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Sludge Production Calculator

Work out sludge production instantly with clear inputs, formula shown and shareable results.

About Sludge Production Calculator

Biological sludge production is BOD removed times the observed yield, which falls with sludge age from about 0.6 at short SRT to 0.3 in extended aeration. Inert solids from the influent add to it. Wet volume depends entirely on solids content — sludge at 0.8% dry solids is over 100 times the volume of the dry mass.

Formulas

Sludge production

Dry solids = BOD removed x observed yield + inert solids load

Wet volume

Volume (m3) = dry solids (kg) / (dry solids fraction x 1000)

Worked example

With the default values below, Sludge Production Calculator returns Dry Sludge Production of 850.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

BOD Removedminimum 0 kg/day
1,300 kg/day
Observed Yieldminimum 0 kg VSS per kg BOD
0.5 kg VSS per kg BOD
Inert Solids Loadminimum 0 kg/day
200 kg/day
Sludge Dry Solidsaccepts 0–40 %
0.8 %

Results

Dry Sludge Production
850.00
Wet Sludge Volume
106.250
Biological Sludge
650.00
Annual Dry Solids
310.250

Step by step

  1. 1Values used
  2. 2Sludge production
  3. 3Wet volume
  4. 4Dry Sludge Production= 850.00
  5. 5Wet Sludge Volume= 106.250
  6. 6Biological Sludge= 650.00
  7. 7Annual Dry Solids= 310.250

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Sewage sludge handling, storage and land application are regulated for pathogens, metals and nutrients. Confirm the applicable biosolids rules.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Sewage sludge handling, storage and land application are regulated for pathogens, metals and nutrients. Confirm the applicable biosolids rules.

Frequently Asked Questions

Why does yield fall with sludge age?

Longer retention allows more endogenous respiration, so a larger fraction of the biomass produced is oxidised again. Extended aeration therefore produces less sludge but consumes more air.

Why is thickening so valuable?

Volume scales inversely with solids content. Thickening from 0.8% to 4% cuts volume by 80%, which transforms the cost of digestion, transport and dewatering.

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