FILTERS:

Water filtration is a separation process that consists of passing a solid-liquid mixture through a porous material which retains the solids and allows the liquid to pass through.

The retained substances will be either non-dissolved particles i.e. dirt, bacteria or organic material or dissolved such as chlorine, pesticides etc. Non dissolved particulate materials are removed by mechanical filtration where the filtration medium traps and retains the particles either as a result of pore size or impingement on the medium as the water rushes through it. The filter medium surface area determines the capacity of the filter.

Dissolved substances are removed by the ability of certain filtration medium to retain molecules on their surface (adsorption), oxidisation/precipitation or by membrane filtration. Certain filtration systems combine all of the above either by interconnecting several modules to form a composite system or by designing different functions into a single unit.

The Everpure BW Series Pre-Coat filters for example, employ powdered activated carbon to mechanically remove all particles down to 0.5 micron in size, reduce chemical contaminants such as chlorine by better than 99% and reduce lead to below the statutory level.

Filtration is a matter of:

• hydraulics
• particle destabilisation
• flow control

There are several levels of filtration:

• particle filtration
• adsorption
• microfiltration
• ultrafiltration
• nanofiltration (membrane softening)
• reverse osmosis

To summarize filtration is aimed at the removal of:

• Nitrates
• Metals
• Odours
• Tastes
• Organic matter
• Sulphates
• Turbidity
• Fluoride
• Chlorine compounds
• Bacteria and Cysts
• Gases