Control systems in fermenter
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Control systems are necessary in fermenters to carefully monitor and regulate parameters like temperature, pH, oxygen levels, agitation and foaming. Sensors integrated directly into the fermenter provide real-time readings of these parameters to control systems which can activate mechanisms to precisely adjust the fermentation process as needed through elements like heating/cooling systems, pumps to add acids/bases and valves to control gas flow. Proper monitoring and control of these critical parameters is essential for optimal microbial growth and product formation.
Control systems in fermenter
- 1. Control systems in fermenter Temperature, Pressure, Aeration, Agitation, Foam, pH Dr. Dhanya KC Assistant Professor, Department of Microbiology St. Mary’s College, Thrissur-680020, Kerala
- 2. Control systems in fermenter Fermenter provides defined conditions for the formation of biomass and product Control temperature, pH, degree of agitation, oxygen concentration, foaming, etc Requires careful monitoring Physical parameters - Temperature, Pressure, Agitator shaft power, Foam Chemical parameters - pH, Redox, Oxygen, Exit-gas analysis, Medium analysis, etc. Monitoring equipment / sensor - information on fermentation progress - link to control system
- 4. Three main classes of sensor: 1. Penetrate into the interior of the fermenter e.g. pH electrodes, dissolved-oxygen electrodes 2. Operate on samples withdrawn from the fermenter e.g. exhaust-gas analysers 3. Do not come into contact with the fermentation broth or gases e.g. tachometers, load cells.
- 5. Three types of sensors in relation to application for process control: 1. In-line sensor - integrated part of the fermentation equipment Measured value directly for process control 2. On-line sensor - integral part of the fermentation equipment Measured value cannot be used directly for control 3. Off-line sensor - not part of the fermentation equipment Measured value cannot be used directly for process control
- 6. Temperature One of the most important parameter to be monitored and controlled mercury-in-glass thermometers, bimetallic thermometers, pressure bulb thermometers, thermocouples, metal-resistance thermometers or thermistors
- 7. Mercury-in-glass thermometer In small bench fermenters In larger fermenters – in a thermometer pocket - delays measurement Not suitable for automatic control or recording Electrical Resistance Thermometers Electrical resistance of metals changes with temperature Bulb of instrument - resistance element wound with sensing element Resistance element - Mica framework - very accurate measurement Ceramic framework - robust less accurate measurement. Sensing element - A platinum wire of 100 Ω resistance Reading - Wheatstone bridge circuit electrical4u.com
- 8. Thermistors Semiconductors - Mixtures of pure oxides of iron, nickel and other metals Large change in resistance with a small temperature change Reading obtained with a Wheatstone bridge Relatively cheap and stable ametherm.com
- 9. Temperature Control In a fermenter - Heat generated by microbial activity & through mechanical agitation If the heat not ideal - have to add or remove heat from the system Laboratory scale - extra heat provided by • thermostatically controlled bath • internal heating coils • heating jacket through which water is circulated In larger vessels - internal coils and cold water circulation moodle.beverleyhigh.net
- 10. Pressure measurement Pressure - crucial measurements - safety concerns Industrial and laboratory equipment - withstand a specified working pressure Devices needed - to sense, indicate, record and control pressure
- 11. Bourdon tube pressure gauge A partial coil having elliptical cross-section Tends to become circular with increasing pressure Difference between the internal and external radii - straightens out Pinion movement - pressure reading sika.net instrumentationtools.com avnet.com Piezoelectric transducer Solid crystals such as quartz - Piezoelectric effect Pressure changes - Change in crystal shape - electric charges Pressure measured by electrodes attached to crystal Diaphragm gauge Suitable for aseptic conditions Changes in pressure - movement of diaphragm capsule Monitored by a pointer
- 12. Pressure control Positive head pressure of 1.2 atmospheres –for aseptic conditions Pressure to be raised during steam-sterilization cycle Pressure maintained - regulatory valves and pressure gauges Safety valves At various places in vessels and pipe layouts Set to release pressure - when pressure increases gcmanway.com
- 13. Agitation control Monitor the rate of rotation (rpm) of the stirrer shaft - Tachometer Detection mechanisms Electromagnetic induction voltage generation Light sensing Magnetic force Laboratory fermenters - a.c. slip motor coupled to a thyristor control Large fermenters - gear boxes, size of wheels and drive belts, changing drive motor www.fluidmixingsolutionsindia.wordpress.com wmprocess.com
- 14. Control of oxygen and aeration Oxygen supplied - as air Laboratory-scale cultures - shake-flask technique Pilot- and industrial-scale - stirred vessels, airlift ferments, bubble column fermenter, etc. Maximum biomass production - Dissolved oxygen concentration greater than critical level
- 15. Measurement and control of dissolved oxygen Steam sterilizable oxygen electrodes - partial pressure of the dissolved oxygen Pressure changes and Temperature influences the reading Galvanic electrodes In small fermenters Lead anode, silver cathode, potassium hydroxide, chloride, bicarbonate or acetate electrolyte The sensing tip - teflon, polyethylene or polystyrene membrane Very sensitive to temperature fluctuations and limited life indiamart.com
- 16. Polarographic electrodes In pilot and industrial fermenters Silver anodes, platinum or gold cathodes, aqueous potassium chloride electrolyte Fast, very precise and pressure and temperature compensated Fluorometric sterilizable oxygen sensor Differential fluorescence quenching of a chromophore In response to partial pressure of oxygen Autoclavable, stable, gives reliable measurements. edaq.com alibaba.com
- 17. Tubing method A coil of teflon or propylene tubing through which helium or nitrogen passed Oxygen diffuses from medium - determined using paramagnetic gas analyser 2 to 10-minute lag, withstand repeated sterilization
- 18. The dissolved oxygen concentration increased by Increasing air flow rate Increasing agitation rate Increasing both Increase the ratio of oxygen to nitrogen in the input gas Agitation - increases oxygen transfer Disperse air into small bubbles Delays escape of air bubbles from liquid Prevents coalescence of air bubbles Decreases the thickness of the liquid film by creating turbulence.
- 19. Foam sensing and control Formation of foam – serious problems if not controlled Foam sensing and control unit - probe is inserted through top plate of fermenter Probe - stainless-steel rod insulated except at tip When foam rises and touches probe tip, a current is passed Current actuates a pump or valve Antifoam is released into the fermenter for a few seconds Mechanical antifoam devices Discs, propellers, brushes or hollow cones fluidhandlingpro.com ravenflo.com
- 20. pH measurement and control pH of an actively growing culture – never constant Rapid changes in pH - reduced - by design of media, incorporating buffers pH measurement - combined glass reference electrode Silver/silver chloride with potassium chloride or Friscolyt as electrolyte ON/OFF controller Signal received Pinch valve opened or a pump started Acid or alkali pumped into the fermenter for a short period of time Addition cycle followed by a mixing cycle After mixing cycle another pH reading
- 21. Control systems Process parameters - controlled using control loops Four basic components 1. A measuring element 2. A controller 3. A final control element 4. The process to be controlled Either Manual Control or Automatic control Automatic control systems – 4 types 1. Two-position controllers (ON/OFF) 2. Proportional controllers 3. Integral controllers 4. Derivative controllers
- 22. • Measuring element senses a process parameter • Generates a corresponding output signal • Controller compares signal with a predetermined set point value • Produces an output control signal. • Final control element receives the control signal • Adjusts the process by changing a valve opening or pump speed • Process property controlled.
- 23. www.horiba.com
- 24. References 1. Industrial Microbiology: An Introduction, M J. Waites, N L. Morgan, J S. Rockey, G Higton 2. Principles of fermentation technology, PF Stanbury, A Whittakker, SJ Hall, 1995, Butterworth-Heinemann publications