Definition of biological aerated filter

Aerated biological filter (BAF) is a new sewage treatment process that integrates biological oxidation and interception of suspended solids, achieving efficient removal of pollutants through biofilm method. The core principle is to use the biofilm on the surface of the filter material for oxidative degradation, while also having physical filtration function, which can effectively remove pollutants such as SS, COD, BOD, and nitrogen and phosphorus. This process has the advantages of high organic load, small footprint, and low investment, but requires high requirements for influent SS and pre-treatment.

The working process of a biological aerated filter generally includes three stages: packing sedimentation, start-up, and stabilization. Firstly, in the sedimentation stage of the packing material, suspended solids in the wastewater are removed through the filtering effect of the filter material, and the filter material gradually forms an attachment layer of microorganisms. Then, during the start-up phase, add an appropriate amount of activated sludge or seed bacteria to the filter material to quickly form a biofilm. In the stable stage, when the wastewater passes through the filter layer, microorganisms degrade organic matter and purify the water quality.

Aerated biological filters have the advantages of simple structure, easy operation, and stable treatment effect, and are widely used in urban sewage treatment plants, industrial wastewater treatment, and rural domestic sewage treatment. However, there are also some problems with aerated biofilters, such as filter clogging and high aeration energy consumption, which require reasonable design and management to improve treatment efficiency and reduce operating costs.

Operating Procedures for Aerated Biological Filters

1、 Preparation before startup

System check

Confirm that the filter layer (volcanic rock/ceramic particles) has no compaction, and the thickness of the supporting layer (pebbles) meets the design requirements.

Check that the aeration system (perforated tube/microporous aerator) is unobstructed and the air volume regulating valve is flexible.Definition of biological aerated filter

The backwash water pump, air compressor, and valve opening and closing functions were tested to be normal.

Preprocessing requirements

Inlet SS ≤ 100mg/L, if necessary, add a primary sedimentation tank or coagulation sedimentation.

Inoculate activated sludge or biofilm, and start biofilm after 24-48 hours of incubation.

2、 Run operation

Parameter control

Hydraulic load: adjusted according to water quality, COD load ≤ 3kg/m ³ · d.

Aeration rate: DO maintained at 2-4mg/L, gas water ratio 3:1-5:1.

Temperature: 15-35 ℃ is recommended, and HRT should be extended at low temperatures.

Daily monitoring

Record COD, NH3-N, pH, and turbidity of incoming and outgoing water every 2 hours.

Observe the color of the biofilm (yellow brown is normal) and promptly clean the floating debris on the surface of the filter material.Definition of biological aerated filter

3、 Backwash operation

Cycle and conditions

Water backwash: Start every 24-48 hours or when the head loss reaches 1.5m.

Air water combined blowback: once a week, first air blowback (30m ³/h · m ²) and then water blowback (15m ³/h · m ²).

Operation steps

Close the inlet valve, turn on the backwash water pump and air compressor.

Inflate with air for 3-5 minutes, rinse with water for 5-8 minutes until the drainage is clear.

Before resuming operation, rinse the filter material with raw water for 2 minutes.

4、 Maintenance and safety

Equipment maintenance

Check the blockage of the aerator every month, acid wash or replace damaged parts.

Supplement lost filter media every quarter and clean up debris in the support layer.

Safety regulations

Personnel are prohibited from entering the filter during backwashing to prevent slipping and falling.

Power off and hang warning signs are required for repairing the aeration system.

The aeration system is used to introduce air into the biological filter to provide the oxygen required by microorganisms. It generally consists of a blower, an air pipeline, and an aeration head, which is usually installed below the filter layer. The drainage system is located at the bottom of the filter tank, mainly used to collect and treat the sewage, and to remove the remaining sludge and detached biofilm in the filter tank. It also has a certain backwashing function to regularly clean the filter material and prevent it from clogging. The supporting layer is located above the water distribution system and is composed of larger gravel or pebbles. Its main function is to support the filter material layer, prevent the loss of filter material, and ensure that the water flow can enter the water distribution system evenly through the filter material layer.