Oxidation-reduction potential is a measure of easily oxidisable or reducible substances in sewage.
An operator can control the process better by knowing if there is a large quantity of reducing substances (e.g., sulphide and sulphite) that may have an immediate, high oxygen demand and may result in an inadequate supply of oxygen for the microorganisms in the secondary process.
Although not specific, the ORP measurement is instantaneous (an electrode is used) and can be used to help maintain dissolved oxygen in the aeration tank.
Another application is to evaluate the progress of digestion and process stability in anaerobic digesters.
O&M issues to be cared for are as follows:
• Regular cleansing of electrode surface
• Precautions against breaking an ORP electrode, which is made of glass and is fragile
• Replacement of the electrode if it is insensitive to changes of potential difference, because of stains accumulated over a long time usage