this presentation is about the control and measurements of pH and red-ox potential in a fermenter or a bioreactor. there are several parameters that should be monitored in order to get the maximum productivity in a fermenter. in that few parameters are very much important to measure as well adjust to its optimum level to get the high yield.

1. PH, Redox Potential control
And Measurements In A
Fermenter
Done by
T.Blessy
E.Brasilda
D.Dhanuprabha
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2. Introduction
1. Fermentation systems must be efficiently controlled in order to
optimize productivity and product yield.
2. The process of fermentation depends on the following factors such
as
• Temperature
• pH
• Agitation
• Redox equilibrium
• Oxygen concentrations etc.
3. The provision of such conditions requires careful monitoring
frequently to produce the maximum yield.
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3. pH measurements and controls
• Control and maintenance of pH at optimum levels inside the reactor is
mediated by sensors (electrodes), along with compatible control
systems.
• pH sensors are internal sensors that should be steam sterilisable and
robust.
• Control of pH is usually a major factor as many fermentations yield
products that can alter the pH of the growth media.
• Fermentation media often contain buffering salts, usually
phosphates, but their capacity to control pH can be exceeded and
addition of acid or alkali may be required. 3

4. • The electrodes may be used
silver/sliver chloride with
potassium chloride as an
electrolyte.
• The pH measurement is routinely
carried out by glass electrode
that will withstand repeated
sterilization at 121*C.
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5. • If the medium is too acidic
the pH can be controlled by
the addition of Ammonium
or sodium hydroxide.
• If the medium is too
alkaline, the pH can be
controlled by the addition of
sulphuric acid.
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6. Redox potential control and
measurements
• Chemically, the oxidation–reduction potential is defined as the
tendency for a molecule to acquire electrons.
• It involves two components known as redox pair during the electron
transfer process, of which the oxidizing one (Ox) attracts electrons and
then becomes the reducing one (Red). This relationship is illustrated
below:
Ox + ne−=Red
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7. • Based on Nernst Equation, the redox potential is
simply determined by the ratio of oxidative state to
reductive state at a fixed temperature, which is
always a constant parameter in most biological
processes. This below picture illustrates three general
approaches to control redox potential in biological
devices.
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Approaches to control redox potential. (A) energy input, (B) redox
reagents, and (C) gas sparging.

8. Control of redox potential
• Bioelectrical reactors (BERs), equipped with anodic and cathodic
electrodes, were developed to regulate redox state in the medium
through an external power source. It was used to replace chemical
electron donor and acceptor in bio system.
• Numerous chemicals with higher or lower standard redox potential
than common metabolic components are supplemented into
fermentation broth in order to alter environmental redox potential.
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9. • Some commonly used reductants and oxidants to
control extracellular redox potential include
• FeCl3,
• Na2S,
• potassium ferricyanide,
• dithiothreitol,
• cysteine,
• methyl viologen,
• H2O2,
• even directly NADH and NAD+ as additives.
• Oxygen and nitrogen are commonly used in aerobic and anaerobic
fermentation, respectively. Thus, sparging pure or mixed gases into
fermentation broth is one of the desired approaches to avoid unwanted
reactions caused by redox salts.
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10. Need for PH and redox
controls
• This provide the progress of fermentation process.
• It indicates the optimum time to harvest.
• It indicates the contamination of the process.
• It also indicates the strain degeneration.
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11. Reference
• Principles of fermentation technology- P.F.stanbury, A.Whitaker, and
S.J.hall.
• Picture courtesy : Google images
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