In addition to di a class of circulating water, other water in the treatment can use multi-media filter, as a MBR reactor follow-up deep du water treatment process on the front-end pretreatment, generally full filtration, this water treatment is characterized by multi-media filter filtration speed is very slow, generally about 10m / h, the removal rate is high, the material if it is carbon steel, generally requires lining 3mm or 5mm of Tianran rubber, mainly to remove suspended solids, colloids, oil stains and ji, etc. There are three main types of water in industry, the water consumption zui is large in circulating leg but water, followed by boiler desalination water, and process water. 

1. Types of filter materials
The general filter material of multi-media filters is quartz sand (or tianran sea sand), and sometimes, the raw water contains some grease, requiring a layer of anthracite coal to be laid on the upper layer. The carbon content of anthracite coal is a very important indicator, common from 30 to 90 percent, the price difference is also very large, the higher the carbon content, the better.

2. Filler height
Taking the common porous plate structure as an example, the general packing height is about 1000~1200mm above the porous plate, the straight section height of the cylinder body is about 2000mm, if there is anthracite coal, the anthracite coal height is about 400mm, and the quartz Rotating sludge scraper sand is about 800mm (200mm cushion + 600mm filter layer).

3. Particle size
Quartz sand is generally about 200mm at the bottom layer of 2 to 4mm, the filter layer is 800mm for 0.5 to 1.0mm, and if it contains anthracite coal, the particle size of anthracite coal is 1 to 2mm. This kind of packing method is used in a wider and wider range, because the design of the filter layer generally takes into account the particle size of the lower layer filter material is smaller than the upper layer filter particle size, in order to ensure that the lower layer of the filter material you are effective and fully utilized, at the same time, the density of the upper layer should be small, to ensure the layered recovery after backwashing, the formation of the upper layer of the filter material to play a coarse filter role, resistance, the loss of water head is small, the lower filter material plays a fine filter role, the ability to intercept pollution is strong, so that the role of the multi-media filter bed is fully utilized, that is, the loss of the water head is small, and the filtration effect is good. Give full play to the advantages of each medium.

4. Zaisheng of the filter material
Multi-media filter in the filtration, the main removal of suspended solids, colloids, oil, etc., a long time in the filter bed, with the increase of the amount of dirt, on the one hand will increase the pressure loss will increase da, on the other hand, the water production will be reduced, a long time, the turbidity of the water will also have an impact, and even the water production will be higher than the turbidity of the incoming water, if not treated may be compacted, after the formation of wormholes, basically lose the mechanism of filtration. Therefore, the filter material zaisheng is very important, mainly relying on the pressure difference (set pressure difference of about 0.8 kg), time (set time about 8 hours) for automatic backwashing zai raw filter material, or manual backwashing. Rely on backwashing to Mechanical fine screen clean off the dirt containment in the filter layer to ensure the filtration effect of continuous water production. Multi-media filter due to the high height of the filler, the variety of filter materials, backwashing will increase the air washing, increase the friction and vibration intensity of the filter material, and then wash, the removal rate is higher. After the backwash is completed, the sewage will be washed again and then filtered.

5. Precautions when using filter material
When the multi-media filter is passed through the water, it must be backwashed, clean the impurities inside, and then filter. The impurities inside may be formed in two aspects, one is the impurities in the system pipe network, and the other is that the filter material is not clean.