The analysis of water may concern different aspects, in order to assess its quality. When this water is used for a given purpose, its quality will be altered. Therefore, it is often necessary to treat the water used before it is discharged into the natural environment, in order to reduce the emission of pollutants.
1. Analysis of physical characteristics or quantities such as:
- pH (acidity, basicity);
- Salinity, mineralization (through conductivity measurements);
- Dissolved oxygen.
2. Assessing the presence of organic matter:
An overall estimate measurement is possible using the quantity of oxygen necessary for oxidation as a reference. Indeed, the presence of oxidizable organic matter will lead to a consumption of oxygen in the environment.
We can use different criteria:
- The permanganate index (in mg O2/L) for water with a low organic matter content, or its equivalent the COD or chemical oxygen demand (in mg O2/L) for water with a high organic matter content;
- The TOD or total oxygen demand (in mg O2/L);
- The BOD5 or biochemical oxygen demand over 5 days (in mg O2/L);
- The oxidizable organic matter or OxOM (in mg O2/L);
- The TOC or total organic carbon;
- The DOC or dissolved organic carbon.
3. Evaluation of nitrogenous and phosphorus matters, responsible for the phenomenon of eutrophication.
Several forms of nitrogen and phosphorus are to be considered when evaluating water quality:
- Total Kjeldahl nitrogen (TKN ou NKj) or organic nitrogen;
- Global nitrogen (NGL);
- Mineral forms of nitrogen (ammonium, nitrites, nitrates);
- Phosphorus derivatives (organic phosphorus compounds and phosphates) determined globally by total phosphorus (TP).
The analytical methods generally used for the determination of these various compounds are techniques of analysis by colorimetry, iodometry or ionic chromatography.
4. Toxic pollution evaluation (often at trace levels) such as organochlorine compounds (chlorinated solvents, chlorinated pesticides, polychlorobiphenyls), the determination of which can be obtained by microcoulometric or chromatographic analysis (possibly after a concentration phase).