Multi media filter is a process of using one or several kinds of filter media to pass the water with high turbidity through the granular or non granular materials with certain thickness under certain pressure, so as to effectively remove the suspended impurities and make the water clear. The commonly used filter materials are quartz sand, anthracite, manganese sand, etc., which are mainly used for water treatment and turbidity removal, softened water, pre-treatment of pure water, etc., and the turbidity of the effluent can reach 3 degrees following.

在水處理上使用的多介質(zhì)過濾器，常見的有：無煙煤-石英砂-磁鐵礦過濾器，活性炭-石英砂-磁鐵礦過濾器，活性炭-石英砂過濾器，石英砂-陶瓷過濾器等。

The common multi-media filters used in water treatment are: Anthracite quartz sand magnetite filter, activated carbon quartz sand magnetite filter, activated carbon quartz sand filter, quartz sand ceramic filter, etc.

多介質(zhì)過濾器的濾層設(shè)計，主要考慮的因素為：

The main factors to be considered in the design of filter layer of multi-media filter are:

1、不同濾料具有較大的密度差，保證反洗擾動后不會發(fā)生混層現(xiàn)象。

1. Different filter materials have large density difference to ensure that there is no mixing phenomenon after backwashing disturbance.

2、根據(jù)產(chǎn)水用途選擇濾料。

2. Select filter material according to the purpose of water production.

3、粒徑要求下層濾料粒徑小于上層濾料粒徑，以保證下層濾料的有效性和充分利用。

3. The particle size of the lower filter material is required to be smaller than that of the upper filter material to ensure the effectiveness and full utilization of the lower filter material.

事實上，以三層濾床為例，上層濾料粒徑 大，有密度小的輕質(zhì)濾料組成，如無煙煤、活性炭；中層濾料粒徑居中，密度居中，一般為石英砂組成；下層濾料由粒徑 小，密度 大的重質(zhì)濾料組成，如磁鐵礦。由于密度差的限制，三層介質(zhì)過濾器的濾料選擇基本上是固定的。上層濾料起粗濾作用，下層濾料起精濾作用，這樣就充分發(fā)揮了多介質(zhì)濾床的作用，出水水質(zhì)明顯好于單層濾料的濾床。

In fact, taking three-layer filter bed as an example, the upper filter material is composed of light filter material with large particle size and small density, such as anthracite and activated carbon; the middle filter material is composed of quartz sand with medium particle size and medium density; the lower filter material is composed of heavy filter material with small particle size and large density, such as magnetite. Due to the limitation of density difference, the selection of filter material for three-layer media filter is basically fixed. The upper filter material plays a role of coarse filtration, and the lower filter material plays a role of fine filtration, so that the multi-media filter bed is fully played, and the water quality of the effluent is obviously better than that of the single-layer filter bed.

而對于飲用水，一般禁止使用無煙煤，樹脂等濾料。

For drinking water, it is generally prohibited to use anthracite, resin and other filter materials.