The use of high pressure CO₂‐facilitated pH swings to enhance in situ product recovery of butyric acid in a two‐phase partitioning bioreactor

Abstract

Through the use of high partial pressures of CO2 (pCO2 ) to facilitate temporary pH reductions in two-phase partitioning bioreactors (TPPBs), improved pH dependent partitioning of butyric acid was observed which achieved in situ product recovery (ISPR), alleviating end-product inhibition (EPI) during the production of butyric acid by Clostridium tyrobutyricum (ATCC 25755). Through high pressure pCO2 studies, media buffering effects were shown to be substantially overcome at 60 bar pCO2 , resulting in effective extraction of the organic acid by the absorptive polymer Pebax® 2533, yielding a distribution coefficient (D) of 2.4 ± 0.1 after 1 h of contact at this pressure. Importantly, it was also found that C. tyrobutyricum cultures were able to withstand 60 bar pCO2 for 1 h with no decrease in growth ability when returned to atmospheric pressure in batch reactors after several extraction cycles. A fed-batch reactor with cyclic high pCO2 polymer extraction recovered 92 g of butyric acid to produce a total of 213 g compared to 121 g generated in a control reactor. This recovery reduced EPI in the TPPB, resulting in both higher productivity (0.65 vs. 0.33 g L(-1) h(-1) ) and yield (0.54 vs. 0.40). Fortuitously, it was also found that repeated high pCO2 -facilitated polymer extractions of butyric acid during batch growth of C. tyrobutyricum lessened the need for pH control, and reduced base requirements by approximately 50%. Thus, high pCO2 -mediated absorptive polymer extraction presents a novel method for improving process performance in butyric acid fermentation, and this technique could be applied to the bioproduction of other organic acids as well.

Enhanced extraction of butyric acid under high-pressure CO2 conditions to integrate chemical catalysis for value-added chemicals and biofuels

“…The reason the pH value under these conditions is higher than 3.06, the calculated pH at pCO 2 50 atm (50.7 bar), is the buffering effect of medium (Additional file 1 : Figure S3). The buffering effects of medium components such as yeast extract and phosphate have been observed in previous studies [ 20 , 31 ]. Ammonium acetate present in the medium seems to strongly resist pH changes, and the filtrate of culture broth exhibited the strongest buffering capacity; a change in pH of ∆pH = 0.08 was found under CO 2 purging at ambient pressure (Additional file 1 : Figure S3).…”

“…The final titer of butyrate was changed after CO 2 pressure–liquid extraction and was measured at 27.4 g under control conditions vs. 36.5/45.1 g under extractive fermentation conditions at 50 bar pCO 2 (Table 1 ). However, the productivity of butyric acid increased from 2.3 up to 3.99 g/L h. Previous studies of solid–liquid phase extraction under 60 bar showed that the productivity was decreased (0.44 vs. 0.50 g/L h), while the final titer was increased (74 vs. 68.4 g) in the batch system [ 20 ]. The productivities reported in previous studies of C. tyrobutyricum are shown in Table 2 .…”

“…CO 2 sparging has been used to achieve temporarily lower pH values for enhancing performance of the extractive fermentation without leaving the accumulation of salts from the large additions of acid and base for pH shifts and without expense of fermentation productivity. Elevated CO 2 pressures with repeated 1-h cyclical exposure up to 60 bar of pCO 2 result in more effective pH swings (up to pH 3.8 in 5 g/L yeast extract) compared with atmospheric CO 2 sparging without having an inhibitory effect on C. tyrobutyricum [ 16 , 20 ].…”

“…Here, we show for the first time the use of high CO 2 pressure for the liquid–liquid extraction of butyric acid from fermentation medium. While a previous study of the application of high CO 2 pressure was conducted through direct absorption between cells and polymeric absorbents [ 20 ], this study used the solvent extraction under high CO 2 pressure and minimized microorganism toxicity of solvent by separation of the cells and the extraction process through cell recovery through the membrane. The aim of this study was to investigate the increase of butyric acid extraction efficiency in liquid–liquid extraction through a temporary decrease in pH using high CO 2 partial pressure.…”

Selecting polymers for two‐phase partitioning bioreactors (TPPBs): Consideration of thermodynamic affinity, crystallinity, and glass transition temperature

“…33 The bioproduction of n-butyric acid is an attractive alternative to current petrochemical processes to supply food, fragrance, pharmaceutical, and chemical industries. [34][35][36] However, the accumulation of n-butyric acid results in low product titers and lost productivity, 9,37 and therefore a TPPB system may have practical utility. 38 This work extends previous binary (solute 1 polymer) PC prediction methods 30 by incorporating experimental water sorption data, enabling ternary polymer phase activity predictions (water 1 n-butyric acid 1 polymer).…”