Redox Reactions for Chemical Oxygen Demand in the Light of Health, Environmental Protection, and Technical Practicability

Abstract

Determination of the important wastewater parameter chemical oxygen demand (COD) in international standard procedures is still based on the use of mercury sulfate and potassium dichromate, which are hazardous to health and the environment (REACH). In order to overcome this environmental paradox, alternative oxidizing agents were compared, and a new wet-chemical method using Mn(III) as an oxidant was developed that works without Cr(VI) and Hg(II). Oxidation of potassium hydrogen phthalate as a reference substance was reproducible in a COD range of 20–500 mg/L with a mean recovery of 88.7% compared with the standard Cr(VI)-method. A high correlation (R2 = 0.9935) to the standard Cr(VI)-method with a mean recovery of 78.1% (± 5.2%) was found for a series of industrial and municipal wastewater samples. Although the results of the new method were not 100% of the standard method, its high correlation with the latter and its reproducibility offer an environmentally benign alternative wet chemical method.