734 Abstracts

growing in dispersed form in submerged cultures. For PeniciUium chrysogenum biomass, volumes of cytoplasmic and vacuolised or degenerated regions can be converted successfully into dry weight estimations. The vacuolation can be characterised in detail for physiological studies. Although off-line, the method is rapid enough to be considered for use as a process control tool. Links between cytoplasmic content and antibiotic production are being sought. The method might be used to provide data for structured models of fungal fermentations, and for control of product formation in those fermentations.

074 Modelling of Filamentous Microorganisms J. Nielsen, pp 45-52

Based on reported mechanisms for filamentous growth, a simple morphologically structured growth model is set up. The model is based on a structuring of the biomass into three types of cells: apical cells, subapical cells, and hyphal cells. The model can describe the morphology of filamentous microorganisms, e.g. the hyphal growth unit, and it is compared with experimental data for the morphology of Geotrichum candidum grown in a submerged culture.

075 Structured Segregated Model for Optimal Profit Control of Baker's Yeast Production J.Q. Yuan, K.H. Bellgardt, pp 53-58

In fed-batch production of baker's yeast the sugar flow profile must regard the Crabtree-Effect and the oxygen transfer capacity of the reactor to avoid loss of yield. This paper describes optimal fed-batch control strategies which also consider the final product quality. Optimization is based on a three-part mathematical process model: the structured growth model, the age- distribution model and the cost model. New parts of the model are presented and simulation results are compared with experimental data. The optimum operation is then investigated. Unlike usual control trajectories, consideration of the quality criterion leads to a pulsed control of substrate flow. The model was verified in laboratory-scale experiments.

076 Modelling the Cyathus Striatus Fermentation Process: Comparison of Three Methods N.A. Jalel, V. Hags, A.R. Mirzal, R. Boeker, A. Munack, J.R. Leigh, pp 59-64

and dissolved hydrogen concentration. The manipulated variable is the dilution rate. Although the responses are model-specific, the methodology can be applied to an actual lab scale or industrial scale bioreactor. The study reveals the intrinsic behaviour of the balances between the assumed bacterial species. The methodology demonstrates the usefulness of advanced control

• techniques to get a better understanding of a process, even if the controller designs are based on incomplete knowledge.

078 Issues in the Optimization, Estimation and Control of Fed-Batch Bioreactors Using Tendency Models P. Tsobanakls, S.H. Lee, J.A. Phillips, C. Georgakls, pp 71-76

The tendency modeling approach for optimization, estimation, and control is applied to bioreaetors. This approach uses a "tendency" or "grey" model based on the available fundamental knowledge of the process and emphasizes the incorporation of new process data such as the power, the oxygen transfer capacity, and the rheological characteristics of the broth. The techniques is demonstrated on simulation studies and preliminary experimental results of penicillin fermentation. The model can be updated periodically, utilizing data collected both on-line and off-line. The updated model can be used off-line to develop optimal feeding policies. On-line, a Kalman filter can utihze the tendency model to estimate poorly, infrequently, or unmeasured states.

079 Substrate Control In Fedbatch Cultivations using a Model-Based Modification of a PI-Regulator P. Hagander, O. Hoist, pp 77-82

A fedbatch process shows exponential growth under ideal conditions. Good substrate concentration control requires that the regulator can track an exponentially growing feed demand. This paper proposes replacing an I-term in standard PI-control with a model-basexl observer for an exponentially growing demand. The regulator can now track the demand without error. Pseudomonas cepacia was grown on salicylate as sole carbon and energy source. On-line measurement of salicylate concentration was carried out using a filtration system. Introducing more instability into the controller requires attention to the anti-windup features. No such problems were found during the cultivations or in simulations of the effect of conceivable disturbances.

In controlling a fermentation process, the most difficult aspect is that of finding a suitable model. This paper describes three different approaches to modelling the Cyathus Striatus fermentation process. First, conventional biotechnological wisdom has been used to develop a set of equations whose parameters have been determined numerically. Second, a linear multivariable model has been fitted to experimentally obtained data. The equations have been integrated to generate a set of time-varying equations. Thirdly, neural nets are trained on experimental data. The approaches are compared in regard to their utility in state estimation and in trajectory- following control.

077 An Analysis of the Impact of Controlled Variables Selection on the Operation of Anaerobic Digestion Processes M. Perrier, D. Dochain pp 65-70

Different adaptive nonlinear controller designs are evaluated for the operation of the anaerobic digestion process. The selected controlled variables are the Chemical Oxygen Demand, propionate concentration,

080 Can we Identify Biotechnical Processes? G. Bastin, L. Chen, V. Chotteau, pp 83-88

The identification problem of biotechnological processes is threefold: (i) determination of the number of biological reactions, (ii) identification of the underlying reaction network, (iii) identification of the kinetics. In most practical cases, these three parts of the identification problem can be completely deeoupled from one another.

081 Some Improvements in the Identification of Bioprocesses A. Munack, pp 89-94

In identification of dynamic models for bioteelmical processes, one is sometimes confronted with the situation, that models with different structure may be equally well fitted to the measured data. Some possibilities for experiment design in order to detect the most suitable model structure are presented and applied to a growth model of Cyathus striatus.