Method for analyzing content of COD (chemical oxygen demand) in sewage with high chloride ion concentration

Abstract

The invention discloses a method for analyzing the content of COD (chemical oxygen demand) in sewage with high chloride ion concentration. The method comprises the following steps: adding 5ml of 1mol / L silver nitrate solution into a sewage sample, mixing, uniformly shaking, precipitating, adding water for dilution till 25mL, performing centrifugal separation, taking 3mL of supernatant liquid, placing into a digestion pipe, adding 1mL of 10% mercury sulfate solution, 1mL of 0.025mol / L potassium dichromate oxidant solution and 5mL of 1% sulfuric acid-silver sulfate catalyst solution, plugging, uniformly shaking, digesting for 15min, taking out, cooling, and determining the COD content in the sample by applying a colorimetric method. According to the method, a silver salt precipitation method and a dilution method are combined and applied, AgNO3 is added into the chlorine-containing sewage sample to precipitate the chloride ions and further eliminate the interference of the chloride ions on the accuracy of COD determination result, the dilution method is further adopted to reduce the influence of nitrate radicals introduced by silver nitrate on an analytical system, the method is suitable for analyzing the content of COD in the sewage sample with the chlorine content of 1200-10000mg / L, and the accuracy in detection result is greatly improved.

Description

technical field [0001] The invention relates to a method for measuring COD content, in particular to an analysis method for COD content in sewage with high chloride ion concentration. Background technique [0002] Chemical oxygen demand (COD) refers to the amount of oxidant consumed when reducing substances in water are oxidized and decomposed under the action of an external strengthening oxidant under certain strict conditions, expressed in mg / L of oxygen. COD reflects the degree of water pollution by reducing substances, including organic matter, nitrite, ferrous salt, sulfide, etc. In general, the amount of inorganic reducing substances in water and wastewater is relatively small, but it is very common to be polluted by organic substances. Therefore, COD can be used as a comprehensive indicator of the relative content of organic substances. [0003] There are many methods for analyzing chemical oxygen demand (COD), such as potassium dichromate method, potassium permangan...

AI Technical Summary

Problems solved by technology

[0003] There are many methods for analyzing chemical oxygen demand (COD), such as potassium dichromate method, potassium permanganate method and rapid closed catalytic digestion method, etc., but with these methods, the measurement results are much higher for sewage with high chlorine content It cannot truly reflect the content of chemical oxygen demand (COD) in sewage, and is not suitable for the determination of sewage solutions with high chloride ion concentration

For the determination of COD content in high chloride ion sewage, there are also literature reports, which can use dilution method, silver nitrate addition method, mercuric sulfate addition method, etc., but for the silver nitrate method, it is reported that nitrate is introduced in the analysis system, and nitric acid Roots are also highly oxidizing and can cause negative bias in results