Growth rate, specific definition

Experimental results of Herbert et al. are compared with predictions of Monod s model in Fig. 16. At long holding times, agreement of the model with experiment is good this is not the case at holding times near the critical, where there is a definite trend not predicted by the model. Thus, it appears that the maximum specific growth rate (//) is faster than that determined from batch experiments also the stoichiometric coefficient a changes as 6 approaches the critical. 

These rates have dimensions of [g T" h" ] or [kJ T h ] and are intensive quantities that may be substituted directly into the mass balance equation. On the other hand, these absolute rates may take on any value and are therefore not characteristic of the system. Comparable variables, which are biologically representative, are the so-called specific rates of production or utilization, which refer to the catalytically active mass (to a first approximation, the concentration of biomass, x, is taken as the dry cell weight). With this, one has the definitions of the specific rates for bioprocesses of Equs. 2.5a-f where, in each case, the specific rate has the dimension [h ]. For growth, the specific rate is p... 

By definition, Z 2/fg = // (specific growth rate) thus the number of bacteria after time t can be expressed by an exponential equaticm as follows ... 

In recent years, it has become obvious that the biofilm mode of growth is associated with a specific expression of genes and altered growth rates. To take into consideration the adoption of characteristic biofilm phenotypes by planktonic bacteria, a modern definition of a biofilm has been given by Donlan and Costerton (2002), who described a biofilm as a microbially derived sessile community characterized by cells that are irreversibly attached to a substratum or interface or to each other, are embedded in a matrix of EPS that they have produced, and exhibit an altered phenotype with respect to growth rate and gene transcription . 

It is important to emphasize the general character of this definition for the volumetric productivity (Py), since it includes all phases of a production cycle in a bioreactor, allowing an evaluation of the impact of bioreactor preparation time and duration of growth and production phases on productivity. As can be observed from Equations 19 to 22, for an industrial bioreactor with a given volume and operation mode, the volumetric productivity depends basically on cell concentration in the production phase and on the specific product formation rate (qp). 

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