Digester Gas and Methane Production
The payoff side of anaerobic digestion, from the volatile solids destroyed: 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 digester-vs-loading's healthy feed rate into the gas-and-energy number the plant budgets around. A planning estimate, not a metered gas measurement.
Formula and source
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.
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