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.
The main factors to be considered in the design of multi-media filter are as follows:
1. The density difference of different filter media is large, which can ensure that there will be no mixing layer after backwashing disturbance.
2. The filter material is selected according to the purpose of producing water.
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.
In fact, taking the three-layer filter bed as an example, the upper filter material has the largest particle size and is composed of light filter materials with low density, such as anthracite and activated carbon; the middle filter material has a medium particle size and a medium density, which is generally composed of quartz sand; the lower layer is composed of heavy filter material with the smallest particle size and the largest 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 the role of coarse filtration, and the lower filter material plays the role of fine filtration, thus giving full play to the role of multi-media filter bed, and the effluent quality is obviously better than that of the single-layer filter bed. For drinking water, it is generally forbidden to use anthracite, resin and other filter materials.
The multi-media filter is mainly composed of filter body, matching pipeline and valve.
The filter body mainly includes the following components: cylinder; water distribution component; support component; backwashing gas pipe; filter material; exhaust valve (external), etc.
Selection basis of filter material
(1) It must have enough mechanical strength to avoid rapid wear and breakage in the process of backwashing;
(2) The chemical stability is good;
(3) It does not contain harmful and toxic substances to human health, and does not contain substances harmful to or affecting production;
(4) The selection of filter media should try to use the filter materials with high adsorption capacity, pollution interception capacity, high water yield and good effluent quality.
In the filter material, pebbles mainly play a supporting role. In the process of filtration, due to its high strength, stable spacing, and large pores, it is convenient for the filtered water to pass smoothly in the forward washing process; similarly, in the backwashing process, the backwashing water and air can pass smoothly. In the conventional configuration, the pebbles are divided into four specifications, and the paving mode is from bottom to top, first large and then small.