Most industrial facilities obtain the water required for production technologies from water sources, use it, and discharge the contaminated water into the receiving environment after purifying it.
Regulations containing limiting criteria are created by states to ensure that the environment and people living in areas close to the facility are not affected by contaminated water. States establish control and monitoring procedures to prevent pollution within the scope of these regulations they put into effect.
Wastewater Discharge Criteria included in the Regulations are determined on a sectoral basis, taking into account the discharge location, which is the boundary point at the exit of the wastewater treatment plants and before the receiving environment where it mixes, such as lakes, streams, coastal and sea waters.
Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD) stand out as the two main indicators of pollution in discharge criteria. However, since COD laboratory values ​​are reached in a shorter time, COD values ​​were adopted as the main discharge criterion. COD (chemical oxygen demand) consists mainly of substances that can be oxidized by strong oxidants, especially organic substances, in the water sample. The oxidation of these substances consumes the dissolved oxygen in the water, creating a chemical oxygen demand. COD (chemical oxygen demand) is an important indicator to measure the degree of organic pollution in water bodies. Excessive content will have a serious impact on the receiving water quality.‌ COD measurement by laboratory analysis is based on the amount of oxidant consumed when reducing substances (mainly organic matter) are oxidized and decomposed in 1 liter of water under certain conditions. Therefore, the COD laboratory analysis result is shown in mg/l units.
The COD value is included in the discharge criteria in the Regulations in our country as mg/l. However, the actual COD load discharged from treatment is the value defined in the unit (kg COD)/day. This value defines the pollution given to the receiving environment in kg per day and is determined by multiplying the laboratory value, which is the mg/l unit of the COD parameter at the discharge point, with the flow rate at the discharge point.
Although using the COD value in mg/l is a criterion for discharge control, it may provide an opportunity to encourage the use of more water from its source as input. Since it will allow the COD amount to be diluted by using excess water, it will also allow the mg/l COD value to be low.

In summary, it is thought that the difference between the COD value in the discharge criteria as (mg COD)/l or (kg COD)/day should be evaluated and which unit of COD value is effective in environmental pollution should be reviewed for pollution control.
Because the design and dimensioning of Wastewater Treatment Facilities are made by taking into account (kg COD)/day, (kg BOD)/day and m3/day flow rate data. For this reason, it is believed that it will be able to be more accurate to use discharge criteria such as (kg COD)/day, (kg BOD)/day and m3/day.