Influencing factors of principle, configuration and efficiency of biological aerated filter 2

Structure of biological aerated filter

The main structure of BAF includes tank body, filter material, supporting layer, air distribution system, water distribution device, backwashing device and drainage system.

Pool body

Its function is to accommodate the treated water and the surrounding filter material, and to support the weight of the filter material and the aeration device. It has three shapes: circular, square and rectangular (aspect ratio is 1.2 ~ 1.5). The structure forms are steel equipment (small amount of water treatment) and reinforced concrete structure (large amount of water treatment). In order to ensure the backwash effect, the single tank area should not be too large (less than 100m2).

Filter material

The filter media is the main body of the biofilter, which has a direct impact on the purification function of the biological filter. Therefore, the filter media should have the characteristics of hard, high strength, corrosion resistance, freezing resistance, high specific surface area, large porosity, and can be used locally to facilitate processing, transportation and other conditions. The material can be made of lightweight ceramsite, slag, quartz sand, coke, zeolite and so on. The particle size is 3-6mm, and the thickness of the filter layer is about 2.5-4.5m.

Bearing layer

The function is to support the filter media, prevent the loss of filter media and plugging the filter head, while maintaining a stable backwash. In order to ensure the stability of the supporting layer and the uniformity of water distribution, the material is required to have good mechanical strength and chemical stability, its shape is as close as possible to the circle, commonly used material is pebble.

Water distribution system

It includes the water distribution chamber at the bottom of the filter and the water distribution filter head on the filter plate.

For the upflow filter, the function of the water distribution chamber is to make the sewage into the filter uniformly mixed in a short period of time. The resistance function of the supporting filter plate and the filter head is that the sewage distributes uniformly under the filter plate and flows evenly into the filter bed through the filter head on the filter plate. When the filter is backwashed, water is used. For the down flow filter, the water distribution system is mainly used for filter backwashing and collecting and purifying water.

Composition of water distribution chamber

Buffer water distribution zone and supporting filter plate. In the buffer water distribution area, the sewage is initially mixed, and then uniformly distributed under the filter plate by the resistance of the supporting plate. The sewage is evenly fed into the filter bed by the filter head on the filter plate. The buffer water distribution zone performs uniform gas distribution when combined with water and gas.

Water distribution filter

Its function is to evenly distribute water to the filter.