Question

What is COD? Which chemical substance is generally used in its measurement?

Answer 1

Hint :
An oxidising agent (oxidant, oxidizer), sometimes known as an oxidising agent (oxidiser), is a compound that has the potential to oxidise other compounds by accepting their electrons. Oxygen, hydrogen peroxide, and halogens are common oxidising agents.

Complete Step By Step Answer:
The chemical oxygen requirement (COD) is a metric for measuring the consistency of water and wastewater. The COD test is often used to track the quality of water treatment plants. This test is based on the fact that, under acidic conditions, a good oxidising agent can fully oxidise almost any organic compound to carbon dioxide. The COD is the quantity of oxygen used to convert organic water pollutants to inorganic end products by chemical oxidation.
Under acidic conditions, COD is often tested using a heavy oxidant (e.g. potassium dichromate, potassium iodate, potassium permanganate). The oxidant is applied to the sample in a quantity that is considered to be excessive. After the oxidation process is complete, the amount of oxidant left in the solution is measured to determine the concentration of organics in the sample. Titration of an indicator solution is commonly used to do this. The mass of oxygen absorbed per litre of solution is measured in milligram per litre of COD.
The COD test takes just a few hours, while the Biochemical (or Biological) Oxygen Demand (BOD) test takes five days. It detects all organic toxins, including non-biodegradable ones. For each particular study, there is a relationship between BOD and COD, but it must be defined empirically. The findings of a COD evaluation will then be used to estimate a sample's BOD. Toxic compounds (such as heavy metals and cyanides) in the samples to be tested have little effect on the oxidants used in the COD test, unlike the BOD test. As a result, the COD test will be used to determine the intensity of wastes that are too harmful to be measured using the BOD method.

Note :
The chemical oxygen requirement is a measure of the amount of oxygen that can be absorbed by reactions in a measured solution of environmental chemistry. It's usually measured in mass of oxygen absorbed per amount of solution, which is measured in mg / litre in SI units.