Chemical Sludge Production Calculator

Phosphorus precipitation and lime add real tonnage to your solids stream. Enter the chemical dose to estimate the extra dry and wet sludge.

Flow

Flow unit

Chemical

Chemical dose (mg/L)As dry product for alum/ferric; as CaO for lime.

Phosphorus removed (mg/L as P)0 if not precipitating phosphorus.

Chemical sludge solids (% by weight)1–3% typical. Default 2%.

Chemical Sludge

Item	Value

How the calculation works

Stoichiometry (mg precipitate per mg reactant)
AlPO₄ from P: 121.95 ÷ 30.97 = 3.94 mg/mg P
Al in dry alum: 2 × 26.98 ÷ 594.3 = 0.0908 mg/mg product
Al consumed by P: 26.98 ÷ 30.97 = 0.871 mg/mg P
Al(OH)₃ from excess Al: 78.00 ÷ 26.98 = 2.89 mg/mg Al
FePO₄ from P: 150.82 ÷ 30.97 = 4.87 mg/mg P
Fe in FeCl₃: 55.85 ÷ 162.2 = 0.344 mg/mg product
Fe consumed by P: 55.85 ÷ 30.97 = 1.80 mg/mg P
Fe(OH)₃ from excess Fe: 106.87 ÷ 55.85 = 1.91 mg/mg Fe
CaCO₃ from lime: 100.09 ÷ 56.08 = 1.79 mg/mg CaO

Totals
Sludge (mg/L) = phosphate precipitate + hydroxide from excess metal (or CaCO₃ for lime)
Dry solids (lb/day) = 8.34 × flow (MGD) × sludge (mg/L)
Wet volume (gal/day) = dry (lb/day) ÷ (8.34 × 1.03 × solids fraction)

Notes & limitations

Ratios are theoretical stoichiometry for the dominant precipitates (Metcalf & Eddy; WEF MOP 8). Real sludge includes co-precipitated organics and inert carryover, so treat the result as the chemical contribution — verify totals against plant mass balances.

For lime, the result is CaCO3 only; magnesium hydroxide and calcium-phosphate co-precipitation are site-specific and not included.
Liquid alum (~48.5%, ~5.33 lb dry per gallon) and ferric solutions need a product-density conversion from the dry-product dose entered here.
Chemical sludge dewaters poorly compared with biological sludge — confirm dewatering capacity before raising doses.

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