...
Dissolved oxygen (DO) is an essential measurement parameter in aerobic bioreactors. The growth of all cells is heavily dependent on DO because it acts as a terminal electron acceptor in aerobic respiration. However, if excessive amount of DO is added to the process, it may limit the growth of the culture and promote undesirable organisms. Consequently, the measurement of DO is critical to effective operation of systems. Today, a variety of sensors are available in the market, each with its own advantages and disadvantages.
...
Dissolved Oxygen
Dissolved oxygen is a physical distribution of oxygen molecules in water. Oxygen does not react with water, but mixes with it. There are two main sources of DO in water: atmosphere and photosynthesis. [2]
...
Also dissolved oxygen data or BOD (biological oxygen demand) is needed to determine effluent water quality. It is a common environmental procedure to determine the amount of microorganisms in a sample. This measurement is used in wastewater treatment, food manufacturing and filtration facilities where this quantity is important for the process and final product. “High concentrations of DO predict that oxygen uptake by microorganisms is low along with the required break down of nutrient sources in the medium” [1].
Types of DO sensors
There are two main types of dissolved oxygen sensors: optical (luminescent) and Clark electrochemical (membrane covered electrode or amperometric). These main types have subtypes, slightly differing from each other, see figure 1.
...
A reduction reaction will occur when a suitable potential is applied to the electrode: ox + ne- → red
Where ox is the oxidized species, red is reduced species, n is the number of electrons transferred and e- is an electron.
A concentration gradient of ox caused by its depletion at the electrode surface leads to mass transport by diffusion. This leads to a flux of ox, Jox (mol/m2s) that related to the reduction current, ired, through the electrode with an area A according to Faraday’s law [5]:
...