Standards Development

Scope

This document specifies a method for the determination of the chemical oxygen demand (ST-COD) using available small-scale sealed tube tests. The test is empirical and is applicable to any aqueous sample, which includes all sewage and waste waters.

Various manufacturers offer small-scale sealed tube tests with different measuring ranges. These are characterized by different accuracies and method detection limits.

Samples with a high chloride concentration will need to be prediluted to give a chloride concentration of approximately 1 000 mg/l respectively 2 000 mg/l or less. Any concentration of chloride present in the sample will interfere if no mercury(II) sulfate is added. Normally mercury(II) sulfate is part of the prefilled reagents. From the whole range of commercially available small-scale sealed tube tests with different measuring ranges, this document refers to four different application ranges:

- ground water, surface water and treated waste water with COD contents up to 60 mg/l O2;

- ground water, surface water and slightly polluted waste water with COD contents up to 160 mg/l O2;

- polluted ground- or surface water and waste water with COD contents up to 300 mg/l O2;

- inflow water of waste water treatment plants with COD contents up to 2 000 mg/l O2. 

Purpose

COD is the most important parameter for the analysis of waste water but used also for measuring theorganic pollution of surface, river, lake, drinking water and many others. The limits for COD aredifferent in the various countries but depends all on laws and regulation. This document covers themeasuring ranges required from the regulators. For in-process control e.g. other measuring ranges canbe useful but will not be covered from this standard.For the specification of the commercial available COD tubes we use either the respective ISO standardof if not applicable a mixture of commercial COD tubes and test the recovery rate to calculate the newrecovery for the standard.The analytical method based on the oxidizing of potassium dichromate and photometric measurement. Preparation of own tubes is not anymore a topic of this standard because it is well understood, that commercial available tubes give more precise and accurate results