COD or Chemical Oxygen Demand is One of the Important and Influential Factors in the Industrial Wastewater Treatment Process, which is Directly Related to the Amount of Oxidizing Substances in Wastewater. COD is the Amount of Dissolved Oxygen That Must Be Present in Water to Oxidize Organic Chemicals Such as Oil.

If Oxidizing Substances in Water is Higher, More Oxygen is Needed for Oxidation. Based On This, Instead of Directly Measuring the Amount of External Materials in Water and Wastewater, the Amount of Oxygen Needed for the Oxidation of All Materials Can Be Calculated. Therefore, the Higher COD Makes More Wastewater Pollution.


One of the Methods of Measuring COD is Classical Method. This Method is Based on Colorimetric Analysis Based on Measuring the Color Formed by Adding the Reagent to the Sample. The Absorbance of the Solution is Measured by the Quartz Reaction Cell at a Specific Wavelength Using an LED Light Source and a Photometer. The Absorption Rate Depends On the Sample Concentration Using Lambert-Beer's Law.


Another Method of Measuring COD is Based On UV Absorption at 254 nm Wavelength by Unsaturated Hydrocarbon Molecules Inside the Water or Wastewater Sample. In Fact, Different Chemical Pollutants in the Solution Absorb a Certain Amount of this Wavelength. In This Method, Light Is Shone into the Solution Using a Lamp. A Sensor Calculates the Received Light Intensity. According to Lambert-Beer's Law, the Amount of Light Absorption Is Proportional to the Concentration of the Mentioned Substances.


Lambert Beer's Law Is as Follows:


C: The Concentration of Hydrocarbons in the Sample
: The Absorption Coefficient Depends on the Nature of Each Molecule

Iin: Intensity of Entering Light to the Sample
: Intensity of the Output Light from the Sample

Absorbance at 254 nm Wavelength is Measured by DIN-C3 38404 Standard.



BOD or Biological Oxygen Demand Is One of the Indicators of Wastewater Pollution and Shows the Amount of Oxygen Consumed by Bacteria and Other Microorganisms to Decompose Organic Matter Under Aerobic Conditions at a Certain Temperature. The Main Difference Between These Two Parameters Is That in COD, the Oxygen Needed to Decompose Organic Matter Is Measured Chemically, while in BOD, the Oxygen Needed to Decompose Pollutants is Calculated Biologically with Microorganisms. Therefore, for a Sample of Wastewater, COD is Always Higher than BOD and Includes BOD as Well.

For each type of effluent, BOD and COD are related to each other. This relationship is the same for Different Types of Water and Industrial Effluents of the Same Type Have Similar Relationships Between BOD and COD. Due to This Fact that COD Provides More and Faster Results Than BOD, In the Science of Wastewater Treatment, It Is Considered as the Standard Test Method of Wastewater Pollution Load, and the BOD Parameter is Calculated Based On the COD Parameter.