The tertiary wastewater treatment includes all further treatment steps to improve the quality of the purified water so that the reuse for multiple purposes is possible.
The use as process water is the most important way treated wastewater can be reused. Examples are:
- Rinsing water for the cleaning of the treatment wastewater plant
- Reuse as industrial process water
- Irrigation of parks, gardens or for landscaping
- Reuse as toilet flushing water
- Infeed in lakes for bathing
- Cooling water for air conditioning
In special cases treatment up to drinking water quality is possible with additional treatment steps.
For the tertiary treatment, there two main processes: mechanical and chemical.
Mechanical treatment steps are all technologies that are based on physical processes. For example:
Sand filtration can be divided into pressure sand filters, which are fed by pumps and often fitted with automatic backwash units and gravity sand filters, which have a relatively big surface on which the filter residue can accumulate and from where it must be removed from time to time.
Disc Filters consist of parallel disk packages. The surface of the single disk has a capillary structure that holds back particles up to a certain size. If the filter is clogged, an automatic backwash in reverse flow will be started.
Activated Carbon Filtration
Activated carbon filters are closed pressure tanks where the activated carbon granulate is found. The activated carbon has the capability to fix many organic compounds such as AOX. If the filter is loaded, the activated carbon is exchanged and reactivated.
Micro filters are very fine sieves that are often installed as rotating drum sieves. The mash width is 10 to 25µm.
Membrane filters use the different size of molecules. The membrane filters are mostly fed under high pressure; smaller molecules pass the membrane while long-chain molecules are retained. Depending on the pore size of the membrane it can be switched between ultra- and nano filtration.
Another application of membrane technology is reverse osmosis. This mainly serves the removal of salts with the use of a semi-permeable membrane. Under high pressure, the water is pressed out of a salt solution against the natural osmotic process. Due to its pore size the separation membrane is permeable then only for water molecules.
With membrane technology it is also possible to remove viruses and bacteria partly from the wastewater.
The chemical treatment steps follow two targets:
Remaining particles of the biological treatment are mechanically converted into separate solids by chemical processes.
The following processes are used:
In precipitation, dissolved components are transformed into solids with the help of different metal salts. The most important precipitation is the phosphate removal.
Flocculation means the transformation of the finest solids into bigger compounds by adding polymers. Long chain molecules are then formed, in which the non-sediment solids are integrated.
Another aim is the hygenization of the treated wastewater so that it is absolutely odorfree, colorfree and safe for the users of the treated water.
Therefore, the water is disinfected with the following processes:
By adding reactive chlorine compounds germs of the treated wastewater are oxidized and hence killed.
With an adequate dosing, a depot-effect is achieved with the hypochlorite process so that a regermination is prevented. After disinfection chlorite salt remains as residue.
In this process the oxidation of the germs is achieved by adding reactive oxygen compounds, in particular ozone (O3). A depot effect cannot be achieved with this process; however, it is better for the environment as no chemical degradation products remain.
The disinfection effect of this process is achieved via ultraviolet light of a specific length. This light is also involved in the oxidizing process. The wastewater passes through reaction pipes that are equipped with adequate UV-lamps. With this process, a depot effect is also not possible.
In many cases System S&P® installs a combination of UV-disinfection and hypochlorite dosing so that the dosing of chlorine compounds can reach a minimum depot effect. That way only minimal traces of chlorite salts come into the environment.
System S&P® is in the position to offer all common filter technologies. For ultra- and nano filtration, as well as reverse osmosis strategic partners have long term experience all over the world.
For the technical treatment of polluted air three common technologies are available:
Activated Carbon Filter
Activated carbon filters fix the organic odor forming constituents of polluted air. The filters are suitable for relatively dry air only, as otherwise biological growth in non-dry air can cause clogging.
Air washers wash out solids and odor causing constituents through finely sprayed water in a reverse flow. By adequate chemicals in the spray water or by integrated surfaces for biological growth, the air filters can be optimized for each specific application.
Biofilters use the effect of natural degradation processes in organic substrates. Via ventilators the contaminated air is pressed through the substrate. The bacteria of the substrate oxidize the odor causing constituents.
System S&P® unites the advantages of air washers and biofilters. By humidifying the contaminated air, the best possible conditions are created for the substrate bacteria. In this way the efficiency of the biofilter is significantly improved.