The difference between cod and permanganate index is that cod is an index representing two methods, and permanganate index is one of them.

COD includes manganese method and chromium method, and the permanganate index refers to the detection value of the manganese method.

The permanganate index is mainly used to measure low-concentration COD, and is used for testing tap water and deep well water. The COD of this type of water is very low (less than 5 mg.l), and the chromium method cannot accurately measure the value. High-concentration COD is mostly tested using the chromium method.

Introduction to Permanganate Index

In the past, there was also a potassium permanganate method called chemical oxygen demand in water quality monitoring and analysis. However, since this method can only partially oxidize organic matter in water under specified conditions, it is not a theoretical oxygen demand, nor a measure of the total organic matter content in the water. Therefore, the term permanganate index is used as an indicator of water quality, which is different from the chemical oxygen demand of potassium dichromate method and is more in line with objective reality.

The chemical oxygen demand measured with potassium permanganate solution as the oxidant was previously called manganese method chemical oxygen demand. In my country's new environmental water quality standards, this value has been renamed the 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, and is not suitable for industrial wastewater.

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