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.