Gould sludge age compares the solids under aeration with the suspended solids entering the aeration basin each day. It does not need wasting data, but it is less directly tied to biology than SRT.
Sludge Age
Formula
Sludge age, days = (Aeration volume, MG x MLSS, mg/L x 8.34)
/ (Flow, MGD x Aeration influent TSS, mg/L x 8.34)
Inputs used
- Aeration basin volume (MG)
- MLSS (mg/L)
- Flow to aeration (primary effluent) (MGD)
- Primary effluent TSS (aeration influent) (mg/L)
Worked example (White River WRRF, fictional)
- MLSS under aeration = 3.6 x 3,000 x 8.34 = 90,072 lb
- TSS entering = 8.0 x 96 x 8.34 = 6,405 lb/d
- Sludge age = 90,072 / 6,405 = 14.1 days
Tips
- Use aeration influent (primary effluent) TSS, not raw influent.
- Compare with SRT; the two often differ.
Results are estimates for operator use. Check units and inputs, and confirm decisions with plant data and procedures.