Two-stage wastewater treatment tank combining sedimentation of settleable solids in an upper compartment and anaerobic digestion of the settled solids in a lower compartment.

The Imhoff tank is a chamber suitable for the reception and processing of sewage. It may be used for the clarification of sewage by simple sedimentation, along with anaerobic digestion of the extracted sludge. It consists of an upper chamber in which sedimentation takes place, from which collected solids slide down inclined bottom slopes to an entrance into a lower chamber in which the sludge is collected and digested.