Bioprocess Kinetics

Abstract

Model building is considered here as an adaptive process (cf. Fig. 2.18): It involves stepwise fitting of the parameters, k, and discrimination of the function, j, itself. All of the models in this chapter should be considered as working hypotheses. The nature of formal kinetic descriptions means that other mathematical functions can always be found that serve the same descriptive function to within the precision of the measurements (see Esener et al., 1983). The lack of basic content in formal kinetic models in comparison with structured models (Harder and Roels, 1981;Roels and Kossen, 1978) can to some extent be compensated for by subsequent analysis (Esener et al., 1983;A. Moser, 1978bA. Moser, , 1984a.The basic kinetic scheme for a typical bioprocess is presented in Fig. 5.1 as the starting point for the analysis (A. Moser, 1980a). A chosen rate, somehow connected with the biological growth process, is plotted as a function of a chosen, relevant quantity-for example, a concentration, the pH, or the temperature. One observes a typical pattern offour regions: maintenance level endogenous metabolism, stimulation, inhibition, and toxicity. The typical biological optimum, with r max intermediate between two critical concentration values, is a consequence of opposing stimulatory and inhibitory factors. The influence of a transport limitation is schematically illustrated by the quantity representing an effective diffusion coefficient Deff in the liquid and/or solid phase. The goal of a formal kinetic analysis is description of the various factors influencing this course of events.To a large extent, the formal kinetic analysis techniques presented in this chapter relate to discontinuous batch operations. Even if the goal is a continuous operation, the batch process kinetic model serves as a start-up. The most significant element of a kinetic analysis is the time dependence of the macroscopic process variables mentioned in Chap. 2. Bacteria, molds, viruses, and yeasts all have different reproduction mechanisms, and formulating a structured kinetic model more closely related to the actual mechanism is a desirable goal. More structured models are desirable not only to deal with active cells but also to extend kinetic analysis to more complex situations involving inactive cells, mixed populations of cells, multiple substrates, and A. Moser, Bioprocess Technology

Oxygen control for an industrial pilot-scale fed-batch filamentous fungal fermentation

“…A linear relationship between viscosity and biomass concentration is adequate to represent experimental observations (data not shown). This is also in agreement with literature data for fermentations of Penicillium chrysogenum and Aspergillus niger [12]. Nevertheless, this relation can be improved by introducing the effect of dissolved oxygen to give:…”

“…In stirred bioreactors, the oxygen transfer coefficient, k L a, depends on the impeller characteristics and the rheological properties of the fermentation medium. The value of k L a can be determined experimentally by the dynamic OTR method (oxygen transfer rate measurement) that gives an average k L a value for the bioreactor [12]. Online measurements of oxygen transfer rate (OTR), viscosity, and DO are available, as well as off-line measurement of the total biomass x t .…”

Microbioreactors for Bioprocess Development

“…The resulting rapid recovery in growth was characterized by the steady increases in absorption and decreases in DO (Figure 3-8). This behavior is consistent with reported phenomena (Larsen and Dimmick, 1964) and kinetic models (Moser, 1988) that incorporate wall growth into the conventional well-mixed continuous stirred tank reactor (CSTR) model. …”

Growth Kinetic Model That Describes the Inhibitory and Lytic Effects of Phenol on Candida tropicalis Yeast

“…Three substrate inhibition models were tested for their ability to describe the relationship between the specific growth rate (μ) and the phenol concentration when the yeast cultures were grown at different initial concentrations of phenol. The tested models were those proposed by Andrews (34), Haldane, and a noncompetitive inhibition model (35). However, these models did not fit as satisfactorily as it was hoped.…”