Filter products

Principles used to granular filter materials

Filter materials need generally to be sufficiently resistant to mechanical, microbiological and chemical attack. After filling, flushing, peeling and start filter media must not transfer any unwanted substances into the water during the filter operation.


3.1 Common filter media

There are a number of common filter materials that perform different tasks. Common are:




Common application

Actived coal


Pure carbon with a residual ash content

Absorbers for non-polar - especially organic compounds that contaminate the water in very low concentrations.

Anthracite coal


(Filter coal N)

Pure Anthracite coalMechanical filtration of solids in multilayer filters

Lignite coke AQUALIN®

(Filter coal H)

Lignite coke

Mechanical filtration of solids in multi-layer filters with adsorptive properties

Silica sand

Quartz gravel


SilicaMechanical filtration in single and multi-layer filters partially with removal of iron and manganese

For pure filter operation less common are:



TypeCommon Applikation
Expanded clays

Aluminum silicates

Mechanical filtration of solids in multilayer filters

PumicePorous rock of volcanic originMechanical filtration and large surface area for biological processes
Calcium carbonateLimestoneMechanical filtration of solids in multilayer filters and deacidification
DolomiteCalcium magnesium carbonate

Mechanical filtration, deferrisation, demanganisation and for part deacidification

GarnetIron-aluminum silicateMechanical filtration and support layer properties
Manganese dioxideManganeseDemanganisation


The substances  listed here have an impact rather on the chemical composition of water.




Is defined as mass per volume and is  specified e.g. in t/m³, kg/L or g/cm³.

Solid density                  


Density of the pure filter material measured on ground sample (no air pockets)

Particle density


Density of the natural grain (incl. possible air pockets)

Storage density


Density after back flushing

Tap density


Density after jolting the filter bed

Bulk density


Density caused by loose filling


The density decreases in this order

3.2.2 Hydraulic Properties

Initial pressure loss


Pressure loss at the beginning of the filter run

Filter resistance

Difference of increased contamination by pressure loss to
initial pressure drop



Velocity of the water in which the particles are in the floating state

3.2.3 Size (on the example of 0.71 – 1.25 mm)

Grain size



Nominal width of the mesh. For example:
Lower nominal grain = 0.71 mm
Upper nominal grain = 1.25 mm



Particles which are larger than the upper nominal grain



Particles which are smaller than the lower nominal grain

Effective size


The value indicates at which (theoretical) size of the sieves to 10% pass through (90 % are bigger than this value). In the example approximately something like 0.8 mm.

Uniformity coefficient


The calculating value caused by division of d60 through d10. It describes together with the d10 the grading curves. The closer the value is to 1, the steeper the slope of the grading curve. Conventional values are 1.3

3.2.4 Grain habitus

Form factor


1             for ideal ball
0.98      for glass beads
0.85      for rounded grains as AQUAGRAN, quartz gravel and sand
0.70      for crushed material such as grit

Specific (grain)



Total surface of the grains based on the total volume of the bed

3.3 Assignment of aggregates to each other

In multilayer filter, the individual aggregates have to be well coordinated both in terms of grain size and with attention to the denisty.  The particle size must be correct, otherwise the individual grains sift down between the larger grains (see 2.2 -. Fig. 4). So should filter sand 0.71 – 1.25 mm not be installed directly on a support gravel with 3.15 - 5.6 mm, because the pore volume is greater than the smallest grain. In such a case, 1.4 - 2.2 mm or 2 - 3.15 mm have to be installed as an intermediate layer. Regarding the density, the expansion behavior is important (how far the bed expands at the same flow pressure).

 An extension of the lighter carbon components over 50% is not desirable, since the risk of washing out is extremely high

The best combination in each individual case must be determined in preliminary tests for each plant, if there are no experience with similar dimensions are present.


 From experience common combinations are:




Product combinations

Grain groups examples


AQUAZIT® (Filter coal N)

  0,8       –          1,6      mm

     1,4       –          2,5       mm


AQUAGRAN® (Filterquartz)

  0,4       -           0,8       mm

  0,71      -           1,25      mm


AQUALIN® (Filter coal H)

  0,6       -           1,6       mm

1,   4       -           2,5       mm


AQUAGRAN® (Filterquartz)

   0,4       -           0,8       mm

  0,71      -           1,25      mm


AQUARBO® (A Activated coal)



AQUAGRAN® (Filterquarz)

  0,63      -           1,0       mm



AQUAZIT®      =          Anthracite coal

 AQUALIN®     =          Lignite

 AQUARBO®   =          Activated coal         



further to:   "Different methodes"



Holger  Vespermann

sales manager, proxy holder

+49 02362 - 2005-30
+49 02362 - 2005-99
direct inquiry