User:Mattryanfry/Sludge age

Sludge age in activated sludge systems is the length of time the particulate matter remains in the reactor and it is the most important and fundamental decision in the design of an activated sludge system. The sludge age selected for a system is dependent on many factors such as the stability of the system, sludge settlability and the quality of the effluent required.

Connection to Hydraulic Retention Time
The nominal hydraulic retention time is the time the liquid and the dissolved material remain in the reactor. Therefore in activated sludge systems without liquid solid seperation (such as an aerated lagoon) the sludge age and the hydraulic retention time are the same. When liquid solid seperation is included the sludge age is longer than the hydraulic retention time.