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

Abstract

Production of organic acids in solid-liquid two-phase partitioning bioreactors (TPPBs) is challenging, and highly pH-dependent, as cell growth occurs near neutral pH, while acid sorption occurs only at low pH conditions. CO2 sparging was used to achieve acidic pH swings, facilitating undissociated organic acid uptake without generating osmotic stress inherent in traditional acid/base pH control. A modified cultivation medium was formulated to permit greater pH reduction by CO2 sparging (pH 4.8) compared to typical media (pH 5.3), while still possessing adequate nutrients for extensive cell growth. In situ product recovery (ISPR) of butyric acid (pKa = 4.8) produced by Clostridium tyrobutyricum was achieved through intermittent CO2 sparging while recycling reactor contents through a column packed with absorptive polymer Hytrel® 3078. This polymer was selected on the basis of its composition as a polyether copolymer, and the use of solubility parameters for predicting solute polymer affinity, and was found to have a partition coefficient for butyric acid of 3. Total polymeric extraction of 3.2 g butyric acid with no CO2 mediated pH swings was increased to 4.5 g via CO2 -facilitated pH shifting, despite the buffering capacity of butyric acid, which resists pH shifting. This work shows that CO2 -mediated pH swings have an observable positive effect on organic acid extraction, with improvements well over 150% under optimal conditions in early stage fermentation compared to CO2 -free controls, and this technique can be applied other organic acid fermentations to achieve or improve ISPR.

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

“…To be competitive with petrochemically derived organic acids, cost reduction is a critical consideration (Kurzrock and Weuster‐Botz, ), and both increased biological performance and improved acid recovery would generate significant benefits, whether through increased productivity, or reduced separation costs. Solid–liquid two‐phase partitioning bioreactors (TPPBs) (Daugulis et al, ) can be used to achieve both these goals simultaneously, by absorbing an end‐product into an inexpensive, easy‐to‐handle absorptive polymer phase, which is typically added directly to the bioreactor, achieving in situ product recovery (ISPR) (Craig and Daugulis, ; Dafoe and Daugulis, ; Daugulis, ; Khan and Daugulis, ; Morrish and Daugulis, ; Peterson and Daugulis, ; Prpich and Daugulis, ). Aside from the ease of recovery afforded by physical separation of solid polymers from fermentation broth, the reduction of end‐product concentrations reduces end‐product inhibition (EPI) during a fermentation, which in turn can improve productivities, yields and titers.…”

“…Partitioning will occur only with protonated species of a given acid (Kertes and King, ), and thus partitioning improves significantly at lower pH values, which can be problematic for fermentations, as they often require near‐neutral pH values during operation. To overcome these mutually exclusive pH values, previous work (Peterson and Daugulis, ) focused on the use of CO 2 sparging during butyric acid fermentations with Clostridium tyrobutyricum to lower pH values temporarily while recycling reactor contents through a column packed with an absorptive polymer, after which the pH could be readily returned to near neutral values. Unlike reactive extraction techniques, which employ toxic extractants to recover organic acids, extraction through CO 2 ‐mediated pH swings does not result in cell toxicity (Peterson and Daugulis, ) and these swings are easily and quickly reversible (Hepburn and Daugulis, ).…”

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

“…Our recent study of polymer–solute thermodynamics found that UNIFAC‐vdW‐FV and Flory–Huggins‐based models were able to predict the equilibrium absorption (PC) of solutes into a single amorphous material, poly( n‐ butyl acrylate). One purpose of this study was to examine the ability of the same thermodynamic models to describe the sequestration of n‐ butyric acid (recently produced in a TPPB system) into a broad range of amorphous materials that were screened from a standard polymer solubility database . The bioproduction of n‐ butyric acid is an attractive alternative to current petrochemical processes to supply food, fragrance, pharmaceutical, and chemical industries .…”

Separation of waste-derived volatile fatty acids from fermented wastewater

“…[24,45,46,76,[85][86][87] Most of these studies have used a solvent already known in the literature to emphasize the importance of the innovation in the operation. Some other studies intended to facilitate the solvent regeneration stage by modifying the relatively simple processes shown in Figure 1, Figure 2 and Figure 3 to significantly improve their efficiencies (see section 4.2).…”

“…In the literature, this practice has been applied on extraction of some carboxylic acids. [24,45,46,85,87,97] In 1983, when Urbas patented a process for enhancing HAc extraction [45], he claimed that by applying any form of CO 2 , solid or gaseous (either atmospheric or pressurized), HAc extraction from a calcium acetate solution can be facilitated.…”