Anaerobic Digestion Calculator

Plan slurry loading, gas yield, and energy recovery. Review retention time, volume, and methane quality. Turn daily waste inputs into actionable engineering outputs fast.

Calculator inputs

Enter feedstock, solids, digestion, gas, and energy assumptions. The form uses a responsive 3-column layout on large screens, 2 columns on smaller screens, and 1 column on mobile.

Total wet feed entering the digester each day.
Used to convert mass flow into slurry volume.
Dry matter fraction of the incoming feedstock.
Biodegradable share of total solids.
Fraction of VS actually converted during digestion.
Expected biogas from each kilogram of destroyed VS.
Typical values often range from 50% to 65%.
Default is close to the lower heating value.
Electric conversion efficiency for CHP or genset use.
Heat recovered from the prime mover or CHP package.
Internal demand from pumps, mixers, and auxiliaries.
Used to size active slurry holding volume.
Adjusts useful energy output for uptime.
Used to estimate electricity displacement benefit.

Formula used

  1. Daily slurry volume = Daily feedstock mass ÷ Slurry density
  2. TS input = Daily feedstock mass × TS fraction
  3. VS input = TS input × VS fraction of TS
  4. VS destroyed = VS input × VS destruction fraction
  5. Biogas production = VS destroyed × Specific biogas yield
  6. Methane production = Biogas production × Methane fraction
  7. Gross energy = Methane production × Methane energy value
  8. Electricity recovery = Gross energy × Generator efficiency × Availability
  9. Heat recovery = Gross energy × Thermal recovery × Availability
  10. Net usable energy = Electricity + Heat − Parasitic load
  11. Digester volume = Daily slurry volume × HRT
  12. Organic loading rate = VS input ÷ Digester volume

How to use this calculator

  1. Enter the wet feedstock mass delivered to the digester daily.
  2. Add slurry density to convert the feed into volumetric flow.
  3. Enter TS, VS of TS, and the expected VS destruction.
  4. Set the specific biogas yield and methane concentration.
  5. Fill in HRT to estimate the working digester volume.
  6. Add generator, heat recovery, parasitic load, and availability values.
  7. Click Calculate to display results above the form.
  8. Use the CSV or PDF buttons to export the current results.

Example data table

Scenario Feedstock (kg/day) TS (%) VS of TS (%) HRT (days) Biogas (m³/day) Digester volume (m³)
Dairy slurry 15,000 8 78 30 393 459
Food waste slurry 12,000 22 90 22 1,009 264
Mixed organics 25,000 12 82 25 1,150 638

These values are illustrative and depend on feedstock chemistry, pretreatment, temperature, and actual digester stability.

Frequently asked questions

1) What does anaerobic digestion calculate here?

It estimates digester volume, biogas production, methane volume, gross energy, useful electricity, useful heat, parasitic demand, loading rate, and annualized benefits.

2) Why is VS more important than TS?

Total solids include biodegradable and inert material. Volatile solids better represent the organic fraction that can convert into biogas.

3) What is a good methane percentage?

Many wet digesters operate around 50% to 65% methane. Lower values reduce energy density, while higher values generally indicate stronger gas quality.

4) What does HRT change?

Hydraulic retention time directly changes working digester volume. Longer HRT increases tank size and usually lowers organic loading rate for the same daily feed.

5) Why include parasitic load?

Digesters consume energy for pumping, mixing, heating support, controls, and gas handling. Ignoring those loads can overstate usable energy.

6) Is this enough for final design?

No. It is an engineering screening tool. Final design still needs lab data, pilot results, foaming review, sulfur control, mixing studies, and safety design.

7) What does the organic loading rate indicate?

It shows how much volatile solids are applied per unit digester volume each day. Higher values may raise productivity but can increase process instability risk.

8) Can this compare feedstock scenarios?

Yes. Change solids, VS destruction, methane fraction, and HRT values between runs. Then export each case to compare results in a spreadsheet.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.