CODMn

CODMn, or chemical oxygen demand using permanganate, is a water quality parameter that measures the amount of oxidizable substances in water or wastewater that can be oxidized by potassium permanganate under specified conditions. It is used as a rapid, economical surrogate for the overall organic load and is related to the more widely used CODCr (dichromate COD) test, but it can respond differently to certain compounds.

In typical practice, a sample is acidified and treated with a standardized KMnO4 solution under controlled conditions. After the oxidation reaction, any excess permanganate is titrated with a standard reducing agent, such as ferrous ammonium sulfate, and the amount consumed is used to calculate the CODMn value. The result is expressed in milligrams of oxygen consumed per liter (mg/L O2).

CODMn is widely employed in drinking-water treatment and wastewater management for rapid process control, screening, and estimating organic loading. It offers advantages of speed and lower reagent toxicity compared with CODCr, but it is not as comprehensive a measure of all oxidizable substances. The method can be affected by interferences and sample characteristics, including certain inorganic species, nitrites, chlorides, iron or manganese, pH, color, and turbidity, which can alter the permanganate demand or the endpoint.

Because CODMn and CODCr do not always correlate precisely, CODMn is typically used alongside other indicators such as BOD and CODCr to assess organic pollution. Standards for CODMn testing are published by various national or international bodies, and laboratories must follow region-specific procedures to ensure comparability of results.