A modified method for the determination of chemical oxygen demand (COD) for samples with high salinity and low organics

This study proposes a modification to the standard method for the determination of the chemical oxygen demand of samples with a salinity up to 40 g NaCl/L and low organic concentrations (20–230 mg COD/L). The masking of chloride by the use of a HgSO4:Cl ratio of 20:1 prior to digestion, and the use of 3 g K2Cr2O7/L in the digestion solution resulted in an error of less than 10% and 12% for samples containing 40 g NaCl/L at 20–190 mg COD/L and 230 mg COD/L, respectively. Comparison of the standard method with the new proposed method using a synthetic sewage highlights the large errors (50–85%) of the standard method in contrast to an error of less than 10% for the proposed modified method.