Structure of biological aerated filter

The structure of BAF is basically the same as that of the three-stage sewage treatment filter, but the filter material is different, and the single homogeneous filter material is generally used. The BAF is mainly composed of eight parts: filter body, filter material, supporting layer, water distribution system, gas distribution system, backwash system, effluent system, pipeline and automatic control system.

1. filter tank body

The function is to hold the treated water and the filter material, and support the weight of the filter material and aeration device. The shape is round, square and rectangular, and the structure forms are steel equipment and reinforced concrete structure.

2. biological filler layer

The filler layer is the carrier of biofilm and has the function of retaining suspended substances. At present, the filter material used in BAF is honeycomb tubular, bundle, circular radiation, shield, mesh and cylinder, etc. the filter materials are mainly porous ceramsite, quartz sand, expanded shale, light plastic, expanded silicon aluminate, plastic module and FRP.

There are some differences in the physical and chemical properties of different particle fillers, some of which are even related to each other. The selection of bio carrier filler is the key to the success of BAF technology. It determines whether the filter material of BAF can operate efficiently. The selection of the filler should be based on the following factors:

a. Good mechanical strength;

b. Generally, porous inert carriers with large specific surface area and high porosity are generally selected, which is conducive to the adsorption, sustainable growth and formation of biofilm;

c. The regular spherical packing is selected to make the distribution of air and water evenly and the flow resistance is small;

d. The surface should have certain porosity and roughness, which is conducive to the attachment and growth of microbial membrane, and the operation of biofilter;

e. The density should be within a certain range;

f. It should have surface electrical property and hydrophilicity, and have good anti backwash ability;

g. The biological and chemical stability is good, and it should have certain chemical stability and corrosion resistance.

3. bearing layer

The supporting layer is mainly used to support the biological filler, prevent the loss of biological filler and block the filter head, and also can maintain the stable backwashing. The supporting layer is made of pebbles. The height of bearing layer is 400-600mm in different positions.

4. water distribution system

The distribution system of BAF mainly includes the water distribution chamber at the bottom of the filter and the water distribution filter head on the filter plate.

5. air distribution system

There are two main purposes for the aerated biological filter to set up the gas distribution system: one is to ensure the aeration needs in normal operation, and the other is to ensure the gas distribution during the backwashing of air and water.

The design of aeration system must be carried out according to the process calculation of the required air supply. The simple aeration device of BAF can adopt perforated pipe. In practice, the same distribution air pipe is used for aeration with oxygen and backwash aeration. However, the air demand for oxygen filled aeration is smaller than that of backwash, so the distribution of gas is not easy to be uniform.

6. backwash system

Backwashing is the key to ensure the normal operation of BAF. The purpose is to make the filter material properly cleaned and recover its function of wastewater interception in a short backwash time. The sequence of air water combined backwashing is usually: first, the air water is used for backwashing separately, then the gas water is used for backwashing, and finally, the backwash is conducted with clean water. In the process of backwash, the washing strength and flushing time must be mastered.

7. water outlet system

The effluent system of BAF can be treated by peripheral water or single weir.

8. pipeline and automatic control system

The pipe is mainly used for water inlet and air intake, and the automatic control system is composed of CPU electric control box and line.