Trickling filter
A trickling (including trickle bed reactor or Rieselstromreaktor called) is an apparatus for waste water treatment. The cleaning takes place by trickling the wastewater over a fixed bed (plastic, lava slag, etc.). The ventilation takes place in countercurrent. Bacterial lawns grown on the fixed bed break down biodegradable waste water constituents. The growing bacterial lawn is washed away by the trickling wastewater and separated in the secondary clarifier.
A special type of trickling filter is the immersed disc trickling filter, in which rotating disks with biomass growth are used that are partially submerged in a waste water basin.
Trickling filters are dimensioned according to the volume load (B R ), i.e. according to the BOD 5 load per cubic meter of filler material in lump-filled systems or according to the surface load, i.e. BOD 5 per square meter of the surface of the filler material in plastic- filled systems. Filling materials made of plastic can have surfaces of 100 to 200 m 2 / m 3 .
Typical volume loads are 0.4 kg BOD 5 / m 3 , d for carbon removal and 0.2 kg BOD 5 / m 3 , d for carbon removal and nitrification , for trickling filters filled with lumps. In the case of plastic fillings, a surface loading of 4 g BOD 5 / m 2 , d carbon removal and with 2 g BOD 5 / m 2 , d carbon removal and nitrification can be achieved.
In the case of small sewage treatment plants , correspondingly lower values would have to be used in order to achieve adequate safety against shock loads.
The final clarification should have a residence time of approx. 2.5 hours with a surface loading of approx. 1 m 3 / m 2 h.
Compared to activated sludge systems, trickling filters have the advantage that they require comparatively simple mechanical equipment and are not endangered by bulking sludge . Furthermore, the trickling filter produces less excess sludge than the activated sludge process.
In the practice of wastewater treatment, trickling filters as the only biological wastewater treatment stage have become rare in Germany. In addition to the considerable structural effort, it was decisive that trickling filters can be used to carry out the step towards biological nitrification, but biological denitrification is difficult to achieve. In other parts of the world, e.g. B. Latin America trickling filters are still used.
Trickling filters can also be used as a further cleaning step after a higher contaminated first stage after the activated sludge process . The secondary clarifier of the first stage is then called the intermediate clarifier. The trickling filter is used as the second biological stage. In the first stage, the carbon compounds (organic contamination measured as BOD 5 or COD ) are essentially reduced. The trickling filter is used for the final cleaning with regard to the carbon compounds and, if designed accordingly, for the oxidation of the nitrogen contained in the wastewater to nitrate. Removing the nitrogen from the wastewater by denitrification is technically difficult with this process and could only be achieved by recirculating the drainage of the trickling filter in the first stage or a further cleaning step (e.g. immersed fixed bed and artificial substrate addition).
In biological waste gas cleaning , the trickling filter principle is used when operating bio- diesel bed reactors , in that the pollutants contained in the waste gas are absorbed by a scrubbing liquid that washes around the microorganisms that have settled on the packing.
Individual evidence
- ^ Walter Reineke, Michael Schlömann: Umweltmikrobiologie . Springer-Verlag, Berlin and Heidelberg 2015, ISBN 978-3-642-41764-1 , pp. 413-414.