10.0 COD determination

10.1 Control of water pollution
10.2 Land Pollution
10.3 Pesticides
10.4 Control of soil pollution
10.5 Green Chemistry: A new route to protection of environment

In COD determination the water sample is treated with a known quantity of an oxidising agent, usually ${K_2}C{r_2}{O_7}$ in acidic medium. This reagent oxidises most of the polluting substances, including those which are resistant to microbial oxidation. The remaining ${K_2}C{r_2}{O_7}$ is determined by back titration with a suitable reducing agent.

From the concentration of ${K_2}C{r_2}{O_7}$ consumed, the amount of oxygen used in oxidation may be calculated using the following chemical equation: $${K_2}C{r_2}{O_7}(aq) + {H_2}S{O_4}(aq) \to {K_2}S{O_4}(aq) + C{r_2}{(S{O_4})_3}(aq) + 4{H_2}O(l) + 3O$$

The results are expressed in terms of amounts of oxygen in ppm, that would be required to oxidise the contaminants. This is called COD.