Imhoff tanks

The Imhoff tank consists of an upper chamber in which sedimentation takes place.

The collected solids slide down an inclined bottom slopes into a lower chamber where the sludge is collected and digested. It normally takes 6-9 months for the sludge to digest. The two chambers of the Imhoff tanks are not connected. The sewage flows through the upper sedimentation chamber and is not permitted to enter the lower digestion chamber. The lower chamber requires separate gas vents and pipes for the removal of the digested sludge. By preventing the mixing of fresh sewage and septic sludge in the same chamber, the Imhoff system�s simple design has eliminated many of the drawbacks of simple single tank septic systems.

The Imhoff tanks are being replaced in sewage treatment by plain sedimentation tanks that use mechanical methods to continuously collect and move the sludge to separate digestion tanks. This arrangement permits both improved sedimentation results and better temperature control in the digestion process, leading to a more rapid and complete digestion of the sludge.

This method of sediment removal is also used in some drinking water treatment facilities, in which the tank is often called an Imhoff cone. As in sewage treatment, the collected sludge must be properly disposed of.

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