Measurement and control of dissolved oxygen in the bioreactor

oxygen level in bioreactors-measurement methods-Types of electrodes used-Tubing methods-Control methods-references

1. PRESENTATION ON MEASUREMENT AND CONTROL OF DISSOLVED OXYGEN IN A BIOREACTOR PRESENTED BY: G.DILIP KUMAR M.EVANGELIN FLORA S.GAYATHRI

2. INTRODUCTION Bioreactors are used to grow cells in the suitable media These cells are sensitive to various conditional changes in the culture such as agitation , oxygen levels , nutrients , pH etc 11.09.19 1

3. Cells that are present in the bioreactors receives oxygen in the form of Dissolved oxygen(DO) The oxygen molecules reaches the bioreactor through sparger It is essential to measure and control the level of oxygen inside the fermentor to maintain the optimum level of the media inside bioreactor 11.09.19 2

4. MEASUREMENT There are two types of electrodes used for monitoring the levels of oxygen inside the bioreactor They are (i) Galvanic and (ii) Polarographic The details of these electrodes are given by Lee and Tsao in 1979 11.09.19 3

5. Galvanic and Polarographic electrodes These electrodes measures the partial pressures of the Dissolved oxygen in the bioreactor It is determined by the following equation, P(O 2 )= C(O 2 )x P T Where, P(O 2 ) -Partial pressure of dissolved O 2 C(O 2 ) -Mole fraction of O 2 -in gas phase P T – Total Pressure 11.09.19 4

6. (a) Galvanic (b) polarographic

7. The reading is expressed in % , partial pressure of oxygen is determined app 160 mmHg If the pressure varies in the broth composition, there will be change in the electrode readings Changes in atm pressure causes 5% back pressure and increase in the readings The solubility of oxygen in aqueous media is influenced by its composition 11.09.19 5

8. GALVANIC ELECTRODES These are used in the small fermentors . It have, - lead anode - silver cathode - Electrolyte - Potassium hydroxide, chloride, carbonate, Bicarbonate or acetate 11.09.19 6

9. ADVANTAGES Measures slow changes in the oxygen concentration Compact size Relatively low cost 11.09.19 7

10. DISADVANTAGES Shows slow response of the order of 60 seconds to achieve 90% reading Very sensitive to temperature fluctuations Electrodes have limited life time because of the corrosion of anode 11.09.19 8

11. POLAROGRAPHIC ELECTRODES Bulkier than galvanic electrodes used in pilot production fermenters The ports is of 12 , 19 or 25 mm in diameter. Removable one needs 25mm port It constitutes of, - Silver anodes-negatively polarized -Reference cathodes- Platinum or Gold -Aqueous potassium chloride -Electrolyte 11.09.19 9

12. ADVANTAGES: Precisely measures even when temperature and pressure are compensated Maintenance costs are lower and the membrane should be replaced DISADVANTAGES: It initially costs 600% more than galvanic 11.09.19 10

13. PHASE FLUOROMETRIC OXYGEN SENSOR

14. The sensor utilizes different quenching of fluorescence life time of a chromophore It is possible to obtain a correlation between fluorescence life time and partial pressure of oxygen 11.09.19 11

15. TUBING METHOD The probe consists of the coil membrane , teflon or polypropylene PARAMAGNETIC GAS ANALYSER : -The oxygen diffuses from the fermentation medium through tubing wall enters inert-gas stream This tubing withstands repeated sterilization for upto 1000 hours 11.09.19 12

16. THERMAL TYPE PARAMAGNETIC GAS ANALYSER

17. Determines oxygen concentration Flow through ring- Detector component Paramagnetic oxygen content of the sample is attracted by magnetic field to the central glass tubes The heated resistors are connected to wheatstone bridge to measure resistance Cool oxygen in incoming gas flow will now get attracted and displace hot oxygen 11.09.19 13

18. This displacement produces convection current This flow rate is the function of oxygen concentration and be detected by resistors The entire gas flow cools both A and B windings 11.09.19 14

19. PARAMAGNETIC GAS ANALYSER

20. PARAMAGNETIC GAS ANALYSER Determines oxygen concentration Has strongest affinity for a magnetic field Analyzers used may be deflector or thermal type The magnetic force acts upon the dumb bell test body that is free to rotate about the axis Magnetic force created around test body is proportional to oxygen concentration When test body swings out of magnetic field, correct electrostatic force must be applied 11.09.19 15

21. CONTROL Changes in oxygen levels is characterized by oxygen transfer coefficient (i.e.) K L a This is important to measure because the bubbles produced inside the reactor contains oxygen Where, K L is the liquid side mass transfer a bubble surface available for diffusion 11.09.19 16

22. It is necessary to keep DO above certain levels Oxygen requirement is most important in bioreactors for the cells to survive If it is above the optimum level, then it is toxic to cells If they are below the optimum condition, then the supply of oxygen will not be sufficient for them to grow 11.09.19 17

23. FACTORS AFFECTING CONTROL OF OXYGEN IN BIOREACTOR Changes in, Pressure Temperature Foaming levels Addition of surface active compounds like fatty acid sulphonates, soaps etc 11.09.19 18

24. FACTORS AFFECTING OXYGEN TRANSFER RATE Gas bubble size Mixing Air flow rate Properties of liquid or medium used Measurement method 11.09.19 19

25. PID CONTROLLER It is a continually monitored control which is used for oxygen controlling There are various factors under this such as, - Process variations - Process model 11.09.19 20

26. CONTROLLER UNIT

27. Process variations Dissolved oxygen tension of 100% corresponds to the solution where the partial pressure is in equilibrium The equation can be written as,

28. Feed Forward Feed forward in the bioreactor used to improve control performance From the recorded process data dynamic relation between feed rate and stirrer speed in relation with control can be monitored 11.09.19 21

29. Process model This determines the mass balance for the dissolved oxygen in bioreactor Equation can be represented as,

30. REFERENCE https://bioprocessintl.com http://nptel.ac.in (DO PARAMETER IN BIOREACTOR) https:/ /youtu.be/y7zbmlEaPas 11.09.19 22