Anaerobic Digester Calculator

Digester Volume is a pure throughput-and-residence-time sizing calculation -- how big the tank needs to be to hold your daily feedstock for the retention time you've specified -- and that sizing doesn't depend on how warm the digestion process runs. Biogas Output, by contrast, models how efficiently the microbial digestion converts feedstock into gas, and that conversion efficiency genuinely does depend on temperature: thermophilic (hotter) digestion generally proceeds faster and yields more biogas per unit of feedstock than cooler mesophilic operation.

Digester Volume is simply Feedstock (m³/day) multiplied by Retention Time (days) -- a direct product, so doubling either input doubles the result by exactly the same amount. This mirrors real digester design: a facility processing twice the daily feedstock needs twice the tank volume to hold it for the same number of days, and a facility wanting to hold material twice as long needs twice the volume to process the same daily feedstock.

Mesophilic digestion runs around 37°C (98°F) and is the more common, more forgiving operating mode for most agricultural and wastewater digesters. Thermophilic digestion runs around 55°C (131°F), generally digests feedstock faster and can yield more biogas per unit of feedstock, but requires more energy input to maintain temperature and is typically less stable -- more sensitive to feedstock changes and temperature swings than mesophilic operation.

This calculator assumes biogas is roughly 60% methane by volume, that methane carries about 10 kWh of thermal energy per cubic meter, and that a biogas combined-heat-and-power generator converts about 35% of that thermal energy into electricity -- together working out to roughly 2.1 kWh of electricity per cubic meter of biogas. These are typical planning figures, not guarantees; actual generator efficiency and gas composition vary by equipment and feedstock.

This calculator's biogas model estimates a daily production RATE from feedstock volume and temperature -- it doesn't separately track how digestion efficiency changes with a longer or shorter residence time. In practice, retention time and biogas yield are related (too short a retention time can leave feedstock only partially digested), but this calculator treats retention time purely as a Digester Volume sizing input, not as a factor in the biogas yield estimate itself.