Production of butyric acid by a continuous fermentation/membrane separation process

This research focused on the production of butyric acid from Clostridium tyrobutyricum by continuous fermentation with membrane separation fermentation. Experiments with fermentation in batch, continuous culture and continuous culture with partial cell recycle by ultrafiltration were conducted. The results show that partial cell recycle via membrane ultrafiltration has a great influence on the selectivity and productivity of butyric acid, with an increase in selectivity from t9% to 95% butyric acid and with productivities as high as 1.13 gl-1h-1.;A comprehensive mathematical model was developed to describe the batch and continuous fermentation of glucose to organic acids with C. tyrobutyricum . The model showed that butyric acid production is a strong function of cell mass while acetic acid production is a function of cell growth rate. Thus, in batch fermentation, high butyric acid selectivity occurs at a high initial cell concentration or high initial glucose concentration. A dynamic model was also developed to describe the kinetics of the continuous fermentation of glucose to produce butyric acid with C. tyrobutyricum. The developed dynamic model fit the experimental results very well. The model was then used to obtain the optimized operating condition to achieve the highest butyrate selectivity and productivity when steady state was achieved. The simulation showed that dilution rate has the most significant effect on butyrate selectivity, and that continuous fermentation can achieve almost the same selectivity and productivity with cell recycle fermentation when dilution rate was at 0.03 h-1. At this condition, the butyric acid selectivity was 0.95, which is close to that of cell recycle fermentation, 0.967. It also showed that the future direction of the research should be to relieve the cell inhibition.;To decrease the inhibitory effect of products and improve butyrate selectivity, a wafer-enhanced electrodeionization (EDI) technique was applied to separate product from the continuous fermentation broth. This developed wafer-enhanced EDI selectively separated butyrate from the fermentation broth. It was found that production selectivity of butyrate increased from 85% to 92%, which was due to the selective separation of butyrate and metabolic shift from acetate to butyrate, and the butyrate productivity increased three fold because the cell mass increased.