Talk about the meaning and difference of COD and BOD

COD, chemical oxygen demand is a chemical method to determine the content of reducing substances (mainly referring to organic substances) that need to be oxidized in water. BOD, Biochemical Oxygen Demand is mainly used to monitor the content of biodegradable organic matter in water. COD-water sample under certain conditions, taking the amount of oxidant consumed to oxidize reducing substances in 1 liter of water sample as an index, converted into the milligrams of oxygen required after each liter of water sample is completely oxidized, expressed in mg/L express. It reflects the degree of water pollution by reducing substances. This indicator is also used as one of the comprehensive indicators of the relative content of organic matter. BOD-organic matter decomposes microorganisms, but microorganisms need to consume oxygen when decomposing organic compounds in water. If the dissolved oxygen in water is not enough to supply the needs of microorganisms, the water body is in a polluted state. BOD5 and CODcr are five-day biochemical oxygen demand and chemical oxygen demand, respectively. The two are a comprehensive indicator of the amount of organic matter in sewage. BOD is an environmental monitoring index, which is mainly used to monitor the pollution status of organic matter in water bodies. Generally, organic matter can be decomposed by microorganisms, but microorganisms need to consume oxygen when decomposing organic compounds in water. If the dissolved oxygen in water is not enough to supply the needs of microorganisms, the water body will be in a polluted state. In order to make the test data comparable, a period of time is generally specified. During this period, microorganisms are cultivated with water samples at a certain temperature and the consumption of dissolved oxygen in the water is measured. Generally, five days are used, which is called the five-day biochemical requirement. The amount of oxygen is recorded as BOD5. The larger the value, the more organic matter the water contains, and therefore the more serious the pollution. Chemical oxygen demand (COD) is the amount of oxidant consumed when a certain strong oxidant is used to treat water samples under certain conditions. It is an indicator of the amount of reducing substances in water. Reducing substances in water include various organic matter, nitrite, sulfide, ferrous salt, etc. But mostly organic matter. Therefore, chemical oxygen demand (COD) is often used as an index to measure the content of organic substances in water. The greater the COD, the more serious the water body is polluted by organic matter. The determination of chemical oxygen demand (COD) varies with the determination of reducing substances in water samples and different determination methods. The most commonly used methods are acidic potassium permanganate oxidation and potassium dichromate oxidation. Potassium permanganate method has a low oxidation rate, but is relatively simple, and can be used when determining the relative value of organic matter in water samples. Potassium dichromate method has high oxidation rate and good reproducibility, and is suitable for determining the total amount of organic matter in water samples.
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