Editing Chemical oxygen demand (section)

==Overview ==
The basis for the COD test is that nearly all organic compounds can be fully oxidized to [[carbon dioxide]] with a strong [[oxidizing agent]] under [[acid]]ic conditions. The amount of [[oxygen]] required to oxidize an organic compound to carbon dioxide, [[ammonia]], and water is given by:
:<math>\mbox{C}_n\mbox{H}_a\mbox{O}_b\mbox{N}_c + \left( n + \frac{a}{4} - \frac{b}{2} - \frac{3}{4}c \right)\mbox{O}_2 \rightarrow n\mbox{CO}_2 + \left( \frac{a}{2} - \frac{3}{2}c \right)\mbox{H}_2\mbox{O} + c\mbox{NH}_3</math>
This expression does not include the oxygen demand caused by [[nitrification]], the oxidation of ammonia into [[nitrate]]:

:<math>\mbox{N}\mbox{H}_3 + 2\mbox{O}_2 \rightarrow \mbox{N}\mbox{O}_3^- + \mbox{H}_3\mbox{O}^+</math>
[[Chromate and dichromate|Dichromate]], the oxidizing agent for COD determination, does not oxidize ammonia into nitrate, so nitrification is not included in the standard COD test.

The [[International Organization for Standardization]] describes a standard method for measuring chemical oxygen demand in ISO 6060 [http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=12260&ICS1=13&ICS2=60&ICS3=50]. However, this ISO standard was withdrawn in 2024.