had been carried out, and the average ethanol productivity was over 2.3 g L^-1 h^-1 with cumulative ethanol production of 610 gL^-1 obtained. During the later period of the CCCF process, the fermentation was inhibited by the accumulative organic acids in the broth, so called the secondary metabolites of the yeast cell. In further experiment, by increasing the pH of the broth in the range of 6.0 and 8.0 at the later period of the process, the inhibition of the organic acids was released and enhanced fermentation could be achieved with higher ethanol productivity, higher cell density, longer fermentation period and hence higher cumulative ethanol production amount.