Retention time describes the time in which a volume of wastewater is stored within the pumping installation, pump sump, pipeline, detention basin and such like. The retention time can be estimated by dividing the holding volume by the discharge flow from the holding structure.
Long as well as short wastewater retention time can be desirable in some situations and undesirable in others. During a 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.
Furthermore, prolonged retention times allow for biological and chemical processes to take place. These processes can in some cases be beneficial (such as oxidation of toxic compounds) whereas other processes might be unwanted (for example the formation of H2S in sewer systems or if sludge retention time in wastewater treatment is too long).
Too short retention times might on the other hand entail that desired biological or chemical processes do not have time to take place (such as the 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 taken into account.
Grundfos ensures a better system design for wastewater networks, helping optimise hydraulic retention time in wastewater treatment.