Discussion on the Determination Method of COD in High Chloride Wastewater

After acid-base neutralization and pressure filtration, the wastewater of printing plates contains a large amount of chloride ions(20000mg/L) and 200 to 400mg/L COD. According to the traditional GB method of the reflow technology within two hours, the detecting precision of COD can't be achieved,and it is a waste of time and drugs. The national standard KI absorption correction method is not suitable for water samples which contain more than 50mg/L COD. The contents of COD in water samples with 10000mg/L chloride ions and 200 to 500mg/L COD are determined by digestion method through 30% mercury sulfate-sulfuric acid solution as a sequestering agent and 0.1M potassium dichromate as an oxidant within one hour. The relative standard deviation is below 2.6%, and the recovery of standard addition is about 105%, so the result is very satisfactory. The problem of measuring the amount of COD in the wastewater from printing plates(PS plate, CTP plate) has been solved. Then a reference for determination of the wastewater in oil, chemical industries was provided.