Evaluation of oxychlorides as chemical oxygen demand interferents: The roles of the different oxidizing agents and the organic carbon source of wastewaters

Abstract

Chemical oxygen demand (COD) is considered to be the most useful analytical parameter to characterize wastewaters in terms of water quality, by providing their organic matter or pollution content. For COD determination, a few interferences have been reported but some of them have not been estimated in detail in scientific literature. Hence constituting a critical issue for COD analysis in wastewater samples. In this research work, the negative interference of oxychlorides in COD measurements has been evaluated at laboratory scale. Specifically, the role of oxychlorides as alternative oxidizing agents in competition with dichromate has been assessed. The COD reduction performance varied widely according to the particular oxidizing agent used and its concentration, as well as, the organic carbon source and amount present in the wastewater. The experimental values of COD removal performance should be considered as dual concentration dependent. On the one hand, for each oxidizing agent the COD reduction performance is directly proportional to the dosage used in the experiment. On the other hand, the influence of OM concentration on COD removal performance was inversely proportional. In addition, chlorate can be considered as the strongest oxidizing agent and the principal interferent responsible for the over-evaluation of the COD removal performance. Furthermore, the interference extent of oxychlorides on COD determination decreased in the order of: Phthalate > Hydrocarbons > Proteins.