A conventional concept referring to the amount of oxygen used in a specific time for the aerobic oxidation of organic matter contained in water or sewage, by live bacteria and extracellular enzymes.

Biochemical oxidation of organic matters takes about 20 days, and it is the most intensive during the first five days. Therefore in Poland, BOD is measured in five days, as BOD5, in the temperature of 20 degrees centigrade. It is one of the most important indications of pollution of water with organic matter, measured to control of water purity, to determine possibilities of biological treatment of sewage, their influence on the receiver and to control the sewage treatment plant operation.

• Wastewater treatment plant
• Surface water