Drinking water 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.

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 coal	Mechanical 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^®)	Silica	Mechanical filtration in single and multi-layer filters partially with removal of iron and manganese

For pure filter operation less common are:

Description	Type	Common Applikation
Expanded clays	Aluminum silicates	Mechanical filtration of solids in multilayer filters
Pumice	Porous rock of volcanic origin	Mechanical filtration and large surface area for biological processes
Calcium carbonate	Limestone	Mechanical filtration of solids in multilayer filters and deacidification
Dolomite	Calcium magnesium carbonate	Mechanical filtration, deferrisation, demanganisation and for part deacidification
Garnet	Iron-aluminum silicate	Mechanical filtration and support layer properties
Manganese dioxide	Manganese	Demanganisation

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	ρ_F	Density of the pure filter material measured on ground sample (no air pockets)
Particle density	ρ_K	Density of the natural grain (incl. possible air pockets)
Storage density	ρ_L	Density after back flushing
Tap density	ρ_R	Density after jolting the filter bed
Bulk density	ρS	Density caused by loose filling

The density decreases in this order

Hydraulic Properties

Initial pressure loss

Δ_ρ

Pressure loss at the beginning of the filter run

Filter resistance

–

Difference of increased contamination by pressure loss to
initial pressure drop

Fluidization

ν_F

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

Size

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

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)

surface

Οs

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

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