The filtration process is basically liquid (water which contains certain physical impurities) passing through a grainy layer of filtering medium or filtering mesh at relatively low flow rates, whereby the particles of impurities are retained by the filtering medium or the filtering mesh.
Sand filters are usually employed for separating small quantities (<10 ppm) of fine particles (<100 μm) from the liquid water phase. Often it is necessary to treat the water beforehand (coagulation, flocculation, sedimentation).
Well-maintained sand filters may reduce water turbidity by up to 90%, and remove up to 80-90% of bacteria, however, not the viruses.
Ultrafiltration (UF) is a procedure by which suspended solids are removed from the water by passing through a semi-permeable membrane. This procedure removes particles in the size range of 0.001 – 0.1 μm, and guarantees 100% reduction in turbidity, and removal of bacteria and viruses. The procedure is not suitable for restoration of chemically contaminated water.
Main advantages of ultrafiltration (UF):
- Complete removal of suspended solids in the water (turbidity)
- Partial removal of dissolved organic matter, depending on the molecular mass
- Effectively removes all bacteria and viruses
-log 6 for bacteria
-log 4 for viruses
- SDI colloidal index < 2
- Equipment protection on the secondary side (RO systems)
- High quality of outgoing water, irrespective of quality change of incoming raw water
- Incorporating several conventional procedures in one
Reverse osmosis (RO)
Osmosis is a process on which nearly all natural metabolic processes are based. If two solutions of varying concentrations are separated in a system by a semipermeable membrane, the solution with the higher concentration will always have a tendency to become more diluted. This process (osmosis) will continue until osmotic equilibrium is reached.
In the process of reverse osmosis, the direction of the osmotic flow is reversed. To achieve this, pressure must be exerted on the concentrated solution. This pressure must be considerably greater than the osmotic pressure that arises due to the natural balancing of differing concentrations.
Synthetic membranes are used in water treatment systems that work on the principle of reverse osmosis. These membranes are permeable for water molecules. The content materials dissolved in the water are held back by the membranes. High pressure causes the concentrated solution (for example drinking water or process water) to flow through these membranes. The result is a separation of this solution into a partial stream with water in which the content materials that are held back are located (concentrate).
Amiad filtering systems
The company Amiad develops and supplies customized filtering solutions for demanding industrial, municipal utility and irrigation systems. A special segment is represented by the self-cleaning filters which – in addition to effectively retaining particles – enable autonomous operation and uninterrupted water supply.
They are distinguished by:
- Automatic cleaning, if pressure drop across the filtering surface exceeds a certain pre-set pressure value
- Uninterrupted water supply as the filter cleans itself in a matter of seconds – without interrupting the flow of water on the incoming side;
- Modular structure with different dimensions, single or serial use possible;
- Flexibility of control options via hydraulically or electronically guided units;
- Rinsing according to pre-set pressure difference and/or timer setting;
- A wide range of different filtration grades ranging from 3500 up to 3 microns.