Retention time

Retention time describes the time, in which a volume of wastewater is stored within the pumping installation, pump sump, pipeline, detention basin etc.

Retention time describes the time, in which a volume of wastewater is stored within the pumping installation, pump sump, pipeline, detention tank etc. The retention time can be estimated by dividing the holding volume by the discharge flow from the holding structure.

Long as well as short retention time of wastewater can in some instances be desirable and undesirable in other instances. During long retention time solid particles from the wastewater might have time to settle if the flow or turbulence is not powerful enough to keep particles in suspension.

Prolonged retention times furthermore allow for biological and chemical processes to take place. These processes can in some cases be beneficial (e.g. oxidation of toxic compounds) whereas other processes might be unwanted (e.g. formation of H2S in sewer systems).

Too short retention times might on the other hand entail that desired biological or chemical processes do not have time to take place (e.g. decomposition of organic matter) but might in other instances be intended.
When designing a sewer system the retention time in pipelines should be estimated and the consequences hereof should be taken into account.





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