What are the definitions and differences between COD and BOD?

COD (Chemical Oxygen Demand) is an abbreviation for Chemical Oxygen Demand, which is an indicator used to measure the organic content in water samples.
COD refers to the amount of chemical oxidant required to convert organic matter in water samples into carbon dioxide and water through chemical oxidation reactions under acidic conditions. By measuring the consumption of oxidants, the concentration of organic matter in water samples can be indirectly calculated.
COD, as a commonly used water quality indicator, can be used to evaluate the degree of organic pollution in water bodies
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It is widely used in fields such as water environment monitoring, wastewater treatment, and water resource management.
The determination of COD usually adopts chemical methods, and commonly used oxidants include potassium perchlorate (KClO3) and sodium perchlorate (NaClO3). During the measurement process, organic matter in the water sample is oxidized to CO2 and H2O by reacting with an oxidant, and then the consumption of the oxidant is measured to calculate the concentration value of COD.


BOD (Biochemical Oxygen Demand) is an abbreviation for Biochemical Oxygen Demand, which is an indicator used to measure the biochemical degradation ability of organic matter in water samples.
BOD refers to the amount of oxygen required by microorganisms (usually bacteria) to decompose organic matter at a certain temperature and for a certain period of time. By measuring the amount of oxygen consumed by the biochemical degradation of organic matter in water samples, the content of organic matter and the quality of water can be evaluated.
BOD is commonly used to assess the degree of organic pollution in water bodies and the health status of aquatic ecosystems.
The determination of BOD requires culturing the water sample with bacteria under certain cultivation conditions, and measuring the difference in dissolved oxygen in the water sample before and after cultivation. The determination of BOD requires a 5-day cultivation period to obtain accurate results.
The higher the BOD value, the higher the organic matter content in the water and the worse the water quality.
The determination results of BOD can help evaluate the degradation ability of organic pollutants in water bodies, guide water quality control and environmental protection work.

The difference between the two:
COD and BOD are both used to measure the content and degree of organic pollutants in water bodies. But there are also some differences
Definition: COD refers to the measured value of chemical oxygen demand in a water sample, which is the amount of oxidant required to oxidize organic matter under specific conditions. BOD refers to the measured value of biochemical oxygen demand in water samples, which is the amount of oxygen required by bacteria to decompose organic matter over a certain period of time.
Measurement method: COD is calculated by chemical oxidation reaction, using oxidants (such as potassium perchlorate) to oxidize organic matter under acidic conditions, and then measuring the consumption of oxidants. BOD is calculated by culturing the water sample with bacteria for a period of time, and then measuring the difference in dissolved oxygen before and after cultivation.
Reaction speed: COD measurement is fast and usually completed within a few hours. The determination of BOD requires a relatively long time, usually requiring a 5-day cultivation period to obtain accurate results.
Application scope: COD is mainly used for rapid assessment of the concentration of organic pollutants in water bodies, and is suitable for monitoring and treating chemical pollutants in water bodies. BOD is mainly used to evaluate the impact of organic pollutants in water bodies on ecosystems, and is more suitable for assessing and monitoring biological pollution in water bodies.