Difference of increased contamination by pressure loss to
initial pressure drop
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 | 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 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 | 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 | 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
| – | |
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: |
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 |
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 | |
further to: "Different methodes"
Dorsten
Dipl.-Ing.
Holger Vespermannsales manager, proxy holder
| +49 02362 - 2005-30 | |
| +49 02362 - 2005-99 | |
| send |