About water Filtration sytems
Practically any water system can benefit from some form of filtration, be it to remove substances that are brought in externally, or substances that have found their way into the water system from within the building. When considering the water filtration systems design, building designers often detail the requirements of softening, ultraviolet treatment and specific mineral removal, and overlook basic filtration. It is a little known fact that our mains water contains particulates. This contamination most likely finds its way into the supply after being treated by the water board, due to internal pipe corrosion or pipe leaks.
If these particulates are allowed to find their way into a building, they can collect in the ‘settling zones’ of a water system, e.g. cold water storage tank, providing a likely habitat for bacteria. This can pose health risks to building users, and increase the frequency of tank disinfection work. Further into the building, they can damage particulate-sensitive equipment, e.g. plate heat exchangers, or cause erosion corrosion in pipework.
Sidestream filters are suited to protecting chilled and heated systems, in both closed and semi-open arrangements. By design, they do not filter the entire system volume of water, but treat a proportion of the flow, maintaining water quality in the system over time.
A relatively small sidestream filter can effectively treat a large system volume, which is beneficial particularly when plantroom space is limited.
- If used in conjunction with a chemical dosing regime, the sidestream filter will keep the system much cleaner, reducing the frequency of mechanical cleaning on equipment such as heat exchangers.
- If applied to a system free of particulate, corrosion inhibitor will provide a protective layer to clean surfaces, thus increasing the life expectancy of equipment.
- Larger organic substances are removed by sidestream filtration, this reducing the demand on chlorine and other biocides.
- Cleaner systems promote more effective heat transfer, reducing a systems tendency for increased energy usage over time.
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Activated Carbon is a specialised filter media used principally for removing chlorine or organic compounds from water. The benefit of this filtration is a significantly improved taste and the elimination of odours, sometimes associated with a “chemical taint” to the water. Activated carbon is also used as a final “polisher” treatment for many water filter systems.
Most of the Activated Carbon used for water treatment is made from baking crushed coconut shell until it produces a charcoal type material. This is then activated with high pressure steam, leaving the carbon with many thousands of minute active pores on its surface. The ability of activated carbon to remove contaminates from raw water is dependent upon the length of time the water spends in contact with the media. Therefore, sizing the filters correctly is crucial for effective performance and should be undertaken by an acknowledged water treatment expert.
Chlorine removal with carbon is a “catalytic” process in which the media does not become blinded or exhausted, but instead it acts as a trigger to the de-chlorination process. The active sites on the surface of the media do eventually become blinded by other contaminants in the raw water (such as iron or colouration), which means that the media will need to be changed every 1 to 3 years (depending upon the local water quality).
With organic removal, the contaminant molecules are trapped and retained in the activated sites on the carbon’s surface, and eventually all of the media will become “blinded” and will need to be changed. The frequency of changing will again depend upon the level of water contamination.
The effectiveness of activated carbon at removing organic compounds such as pesticides and solvents varies according to the precise nature of the contaminant.
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With the increasing demands for new housing developments, the demand on our water infrastructure is greater than ever before. We have an increasing responsibility as building engineers, to produce sustainable solutions for the demand on our resources, and provide efficient designs that meet current regulations.
As a result of this, there are an increasing number of water recovery schemes coming to market, such as rainwater and greywater harvesting, and a growth in the number of borehole derived water supplies. Given the nature of these water sources, there is often a chance that the water could contain an undesirable substance, which needs to be removed before the water is fit for purpose.
If, for example, there is a manufacturing facility that has a waste water discharge containing manganese, a borehole that is drilled in the locality of this plant may require a specialist filter containing media that targets manganese.
Typically, these selective mineral filters are vessel-type filters that resemble water softeners, and may or may not utilise some form of chemical regenerant.