A METHOD AND A DEVICE FOR TREATMENT OF MEDIUM

摘要

The invention relates to a method and an arrangement for the separation of lighter particles (10) from heavier particles (3) in a liquid medium, which contains lighter particles and heavier sinking particles which require to be washed, in particular sand, and in particular at sewage works in the incoming waste water, where the heavier particles are removed at the lower end of a vessel and the lighter particles are removed at a level above the outlet for the aforementioned heavier particles. In accordance with the invention the level in the vessel (13) of the process water intended for washing the sand (3) is varied, so that a hydraulic pressure difference is achieved and the sedimented lighter material (10) that is not intended to be washed can be removed by decanting for a predetermined period of time by causing rotation (20) of the lighter material (10) so that it makes its way towards the centre at a level (14) above the upper level (22) of the sand. Washing water (23) and/or other fluid for washing the sand is also supplied.