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The service life of pipes, boiler systems, pumps and fittings in thermal hot-water and steam-boiler systems is determined to a great extent by the quality of the boiler water. Water contains different amounts of oxygen (O2) and carbon dioxide (CO2) - depending on the pressure and temperature. Both gases cause particular types of damage to metallic boiler materials: Oxygen has an oxidising effect, and carbon dioxide (carbonic acid) is aggressive.
Fine filtration
When using drinking water from the community water supply, the raw water from kilometres of pipe networks can be contaminated with rust, sand, broken out incrustations and other solids. These solids can be filtered out with cartridge filters. Cartridge filters are not suitable for removing larger quantities of dirt. In case of large quantities of dirt, the agglomeration of solids on the cartridge surface can lead to a rapid increase in the differential pressure.
Gravel filtration / Multi-layer filtration
 In contrast to cartridge filtration, gravel filtration, in particular the multi-layer filtration variant (filter gravel + hydro-anthracite) is a type of deep-bed filtration. With multi-layer filtration, the water passes through various layers of filter material with increasing fineness in the direction of filtration. Dirt is agglomerated in the various layers of the filter depending on its size. Multi-layer filters can take up large quantities of solids. Gravel filtration / resp. multi-layer filtration, especially in conjunction with flocculation, is used in the treatment of river water. In these cases, a sedimentation stage or other suitable pre-treatment is to be found upstream of filtration as an initial process step. Gravel and multi-layer filters must be cleaned regularly via back-flushing.
Iron removal
 Water with higher iron concentration must be treated. Water containing iron is generally reduced water or low-oxygen water in which the iron is usually dissolved in bivalent form. Compressed air or oxygen is introduced into the raw water upstream of the filter and mixed with it for oxidation of the iron. The bivalent iron oxidises with oxygen and forms undissolved rust, which is held back in the filter bed. The held back iron leads to an increase in the differential pressure in the filter.
Demanganisation
Dissolved manganese is usually present in water containing iron. The oxidation of manganese is more difficult, due to the fact, that manganese is oxidised after iron. In addition to chemical and biological demanganisation, catalytic filter materials are primarily used. Demanganisation can occur in one or two filter stages, depending on the manganese content of the raw water.
Arsenic removal
In addition to iron and manganese, arsenic is trace substance occurring especially in reduced groundwater. When using ozone, the arsenic removal can occur also parallel to iron removal and demanganisation in one single filter stage. Alternatively, filtration via granulated iron hydroxide (GIH) is possible. In this process, arsenic agglomerates at the GIH material.
Deacidifaction
Natural water sometimes contains excessive amounts of carbonic acid, which has a negative effect on downstream pipelines and consumers.Filtration via materials containing calcium carbonate (half-burnt dolomite, marble or Jurassic limestone) causes neutralisation of the free carbonic acid until a balance between hydrogen carbonate and carbon dioxide is achieved. The free carbonic acid reacts with calcium carbonate from the filter material.
Filtration via activated carbon
Filtration via activated carbon is primarily used to remove excess chlorine, odour, colour, taste, halogenated hydrocarbons, pesticides etc.. The substances are adsorbed on the interior of the activated carbon here. The activated carbon must be exchanged when fully loaded. Loaded activated carbon can be thermally regenerated using special equipment.
Membrane filtration
 The following processes are grouped together under membrane filtration:
- Microfiltration (MF)
- Ultrafiltration (UF)
- Nanofiltration (NF)
- Reverse osmosis (RO)
Membrane filtration technologies are used for the widest variety of applications in the water treatment field, often in conjunction with classical processes.
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Overview
