Imhoff tank

Typically, well-designed and operated Imhoff tanks are expected to remove suspended solids with an efficiency between 50-70%.

[4] Effluent coming out from Imhoff tanks can be either discharged in the environment, sent to a centralized wastewater treatment facility, or sent to constructed wetlands for disinfection and nutrient removal.

This wastes the energy potential recovery of the technology and increases its carbon footprint, given the high content of methane which has a global warming potential about 25 times larger than the one of carbon dioxide.

A test for settleable solids in water, wastewater and stormwater uses an Imhoff cone, with or without stopcock.

The volume of solids is measured after a specified time period at the bottom of a one-liter cone using graduated markings.

Imhoff tank. a - upper chamber, b-c - outlet for sludge, d - outlet for biogas (would need to be higher), f - lower chamber, g - slot for sludge to pass from the upper to the lower chamber, h - height.
View from above an empty Imhoff tank