Granular media filtration

Gemwater is able to provide the design of several types of Granular Media Filters, depending on the specific water composition and environmental condition. The process solutions are studied in order to comply with Client requirements.
Depth filtration through a filter bed is suitable for slow or rapid filtration of water when it is desired to merely reduce the concentration of suspended solids, without acting upon the colour or organic matter content.
Depending on the proprieties of the particles to be retained, it may be best to use one layer (of varying depth) of a uniformly sized material, two or more layers of different grain size (each layer being uniform), or one of more layers of materials of completely heterogeneous grain size. The most common filter media in water treatment are sand and anthracite.

Through a header water is distributed in order to homogeneously cover the bed below. The filter media is composed by fine sand on the top and then gradually coarser sand in a number of layers followed by gravel on the bottom, in gradually larger sizes. The top sand physically removes particles from the water.
The role of the subsequent layers is to support the finer layer above and provide efficient drainage.
When clogging becomes excessive, or the filtrate quality being to suffer, the filter bed must be washed.
This washing operation must restore the original proprieties of the bed, or otherwise the filter would become less effective. Backwashing can be performed with uniform distribution of water or with water + compressed air, which pass through the filter and removed the dirt which was retained by the media.
While filtration occurs normally down ward, backwashing is carried out upwards.
A filter will only operate effectively if there is a perfect distribution through the filtering mass of the water to be filtered, of the wash-water and of the air (if used) utilized for washing.

The main reason for selecting a pressure filter is that by disposing a sufficient pressure the filtration rate can be increased and/or the filter runs can be prolonged. Therefore gravity filters are normally used when a low filtration rate is required and when the plant capacity is high (because large size filters can be cheaply executed in reinforced concrete). The backwash procedure does not differ in both cases.

The activated carbon material is normally used to remove the dissolved organics matters, color, free chlorine, hydrocarbons, unpleasant taste in waste water treatment and in potable water treatment.
The substances removed by the activated carbon occur by adsorption process; this is depending by:
the activated carbon filling material (porous structure, active surfaces);
the chemical characteristics of organic substances to be removed (molecular weight and structure, polarity and
  solubility in water, presence of specific functional groups);
operating temperature;
contact time.