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How to quickly distinguish BOD and COD

by:BOQU     2023-03-10
Generally, people who are new to the sewage industry often hear a few concepts that are a few indicators in the discharge standard. The following three are easy to understand: BOD, COD, TP, TN and SS. The three concepts of total phosphorus, total nitrogen and suspended solids are very specific. But BOD and COD, one is biochemical oxygen demand and the other is chemical oxygen demand. These two are dizzy just by looking at their names. Newcomers who have just entered the industry may not be able to tell the difference. In fact, these two oxygen requirements represent the content of organic matter in wastewater. 1. Why use BOD and COD as pollutant indicators? In sewage and wastewater, most of the pollutants are organic matter. However, the types of organic matter in wastewater may range from dozens to hundreds or even thousands of species. It is impossible for us to take out every type of organic matter as an indicator of effluent. At this time, a unified indicator is needed to represent the organic matter in the wastewater. We know that organic matter is composed of hydrocarbons, which can be oxidized by strong oxidants or oxidized and decomposed by microorganisms, and the products are carbon dioxide and water. Oxygen is consumed during the oxidation process. The more oxygen consumed, the more organic matter in the wastewater. Therefore, chemical oxygen demand and biochemical oxygen demand, namely COD and BOD, are used to represent the content of organic matter in wastewater. 2. What are BOD and COD? BOD refers to the amount of dissolved oxygen needed by microorganisms to decompose organic matter. In the actual determination of dissolved oxygen consumption in water, 5 days are generally used as a cycle called BOD5. COD refers to the amount of oxidant consumed by reducing substances in a unit volume of water sample under certain conditions. Generally, the potassium dichromate method is called CODcr. The higher the value of BOD and COD, the more serious the water pollution. 3. What is the difference between BOD and COD? Organic matter in wastewater is divided into degradable organic matter and non-degradable organic matter. Microorganisms can use only degradable organic matter, while strong oxidants can oxidize all organic matter, so BOD means degradable organic matter. COD represents all organic matter, and the difference between these two data represents non-degradable organic matter. In the absence of measurement errors, COD must be greater than BOD. Generally, the value of BOD/COD can be used to roughly represent the biodegradability of wastewater. Generally, when it is greater than 0.3, the wastewater is considered to be biodegradable. The larger the ratio between the two, the higher the biodegradability of wastewater.
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