What's the Chemical Oxygen Demand(COD) ?
What's the Chemical Oxygen Demand(COD) ?
Chemical oxygen demand (COD) refers to the oxygen content of the oxidant needed to oxidize the organic matter in sewage by chemical method. When potassium permanganate is used as oxidant, the measured result is customarily called oxygen consumption, which is expressed by OC. When potassium dichromate is used as oxidant, the measured result is called cod. The difference between the two lies in the choice of oxidant. With potassium permanganate as oxidant, it can only oxidize straight chain organic compounds in sewage, while with potassium dichromate as oxidant, its action is stronger and more complete than the former. Besides straight chain organic compounds, it can oxidize many complex organic compounds that potassium permanganate cannot oxidize. Therefore, COD value of the same sewage is much higher than OC value. Especially when a large amount of industrial waste water enters the sewage plant, the chemical oxygen demand of the method of potassium bichromate should be measured generally. The COD value of municipal wastewater treatment plant is generally about 400-800mg / L.
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