The meaning of filtration is that in the process of water treatment, filtration generally refers to the process of using filter media layers such as quartz sand and anthracite to retain suspended impurities in water, thereby clarifying the water. The porous material used for filtration is called filter material, and quartz sand is the most common filter material. There are various types of filter media, including granular, powdered, and fibrous. Common filter media include quartz sand, anthracite, activated carbon, magnetite, garnet, porous ceramics, plastic balls, etc.

Multi media filter (filter bed) is a medium filter that uses two or more media as the filter layer. In industrial circulating water treatment systems, it is used to remove impurities, adsorbed oil, etc. from wastewater, so that the water quality meets the requirements of recycling. The main function of filtration is to remove suspended or colloidal impurities in water, especially small particles and bacteria that cannot be removed by sedimentation technology. BOD5 and COD also have a certain degree of removal effect. The performance parameters are shown in the table below:

Multi medium filters are widely used in water treatment processes, and they mainly consist of the following parts: supporting pipelines and valves. The filter body also includes: ① cylinder body; ② Backwashing the trachea; ③ Water distribution component; ④ Supporting components; ⑤ Filter material; ⑥ Exhaust valve (external), etc

The multimedia filter material inside the filter is high-quality uniform gravel, quartz sand, magnetite, anthracite and other filter materials. These filter materials are scientifically and orderly distributed in the filter tank according to their specific gravity and particle size. For example, anthracite with small specific gravity and slightly larger particle size is placed at the top of the filter bed, quartz sand with moderate specific gravity and small particle size is placed in the middle layer of the filter bed, and gravel with large specific gravity and particle size is placed at the bottom layer of the filter bed. This ratio ensures that the filter does not produce disordered layers during backwashing, thereby ensuring the retention capacity of the filter material.

A multimedia filter (also known as a mechanical filter) is a typical multimedia filter that uses layered anthracite, sand, fine garnet, or other materials as the bed layer.

The top layer of the bed is composed of the lightest and coarsest materials, while the heaviest and finest materials are placed at the bottom of the bed. The principle is depth filtration - larger particles in the water are removed at the top layer, while smaller particles are removed at a deeper depth in the filter medium. Thus, the water quality can reach the standard after coarse filtration.

The equipment is pressure type, and its principle is that when the raw water passes through the filter material from top to bottom, the suspended solids in the water are intercepted by the surface of the filter layer due to adsorption and mechanical blockage; When water flows into the middle of the filter layer, due to the tighter arrangement of sand particles in the filter material layer, particles in the water have more opportunities to collide with the sand particles. As a result, flocs, suspended solids, and sand particles in the water adhere to each other, and impurities in the water are trapped in the filter material layer, resulting in clear water quality. The suspended solids in the filtered effluent can be below 5 milligrams per liter.

1. Porous media filters are widely used in water treatment processes and can be used alone, but most of them are used as pre filters for advanced water treatment (exchange resin, electrodialysis, reverse osmosis).

2. Multi media filters are commonly used pre-treatment devices for deep water purification, which can be filled with different filter media according to process requirements.

3. The material of the multimedia filter can be fiberglass, A3 steel anti-corrosion or rubber lined, and all stainless steel. There are two forms of operation: fully automatic and manual. Automatic control adopts automatic controllers imported from the United States and pneumatic and hydraulic valve control, which is easy to operate and maintain. It is widely used in pre-treatment devices of water treatment processes in various industries.

4. The filtering material of a multimedia filter (including a dual filter material filter) should have sufficient chemical stability, and there should be certain differences in the relative density and particle size of each medium. The dual filter material filter composed of anthracite and quartz sand uses anthracite with a relative density of 1.4-1.6, particle size of 0.8-1.8mm, quartz sand with a relative density of 2.6-2.65, and particle size of 0.5-1.2mm; In addition to the above two types of filter media, a three-layer filter can also use heavy ores such as manganese sand and magnetite, with a relative density of 4.7-5.0 and a particle size of 0.5-4mm.

(1) It must have sufficient mechanical strength to avoid rapid wear and breakage during the backwashing process;

(2) Good chemical stability;

(3) Does not contain harmful or toxic substances to human health, and does not contain substances that are harmful or affect production;