Development and Verification of the Control System for Fed
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1. S4 Wo lt 88 Fig 3 Sequential diagram States description S1 the program comes to the state S1 in the beginning automatically starting state S2 S2 takes on when the operator enables to add the next dose automatically S3 S3 is the so called dosing state it is ac tive in the time when substrate is added S4 after the end of the dose the cycle comes to the state S4 The cycle waits in the state S4 up to saturation by oxygen decreases bellow 88 gener ally Wo control level minus 2 Then it comes to the state S1 In this manner it is ensured that the program does not respond to momentary overshoot around the 90 level but it waits for a real fall un der 90 Wo level that was used during the real experiments The control strategy described above was real ized by the program in MFCS win system The pro gram was written by defining on line calculations which are calculated every 5 seconds and their re sults are stored to the controller variables and the cyclic variables Every 5 seconds the program in MFCS win sends the control signal to the pump if to dose or not The upgrade of the control program in MS Excel Unfortunately the user interface of program MFCS win in version 1 1 does not allow the opera tor to change parameters of the control program easily but this function is essential during the ex periments These changes can be performed from MS Exc2. sion content was taken off to achieve the initial vol a 4 2 ml 123 mg I were examined See figure 9 ume of 1 5 in the cultivation time of 23 5 hours for the calculated phenol concentrations after the The figure 8 shows the course of saturation of dose taking into account the changes of medium the medium by oxygen during the cultivation Inter volume caused by dosing and sampling esting course of envelope of the wo declines is Several manual phenol doses were added in the probably caused by a number of influences For in beginning of the experiment before the saturation stance increasing Kya with increasing volume by oxygen declined under the executing level could have the effect on the course of the wo de Cak phn cone aber dose jng 66 V VOJTA et al Development and Verification of the Control System for Fed Batch Chem Biochem Eng O 16 2 59 67 2002 clines in cultivation time of 14 23 hours The effect of the addition of the antifoam agent is also evident e g in 25 hours The table 4 presents the average values attained in the individual sections of cultivation defined by different dosing conditions The phenol specific con sumption rate decreases during the whole cultivation as before disregarding the increasing amount of dose in the second half of the experiment This ob servation supports the idea that the rate of phenol degradation does not depend on amount of doses when dosing in th
3. j the quantity of dosage and then increased it again Decrease ofr bame oo i Ki Wij 40 ca Table 3 Conditions of the experiment 2 Cultivation time jh Stirrer speed 800 600 min Fig 9 Specific consumption rate of phenol dotted line or LLL min The calculated concentration of phenol in the reac eration min tor after the dose solid lines Concentration of phenol water 50 g i The amount of degraded phenol 32 33 g 343 94 mmol 90 to allow the system to take control over sub itial soli 1 Initial solid Lgl strate dosing At 800 min however extensive Final solid 7gf foaming took place and the cells entered the foam That is why it was necessary to add the antifoam oil which distinctively affects K a lower the stirrer To be able to add comparable substrate dosage speed and recalibrate the oxygen electrode as it was done in the previous experiment and also to prevent the oxygen limitation it was necessary to level up the aeration to 1 L L min and stirrer speed to 600 min The initial dose was 3 ml again With respect to higher oxygen supply the deg radation rate was much higher than in the previous cultivation Thus increments of phenol and NaOH In this case the final concentration of phenol after were higher then before and increase of the medium the dose in the fermenter was 100 mg I Next the volume was serious Therefore a palt of the Suspen doses 1 8 ml 51 9 mg I 3 6 ml 108 4 mg I
4. satu 60 V VOJTA et al Development and Verification of the Control System for Fed Batch Chem Biochem Eng O 16 2 59 67 2002 ration by oxygen At this moment one half of reac tor content was changed by fresh medium This work deals with implementation of a suit able method for the fed batch phenol biodegrada tion The goal was to create a user friendly and widely applicable control system that allows con trolling the fed batch phenol degradation in a way that it prevents the substrate inhibition The pro posed control strategy is based on dosing of phenol according to on line measurements of dissolved oxygen tension in the medium The main idea of this strategy can be described as follows When the phenol dose is added the cells start to utilize it as carbon source they respire and woz decreases Sub sequent increase of wo indicates total substrate de pletion so the conditions for addition of the next dose are fulfilled For this phenol fed batch biodegradation con trol strategy a control program was developed and implemented in MFCS win software package Be cause the user interface of the MFCS win program version 1 1 that was used does not allow the opera tor easily to change the parameters in the program during the experiment another cooperating applica tion was designed in MS Excel that allows changes of the important parameters in MFCS win during the experiments from new user displays These pa ramete
5. was used for inoculation of twelve Erlenmeyer flasks containing the same me dium The second cultivation proceeded 24 hours only The biomass was centrifuged and washed by sterile water For the fed batch experiments the BSM medium was used the composition of which is KH PO 4 30 g 1 K HPO 3 40 g I NH SO 2 00 g I MgCl 6 H O 0 34 g I plus trace elements 1 ml I FeSO 7 H O 0 5 mg I ZnSO 7 H O 0 5 mg I MnSO 7 H O 0 1 mg I CuSO 5 H O 0 1 mg I CoCl 6 H O 0 1 mg I NaBO 0 1 mg I Na Mo 0 0 1 mg I Conditions during the experiments The threshold level of pwo for the substrate dosing was set to 90 The initial volume of the medium was 1 5 The temperature was kept at 30 C and pH value at 5 2 The aeration was 0 5 and 1 L min and the stirrer speeds were 400 600 and 800 min The mass concentration of phenol water solution was 50 g I The doses of phenol were 0 4 1 33 1 8 2 4 3 3 6 4 and 4 2 ml The NaOH solu tion for pH value control had the concentration 0 1 mol F Note The doses of phenol were so small so that the substrate inhibition would not occur Measurement and control system The control system Fig 1 consists of the digi tal control unit Micro DCU 300 controlling a 2 litre bioreactor Biostat 2A B Braun Biotech In ternational and the personal computer with proces sor AMD K6 2 266 MHz and 64 MB of operation memory Both parts are connected
6. V VOJTA et al Development and Verification of the Control System for Fed Batch Chem Biochem Eng O 16 2 59 67 2002 59 Development and Verification of the Control System for Fed Batch Phenol Degradation Processes V Vojta J N hl k J Paca and E Komarkova Department of Computing and Control Engineering Department of Fermentation Chemistry and Bioengineering Institute of Chemical Technology Prague Technicka 5 166 28 Prague 6 Czech Republic E mail vaclav vojta vscht cz Original scientific paper Received September 15 2001 Accepted February 8 2002 The structure of a control system for the control of the fed batch phenol degradation is described In the software environment of MFCS win and MS Excel a control strategy for phenol dosing on basis of measuring the saturation of the medium by dissolved oxy gen was designed This strategy is able to prevent the substrate inhibition and to keep the biodegradation process in operation as long as possible In addition it enables the opera tor to change important parameters such as the amount of the dose of carbon and energy source and the control level of dissolved oxygen during the cell cultivation The program was experimentally verified under conditions of oxygen excess and oxygen limitation in fed batch cultivations of the yeast Candida tropicalis A correlation between the phenol degradation rate and the amount of phenol dose was especially studied The system
7. agen 100 mg l i 5 mgl TAT og ag Hi mg f i p w A ddiin af ant iia agent Lg x j presaj rae Cuklivalion time h Fig 6 The course of dissolved oxygen a i E ee ne Ls all La Li WW i n ee i x ih apa id DARREL TE ET w o oi fi i Hi y Hi j kaa Duhn e h Fig 7 Specific consumption rate of phenol dotted line and the calculated concentration of phenol in the reactor after the dose solid lines following doses could be reduced to 2 4 ml of phe nol That caused the resultant concentration equal to 71 7 mg I after the dose During the rest of the cultivation the 1 33 ml 39 mg F a 0 4 ml 11 mg 1 doses were examined See figure 7 for the cal culated phenol concentrations after the dose taking into account the changes of medium volume caused by dosing and sampling Figure 6 shows the course of saturation by oxy gen during the cultivation given by the imple mented control strategy Figure 7 shows specific phenol consumption rate against time together with the progress of the calculated phenol concentration after dosing Table 2 presents the average values attained in the individual sections of cultivation The effect of the oxygen limitation is manifested by a high differ ence of phenol specific consumption rate before and after 4 6 hours of the cultivation time As we can Si Cale phoma cone after dearer riy V VOJTA et al Development and Ve
8. e beginning of the experiment Next the user is allowed to choose the variables which will be in the graph plotted against cultivation time Finally the operator can choose an appropriate time span for the display of data One of the choices is to draw all recorded data the next allows to com prehend to the graph the certain number of the last V VOJTA et al Development and Verification of the Control System for Fed Batch Chem Biochem Eng Q 16 2 59 67 2002 63 Fig 5 Historical file display 64 V VOJTA et al Development and Verification of the Control System for Fed Batch Chem Biochem Eng O 16 2 59 67 2002 values only and the last choice is to display data from the selected past time interval The course of the variables is drawn after activation of the list that names Graph This graphical interface enables to the operator to operate the cultivation only through the displays in the created MS Excel application The experiments Several experiments of phenol fed batch degra dation by the yeast Candida tropicalis were carried out Besides testing the software control system the aim was to study the influence of the amount of phenol dose on the degradation rate in BSM me dium Here we will describe two experiments The first cultivation was carried out under the conditions of oxygen limitation while the second one under the conditions of oxygen in excess Both experi ments ran approximately 50
9. e range without limitation of oxy gen and without phenol limitation but on other pa rameters as intermediate accumulation Table 4 Phenol specific q and total q consumption rates q phenol Dosage m Medium Phenol q phenol volume consumption mgt g mmol g h mmol r h mmol h 100 1 81 1 56 14 28 3 46 4 01 92 3 2 42 1 67 25 27 3 19 4 62 51 9 3 82 1 65 142 31 2 12 4 89 94 9 6 20 1 61 16 62 0 99 3 81 108 4 7 16 1 67 18 72 0 88 3 77 123 10 45 1 79 101 33 0 64 3 73 Discussion In this study the main functions of the control program in MFCS win system controlling the dos ing of phenol in a way that prevents the substrate inhibition during its biodegradation were de scribed Next an upgrade to this system was devel oped Its benefit for the user is to change parame ters easily such as the amount of dose and the con trol level of oxygen by means of the displays in the MS Excel program The system was successfully tested in several actual cultivations The experiments proved full functionality of the control program including the communication of the MFCS win system with the MS Excel application The designed system enables easier and more sophisticated research of the fed batch biodegradations and it can also be used for various types of biodegradations It is commonly in use at Department of Fermentation Chemistry and Bioengi neering Institute of Chemica
10. el application cooperating with MFCS win by means of DDE communication Since the com munication is a two way kind it is not only possi ble to operate the control system but also to display actual and historical values on the displays in MS Excel according to the specific requirements Therefore the next goal was to create a suitable user interface for the simple and intuitive work with this program For cooperation of both the programs it is nec essary while creating the input variables in the MFCS win to determine from which cell and from which file of MS Excel will be its value acquired All measured variables pH value wo stirrer speed temperature amount of added phenol and NaOH and the cultivation time are sent from MFCS win to MS Excel The operator commands are sent in the opposite direction The commands can be switch on or off of the automatic dosing change the control level of dissolved oxygen change the amount of phenol dose and finally the manual dosing Fig 4 Moreover in MS Excel environment the opera tor can monitor the actual state of all measured vari ables the cultivation and real time on the historical file display Fig 5 and a graphical display He is able to choose any group of the displayed variables and set their logging periods The system MFCS win creates its own historical file and mea sured variables are stored every minute there The variables and the interval can be set only prior to th
11. fication of the Control System for Fed Batch Chem Biochem Eng O 16 2 59 67 2002 67 Nomenclature Wo dissolved oxygen tension in the medium Yphenot Phenol specific consumption rate mmol eth pheno Phenol total consumption rate mmol rh m biomass dry mass g DCU Digital Control unit DDE Dynamic Data Exchange GUI Graphical User Interface MFCS win Multi Fermenter Control System for Win dows NT S1 S2 S3 S4 states of the control program SCADA Supervisory Control And Data Acquisition References 1 Ruiz Ordaz N Hernandez Manzano E Ruiz Lagunez C J Cristiani Urbina E Galindez Mayer J Biotech nol Prog 14 1998 966 Lallai A Mura G Chem Eng J 53 1994 B47 B55 Wang S Loh K Enzyme Microb Technol 25 1999 177 Mordocco A Kuek C Jenkins R Enzyme Microb Technol 25 1999 530 Moreno J Buitron G Water Sci Technol 38 1998 219 Dikshitulu S Baltzis B C Lewandowski G A Bio technol Bioeng 42 1993 643 Brack G Volk N Roser M Neuking F Chem Tech 46 1994 186 L onard D Youssef C B Destruhaut C Lindley N D Queinnec I Biotechnol Bioeng 50 1999 407 Schr der M M ller C Posten C Deckwer W D Hecht V Biotechnol Bioeng 54 1997 567 Hughes S M Cooper D G Biotechnol Bioeng 51 1996 112 Braun B Biotech International Gmbh Micro DCU 300 use
12. hours and the level of the dissolved oxygen at which the next substrate dose was automatically added was set to 90 The measured variables were stored every minute to the memory file These variables were as follows total amount of added phenol total amount of added NaOH saturation of the medium by dissolved oxy gen temperature pH value and stirrer speed Table 1 Conditions of the experiment 1 Stirrer speed 400 min Aeration 0 5 L L min Concentration of phenol water 50 g j 15 21 g 161 81 mmol ligt 3g ie The amount of degraded phenol Initial solid Final solid Cultivation No 1 The goal of this cultivation was to examine the dependence of the specific phenol degradation rate on the quantity of the individual doses under the conditions of oxygen limitation That is why we added so high phenol doses so that the saturation by the oxygen during the degradation always de creased close to zero or to zero The effect of the gradually lowering substrate doses was investigated In the beginning the 3 ml phenol dose was selected It ensured the concentra tion of phenol in the fermenter immediately after the dose to be equal to 100 mg I Because phenol is fully consumed by the yeast before the next dose the 100 mg I concentration will never be ex ceeded In this way the dosing does not cause the substrate inhibition The saturation by oxygen de creased to 0 progressively and that is why the Tisselwed d
13. is commonly used at Department of Fermentation Chemistry and Bioengineering ICT Prague Keywords Control strategy aerobic degradation fed batch Candida tropicalis phenol Introduction In the twentieth century phenol pollutes the en vironment considerably It is present in many kinds of industrial waste from which it is eliminated by expensive but often ineffective physical or chemical methods A biodegradation has been studied as a possible alternativ due to relatively low expenses and complete xenobiotic mineralization On the other hand it is nonapplicable to solve the cases with high contamination level Many scientists deal with phenol biodegrada tion Ruiz Ordaz et al showed in his study that Candida tropicalis has high allowance against phe nol They show that growth of yeast can be inhib ited by phenol or it can even cause break up of cells or their parts Lallai and Mura also deal with inhibition and inhibition models of phenol degrada tion process They state that it is necessary to con sider temporary biomass growth on reactor walls while modeling Wang and Loh point out in his re search significance of metabolic intermediates in kinetics of phenol biodegradation They demon strate that intermediates play a critical role in mod eling of these processes Many researchers also deal with immobilized systems The advantage of immo bilized cells is that they are not washed out from the reactor and it was
14. l Technology Prague Although the system was originally developed for solving a special problem its applicability is much higher It can be applied not only for fed batch cultivation that requires this sort of process control but after little adjustment also in cases where there is a need to expand the scope of MFCS win by a new nonstandard functions of computational opera tional and also visual character During experiments it was experimentally veri fied that the oxygen supply has a significant effect on the phenol degradation rate For a high degrada tion rate it is necessary to eliminate the limitation by oxygen It is easy to control the biodegradation so that the limitation by oxygen does not occur only by the suitable setting of the amount of dose by us ing suggested control strategy From the experimental results it can be seen that the phenol specific consumption rate Tab 2 4 does not depend much on the amount of phenol dose This rate gradually lowered in the course of degradation although the control strategy managed to keep the concentration of phenol in the medium during the whole cultivation on the levels when the substrate inhibition did not occur Sequential de crease of the degradation rate was caused by other effects One of them could be the accumulation of intermediates in the reactor Using proposed control strategy in the excess of oxygen the average specific phenol consumption rate 1 63 mm
15. lized The operator must be able also to change process control parame ters simply such as the control of wo level when the next substrate dose is added and the quantity of individual dose Another required function ensures that the user can simply switch off and switch on the automatic quantitatively constant substrate dosing and in the meantime he can add through the user s interface several doses of various amounts according to his own consideration 62 V VOJTA et al Development and Verification of the Control System for Fed Batch Chem Biochem Eng O 16 2 59 67 2002 Implementation of the program in MFCS win To eliminate the substrate inhibition it was necessary to apply the sequential control approach in the program because phenol dosing according to the requirements above mentioned required differ entiation of several states within the dosing cycle The sequential dosing cycle depicted as sequential diagram in Fig 3 runs over always with every next substrate dose After adding the first phenol dose Wo decreases and then increases after depletion of substrate again Exceeding of the adjusted wo level shows that all phenol was consumed and the cycle comes to the state 1 again etc This ensures that phenol does not accumulate in the medium and therefore substrate inhibition does not occur El Automatic dosing Yes S2 Wo gt 90 Dosing End of dose
16. nergy does not grow and does not consume oxygen The saturation of media by oxygen wo is increasing to 100 Next the first phenol dose is added the cells start to utilize it they respire and w de creases Subsequent increase of wo indicates full substrate depletion and so the possibility for adding its next dose The manner of dosing is shown in fig ure 2 In this particular example the level of Wop at which the next dose of substrate was added was set on 80 In case of exceeding this level the phenol dose was added which caused decrease of wo to approximately 30 After utilizing the substrate dose wo started to increase again and the whole cycle was repeated The advantage of this manner of dosing is in the easy determination of the mo ment before the next dose when the concentration of phenol in the reactor is zero Since the next phe nol dose of an appropriate size is added just upon the previous one is completely consumed by the yeast this strategy prevents the substrate inhibition li Bi ii fj fl A 7 al r il i 40 1 r fT A oy yy A ka ti Zi 7 aa Dose of phenol 740 TM Tt 7 7 7 al Pa KAHI 10 Cuira ten fh Fig 2 The course of dissolved oxygen during the control The automatic dosing of substrate is therefore the main requirement for the control program which has to guarantee that the next dose is added just upon the previous one is completely uti
17. ol g h was achieved and the average total phenol consumption rate during the whole ex periment was 3 97 mmol g h These results are fully comparable with data mentioned in literature where the average total phenol consumption rates are between 0 62 and 8 42 for different microorganisms and methods of cultivation Fed batch process of phenol degradation con trolled by automatic dosing according to the satura tion of the medium by oxygen would be transformed to the process similar to continuous one Always be fore adding the next dose when the concentration of phenol in the medium is zero the amount of medium without the cells complete cells recycle of a quan tity that equals the previous dose would be taken away For improved efficiency of the process the possibility to set automatically the amount of phenol doses during the cultivation would contribute greatly The amount of the next phenol dose could be deter mined on line in order to reach the prespecified min imal value of dissolved oxygen concentration be tween two consecutive doses At the current level of computer control this method is easy to apply ACKNOWLEDGEMENT The work was financially supported by the Grant Agency of the Czech Republic Grant No 104 00 0575 by the fund No MSM 223400007 of Czech Ministry of Education and by the European Commission Fifth Framework Programme under contract No OLK3 CT 1999 00004 V VOJTA et al Development and Veri
18. proved that immobilized cells degrade phenol better at dilution rate Dei iy Most scientists are engaged in batch or contin uous phenol biodegradation This study belongs to the one that deals with fed batch phenol biodegra dation Brack et al treat especially models and optimal control of fed batch reactors for phenol bio degradation Other research workers come up with another ways of the control e g L onard et al laid hold of the fact that semialdehyde of 2 hydroxy muconic acid the main intermediate of phenol bio degradation colors the medium yellow The pro duction of this dye directly correlates with the bio degradation rate This relation between the change of the color and metabolic activity was used to pro pose the control strategy for optimal phenol degra dation The PI controller was applied to maintain stable concentration of phenol in the reactor at set point 0 1 g I it corresponds with specific growth rate of 0 3 h Schr der et al used CO concen tration in exhaust gases as controlled variable and dilution rate as manipulated variable to control this process Hughes and Cooper deal with self cycling fermentation processes They put to use values of fraction media saturation by oxygen which was continually monitored to control this bioprocess The next cycle always began after complete utiliza tion of phenol in the previous cycle This state was distinguished just from the course of medium
19. r manual 1996 Braun B Biotech International Gmbh MFCS win 1 1 user manual 1996
20. rification of the Control System for Fed Batch Chem Biochem Eng O 16 2 59 67 2002 65 Table 2 Phenol specific and total consumption rate 1230 bai bhi eae raw dam renr Faa ai PEI TE aia wii EE mj Medium Phenol i A volume consumption q e i 4 Daf 10 iy l mg I g l mmol ir mmol g h mmol I h Z P i 100 1 88 1 53 17 42 2 03 2 49 95 3 12 1 62 30 08 0 66 1 28 7 71 7 4 32 1 69 12 87 0 52 1 32 F Ww 39 5 16 1 75 35 00 0 41 1 22 BO 11 5 77 1 80 10 24 0 32 1 04 w P ELESE Kay shh gies el s pO ecient see in the table 2 the phenol specific consumption o 10 yi 3 rate decreases with the decreasing quantity of the Colivation time h dose However the intermediates accumulated in Hetan sohe the reactor might cause the inhibition of the degra pre e The Galera 0f Rissdived oxygen dation too So it is not possible to state with the certainty that the phenol specific consumption rate decreases with reducing amount of the dose as ta __ i Cultivation No 2 7 i a 10 4 a i ee a L The goal of this cultivation was to find out the D relation between the phenol degradation rate and 20 lt the amount of the individual doses under the condi jj r a tions of oxygen in excess To eliminate the simulta ie s r neous effect of the quantity of doses and other ef 1a ens fects on the biodegradation rate we first decreased a tsss
21. rs are for example the amount of substrate dose and the level of oxygen when the next sub strate dose is added The control system was experimentally verified under conditions of excess and limitation of oxygen in phenol fed batch degradation by the yeast Can dida tropicalis Furthermore correlation between the rate of phenol biodegradation and the amount of dose was studied In this paper the control system which was developed for this purpose will be de scribed followed by the results achieved in testing experiments Materials and methods Microorganisms medium and culture conditions In the experiments the yeast Candida tropicalis Ct2 from the biodegradation laboratory collection of prof Paca Department of Fermentation Chemis try and Bioengineering Institute of Chemical Tech nology Prague was used The yeast was isolated from the soil contaminated by phenol substances The cells were subsequently long range adapted to higher phenol concentrations The inoculum was prepared in two steps by cultivation in YNB me dium with glucose and phenol YNB base 1 7 g I NE S0 521 KH PO 1 g 1 MgS0 05 1 NaCl 0 1 g I solution of amino acid 1 ml I glu cose 4 g I phenol 350 mg The cultivation proceeded in Erlenmeyer flasks 500 ml 100 ml of medium on shakers at the temperature of 30 C The first cultivation was inoculated by resting cells from an agar solid medium and proceeded 36 hours This cell suspension
22. through a serial interface RS 422 Micro DCU 300 provides stan dard functions such as temperature and pH mea surement and control stirring and dosing The con trol software MFCS win Multi Fermenter Control System for Windows NT is installed on the PC in Windows NT 4 0 Workstation operating system en vironment It is a 32 bit Windows application which can exchange data with other Windows ap plications using Dynamic Data Exchange DDE protocol This software is used together with MS Excel program for the automatic bioprocess control The fermenter was equipped with a combined pH electrode the oxygen electrode Mettler Toledo the temperature resistance sensor Ptl00 and the V VOJTA et al Development and Verification of the Control System for Fed Batch Chem Biochem Eng Q 16 2 59 67 2002 61 Biostat 2A C T D Micro DCU 300 Micro DCU 300 mew ae 206 o moe ea mm Mans CEES Ry E Windows NT 4 0 MFCS win MS Excel F PC 1 1 Fig 1 Measurement and control system stirrer Two peristaltic pumps for dosing the NaOH and phenol dilutions into the fermenter were in stalled A hollow needle and a plastic hypodermic needle guaranteed the sampling Heating was pro vided by external heating wrapper cooling by the flow of water through the inner construction The airflow
23. was measured by means of the flow meter and set manually The oxygen electrode was calibrated by means of the sulfite dilution wo 0 and the level of oxy gen saturation in the fermenter under the aeration conditions of the cultivation was set up Con sidering the formation of the acid intermediates dur ing the cultivation the pH value was controlled by the addition of NaOH solution only according to the signal of the pH electrode The biomass concentra tion was determined by a gravimetric method and a photometric method by the analyzer Spekol 11 Carl Zeiss Germany measuring the absorption of diluted cell suspension at the wavelength 500 nm The probes thermometer pH electrode wo electrode in the fermenter are connected to Mi cro DCU 300 and through this unit their signals are consecutively monitored on the user displays in system MFCS win and in MS Excel on PC moni tor and archived in memory files Software MFCS win 1 1 which is installed on the control computer controls through Micro DCU 300 the pumps of substrate and base and sends setpoint val ues of temperature pH and stirrer speed into this unit Results The control strategy and requirements for the control program The proposed control strategy is based on on line measurements of dissolved oxygen tension in the medium and works as follows The yeast is in the bioreactor without phenol in the beginning and so it does not have a source of carbon and e
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