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Pressure Filtration

General Description

Pressure filtration is a broadly applied process used for removing various solids and contaminants from water.The basic concept is to let water pass under pressure through a vessel that contains filter media. The type and size of filter media determine the filtration effect and the contaminants to be removed.

Advantages - Benefits of the Technology

Pressure filtration does not face great competition. There are not many other solid or contaminant removal processes that are this fast, effective, require such a small footprint, are easily monitored with inexpensive controls and are easily adjustable.

Applications

Depending on the type, size and quantity of filter media used, pressure filtration serves a great variety of applications including:

Filtration of biologically treated sewage or industrial wastewater as a polishing stage to reduce furthermore the concentration in suspended solids and organic load
Filtration of borehole water for iron and manganese removal
Filtration of cooling water to prevent heat exchanger fouling
Filtration of potable water

Basic Process Stages

The filtration process is straightforward. Water is pumped at a predetermined pressure and flow rate before it passes through the filtering unit. The filtering unit consists of the vessel (usually made of carbon steel, stainless steel or grp), the filtering media (depending on the incoming water and the expected results these can be gravel, sand, anthracite, granular activated carbon or other).

Water enters the top of the vessel, flows downwards through the bed of media and leaves through an outlet at the bottom. Solids and contaminants are either retained or absorbed depending on the chosen media.

Water is passed through the filter vessel until either the pressure loss across it rises to a preset value, or contaminant breakthrough is detected. It is then taken out of service and cleaned by backwashing with clean water.

The backwash water enters the bottom of the filter vessel and flows upwards through the media bed, which starts to fluidize, that is the media grains begin to separate from each other and float freely. The fluidization of the media releases the retained or absorbed contaminants, a process which may be assisted by bubbling air through the bed (air scouring) which causes the sand grains to rub against each other dislodging the retained or absorbed contaminants from the surface. The contaminants are then washed of the filter bed and released out of the filter vessel to waste.