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:

 

Description

Type

Common application

Actived coal

AQUARBO®

Pure carbon with a residual ash content

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

Anthracite coal

AQUAZIT®

(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

(AQUAGRAN®)

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

For pure filter operation less common are:

 

Description

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.

 

 

Density

 

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

Solid density                  

ρF            

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

Particle density

ρK

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

Storage density

ρL

Density after back flushing

Tap density

ρR

Density after jolting the filter bed

Bulk density

ρS

Density caused by loose filling

 

The density decreases in this order

3.2.2 Hydraulic Properties

Initial pressure loss

Δρ

Pressure loss at the beginning of the filter run

Filter resistance

Difference of increased contamination by pressure loss to
initial pressure drop

Fluidization

νF

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

Oversize

-

Particles which are larger than the upper nominal grain

Undersize

-

Particles which are smaller than the lower nominal grain

Effective size

d10

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

d60/d10         

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

f      

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)

surface  

Οs   

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


Above

AQUAZIT® (Filter coal N)

  0,8       –          1,6      mm

     1,4       –          2,5       mm

Below

AQUAGRAN® (Filterquartz)

  0,4       -           0,8       mm

  0,71      -           1,25      mm


Above

AQUALIN® (Filter coal H)

  0,6       -           1,6       mm

1,   4       -           2,5       mm

Below

AQUAGRAN® (Filterquartz)

   0,4       -           0,8       mm

  0,71      -           1,25      mm


Above

AQUARBO® (A Activated coal)

                        K814

Below

AQUAGRAN® (Filterquarz)

  0,63      -           1,0       mm

 

 

AQUAZIT®      =          Anthracite coal

 AQUALIN®     =          Lignite

 AQUARBO®   =          Activated coal         

 

 

 

further to:   "Different methodes"

DORSTEN
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Dipl.-Ing.

Holger

Vespermann

DEEN
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