Oxidation-reduction potential, or ORP, has been used for many years in facilities that process wastewater generated by metal finishing plants, but recently it has become prominent in municipal wastewater treatment plants.  When using a typical ORP device, an operator inserts a probe directly into a plant’s tank or waste stream.  The probe contains a sensor that measures electrical charges from particles, called ions, and these charges are converted to millivolts (mV) that can be either negatively or positively charged.  Unlike “wet Chemistry” analysis that can be time-consuming and complex, ORP readings are instantaneous and easy to perform.  And like all sampling measurements taken by operators, they are snapshots in time that can indicate process efficiency and identify treatment problems before they affect effluent quality.  When using continuous monitoring and control instrumentation, this snapshot can become a real-time indicator. 

Nitrification

Denitrification

Biological Phosphorus Removal

Sulfide Formation and Fermentation (Biological Malodor Production)

cBOD Degradation with Free Molecular Oxygen

Methane Production

Methane (CH4) production is highly desired in an anaerobic digester and undesired in a sewer system.  Methane production is performed by methane-forming bacteria and occurs over a large range of ORP values, from -175 to -400 mV.