Primary Sludge Volume Calculator
Primary sludge pumping is sized on wet volume, but the solids come from the TSS removed. Convert between dry pounds and pumpable gallons here.
Primary Sludge
| Item | Value |
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How the calculation works
Formulas
TSS removed (mg/L) = influent TSS − effluent TSS
Dry solids (lb/day) = 8.34 × flow (MGD) × TSS removed (mg/L)
Wet sludge (gal/day) = dry solids (lb/day) ÷ (8.34 × specific gravity × solids fraction)
Pump rate (gpm) = wet sludge (gal/day) ÷ 1,440
TSS removed (mg/L) = influent TSS − effluent TSS
Dry solids (lb/day) = 8.34 × flow (MGD) × TSS removed (mg/L)
Wet sludge (gal/day) = dry solids (lb/day) ÷ (8.34 × specific gravity × solids fraction)
Pump rate (gpm) = wet sludge (gal/day) ÷ 1,440
Notes & limitations
The 8.34 lb/gal conversion and the dry-to-wet volume relation are standard (Metcalf & Eddy; WEF MOP 8). Percent solids is the dominant variable — a 1-point change in % solids changes the pump volume by roughly 25%.
- Verify % solids with lab total-solids testing; hopper sludge is often thicker than the pumped average.
- Size pumps and piping for the peak-day sludge blanket, not the average — add capacity for scum and washdown solids.
- This covers primary sludge only; add waste activated sludge and chemical sludge separately for the total to digestion or dewatering.
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