The concentration of the activated sludge solids and the condition of those biological solids determines the effectiveness of an activated sludge process. Too few or too many organisms in a system will cause operational control problems, reducing treatment plant efficiency and causing an added pollution load on the receiving waters.
Sludge age is defined as the average time in days the suspended solids remain in the entire system. To successfully maintain a viable biological population and to maintain the proper concentration of solids, the system requires continuous observation and monitoring by the operator.
Sludge age is one of the methods or tools available to the operator to help maintain the desired amount of solids in the aeration tank.
Sludge age is a relatively easy control parameter to monitor because the suspended solids in the aeration tank are easy to measure.
Sludge age considers the:
solids entering the aeration basin; measured as primary effluent
suspended solids in mg/L, and
solids or organisms available to degrade the wastes; measured
as Mixed Liquor Suspended Solids, mg/L
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