Lecture 6: Bioreactor Monitoring and Control
Measurement of cell culture parameters
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On-line measurements using in-situ sensors
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Temperature, pH, Dissolved oxygen (DO), dissolved CO2
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Disposable sensors
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Measurement of gas flow rates
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Off gas analysis
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On-line measurements of metabolite and product concentration
Real-time monitoring of cellular activities
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Growth, metabolic, and production rates
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Oxygen consumption rate
Monitoring or estimating cell density
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Cell density probes
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Estimates based on metabolic rates
Process Control
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Principles of process control
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On-off (bang–bang) control
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feedback control
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PID control
On-Line Bioreactor Monitoring and Control
Overlay air
in the headspace to minimize CO2 + O2 accumulation
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Air, CO2, N2, and O2 are added at the same time based on the computer
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Mass flow controllers are digital and can be controlled by the computer
Agitator (RPM) is set by the control system
On-Line Bioreactor Monitoring and Control
Five Components
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Probes/Sensors
- measurement
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Meters/Amplifiers
gives you pH, temp, etc
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Mass Flow Meters
(MFCs) for Gas
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Pumps for Liquids
connected to the system
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Controller Unit
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Has I/O interface
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In amps or mvolts
Measurement of Temperature, pH, Dissolved Oxygen, Dissolved CO2
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Temperature in bioreactors is measured using
Resistance Temperature Detectors
(RTDs). The change in resistance due to temperature change is measured
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Basically a wire and the tip of the wire has a resistance, the resistance changes by
the temperature
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pH, dissolved oxygen, and dissolved CO2:
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Sensors (probes) are available for off-line and on-line measurements
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On-line measurements in bioreactors require sterilizable probes
Measurement of pH
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Calibration using pH buffers (pH 7.0 first, then either pH 4.0 or 10.0 buffer)
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Temperature compensation
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Maintenance and care during storage
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check the response time of the electrode
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Sterilization may change the calibration, typically one-point recalibration is performed
after sterilization
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Uses a glass probe
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pH buffer goes bad, has to change them or youll be in trouble for calibration
Measurement of Dissolved Oxygen (DO)
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Two types of sensors, Galvanic and Polarographic (more common)
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Calibration of DO probes (100% in air at 1 atm, electronic zero, and/or use of N2)
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Calibrated in air, 100% means 100% air saturation
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Polarization of the electrode (2-8 hrs) is needed
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Voltage is constant (-0.7 V), current is proportional to DO
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Temperature and pressure can change the calibration
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Maintenance: Membrane and electrolyte change
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Sterilization may change the calibration, typically one-point recalibration is performed
after sterilization
DO Probe Reading and Dissolved Oxygen Concentration
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DO probes are calibrated in air to read 100% air saturation (air is 21% oxygen)
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if DO probe is exposed to 100% oxygen, it will read 476% air saturation
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A reading of 50% saturation is equivalent to 10.5% oxygen
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Concentration of oxygen in mmol
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100% air saturation at 37oC and at 1 atm ~ 0.2 mM (depends on solution)
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Temperature and pressure should be included in the calibration of DO probe
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