Sludge Volume Calculator
Estimate sludge production for a sewage treatment plant (STP), effluent treatment plant (ETP), or water works. Get dry mass of sludge in kg/day with and without chemical precipitation, convert that mass to wet sludge weight and volume using solids % and density (kg/m³), then size preliminary sludge tank capacity.
Educational estimate. Calculator results are for planning and information only, not financial, tax, medical, legal, or engineering advice. Verify important decisions with official sources or a qualified professional.
Sludge Volume Calculator
Dry Mass kg/day, Sludge Weight, Tank Capacity & Chemical Precipitation
📐 Formula & Method
Dry Mass without Chemical Precipitation
One mg/L equals 0.001 kg/m3. Leave BOD at zero for a TSS-only or physicochemical ETP estimate.
Chemical Precipitation Dry Solids
Default factors: liquid alum 0.44 kg DS/kg product (EPA residual equation), ferric chloride about 0.66 as Fe(OH)3/FeCl3, lime 1.0 for screening only.
Dry Mass with Chemical Precipitation
Both results are reported so exam and plant-comparison problems can be read side by side.
Wet Sludge Weight
At 3% solids, wet sludge weight is about 33 times the dry mass. This is the sludge weight used for hauling and tank mass checks.
Sludge Volume
Raw, thickened and dewatered cake each use their own wet density. Wet weight is unchanged by density. The default 1,020 kg/m3 keeps all three stages on the same planning basis; cake volume is then an approximation because real cake is often 1,100–1,300 kg/m3.
Sludge Tank Capacity
This is working capacity only. Add freeboard, dead volume, mixing, and redundancy in detailed design.
📋 How to Use
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1
Enter plant flow and select m³/hour, m³/day, ML/day or MGD.
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2
Enter influent TSS and the expected or measured TSS removal percentage.
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3
For biological STP sludge, enter BOD, BOD removal and observed yield; leave BOD at zero for ETP physicochemical or water-treatment residuals.
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4
To compare dry mass with and without chemical precipitation, choose alum, ferric, lime or a custom factor and enter the product dose.
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5
Enter raw, thickened and dewatered total solids plus a wet density for each stage. Cake volume is an approximation if cake density is left equal to raw-sludge density.
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6
Set storage days and margin to estimate sludge tank capacity, plus available pumping hours.
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7
Read dry mass kg/day (with and without chemicals), wet sludge weight, volumes and tank working capacity.
🧮 Worked Examples
TSS-only dry mass and sludge weight
100 m³/h for 24 h/day, 200 mg/L TSS, 90% removal, 3% raw solids and density 1,020 kg/m³. No chemicals.
Dry mass with vs without chemical precipitation
Same flow and TSS, plus 30 mg/L liquid alum at residual factor 0.44.
Combined municipal wastewater example
Add BOD-derived biological solids and compare 3% raw, 6% thickened and 20% dewatered material.
Dry Mass, Sludge Weight, Density and Tank Capacity
Sludge calculations start with dry solids, not flow. The dry mass of sludge in kg/day is the captured TSS plus any biological yield and any chemical-precipitation solids. Wet sludge weight and sludge volume then follow from total-solids percent and wet-sludge density in kg/m3.
Without chemical precipitation, dry mass is Flow × TSS × removal ÷ 1000, plus an optional BOD × yield term. With chemical precipitation, add Flow × coagulant dose × residual-solids factor ÷ 1000. The calculator reports both kg/day results so STP, ETP and exam problems can be compared directly.
Sludge weight usually means the wet mass: dry mass divided by the solids fraction. At 3% total solids, 432 kg DS/day is about 14,400 kg/day of wet sludge. Volume is that wet mass divided by the density of that stage. Use separate raw, thickened and cake densities when you have them. A shared planning density of 1,020 kg/m3 is typical for raw or thickened sludge; if cake also uses 1,020 kg/m3, the cake volume is an approximation because dewatered cake is often 1,100–1,300 kg/m3.
Sludge tank capacity is daily volume × storage days × (1 + margin). That figure is working volume for holding raw or thickened sludge, not a finished tank design. Add freeboard, unusable volume, mixing, odor control and standby capacity separately.
This tool is a production and storage mass balance. It is not a sludge volume index (SVI) calculator. SVI uses 30-minute settled volume and MLSS to describe activated-sludge settleability — use the SVI calculator for that.
Storage, pumping and cake outputs are preliminary. Final design must consider peak and seasonal loading, volatile solids, return liquors, polymer or coagulant addition, equipment capture efficiency, standby capacity, mixing, odor, pump rheology, local regulations and representative bench or pilot testing.
🔬 Methodology & Accuracy
Formula: Dry-solids mass balance combining captured TSS, optional observed-yield biological solids and chemical-precipitation solids from dose × residual factor (plus any extra known solids). Wet sludge weight is dry mass ÷ solids fraction and does not depend on density. Raw, thickened and cake volumes each use Volume = wet weight ÷ that stage’s wet density. Shared 1,020 kg/m3 defaults preserve existing test cases; cake volume is then an approximation.
Data sources: US EPA Biosolids Technology Fact Sheet: Gravity Thickening (EPA 832-F-03-022); US EPA Technology Transfer Handbook: Management of Water Treatment Plant Residuals (alum residual-solids factor); standard wastewater dry-solids mass-balance and observed-yield methods.
Last reviewed: August 2026 · General formula used: Dry Mass without Chemical Precipitation · Accuracy: Results are precise to two decimal places using IEEE-754 double-precision arithmetic. Intended for educational and planning use only.
For informational purposes only. Results are estimates based on the inputs and formulas provided. For financial, tax, medical, or legal decisions, consult a qualified professional. Rates and regulations change — always verify current figures with official sources.