Trickling filter

A trickling filter (also called trickle-bed reactor or Rieselstromreaktor ) is a device for wastewater treatment. The cleaning is carried out by coulure the wastewater through a fixed bed (plastic, lava slag, etc.). The aeration is carried out in countercurrent. In the fixed bed grown bacterial lawns make the reduction of biodegradable waste water constituents. The overgrowing bacteria colonies are washed away by the durchrieselnde wastewater and removed in the secondary clarifier.

A special form of the trickling filter is the rotating biological trickling filter, which uses the rotating disks in a sewage tank partially submerged biomass nursery.

Trickling filter designed in accordance with the loading rate (BR), ie after the BOD5 loading per cubic meter of fill material in boulder -filled equipment or after the wing loading, ie BOD5 per square meter of the surface of the filler material in plastic- filled systems. Plastic fillers can have surfaces of 100 to 200 m2/m3.

Typical loading rates are for carbon removal 0.4 kg BSB5/m3, d and for carbon removal and nitrification 0.2 kg BSB5/m3, d at chunk -filled trickling filters. In plastic fillings d Kohlenstoffentferungen and nitrification can be achieved with surface loading of 4 g BSB5/m2, d Kohlenstoffentferung and 2 g BSB5/m2.

In small treatment plants would be correspondingly lower values ​​apply in order to achieve a sufficient security against shock loads.

The final clarification should have a residence time of about 2.5 hours at a surface loading of approximately 1 m3/m2, h.

Compared with activated sludge plants, trickling filters have the advantage that they require a relatively simple mechanical equipment and are not blähschlammgefährdet. Further falls in the trickling filter to less excess sludge than in the activated sludge process.

In practice, the wastewater trickling filters have become more rare still the only biological treatment stage. In addition to the substantial construction effort was instrumental to that with trickling filters, although the step for biological nitrification can be accomplished, but is difficult to achieve the biological denitrification.

Trickling filter can be followed as a further purification step behind a highly loaded first stage after the activated sludge process. The first-stage sedimentation tank is then referred to as an intermediate clarifier. The trickling filter is used as a second biological stage. In the first stage, the carbon compounds (organic impurities expressed as BOD5 or COD ) can be substantially reduced. The trickling filter is used for cleaning in terms of carbon compounds and an appropriate design of the oxidation of the nitrogen present in the wastewater to nitrate. However, removal of nitrogen from wastewater by denitrification process is technically difficult in this process and could only be achieved by recirculation of the expiry of the trickling filter in the first stage or a further purification step (eg submerged fixed bed and artificial substrate addition).

• Wastewater treatment