The 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. The greater the COD, the more serious the water body is polluted by organic matter. At present, the most commonly used methods are acidic potassium permanganate oxidation and potassium dichromate oxidation. Potassium permanganate (KMnO4) 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 (K2Cr2O7) method has high oxidation rate and good reproducibility, and is suitable for determining the total amount of organic matter in water samples. The COD351 COD sensor of Daruifuno is different from the traditional chemical measurement method. It uses the ultraviolet absorption method. Its principle is to use the characteristics of ultravi…