The Imhoff tank, named for German engineer Karl Imhoff (1876–1965), is a chamber suitable for the reception and processing of

sewage Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produced by a community of people. It is typically transported through a sewerage, sewer system. Sewage consists of wastewater discharged fro ...

. It may be used for the clarification of sewage by simple

settling Settling is the process by which particulates move towards the bottom of a liquid and form a sediment. Particles that experience a force, either due to gravity or due to Centrifuge, centrifugal motion will tend to move in a uniform manner in the ...

and

sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to th ...

, along with

anaerobic digestion Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to Waste management, manage waste or to produce fuels. Mu ...

of the settled sludge. It consists of an upper chamber in which sedimentation takes place, from which settled solids slide down on the inclined bottom slopes towards a lower chamber in which the sludge accumulates. The two chambers are otherwise unconnected, with the more liquid sewage flowing only through the upper sedimentation chamber and only a slow flow of sludge in the lower digestion chamber. The lower chamber requires separate

biogas Biogas is a gaseous renewable energy source produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, Wastewater treatment, wastewater, and food waste. Biogas is produced by anaerobic ...

vents and pipes for the removal of digested sludge, typically after 6–9 months of digestion. The Imhoff tank is in effect a two-story

septic tank A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (sewage) flows for basic sewage treatment. Settling and anaerobic digestion processes reduce solids and organics, but the treatment ...

and retains the septic tank's simplicity while eliminating many of its drawbacks, which largely result from the mixing of fresh sewage and septic sludge in the same chamber. Typically, well-designed and operated Imhoff tanks are expected to remove suspended solids with an efficiency between 50-70%. Effluent coming out from Imhoff tanks can be either discharged in the environment, sent to a centralized

wastewater treatment Wastewater treatment is a process which removes and eliminates contaminants from wastewater. It thus converts it into an effluent that can be returned to the water cycle. Once back in the water cycle, the effluent creates an acceptable impact on ...

facility, or sent to constructed wetlands for disinfection and nutrient removal. As a result of anaerobic digestion of settled sludge, methane, carbon dioxide, hydrogen and hydrogen sulphide are typically formed. While in the past this gas mix used to be exploited for energy production given the relatively high methane content, nowadays gas from Imhoff tanks is typically vented out in the environment. 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. Imhoff tanks are being superseded in

sewage treatment Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water p ...

by plain sedimentation tanks using mechanical methods for continuously collecting the sludge, which is moved 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. A test for settleable solids in water, wastewater and stormwater uses an Imhoff cone, with or without

stopcock A stopcock is a form of valve used to control the flow of a liquid or gas. The term is not precise and is applied to many different types of valve. The only consistent attribute is that the valve is designed to completely stop the flow when clo ...

. The volume of solids is measured after a specified time period at the bottom of a one-liter cone using graduated markings.Imhoff Cone
Retrieved 2012-05-29.

References

External links

''Imhoff Tank implications''

''Imhoff OM guide, Texas''
{{Wastewater Anaerobic digester types Sewerage infrastructure

See also

References

External links