Traditionally, settlement tanks were large vats in which water was left for sediment to settle to the bottom. This used considerable space and the process could not be accelerated as an increased flow rate would disturb the sediment formation. They also had to be completely emptied to remove debris, which incurred plant down-time.
Today, primary water treatment systems tend to prefer to use lamella clarifiers which are not only more controllable, but also require considerably less footprint. This works by using inclined plates or pipes to increase the surface area for sediment to settle on. With the water being dispersed evenly as it enters the clarifier, this reduces the amount of turbulence which could dislodge previously settled particles.
As the sediment accumulates, it forms a sludge in the hopper at the base of the clarifier. This sludge can then be removed via integrated pipework at the bottom of the tank without interruption to the process. Whilst this is happening, clear water is removed as it flows over the weirs in the top of the clarifier.
These weirs are very important as they retain any foam, or surface sediment which may be floating. As the sludge drain can be operated by an electronic valve actuator, the lamella clarifier systems can run almost continuously without the need for manual intervention. This makes them a very efficient and economical solution for effluent pre-treatment.
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