This document discusses process control for bioreactors. It defines process control and its goals of producing quality products at low cost. Process control is important for process optimization, constant product quality, early problem detection, and quality assurance. Bioreactors can operate as batch or steady state processes, with the latter allowing for simpler feedback control. Sensors enable process monitoring while actuators make changes to the process. Common control schemes include open-loop, closed-loop, inferential, and combined feedforward and feedback control.

3. Process ControlGuidance of the process along a certain
path to produce a product that meets
predefined quality specifications
The Aim
To produce the product of interest at a
minimum of operating costs (ie. Increase
the cost/benefit ratio)

4. Reasons for Process Control
 Easier optimisation of the process
 More constant product quality
 Detection of problems and their
location at an early stage
 Greater quality assurance

5. (1) Bioreactor
Batch process
• significant changes of process variables over time
• requires more complex control
• requires experience with the process (feed
forward control)
Steady state processes (chemostat)
• constant process conditions
• more simple process control
• feedback control often sufficient

6. (2) Sensors (Measuring Devices)
 Enable monitoring of the state of the
process
– e.g. temperature, DO concentration,
biomass conc.
 Measurements can be on-line or off-line.

7. On-line Measurements
 Performed automatically
 Results directly available for control
 Monitored continuously
Off-line Measurements
 Require human interface
 Less frequent and usually irregular
 Best suited for checking and calibrating

8. Types of On-line Measuring Equipment
Physical Measurements
 Temperature
 Weight
 Liquid flow rates
 Gaseous flow rates
 Liquid level
 Pressure inside vessel
10.12 kg

9. (3) Actuators
 Devices which make the changes to
the process, e.g.
 Aeration pumps
 Stirrers
 Feed pumps
 Chemical dosing pumps
 Inoculation ports
 Recycle pumps

10. Basic Control Schemes
 Open-Loop Control (Feedforward)
 Closed-Loop Control (Feedback)
 Inferential control
 Combined feedforward and feedback
(model-supported control)

11. Devices that decide on the appropriate action
to be taken to keep the process running along
the desired path
◦ Computers
◦ “Biocontrollers”

12. Examples of feedback loops:
 Temperature control
 pH control
 Oxygen control (e.g. SND)

13.  The pattern of the manipulable variable is
predetermined, and directly adjusts the actuator
 There is no feedback from the process to the
controller
 Requires no measurement of the variable
 Often model-based  requires reliable model
 Large deviations of the process from the required
path are not corrected for
 Sounds very theoretical (examples?)

14.  Simplest type – digital
on-off switching, e.g. thermostat
 PID control (very common and
important)
 Fuzzy logic control, Adaptive
Controllers, Self learning systems
(not covered in this unit)

15.  Measurements give indirect information
about critical variables in the process (e.g.
biomass activity, biomass concentration,
substrate concentration etc.)
 Using the on-line measurements to estimate
the current state of the biomass
 state estimators (e.g. SOUR)
 Advantage: enables on-line control of a
variable that cannot be measured on-line
 Modelling plays important role

16.  Measurements give indirect information
about critical variables in the process (e.g.
biomass activity, biomass concentration,
substrate concentration etc.)
 Using the on-line measurements to estimate
the current state of the biomass
 state estimators (e.g. SOUR)
 Advantage: enables on-line control of a
variable that cannot be measured on-line
 Modelling plays important role

17. If the input signal does not immediately affect
the output  delayed action typical of on/off
controllers
Caused by things such as;
 feed pump too large for required dosage
 delay in sensor response
DO
mg L-1
Time
1
2

18. error
Controller Process
Actuator
Measured
output

19.  Conventional and most common type of control
scheme … “safest”
 Measurements from the process are used to
calculate a suitable control action
 Appropriate when the accuracy requirement is
higher
 Deviations between the variable and its setpoint
are used to change the process
 smaller deviations