somniferum Ad/Ar: 1 (1992)
Datura
stramonium
1.2L ALR
Ad/Ar: 0.69Qg: 0.69 vvm N/A 0.05 Ballica & Ryu
(1993)Chenopodium 20 L ALR Qg: 0.155 vvm N/A 0.013 Fischer et al.
(1994)
rubrum Ad/Ar: 4
aestimated using equation (3), for STRs, under non-aerated conditions; using equation (4) for
ALRs; assumed broth density of 1000 kg m−^3.
bapparent viscosity of 2 cP assumed by Meijer et al. (1994) and applied here to the data of Ho et al.
(1995) for comparison purposes.
are of the order of 1 W kg−^1 , although levels can vary by an order of magnitude between
laboratory and large-scale vessels. Representative values for plant cell systems are
presented in Table 14.5. Reductions in power due to gassing are strongly dependent on
impeller geometry, fluid viscosity and aeration conditions. Gassed-to-ungassed power
ratios of about 0.4–0.6 are common for Rushton turbines, while values for up-pumping
impellers are higher, typically about 0.8 (Nienow, 1998).
To take account of the combined effects of aeration and agitation, the initial oxygen
mass transfer coefficient (kLa), i.e. as measured in cell-free medium, has been employed
as an indicator of the intensity of the environment (e.g. Kato et al., 1975; Leckie et al.,
1991a). Application of initial kLa values as a design criterion is limited by subsequent
variations in the prevailing kLa, due to increases in biomass levels and broth viscosity and
addition/accumulation of surfactants including anti-foams and extracellular proteins.
However, for individual cell lines, this approach can yield useful information.
More recently, the concept of a critical shear stress (e.g. Ballica and Ryu, 1993;
Kieran et al., 1995) or a critical energy dissipation rate has been superseded by the use of
cumulative energy dissipation (i.e. the product of energy dissipation rate and exposure
time) as a correlating parameter for cell damage. In an aerated, agitated bioreactor, a
representative specific power input of 0.5 kW m−^3 corresponds to a daily cumulative
energy dissipation level of approximately 4×10^7 J m−^3. However, evaluation of this
quantity depends on the choice of an appropriate dissipation volume (e.g. the entire
vessel
Bioreactor design for plant cell suspension cultures 431