Activated carbon filters are used for dechlorinatio n and adsorption. Dechlorination is a very rapid process, in which the activated carbon participates in the reac tion and the free chlorine is converted to chloride.
The reaction takes place within seconds in the upper 10 cm of the filter bed. In the case of adsorption, which is used for THM re moval (tri-halo-methane) or the elimination of unwanted o dour and colour, the activated carbon filter is used as a chromatographic bed. Depending on the concentration and the polarity of the constituents to be removed and their mutual interference, the contact time is dete rmined which is typically between 80 and 20 minutes.
For THM adsorption monitoring of the treated water quality is required. At breakthrough, the carbon mu st be replaced immediately. New plants are equipped with steam devices to strip out the volatile components at high temperatures of 140°C. This operation extends the life of the carbon up to five times.
Furthermore it is important to construct the filter vessel so that proper sterilisation with either hot water (min. 95°C) or steam (up to 140°C) is possible. The only suitable material is stainless steel, whose quality is selec ted depending on the chloride content of the water. In addition, a nozzle plate for even distribution of c lean water and steam across the carbon bed should be installed, and the nozzles should be covered with f ilter gravel.
The sterilisation of an activated carbon filter sho uld generally be done at least once a week or more often if the microbiological parameters are deteriorating. Furth ermore, if the carbon filtration consists of more than one ves sel, it is recommended to always operate all carbon filters in parallel. A filter should only go out of operation for sterilis ation and / or backwashing, because a continuous operation is an e ffective way to prevent early microbiological growth on the carbon.
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