scope:

This part of ISO 5815 specifies the determination of the biochemical oxygen demand of waters by dilution and seeding with suppression of nitrification after 5 d incubation time. This part of ISO 5815 is applicable to all waters having biochemical oxygen demands usually between 3 mg/l and 6 000 mg/l. It applies particularly to waste waters. For biochemical oxygen demands greater than 6 000 mg/l of oxygen, the method is still applicable, but the errors caused by the necessary dilutions can influence the analytical quality of the test method. Then the results are to be interpreted with circumspection. The results obtained are the product of a combination of biochemical and chemical reactions with participation by living matter which behaves only with occasional reproducibility. They do not have the rigorous and unambiguous character of those resulting from, for example, a single, well-defined, chemical process. Nevertheless, they provide an indication from which the quality of waters can be estimated.