Among the many parameters used to determine the degree of pollution of domestic and industrial wastewaters, the most important is the need for chemical oxygen. Chemical oxygen demand (COD) is the amount of oxygen required for chemical oxidation of substances suitable for oxidation in wastewaters.

Unlike the determination of biological oxygen demand (BOD), this method is based on the oxidation of organic matter by redox reactions, not by biochemical reactions. During this process, the carbonaceous organic substances in the oxidation medium are converted into carbon dioxide and water, and the nitrogenous organic substances are converted to ammonia.

The most important advantage of chemical oxygen demand determination over biological oxygen demand determination is that this process is performed and concluded in a short time. Because the process for the determination of biological oxygen demand takes five days, the result is three hours for the determination of biological oxygen demand.

Determination of chemical oxygen demand is a very important method in the studies of river water and industrial wastes and results are obtained very quickly. If the wastes do not contain toxic substances and contain only readily decomposable organic substances, the COD obtained is approximately equal to the BOD value.

However, COD value is always higher than BOD value since chemical oxygen demand determination can be followed by some substances which do not decompose biologically by differentiating from biological oxygen demand determination.

The oxidizing agent commonly used when determining the chemical oxygen demand is potassium di chromate. This method is very suitable for measuring the concentration of organic matter in domestic and industrial wastewaters containing toxic substances for biological life. Because chemically oxidizable compounds are more than biologically oxidizable compounds.

In accredited laboratories, chemical oxygen demand (COD) determination procedures are carried out to determine the oxygen to be added until the carbonaceous substances in the waters are converted to carbon dioxide. The oxygen demand obtained by laboratory measurements is an indirect measure of the carbon content in the wastewater.