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
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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
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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
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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(O2)= C(O2)x PT
Where, P(O2)-Partial pressure of dissolved O2
C(O2)-Mole fraction of O2-in gas phase
PT – Total Pressure
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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
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8. GALVANIC ELECTRODES
• These are used in the small fermentors. It
have,
-lead anode
-silver cathode
-Electrolyte- Potassium hydroxide, chloride,
carbonate, Bicarbonate or acetate
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9. ADVANTAGES
• Measures slow changes in the oxygen
concentration
• Compact size
• Relatively low cost
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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
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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
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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
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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
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16. 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
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17. THERMAL TYPE PARAMAGNETIC
GAS ANALYSER

18. • 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
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19. • 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
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20. PARAMAGNETIC GAS ANALYSER

21. 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
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22. CONTROL
• Changes in oxygen levels is characterized by
oxygen transfer coefficient (i.e.) KLa
• This is important to measure because the
bubbles produced inside the reactor contains
oxygen
Where, KL is the liquid side mass transfer
a bubble surface available for diffusion
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23. • 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
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24. FACTORS AFFECTING CONTROL OF
OXYGEN IN BIOREACTOR
Changes in,
• Pressure
• Temperature
• Foaming levels
• Addition of surface active compounds like
fatty acid sulphonates, soaps etc
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25. FACTORS AFFECTING OXYGEN
TRANSFER RATE
• Gas bubble size
• Mixing
• Air flow rate
• Properties of liquid or medium used
• Measurement method
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26. 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
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27. CONTROLLER UNIT

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

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

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