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SEDIMENTATION TANK

Separating solid material (sludge) from liquids by means of sedimentation. 
Separating solid material (foam, oil, residuals) from liquids by means of flotation.

Types:

  • Horizontal flow
  • Inclined surface
  • Solid contact tank

Some unsettled solid material is removed from raw waste water. So, organic load to be purify in the biological purification unit is decreased. Decrease in organic load causes decrease in oxygen amount required to be delivered into system under biological purification unit, and declines the energy requirement and active sludge amount. 

HORIZONTAL FLOW SEDIMENTATION TANKS 

HORIZONTAL FLOW RECTANGULAR TANKS
Advantages and disadvantages comparing with circular pools

Advantages:
• Multiple pools cover less places. 
• The construction cost decreases as the multiple pools require less wall building.
• Surface can be easily covered in case of odor. 
• It has longer road for sedimentation. 
• Short-circuit flows are less. 
• Sludge collection and disposal require less energy. 

Disadvantages:

  • There are dead spaces. 
  • It is sensitive against flow fluctuation. 
  • The width is limited to the dimension of sludge collecting equipment (8-12 m)

HORIZONTAL FLOW CIRCULAR PRE-SEDIMENTATION TANK
Central feeding is performed in circular sedimentation tanks. Waste water moves from center to outer wals and gets out from canals through the outer parts. The settled sludge is pushed by strippers to the center. The floating materials on the upper surface are collected by a turning stripper, and accumulated in the tank. 

SOLID CONTACT POOLS 
When the inlet waste water is delivered to the dense layer on the point close to bottom of the pool, this layer provides effect like a blanket, and the solid materials crash together and settled. The hydraulic conditions of this kind of pools are quite good, and they can reach to the horizontal flow performance in a shorter waiting period. It is frequently used to settle chemical sludge rather than the biological sludge. 

INCLINED SURFACE POOLS
There are surfaces or tubes placed in an inclined way in these pools. The settlement depth of particules is decreased by means of them. It has 2 types as the ones with tube  and parallel surface separator. There is not wind effect and the flow is laminar in this kind of pools. 

Disadvantages:

  • Sludge accumulation may occur between the layers and septic conditions may happen.  
  • The exit water quality decreases when the bottom sludge is removed. 
  • Chock may occur in canals or tubes. 
  • Short circuit flows may occur when the temperature of inlet waste water is higher than the pool temperature