Filtration - How does it work?
The process of filtration involves the flow
of water through a granular bed, of sand or another suitable
media, at a low speed. The media retains most solid matter while
permitting the water to pass. The process of filtration is usually
repeated to ensure adequate removal of unwanted particles in
the water (Ramstorp, 2003). This type of slow filtration over
a granular bed is generally known as slow sand filtration. It
is the oldest method of filtration but still widely used in
municipal water treatment plants today.
More modern filtration systems use carbon as the main constituent
material of the filter. This carbon is compressed into a solid
block form, as opposed to the more loosely structured, granular,
sand filters. Such filters often include other media substances,
in addition to the compressed, solid carbon. This type of water
filter is known as a multimedia filter. These filters clean
water through both physical
and chemical processes. Physically, they perform the same
function as slow sand filters, blocking the passage of unwanted
materials with molecular structures that are larger than water.
Chemically, the carbon or multimedia filters perform an added
filtration function. Through the process of adsorption,
the atomic charge of the carbon and other media encourages unwanted
particles to abandon their bond with the water and chemically
attach to the media (Ramstorp, 2003). The water then passes
through the filter, cleansed of undesirable materials. The addition
of extra media to the standard filter constitution of sand or
carbon allows for more particles to chemically bond to the media,
resulting in greater filter performance and efficiency.
Water is generally directed through several stages carbon and
multimedia filters to ensure the removal of all unwanted materials.
The first filtration stage will remove the most concentrated
chemicals, like chlorine, while subsequent stages will remove
smaller and more evasive chemicals, like pesticides.