What is a deep two-storied sewage tank that features an upper sedimentation chamber and a lower chamber called?

A deep two-storied sewage tank featuring an upper sedimentation chamber and a lower chamber is known as an Imhoff tank. This type of tank is designed to facilitate the preliminary treatment of sewage. In the upper chamber, solids settle out from the wastewater, forming sludge, while in the lower chamber, the settled solids undergo anaerobic digestion. This two-chamber design effectively separates solids from the liquid waste and promotes the breakdown of organic material through biological processes. The Imhoff tank is particularly useful for handling high organic loads and improves the quality of effluent before it undergoes further treatment processes.

This design is advantageous because it not only provides a means for sedimentation but also allows for the stabilization of waste materials, minimizing odors and the volume of sludge produced. Other options, like detritus tanks, septic tanks, and elocculating tanks, do serve specific functions in waste treatment but do not feature the dual-chamber system characteristic of an Imhoff tank.