Besides the chemical oxygen demand (COD), the biochemical oxygen demand after 5 days (BOD5) is the most important cumulative effect parameter for the assessment of the degree of contamination of a water body.
The BOD is defined by the volume-related amount of oxygen which is consumed by microorganisms to degrade the organic matter present in the water at 20 °C by oxidation. In general, this determination is made after 5 days, why it is often referred to as the BOD5 value.
The BOD content is determined by measuring the oxygen concentration. Microorganisms consume oxygen during the degradation of organic substances into carbon dioxide.
The simplified determination of the biochemical oxygen demand after 5 days (BOD5) is done with undiluted samples and without using a control in accordance with the German norm DIN EN 1899-2-H52. The oxygen-enriched, undiluted sample is incubated in a test tube for 5 days at 20 ± 1 °C in the dark. The determination of the dissolved oxygen after 5 days is based on the Winkler method. The incubation of the sample and the oxygen measurement (after 5 days) take place in the same test tube (REF 985825). In the standard method, the BOD5 is determined according to the so-called dilution principle. The oxygen concentration is measured immediately after sample preparation and after five days of incubation in Winkler bottles (REF 985 822). This method is in accordance with the German norm DIN EN 25813-G21.