Anaerobic Digester Calculator: Organic Waste to Biogas & Electricity
Anaerobic digestion breaks down organic waste — food waste, manure, wastewater sludge, agricultural residues — in an oxygen-free environment, producing biogas that is roughly 60% methane. That biogas fuels a combined-heat-and-power (CHP) engine to make firm, around-the-clock electricity, plus usable heat and a fertilizer byproduct called digestate. Unlike burning dry municipal waste (mass-burn incineration), digestion handles WET organic material — which is exactly why it is the right pathway for food waste and manure, feedstocks that are too wet to burn efficiently. The digester is a biological reactor, not a furnace: microbes do the work at modest temperatures, and the methane they release becomes dispatchable power rather than a greenhouse gas escaping from a landfill or manure lagoon. This calculator turns a feedstock stream — tons per day of organic material — into the biogas volume, the continuous megawatts a CHP engine can reliably deliver, the annual generation in GWh, the equivalent homes powered, the usable heat co-product, and the dual-revenue breakdown (energy sales plus tipping fees for accepting the waste). Actual output depends heavily on feedstock type and quality, so treat this as a planning-level estimate, not a performance guarantee.
Wet tons of organic material. A mid-size food-waste / mixed-organics digester; large facilities process 250–500+ tons/day.
Cubic meters of methane per kg of volatile solids destroyed. Food waste ~0.3–0.5; manure lower ~0.2.
Industrial/wholesale rate — $0.06–0.10/kWh. Do NOT use a residential rate; this is grid/data-center generation.
What the digester is PAID to accept organic waste — food-waste digesters are often paid to take feedstock. Typical ~$20–60/ton.
firm, around-the-clock baseload from a CHP engine burning the biogas
9,772,875 kWh/yr after CHP efficiency and uptime
million cubic meters of biogas per year at 60% methane
at ~10,500 kWh/yr per U.S. home
CHP co-product — the digester uses some to keep itself warm; the rest can serve nearby thermal loads
35% of total — selling the power
65% of total — paid to take the organic waste
dual revenue: paid for the waste AND the electricity — plus digestate byproduct usable as fertilizer
Results update live as you type. For planning and field-check estimates — always verify against applicable standards and equipment ratings.
How we calculate this →How anaerobic digester biogas output is calculated: from organic feedstock to firm megawatts
The calculation starts with the feedstock stream and works through the biology to the electricity. Annual feedstock (tons/yr) = tons per day × 365. A 100 ton/day digester processes 36,500 wet tons of organic material per year.
Not all of that wet weight is digestible. Total solids (tons/yr) = annual feedstock × (total solids % ÷ 100) — the share that is solid rather than water. At 25% total solids, 36,500 tons becomes 9,125 tons of dry solids. Volatile solids (tons/yr) = total solids × (volatile solids fraction ÷ 100) — the portion of solids the microbes can actually break down. At 85% volatile solids, that is 7,756 tons, or 7,756,250 kg of volatile solids per year.
Methane produced (m³ CH₄/yr) = volatile solids (kg) × methane yield (m³/kg). At a food-waste-typical 0.35 m³/kg, the digester produces about 2.71 million cubic meters of methane. Biogas volume (m³/yr) = methane produced ÷ (methane content ÷ 100), because biogas is only ~60% methane with the rest mostly CO₂ — so 2.71 million m³ of methane becomes about 4.52 million m³ of raw biogas.
Gross biogas energy (kWh/yr) = methane produced (m³) × 10, using methane's heating value of roughly 10 kWh per cubic meter. That gives about 27.1 million kWh of thermal energy in the methane. Electricity generated (kWh/yr) = gross biogas energy × (CHP electrical efficiency ÷ 100) × (capacity factor ÷ 100) — the engine converts ~40% of that energy to electricity and runs ~90% of the hours in a year, yielding about 9.77 million kWh/yr.
Firm electrical capacity (MW) = electricity generated ÷ (8,760 × capacity factor ÷ 100) ÷ 1,000 — the continuous megawatts the CHP engine reliably delivers, about 1.24 MW at these defaults. Annual generation (GWh) = electricity generated ÷ 1,000,000. Homes powered = electricity generated ÷ 10,500 kWh (the average U.S. home's annual use).
The CHP heat co-product: a combined-heat-and-power engine produces roughly as much usable heat as electricity — typically slightly more. Usable heat available (kWh-thermal/yr) ≈ electricity generated × 1.1. Digesters use some of this heat to maintain their own warm operating temperature (mesophilic ~35–40°C or thermophilic ~50–55°C); the remainder can serve nearby thermal loads such as district heating, greenhouses, or industrial processes.
The dual-revenue breakdown mirrors other waste-to-energy pathways. Energy revenue ($/yr) = electricity generated × electricity rate. Tipping-fee revenue ($/yr) = annual feedstock × tipping fee — the gate fee the digester is paid to accept organic waste that would otherwise go to a landfill. Total annual revenue is the sum. At the default assumptions, a 100 ton/day food-waste digester earns roughly $0.78M/yr from power and $1.46M/yr from tipping fees — it is paid twice, once to take the fuel and once to sell the power. Anaerobic digestion also produces digestate, a nutrient-rich material that can be used as fertilizer, an additional value stream not captured in this calculator.