Notes to table
Water filtration media are identified by two groups of indexes. The first group relates to the characteristics of the filter media that is supposed to be used for a filter-bed, and the second group directly to the filter-bed.
The first group of characteristics concerns the granulometric structure and heterogeneity of filter media, its density and the form of grains, physical integrity and chemical stability, and also its sanitary measurements.
One of the important characteristics of separate grain of the filter media, defining characteristics of a granular layer during backwashing is the hydraulic size (speed of grain movement in water). This index depends on density of a material and size of grains.
Technological characteristics of filters are defined by filter bed characteristics as a whole: by the porosity of filter bed, a specific surface of filter media in unit volume of a layer and distribution of size grains on filter-bed height.
The density of grains influences demanded intensity of washing as the greater speed of water stream is necessary for weighing of heavier filter materials. The least admissible density of grains is limited by washing conditions.
Full removal of the washed impurities from the filter is provided by intensity not below 12-13 (l/s∙m ²), therefore, in order to prevent the removal of separate grains out of the filter together with impurities, their density should not be less than 1,6-1,7 g/sm ³.
The durability of a filter material is defined by its physical integrity and chemical stability. Physical integrity is characterized by indicators of attrition and grindability.
Mechanically strong loadings are those to have attrition not exceeding 0,5%, and detachability of 4%.
Chemical stability is defined in alkaline, acid and neutral according to the increase of the dry residue and oxidability of water as a result of contact of a filter media to these solutions. As a result granular filter media with satisfactory chemical stability should give an increase in the dry residue not more than 20 mg/l and an increase in oxidability not more than 10 mg/l in water.
The major geometrical characteristics of the filter bed made of separate grains are porosity and a specific surface. The granular filter media represents a set of the channels (pores) of the various form and size. The relation of volume of a pores to layer to total amount defines the porosity of media.
The higher porosity and a specific surface are the more effective the filter work is. These parameters are also connected with the increase of porosity of the specific surface. Usually the raised porosity takes place, when the filter bed is made of grains with the developed surface.
The important requirement to anthracite filter media is the form of grains. The manufactured grains should have the form, close to cubic or spherical. If manufactured grains have the flat form such material is not suitable for the filter-bed device as such loading has low intergrain porosity, the raised carrying out of a material is badly washed out.
Actual indicators of «AQUALAT®» filter media completely correspond to requirements of SSS State Standards, are in borders of specifications and are essentially better than normalized sizes of production schedules for clearing household and industrial waters.
In the long term these advantages provide the following services:
By grindability and attrition:
By chemical stability: