Chemical oxygen demand (COD) measures the total quantity of oxygen required to chemically oxidize all organic and inorganic matter in a water sample. It provides a broader assessment of water contamination than BOD.
Chemical oxygen demand (COD) is a laboratory test that determines the amount of oxygen equivalent consumed during the chemical oxidation of organic and oxidizable inorganic compounds in water. Unlike BOD, which relies on biological decomposition, COD uses a strong chemical oxidant such as potassium dichromate to oxidize virtually all organic material, including compounds resistant to microbial breakdown. The COD test can be completed in about two to three hours, making it much faster than the five-day BOD test. COD values are always equal to or higher than BOD values because the chemical oxidation process breaks down more substances than biological processes can. The ratio of BOD to COD is often used to assess the biodegradability of wastewater: a BOD/COD ratio above 0.5 suggests the waste is readily biodegradable. Industrial wastewater may have COD values exceeding 10,000 mg/L, depending on the type of manufacturing process. COD is widely used for monitoring treatment plant performance and for regulatory compliance in both municipal and industrial settings.