Sedimentation tanks, flow-through

Figure 3. Flow-through characteristics of investigated sedimentation tanks.

Filtration is more normally used as a post-treatment process, further to improve the water quality. However, oil-water separators are also designed on a filtration basis. When two non-miscible liquids of different densities flow by gravity through a porous medium, they wiU have different penetrability rates. In such a filter, the oil-water mixture first enters a sedimentation tank, where heavier particles settle out. The oil-water mixture then enters an inlet basket and flows into the porous medium, where the oil separates from the water. The water flows on down through a screen at the bottom, then up and over a water weir, which creates the water table supporting the oil longer. The oil travels horizontally on top of the water into the oil trap and then over an adjustable oil weir, which is set at a position slightly above the maximum water level. 

In sedimentation the water to be treated flows slowly through a tank, allowing the suspended material in the water to fall to the base of the tank. The use of coagulating compounds, such as aluminum and ferric sulfate, increases the efficiency. 

Cross-flow devices. Equipment manufacturers have modified the CPI configuration for horizontal water flow perpendicular to the axis of plate corrugations. This allows plates to Lie installed at a steeper angle to facilitate sediment removal and enables the plate pack to be more conveniently packaged in a pressure vessel. The latter advantage is critical if gas blowby through an upstream dump valve could cause relief problems in an atmospheric tank. 

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