# Redox potential measurement (ORP)

• ORP measurement in MINIFOR fermentor – bioreactor with redox measurement unit and combined redox, pH & temperature probe
• No additional connectors, cable or side ports needed for redox implementation
• Redox potential measured in mV
• Regulation of redox potential and data saving by SIAM fermentation software
• Possibility to control the fermentation process at a desired redox value (e.g.: automatic pumping of reducing agent to maintain redox value negative)

## LAMBDA REDOX measurement

LAMBDA REDOX measurement unit allows the measurement of the Red-Ox potential and the digital transfer of the data to the PC via RS-485 interface. The measured data can be visualized and recorded, for example by the fermentation software SIAM. The redox potential (ORP) is measured in mV. The working range of the LAMBDA REDOX measurement unit is from -999 to +999 mV. Negative values are indicated by lighting of the yellow “MINUS” LED.

The redox measurement unit does not require any additional connector, cable or side neck. However, the MINIFOR fermenter-bioreactor must have been electronically equipped with the redox option in advance. The output RedOx signal is then provided on the “PUMP” socket at the rear side of the MINIFOR laboratory fermentor-bioreactor control unit.

With the SIAM industrial fermentation software, it is possible to visualize, regulate and record data of the redox potential. It is also possible to set-up a fermentation experiment with constant redox value by PID controller using SIAM software.

## Nernst equation

The measurement of Red-Ox potential can be made with the laboratory fermenter-bioreactor LAMBDA MINIFOR, using a sterilizable combined pH/temperature probe with an additional Pt electrode fixed on its glass body. The combined redox, pH & temperature probe can be connected to the MINIFOR fermenter-bioreactor in the same way as the standard pH probe.

The electrode behaviour is defined by the Nernst equation:

$E&space;=&space;E_{0}&space;-&space;\frac{R\cdot&space;T}{n\cdot&space;F}ln\frac{C_{ox}}{C_{red}}$

where,
E = measured potential (mV) between the platinum and the reference electrode
Eo = measured potential (mV) between the platinum and the reference electrode at a concentration of Cox = Cred
R = Universal gas constant (R = 8.314 J mol-1 K-1)
T = Temperature in K (Kelvin), where T (K) = 273.15 + t°C and t is the temperature of the measured solution
F = Faraday constant (96485 C mol-1)
n = electrical charge of the ion
Cox = oxidant concentration in moles/L
Cred = reductant concentration in moles/L

## Monitoring fermentation with ORP or Eh

The redox potential measurement represents the sum of the potentials of all oxido-reduction processes in a particular fermentation. Redox potential (ORP or Eh) can be used to monitor the progress of fermentation by the detection of metabolic activity and/or growth of anaerobic as well as aerobic microorganisms (e.g.: Methanospirillum, Methanocorpusculum, Thermotoga sp., Proteus vulgaris, Clostridium paraputrificum, Candida utilis, Lactobacillus sanfranciscensis, Lactococcus lactis, Clostridium acetobutylicum, Acetobacterium malicum, Candida guilliermondii, etc.). The redox potential also used as a key control parameter in the on-line estimation of viable cells in a hybridoma culture at various DO levels.

LAMBDA offers a possibility to regualte the fermentation process based on the desired redox potenial using the SIAM fermentation software, for example: automatic pumping of reducing agent to maintain the set negative redox value.