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COD determination method and national discharge wastewater standard

by:BOQU     2022-10-10

1. What is COD?

Chemical oxygen demand COD (Chemical Oxygen Demand) is a chemical method to measure the amount of reducing substances that need to be oxidized in a water sample. Wastewater. The oxygen equivalent of substances (usually organic) that can be oxidized by strong oxidants in effluent and contaminated water from wastewater treatment plants. In the study of river pollution and industrial wastewater properties and the operation and management of wastewater treatment plants, it is an important and fast-determined organic pollution parameter, often represented by the symbol COD.

Under certain conditions, the amount of oxidant consumed by oxidizing reducing substances in 1 liter of a water sample is used as an indicator, which is converted into the milligrams of oxygen required for each liter of water sample after all the oxidation, expressed in mg/L. It reflects the degree of contamination of water by reducing substances. This indicator is also used as one of the comprehensive indicators of the relative content of organic matter.

2. What is the measurement principle of COD?

The national standard method of COD uses the reflux digestion titration method, which has a long digestion time (2 hours), high energy consumption, high reagent cost and low detection efficiency, which are the main factors that often trouble the actual operator. At present, the COD detector performs more rapid digestion spectrophotometry to detect COD. The detection principle is that potassium dichromate solution is in a strong acid medium, and silver sulfate is used as a catalyst. After high-temperature digestion, the COD value is determined by spectrophotometry. When the COD value in the sample is 100mg/L to 1000mg/L, at 600nm± The absorbance of Cr3+ produced by the reduction of potassium dichromate is measured at a wavelength of 20 nm. The COD value in the sample is proportional to the increase in the absorbance of Cr3+, and the absorbance of trivalent chromium Cr3+ is converted into the value of sample COD.

National discharge wastewater COD standard Chemical Oxygen Demand (COD) The national discharge wastewater standard is unit: mg/L Industry first-level discharge standard Second-level discharge standard Third-level discharge standard Tiancai sugar. Synthetic fatty acids. Wet fiberboard. Dyes. Wool washing. Organophosphorus pesticide industry 100200100 monosodium glutamate. Alcohol. Pharmaceutical raw materials. Biopharmaceuticals. Ramie degumming. Leather. Chemical fiber pulp industry.

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