The use of CO₂ for reversible pH shifting, and the removal of succinic acid in a polymer‐based two‐phase partitioning bioreactor

Abstract

BACKGROUND: Succinic acid (SA) is an intermediate in the production of commodity chemicals, but SA bioproduction has not yet been commercialized due to end product inhibition and high product separation costs. Two-phase partitioning bioreactors (TPPBs) can increase volumetric productivity through in situ product removal, although SA uptake by polymers requires a pH below the pK A2 of SA (4.2). It was proposed to reversibly reduce the pH with CO 2 sparging for absorption of SA, followed by nitrogen stripping to allow continued bioproduction after returning to metabolic pH levels.

Demonstration of in situ product recovery of butyric acid via CO2‐facilitated pH swings and medium development in two‐phase partitioning bioreactors

“…If a sequestering phase with a partitioning coefficient an order of magnitude higher was employed, and CO 2 sparging afforded a 40% increase in partitioning, this could make a marked improvement in extraction. ISPR of butyric acid has been demonstrated elsewhere (Wu and Yang, ), with similar studies proposed for succinic acid (Hepburn and Daugulis, ) and lactic acid (Krzyzaniak et al, ) and it is possible that the use of CO 2 –N 2 sparging could generally improve ISPR of organic acids by facilitating further pH‐dependent uptake. Previous work has shown that partitioning of an organic acid under acidified conditions can reach equilibrium in under 1 h (Hepburn and Daugulis, ) suggesting that this process is limited by pH and polymer‐solute affinity.…”

“…ISPR of butyric acid has been demonstrated elsewhere (Wu and Yang, ), with similar studies proposed for succinic acid (Hepburn and Daugulis, ) and lactic acid (Krzyzaniak et al, ) and it is possible that the use of CO 2 –N 2 sparging could generally improve ISPR of organic acids by facilitating further pH‐dependent uptake. Previous work has shown that partitioning of an organic acid under acidified conditions can reach equilibrium in under 1 h (Hepburn and Daugulis, ) suggesting that this process is limited by pH and polymer‐solute affinity. Thus in this specific case, improvements in yield and titre could be achieved through higher partitioning by both selecting polymers with increased polymer‐solute affinity and improvement of pH swings through the use of elevated CO 2 pressure.…”

“…To maximize the ability of CO 2 to decrease pH, minimization of buffering medium component concentrations is important; however, any reduction in component concentrations cannot negatively affect cell growth and acid production. Previous studies in our group determined that yeast extract and dibasic phosphate were responsible for the majority of the buffering capacity observed in media used for organic acid production (Hepburn and Daugulis, ). As shown in Figure , medium studies investigating the effect of yeast extract on growth and butyric acid production showed a direct relationship between yeast extract and microbial activity, with any reduction in yeast extract concentration showing a negative impact on both response variables.…”

“…However, further work must be done to confirm the validity of these corrections before they are fully adopted. Regardless, the polymers selected using these approaches have shown a marked improvement in partitioning compared to previous studies with organic acids (Hepburn and Daugulis, 2012), and further study of these strategies is merited. In the case of these experiments, as the low melting temperature of Pebax 1 2533 (130 C, Arkema datasheet) could prove problematic during steam sterilization, Hytrel 1 3078 was ultimately used for the ISPR studies as it shares the same soft segment (PBO), while possessing a higher melt temperature (177 C, DuPont datasheet; DuPont Co, 2013) making it suitable for autoclaving and thus was used for all subsequent experiments.…”

Characterization of transport through polymers for fracking fluid treatment and organic acid concentration in extractive membrane bioreactors

“…Several studies have used various grades of the DuPont polymer Hytrel™ for the treatment of a variety of wastewater types including high salinity synthetic tannery wastewater or for the bioproduction of commodity chemicals . Other studies have demonstrated the effectiveness of Hytrel™ beads in sequestering a variety of xenobiotic compounds for biodegradation in solid–liquid two phase partitioning bioreactors (TPPBs) .…”