Determination of Chemical Oxygen Demand for Saline Wastewater

The interference of the chloride ion (Cl^-) on the standard method for chemical oxygen demand (COD) determination proposed by American Publican Health Association (APHA) cannot be ignored, especially for samples with high salinity. Increasing the ratio of HgSO₄:Cl- and adding some masking agents such as AgNO₃, Cr³⁺, Al³⁺ are all good modifications of the standard method to eliminate the Cl^- interference. Correction method can also be used to calculate the real COD value by analyzing the interfering COD value and the measured COD value. In addition, new techniques such as chemiluminescence (CL) system, chemiluminescence combined with flow-injection method, and new assisted digestion methods can tolerate Cl^- at a certain extent and save time simultaneously.