Gas Hold‐Up and Oxygen Transfer in Three‐Phase External‐Loop Airlift Bioreactors: Non‐Newtonian Fermentation Broths

Abstract

The effects of solids loading on gas hold-up and oxygen transfer in external-loop airlift bioreactors with non-Newtonian fermentation media are discussed. Experiments were performed in two model external-loop airlift bioreactors with aqueous solutions of carboxymethyl cellulose (CMC) and xanthan gum representing non-Newtonian flows. Low-density plastic particles of 1030 and 1300 kg m-3 were used and the solids loading was varied in the range 0-20% (v/v). For the inelastic non-Newtonian CMC aqueous solutions, the presence of low-density solid particles slightly increased the riser gas hold-up, &gr, but decreased the volumetric mass transfer coefficient, k,a. On the other hand, #gr decreased but k,a increased with solids loading in the viscoelastic non-Newtonian xanthan gum aqueous solution. The extent of these effects depended on non-Newtonian flow behavior. Theoretical models of riser gas hold-up and volumetric mass transfer coefficient have been developed. The capability of the proposed models was examined using the present experimental data obtained in the model external-loop airlift bioreactors and the available data in the literature. The data were successfully correlated by the proposed correlations except the results for k,a coefficient in the xanthan gum solution.Key words: three-phase external-loop airlift bioreactor, non-Newtonian fermentation broths, gas hold-up, volumetric mass transfer coefficient. a A d Ar C CAL D Dd D r EXP 9 Hd kI. NOTATION Specific surface area (m-') Downcomer cross-sectional area (m2) Riser cross-sectional area (m2) Coefficient Calculated Diffusivity (m2 s -l ) Downcomer diameter (m) Riser diameter (m) Experimental Gravitational acceleration (m s -2, Length of vertical portion of downcomer (m) Liquid-phase mass transfer coefficient (m s -') K R n Usgr V L 3 & PI P S PI 0 z +v * To whom correspondence should be addressed. 325 Consistency index in a power-law model (Pa s") Effective consistency index in a power-law model for (solid-non-Newtonian liquid) two-phase system (eqn (2)) (Pa s") Flow index in a power-law model Superficial gas velocity in the riser (m s -l ) Liquid volume (m3) Shear rate (SKI) Energy dissipation rate per unit mass (W kg-') Liquid density (kg m-3) Solid density (kg m-3) Effective density of (solid-liquid) two-phase system (eqn (2)) (kg m-3) Surface tension (N m-') Shear stress (Pa) Riser gas hold-up J . Chem. Tech. Biotechnol. 0268-2575/96/$09.00 0 1996 SCI. Printed in Great Britain

Rheology, oxygen transfer, and molecular weight characteristics of poly(glutamic acid) fermentation by Bacillus subtilis

“…Other fermentation systems are also used, such as airlift bioreactors (Roukas and Mantzouridou, 2001;Kawase and Hashimoto, 1996;Moo-Young et al, 1987) and bubble columns (Godbole et al, 1984). However, there is an upper viscosity limit for bubble columns (Van Reit and Tramper, 1991), beyond which the oxygen mass transfer decreases drastically.…”

“…4a,b). It is well known that k L a is dependent on many factors, including viscosity, the presence of solids, the presence of surfactants, and the ionic strength of the liquid phase (Kawase and Hashimoto, 1996;Ozturk and Schumpe, 1987;Godbole et al, 1984). The presence of microbial cells and PGA may influence the physical properties of the gas-liquid interface during the course of fermentation, and therefore influence the volumetric mass transfer coefficient, k L a.…”

Flow and mass transfer of fully resolved bubbles in non‐Newtonian fluids

“…Similar observations can be made for the properties needed to precisely predict transport of metabolites, nutrients, or CO 2 . So far, most studies are based on experimental investigations, which are usually interpreted with simple theoretical models 3, 4, 8–11. First‐principles methods to predict mass‐transfer coefficients, transport rates, and other parameters in non‐Newtonian fluids have not been reported so far.…”

Prediction of mass transfer coefficients in non‐Newtonian fermentation media using first‐principles methods

“…Most data on non-Newtonian liquids are derived from experimental studies, which are usually interpreted with simple theoretical models (Doran, 1999;Jin et al, 2005;Kawase and Hashimoto, 1996;Kieran et al, 1997;Li et al, 2004;Sánchez et al, 2002). However, so far there have been no reports on the prediction of mass transfer coefficients in non-Newtonian fluids based on first-principles methods.…”