Digester Gas Production Calculator
Destroyed volatile solids become biogas. Enter your VS feed and destruction rate to estimate daily gas volume, methane yield, and recoverable heating value.
Biogas Production
| Item | Value |
|---|
How the calculation works
Formulas
VS destroyed (lb/day) = VS fed (lb/day) × VS reduction% ÷ 100
Biogas (ft³/day) = VS destroyed (lb/day) × gas yield (ft³/lb VS destroyed)
Methane (ft³/day) = biogas (ft³/day) × methane fraction
Energy (BTU/day) = biogas (ft³/day) × 600 BTU/ft³ (typical biogas heating value at ~65% methane)
VS destroyed (lb/day) = VS fed (lb/day) × VS reduction% ÷ 100
Biogas (ft³/day) = VS destroyed (lb/day) × gas yield (ft³/lb VS destroyed)
Methane (ft³/day) = biogas (ft³/day) × methane fraction
Energy (BTU/day) = biogas (ft³/day) × 600 BTU/ft³ (typical biogas heating value at ~65% methane)
| Parameter | Typical value |
|---|---|
| Gas yield per lb VS destroyed | 12 – 18 ft³/lb |
| Methane fraction | 60 – 70% |
| Biogas heating value | ~600 BTU/ft³ |
| VS reduction, mesophilic | 45 – 60% |
Notes & limitations
Gas-yield and VS-reduction ranges are from Metcalf & Eddy wastewater engineering references. Actual yield depends on feedstock (grease and food waste boost it; WAS alone is lower), temperature, and SRT — calibrate against your gas meter.
- This is a planning-level estimate. Use measured gas flow for energy contracts, flare sizing, and engine fuel planning.
- VS reduction below ~40% suggests under-digestion (short SRT, low temperature, or toxicity) — investigate before counting on the gas numbers.
- The 600 BTU/ft³ heating value assumes ~65% methane. Raw biogas also carries H2S and moisture that engines and boilers must handle.
- Gas production swings with feed — batch feeding and weekend shutdowns show up in the meter within a day or two.
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