What is the permanganate index ?
Under certain conditions , with potassium permanganate ( KMnO4 ) as the oxidant , the amount of oxidant consumed in the treatment of water samples is called the permanganate index , and the unit is expressed in mg / l of oxygen ( O2, mg/l ) .
Permanganate index In the past water quality monitoring and analysis , there is also a potassium permanganate method called chemical oxygen demand . However , because this method is under specified conditions , the organic matter in the water can only be partially oxidized , not The theoretical oxygen demand is also not a measure of the total organic matter content in the water body . Therefore , the term permanganate index is used as an indicator of water quality , which is different from the chemical oxygen demand of the potassium dichromate method. , which is more in line with objective reality . The chemical oxygen consumption measured by potassium permanganate solution as the oxidant was formerly called the chemical oxygen consumption of manganese method . In China's new environmental water quality standards , this value has been renamed permanganate Index , and only the value measured by the acid potassium dichromate method is called chemical oxygen demand . The International Organization for Standardization (ISO) recommends that the potassium permanganate method is limited to the determination of surface water, drinking water and domestic sewage , not suitable for industrial waste water .
Initially, in order to distinguish COD by potassium dichromate method and potassium permanganate method , CODCr and CODMn were used to represent respectively, and later the latter was named "permanganate index" internationally.
CODcr refers to the use of potassium dichromate as an oxidant to oxidize all reducing substances in a 1L water sample. The amount of oxidant consumed is expressed in mg/L of oxygen, and CODmn is the permanganate index.