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Sedimentation

Sedimentation

Process description

Sedimentation entails the removal of suspended particles from water under the force of gravity. In conventional sedimentation, the sedimentation takes place in a relatively large basin in which the particles sink to the bottom. If the pitch of the bottom is steep, the particles collect at the bottom and can be drained off and processed further, if required. In the case of large sedimentation tanks, the pitch of the bottom is shallow and the particles are collected in the middle of the tank with the aid of mechanical scrapers.

A variant on the conventional sedimentation tank is the lamella sedimentation tank. The theory of sedimentation is based on the fact that the sedimentation process is determined primarily by the surface area and not by the retention time in the tank. In a lamella sedimentation tank, or lamella separator, a large number of plates/tubes are placed parallel at an angle, thus creating a large surface for sedimentation. The illustration below shows a number of different types of lamella separators. The projected surface of the lamella separator, distance between plates and flow are important factors here.

lamelleseparator_LWT_

The benefits of lamella sedimentation over conventional sedimentation are as follows:
  • Compact/ small surface;
  • No moving parts;
  • Simple to try out (see also Logisticon Rental fleet).
One disadvantage is that:
  • •at high sludge loads, this technology is more prone to blockages, which disrupt flow.

Area of application

Conventional sedimentation tanks (including Dortmund tanks) have already been used on a large scale for the chemical and biological treatment of waste water for decades. Lamella separators have, as yet, not been used to a very large extent for the treatment of household waste water, but have primarily been used in the process, paper and food industry.

Process interruptions

As is the case with membranes, separation by sedimentation is not absolute. If, because of an excessively slow sedimentation rate, particles cannot be removed (and there are many reasons why this may be the case), they are discharged with the effluent.