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- Axelsson, Jan Peter, et al.
(författare)
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Substrate Control of Biotechnical Fedbatch Processes. Robustness and the Role of Adaptivity
- 1990
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Konferensbidrag (refereegranskat)abstract
- Results from experiments on laboratory scale fedbatch processes are presented as well as analysis and design of the control system. The main reason for control is to track the drastic growth in feed demand during a cultivation. Variations in the amount and quality of the inocculum makes precalculated dosage schemes of limited value to obtain reproducible cultivation conditions. Two processes have been studied on a laboratory scale, production of bakers' yeast, and production of the enzyme salicylate hydroxylase using a strain of bacteria. Direct measurement was used to monitor the feed demand. A regulator structure is proposed based on an observer for the exponentially growing feed demand. It can be viewed as a modified PID regulator around a dosage scheme, but it is less sensitive to errors in the dosage scheme than conventional PID control. The a priori knowledge of the feed profile is further relaxed by introduction of adaptation of the growth rate parameter. The obtained non-linear control system has a simple structure and stability is garanteed for a wide range of initial values using the technique of Liapunov function. The linearized system is analysed in the frequency domain and the adaptation is shown to have negligible influence on the loop phase margin. The adaptive regulator is tested in simulation against real feed profiles and shows good results.
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| 2. |
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| 3. |
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| 4. |
- Holst, Olle, et al.
(författare)
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Substrate Control in Fed-Batch Cultivations Using a Model-Based Modification of a PI-Controller
- 1992
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Ingår i: Proceedings of the 2nd IFAC Symposium on Modelling and Control of Biotechnical Processes.
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Konferensbidrag (refereegranskat)abstract
- A fedbatch process shows exponential growth under ideal conditions. To obtain good substrate concentration control it is necessary that the regulator can track an exponentially growing feed demand, and standard PI-control has to be supplemented with an estimated basic dosage to get reasonable control. However, an exponentially growing concentration error is impossible to avoid. An I-term could be interpreted as an observer of a constant demand, and we have proposed to replace it with a model-based observer for an exponentially growing demand. In the resulting controller the integrator is replaced by an unstable pole at s = μ, the specific growth rate, and the initial condition of this term is equivalent to the basic dosage part. The regulator can now track the exponentially growing feed demand without error. Pseudomonas cepacia was grown on salicylate as sole carbon and energy source. Salicylate is a toxic substrate, so it is important to have good substrate control. On-line measurement of salicylate concentration was carried out using a filtration system from which cell-free permeate was passed to a flow-through spectrophotometer. 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 like pump-failure, air-bubbles in the spectrofotometer, and low oxygen concentration induced growth-rate reduction.
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| 5. |
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| 6. |
- Larsson, L, et al.
(författare)
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Oxidation of Pyrite by Acidianus brierleyi: Importance of Physical Contact Between the Pyrite and the Microorganisms
- 1993
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Ingår i: Biotechnology Letters. - 1573-6776. ; 15:1, s. 99-104
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Tidskriftsartikel (refereegranskat)abstract
- Experiments were done in order to study the thermophilic archaebacterium Acidianus brierleyi during oxidation of pyrite (FeS2). The microorganisms were grown both separated from the pyrite by a membrane and in close contact with the pyrite. From the results it can be concluded that direct contact is needed for good growth of the strain studied. The obtained results indicated that the direct contact mechanism may be applied to oxidation of sulfidic minerals by A. brierleyi.
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| 7. |
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| 8. |
- Olsson, G, et al.
(författare)
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Desulfurization of Low Sulfur Coal by it Acidianus brierleyi: Effects of Microbial Treatment on the Properties of Coal
- 1993
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 33:2, s. 83-93
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Tidskriftsartikel (refereegranskat)abstract
- The effect of microbial desulfurization of two different low-sulfur coals by the thermophilic archaebacteria Acidianus brierleyi was studied with respect to the following properties of the coal: porosity, surface area, pore diameter, particle size, heating value, proximate and ultimate analyses as well as ash composition. About 35-40 percent of the sulfur was oxidized microbially. The microbial treatment only had a slight or negligible effect on most properties. Significant increases were seen with respect to oxygen content and volatile matter for one of the coals. The ash content had a significant increase in phosphorus which originated from the growth medium. Furthermore, jarosite formation was significant, especially for one of the coals investigated. For the same coal a large increase in porosity was seen and the surface area decreased significantly at the same time.
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| 9. |
- Olsson, Gunnel, et al.
(författare)
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Kinetics of coal desulphurization by Acidianus brierleyi
- 1993
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Ingår i: Chemical Engineering & Technology. - : Wiley. - 1521-4125 .- 0930-7516. ; 16:3, s. 180-185
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Tidskriftsartikel (refereegranskat)abstract
- Acidianus brierleyi was demonstrated to remove pyritic sulphur from coal. A. brierleyi was also found capable of catalyzing the removal of what is normally reported as organic sulphur from coal 171US34. A kinetic analysis was performed by assuming a first order reaction. The first order kinetics allowed a comparison with literature data for Thiobacillus ferrooxidans. Also, formation of jarosite was taken into account in the analysis. The simple first order kinetics was observed to fit the data on removal of sulphur satisfactorily.
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| 10. |
- Olsson, G, et al.
(författare)
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Microbial Desulfurization of Coal by T. ferrooxidans and Thermophilic Archaea
- 1994
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 40:2-3, s. 277-282
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Tidskriftsartikel (refereegranskat)abstract
- Several different microorganisms have been suggested for coal desulfurization. In the present investigation, the thermophilic archaea Acidianus brierleyi (DSM 1651), Sulfolobus acidocaldarius (DSM 639) and Sulfolobus solfataricus (DSM 1616) were compared with the mesophilic bacterium Thiobacillus ferrooxidans (DSM 583) concerning their capability of removing sulfur from coal. The desulfurization rate as well as the amount of sulfur removed by the microorganisms was studied. Two of the investigated microorganisms, Thiobacillus ferrooxidans and Acidianus brierleyi, were capable of oxidizing pure pyrite as well as oxidizing sulfur in coal. A kinetic analysis was performed assuming first order reactions. The rate constant for oxidation of pure pyrite by A. brierleyi was observed to be higher than for T. ferrooxidans, The values of the rate constants for sulfur removal from coal were comparable for the two microorganisms, but were higher than for oxidation of pure pyrite.
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