Digester Gas and Methane Production
The payoff side of anaerobic digestion, from the volatile solids destroyed.
Example
You enter
- Volatile solids fed (lb/day) 10000
- VS reduction (%, typical 50-60) 55
- Gas yield (ft³ per lb VS destroyed) 15
- Methane fraction of gas (%) 65
You get
- VS destroyed 5500 lb/day
- Digester gas 82500 ft^3/day
- Methane 53625 ft^3/day
- Recoverable energy 51.5 MMBtu/day
Details, formula, and sources
gas = VS_destroyed x yield (12-18 ft^3/lb, default 15), methane = gas x ~65%, energy = methane x 960 BTU/ft^3. A digester destroying 5,500 lb VS/day makes about 82,500 ft^3 of gas, 54,000 ft^3 of methane, and 51 MMBtu/day - enough to heat the digester and run a cogeneration engine. Turns a healthy digester feed rate into the gas-and-energy number the plant budgets around. A planning estimate, not a metered gas measurement.
VS_destroyed = VS_fed x reduction/100; gas = VS_destroyed x yield; methane = gas x methane_pct/100; energy = methane x 960 BTU/ft^3.
Anaerobic digester gas production (WEF; university operator courses), by name.
The digester-gas production relation and its typical yields are public wastewater-operations results; the digester monitoring and the operator govern.
Estimate. AHJ and licensed professional govern.
Field names used by the API: vs_fed_lb_day, vs_reduction_pct, gas_yield_ft3_lb, methane_pct, vs_destroyed_lb_day, gas_ft3_day, methane_ft3_day, energy_mmbtu_day
- Gas yield 12-18 ft^3 digester gas per lb VS destroyed (default 15); feed- and temperature-dependentWEF / operator courses
- Methane and energy gas is ~65% methane; recoverable energy is methane x ~960 BTU/ft^3 (the CO2 carries none)WEF / operator courses