Calculating Sludge Age

Sludge age in the activated sludge process is the measure of the length of time a particle of suspended solids has been undergoing aeration. This time is expressed in days and is calculated using the pounds of Mixed Liquor Suspended Solids (MLSS) in the aeration basin and the pounds of Total Suspended Solids TSS) in the influent. Young sludge is indicated by excessive white, billowy foam and low MLSS concentration and high food to microorganism ratios. An overabundance of dark brown and greasy foam is an indicator of old sludge, which also has a high MLSS concentration and low food to microorganism ratios.

The influent flow to a 8.0 MGD facility is 6.4 MGD with an influent TSS concentration of 166 mg/L and a MLSS concentration of 3,653 mg/L. What is the sludge age in days at this facility?

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