The amount of oxygen used by microorganisms during biochemical oxidation of organic substances living in water is called biological oxygen demand. In other words, it is the amount of oxygen that organic substances need when converting to carbon dioxide.

While organic substances are decomposed by microorganisms together with oxygen, carbon dioxide, new cells and energy are released. The amount of oxygen required during this disintegration gives rise to the need for biological oxygen.

The determination of biological oxygen demand (BOD) is generally done in order to measure the amount of organic carbon in wastewater and to determine the organic loads coming to the treatment plants. These analyzes are also necessary to determine the time required to meet the biological oxygen demand and to determine the efficient operation of the treatment plants in this respect. With these analyzes, it is understood whether the wastewater plant meets the discharge standards.

Since organic substances are present in wastewater, their concentrations are considered as a measure of the degree of pollution. However, the composition of wastewater is quite different. For this reason, the ingredients are usually expressed by their concentration. As a measure of organic substances, the amount of oxygen consumed during the oxidation of the carbonaceous substances contained is based on the biological oxygen demand (BOD). Biochemical oxidation is a combustion event that develops in the wastewater and during this combustion oxygen dissolved in the wastewater is used. The more oxygen is used, the higher the amount of organic matter in the wastewater.

The oxygen demand of the waters containing organic matter increases until the carbonaceous substances are completely converted to carbon dioxide. This is the maximum 10 day. At the end of this period, all carbonaceous substances in water are decomposed. If the sewage system is operating effectively, the BOD is usually around the average 54 g / person-day.

In the laboratories, biological oxygen demand determination studies are carried out within the scope of chemical tests. During these studies, the standards issued by domestic and foreign organizations are complied with.