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What exactly is COD in wastewater?
Chemical Oxygen Demand (COD) is the amount of reducible substances in a water sample that need to be oxidized, as measured by chemical methods. The oxygen equivalent of substances (usually organic compounds) that can be oxidized by strong oxidants in wastewater, effluent from wastewater treatment plants, and polluted water. In the study of river pollution and the properties of industrial wastewater, as well as in the operation and management of wastewater treatment plants, it is an important organic pollution parameter that can be measured relatively quickly; it is often denoted by the symbol COD. Testing methods: the chromate method, potassium permanganate method, spectrophotometric method, rapid digestion method, and rapid digestion spectrophotometric method comply with **Standard HJ-T399-2007 for the determination of chemical oxygen demand in water quality.
The so-called Chemical Oxygen Demand (COD) refers to the amount of oxidizing agent consumed when a water sample is treated with a certain strong oxidizer under specific conditions. It is an indicator of the amount of reducing substances in water. Reducing substances in water include various organic compounds, sulfites, sulfides, ferrous salts, and so on. But the main component is organic matter. Therefore, Chemical Oxygen Demand (COD) is often used as an indicator to measure the amount of organic matter in water. The higher the chemical oxygen demand, the more severe the pollution of the water body by organic substances. For the determination of chemical oxygen demand (COD), the most commonly used methods at present are the oxidation with acidic potassium permanganate and the oxidation with potassium dichromate. The potassium permanganate (KmnO4) method has a low oxidation rate, but it is simple to use; it can be employed for determining relative values of organic matter content in water samples. The potassium dichromate (K-2Cr2O7) method features a high oxidation rate and good reproducibility, making it suitable for determining the total amount of organic matter in water samples.