Substrate mass transport in two-phase partitioning bioreactors employing liquid and solid non-aqueous phases

Abstract

The mass transfer of phenol and butyl acetate to/from water was studied in two-phase partitioning bioreactors using immiscible organic solvents and solid polymer beads as the partitioning phases in a 5-L stirred tank bioreactor. Virtually instantaneous mass transfer was observed with phenol in water/2-undecanone, and with butyl acetate in water/silicone oil systems. The mass transfer of butyl acetate to silicone oil was rapid irrespective of the viscosity of the partitioning phase. When Hytrel® polymer beads were employed as the partitioning phase, substrate transport to the polymer was found not to be externally mass transfer limited, but rather internally by substrate diffusion into the polymer. In contrast to gaseous, poorly soluble substrates studied in other works, mass transfer of soluble substrates such as phenol and butyl acetate to the polymer was unaffected by impeller speed but rather by polymer mass fraction.

Mass transfer considerations in solid-liquid two-phase partitioning bioreactors: a polymer selection guide

“…The PC values for the various polymers are also shown in Table , and reflect the slightly different chemical compositions of the various grades of Hytrel. Partition coefficients determined at equilibrium for the Hytrel 8206 polymer sizes were all approximately 41, which is also close to values reported previously . The overall mass transfer coefficients (Table ) decrease as the polymer size increases (within Hytrel 8206), or as the diffusivity of the polymer decreases (across the various Hytrel grades), also as expected.…”

“…Although thermodynamic affinity considers the extent to which a polymer will sorb a solute, implementation of the TPPB technology platform also requires that the rate of uptake/release be sufficiently fast such that the overall process is reaction, rather than mass transfer rate, limited. This was seen in some of our earlier work, and was confirmed recently when we showed that although liquid–liquid TPPB systems may generally not be mass transfer limited because of the small droplet size of the dispersed organic phase, polymer TPPBs, operating above a few hundred rpms where external mass transfer limitations become negligible, may have significant mass transfer resistance due to the rate of solute diffusion within the polymer structure. Another recent article identified that the substrate mass transfer between the polymer phase and the aqueous phase may be too slow in a high rate biological system, and that a thorough investigation of mass transfer is urgently needed…”

“…As was previously demonstrated, as long as mixing in small scale bioreactors exceeds 200 rpm, the overall resistance to mass transfer of a solute between an aqueous phase and a polymer bead resides exclusively within the polymer itself, and depends on the diffusional path length and the solute diffusivity. Both aspects were independently examined via abiotic dynamic uptake experiments at 300 rpm for different polymer bead sizes of a single grade of Hytrel (8206) and three grades of Hytrel possessing different phenol diffusivities (8206, 3548 and 5544), in conjunction with data fits to the Crank Equation as previously described .…”

2,4-Dichlorophenol removal in a solid–liquid two phase partitioning bioreactor (TPPB): kinetics of absorption, desorption and biodegradation

“…This assumption is generally considered to be valid in two phase bioreactors operating with polymers, and a good experimental demonstration of its validity is given in a recent paper [25] with tests performed under different mixing conditions showing that the mass transfer was not externally controlled by the extent of mixing in the aqueous phase, but by substrate diffusion into the polymer.…”

Towards a continuous two-phase partitioning bioreactor for xenobiotic removal

“…The use of rationally-selected polymer tubing in C-TPPBs could extend the application to the treatment of broad classes of pollutants, arising from the "tailoring" of the polymer for specific contaminants as has recently been demonstrated using first principles' thermodynamic methods [11]. Previous studies of EMBs have mainly been focused on the removal of VOCs [12,13], and the bioreactors were operated with a silicone rubber membrane, which was effective for these hydrophobic compounds, but could be limited by the solvation capabilities of the membrane used [14], and the limited capacity of this single type of material (silicone rubber) to sorb other types of important organic molecules such as phenols [15].…”