Search

Several investigators recently have explored the use of cell population balance equation (PBE) models for the design of biochemical reactor control strategies. A major disadvantage of the PBE modeling approach is that the incorporation of intracellular reactions needed to accurately describe cellular processes leads to substantial computational difficulties. We investigate an alternative modeling technique in which the cell population is constructed from an ensemble of individual cell models. The average value or the number distribution of any intracellular property captured by the cell model can be computed from ensemble simulation data. To illustrate the basic procedure, a single cell model of yeast glycolytic oscillations is used to construct large cell ensembles for the investigation of cell population synchronization. The potential use of cell ensemble models for bioreactor controller design are discussed.

In this contribution some new aspects in the design of structured models for stirred tank bioreactors are discussed. Numerical solutions of the set of momentum equations for gas and liquid phase are presented The results of this computational fluiddynamic calculations (CFD) are then used for solving the material balances of a biological (oxygen sensitive culture of Bacillus subtilis ) and a physico-chemical (pH-calculation) model. In these models microbial and chemical reactions do not affect fluid dynamics, so that a strict separation of the solution of momentum and material balances is possible.

In this contribution new hardware and software concepts are presented for on-line supervision and control of fermentation processes. The concepts consist of components which are connected to instrumental network. With the aid of micro-robot systems the implementation of a high sophisticated analytic module is possible. Automation of sample preparation steps and the instrumental network of process control system, host computer lead to a better quality of control and state estimation. All components (software and hardware) are flexible and commercially available, so that their adaptation and transfer into industrial production processes is feasible.

A mathematical model has been developed to simulate the dynamics of key reactions of the catabolism in growing cells of Saccharomyces cerevisiae. The structured model considers the reactions of glycolysis, tricarbon acid cycle, pentose phosphate shunt and respiratory chain. The mathematical description of the metabolism comprises of 22 dynamic mass balances which contain 21 reaction rates. The proposed model is able to predict the time-dependent states of Saccharomyces cerevisiae under in-vivo conditions during metabolic features of short-time dynamics of glycolysis satisfactorily.

The paper deals with the application of a symbolic computer language (MAPLE V) for quantitative studies of stabilities of mixed populations which is an essential task for the design of various treatment process for xenobiotic compounds. The prominent feature of these powerful computation tool will be elaborated with the aid of two examples: (1) derivation of a general analytical solution of stability for mixed populations which consist of n-species competing for a common substrate with unstructured growth kinetics μ i ( c s ) ( i =1,. n ) and (2) stability analysis of a two-species mixed population whose mutualistic interaction during degradation of sulfanilic acid has been modelled with the aid of a structured model. The main emphasis of the studies lies in the use of symbolic computer languages for solving problems of coexistence in complex systems which are difficult to tackle with conventional analytical or numerical tools for stability analysis.

In recent years considerable emphasis has been placed on the application of computer control to substrate feeding in baker's yeast production. Many investigators have studied the dynamics of different control loops and also first steps have already been taken to optimize the control algorithms. As far as the experimental verification of different strategies is concerned, the published work is, however, restricted to laboratory scale only. From current practice in baker's yeast industry which is most often based on open loop control with fixed schedule for carbon substrate addition, it is well known that mixing of substrate is playing an important role. The effects of the dynamics of mixing process in mechanicaly stirred tanks upon the performance of baker's yeast fermentation with fixed schedule have been investigated earlier by using a circulation model (Bajpai and Reuss, 1982). In the present contribution this framework is used in conjunction with a closed computer control of carbon substrate feeding based on exhaust air analysis. From experimental results for computer controlled fermentation in 10 and 2 000 l scale a decrease of productivity with increasing circulation times of liquid is observed. These results can be confirmed with the model calculations.

The major bottleneck for computer-coupling of fermentation processes is the lack of reliable, sterilisable and robust sensors for process key variables like biomass, substrate and product concentrations. Principally there are two ways to overcome this difficulty: a) construction of new sensors like product specific electrodes for in situ application or b) automatic coupling of powerful analyser systems like HPLC. This work is aimed to present a new system for coupling automatically an HPLC-System to fermentors. Furthermore this system is able to measure automatically filtration characteristies of the fermentation broth. The relationship between filtration characteristics, the height of the filter cake and its density was applied to the determination of morphology parameters of Penicillium by Nestaas and Wang (1981). Similar to other attempts for coupling autoanalyser systems, their concept was based on a filter unit with backflushed filter media. Problems in the use of such concepts for industrial media had been described several times in literature. Therefore in this work the concept of renewable filters.is chosen.The filter media is a band of filter paper or membrane filter (dependinq on the process), which lies between the media support and the'filter body.The sequence of the different operations : sterilisation, sampling, filtration, HPLC-analysis of the filtrate cleaning and finally transportation of the filter media is computer controlled. During filtration the computer registers the data for weight of the filtrate (load cell) filtration time and height of the filter cake from a couple of reflection light barriers. Using this information! the computer predicts filtration and morphology parameters. Examples for the application of this automatic system will be discussed with the aid of fermentations with a mycelial organism and yeasts. In all of these examples the emphasis of discussion is placed on both filtration parameters and HPLC-coupling.

Oxygen supply is a critical factor for many aerobic fermentation processes. It is no wonder then, that the study of oxygen transfer and reaction has attracted many researchers. There is a tendency, however, to treat these two subjects in isolation. The present contribution will emphasize the concept of interaction of these two topics because both of them individually and jointly affect the overall performance of an aerobic process. The choice of an appropriate mathematical model with which effects of oxygen supply on microbial activities can be quantitatively explained is dictated by the nature of biomass suspension, reactor configuration and scale of operation. Some examples of practical interest will be presented to throw light upon the role of oxygen transfer gas-liquid, liquid-biomass, diffusion and reaction. Special emphasis is given to problems of feed back from biomass to oxygen transfer via physical properties of the broth. Because physical environment that biomass encounters in production scale can be drastically different to that in a pilot plant a mechanistic framework is developed in which the concept of diffusion depending oxygen consumption in mycelial broths is used in conjunction with local energy dissipation and circulation models for the liquid.