Pretreatment
In addition to sedimentation to separate coarse material, pretreatment also includes precipitation (addition of Fe or Al salts) and flocculation (addition of polymers). The latter two processes serve to form micro or macro flocs to accelerate the subsequent sedimentation. Typical measuring parameters are (measuring technique see below):
- Salt or polymer concentration and filling level
- Turbidity
- SAC
- Sludge level
Filtration
The filtration process can be divided into filtration through a matrix (e.g. sand filter with or without activated carbon) and filtration on a surface (e.g. membrane filtration).
Sand filtration is used for the separation of solids as the raw water flows through the filter and the solids adhere and remain in the matrix. As the filter has to be rinsed regularly, often several filters are operated to clean the raw water on the other filters in the meantime. In addition, a biologically active layer builds up on the filter surface, which must be regularly removed. If an activated carbon layer is embedded, dissolved organic substances or impurities that are difficult to degrade are also removed. Monitoring parameters are (measurement technique see below):
Depending on the pore size, membrane filtration is able to remove not only solids but also dissolved particles and also has a disinfecting effect. However, membrane filtration is not approved for disinfection at least in Germany. Depending on the pore size, a distinction is made between micro (0.1–10 µm), ultra (0.001–0.01 µm), nano filtration (0.0005–0.007 µm) and reverse osmosis (<0.001 µm). Monitoring parameters are:
- Particle/solid
- Hygienic parameters
- Turbidity
Disinfection
For disinfection, the addition of chlorine, chlorine dioxide, ozone (chemical disinfection) or UV treatment (physical disinfection) can be considered. In Germany, ozonation is not permitted as the sole disinfection method.
In the chemical processes, microorganisms are inactivated. The inactivation depends on the c*t values, i.e. on the concentration (c) to which the microorganisms are exposed over a certain time (t). The disinfection performance is limited by the presence of ammonium (formation of chloramines) and at higher turbidity levels (>1 NTU). Chemical oxidation of inorganic or organic components also takes place in all processes. For ozonation this is the primary objective. Monitoring parameters are (see below for measurement technology):
- Chlorine
- chlorine dioxide
- O3
- pH
- UV transmission
- Turbidity
Physical disinfection damages the DNA of microorganisms and thus deprives them of their ability to divide. The performance here depends on the UV dose and requires a low turbidity (<1 NTU). Chemical oxidation only takes place in the presence of H2O2.
Others (e.g. activated carbon, Deferrization/Manganese removal)
Among the numerous other processes, activated carbon and deferrizing/demanganization are the most common.
The activated carbon removes dissolved organic and hardly degradable (micro) impurities. In addition, it also promotes biological degradation and provides protection in the event of short-term exposure shocks. The process can be carried out using its own filter bed, stored in other filters or integrated into the treatment process using powdered activated carbon. Depending on the raw water and rinsing processes, it can take one month or one year until the carbon is fully loaded. Afterwards the coal has to be regenerated or burned. Typical monitoring parameter is (measurement technology see below):
- SAK before and after the treatment stage
Iron and manganese removal is a combination of oxidation and subsequent filtration. In oxidation, Fe3+ or Mn4+ are oxidized to Fe2+ or Mn2+. The iron precipitates from the beginning in the subsequent filter. The manganese is removed with some delay by manganese eating bacteria. The delay results from the fact that these bacteria must grow in sufficient quantity first. To be measured:
- Oxygen in the oxidation
- Iron/manganese after filtration