Continuous Fermentation of <em>Clostridium tyrobutyricum</em> with Partial Cell Recycle as a Long-Term Strategy for Butyric Acid Production

Abstract

In making alternative fuels from biomass feedstocks, the production of butyric acid is a key intermediate in the two-step production of butanol. The fermentation of glucose via <em>Clostridium tyrobutyricum </em>to butyric acid produces undesirable byproducts, including lactic acid and acetic acid, which significantly affect the butyric acid yield and productivity. This paper focuses on the production of butyric acid using <em>Clostridium tyrobutyricum</em> in a partial cell recycle mode to improve fermenter yield and productivity<em>.</em> Experiments with fermentation in batch, continuous culture and continuous culture with partial cell recycle by ultrafiltration were conducted. The results show that a continuous fermentation can be sustained for more than 120 days, which is the first reported long-term production of butyric acid in a continuous operation. Further, the results also 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 ≈9% to 95% butyric acid with productivities as high as 1.13 g/Lh. Continuous fermentation with low dilution rate and high cell recycle ratio has been found to be desirable for optimum productivity and selectivity toward butyric acid and a comprehensive model explaining this phenomenon is given.

Keywords

• butyric acid
• continuous fermentation
• ultrafiltration
• &lt;em&gt;Clostridium tyrobutyricum&lt;/em&gt;