In our refinery, the COD (chemical oxygen demand) of treated wastewater is analyzed in both laboratory and field analyzers. Lately, the COD in the analyzer has been increased by 4 times compared to the COD in the laboratory. We use the same method-Acidic Permanganate for both, but the additional AgNO3 is used for only the laboratory. However, the chloride content in treated wastewater hasn't been increased. What is the reason for the difference between the field analyzer and laboratory?Sep-2021
Peter Norman, Suez Water Technologies & Solutions, email@example.com
Sounds to me like the chloride went up enough to cause positive interference. Alternatively, nitrogen contamination (e.g. amines) increased, making the existing chloride interference much worse.