Biogas Digestate & Biochemical Methane Potential (BMP

Bioenergy Engineering & Waste-to-Value: Anaerobic Digestion

Anaerobic digestion (AD) breaks down organic waste in the absence of oxygen through a four-stage microbial cascade (Hydrolysis Acidogenesis Acetogenesis Methanogenesis):

• Total Solids (TS) vs. Volatile Solids (VS):

• Total Solids (Dry Matter): Mass remaining after evaporating water at 105°C.

• Volatile Solids (Organic Fraction): Mass combusted at 550°C; only volatile organic solids can be converted into methane by methanogenic archaea.

• Biochemical Methane Potential (BMP): Measures the maximum volume of methane produced per kilogram of volatile solids (food waste has ~2x higher BMP than cattle manure due to high lipid and carbohydrate density).

• RNG vs. CHP: Raw biogas (~60% CH_4) can be combusted in a CHP engine for on-site electricity and heat, or upgraded via membrane separation to 98%+ Renewable Natural Gas for pipeline injection.

How to Use This Calculator

Enter your Daily Feedstock Substrate Inflow (Tons / day) (e.g. 50 (50 tons/day organic biomass or manure)), Organic Feedstock Substrate Category — choose from Dairy Cattle Manure (12% TS | 80% VS | ~0.24 m³ CH₄/kg VS), Commercial Food & Restaurant Waste (20% TS | 90% VS | ~0.45 m³ CH₄/kg VS), Agricultural Corn Silage (33% TS | 92% VS | ~0.34 m³ CH₄/kg VS), Feedstock Total Solids Content (TS %) (e.g. 12 (12% dry matter)), Volatile Solids as % of Total Solids (VS %) (e.g. 80 (80% organic volatile matter)), Biochemical Methane Potential (BMP [Nm³ CH₄ / kg VS]) (e.g. 0.25 (0.20 to 0.45 m³ methane per kg VS)), Biogas Methane Concentration (CH₄ %) (e.g. 60 (55% to 65% CH₄ concentration)), and CHP Cogeneration Electrical Efficiency (%) (e.g. 38 (38% electrical / 45% thermal efficiency)). Results update instantly as you type — adjust any value to compare scenarios.

The Formula

VDI 4630 & EPA AgSTAR Anaerobic Digestion equations:

Volatile Solids Loading (kg VS/day) = Feedstock (kg) × ((TS %) / (100)) × ((VS %) / (100))

Daily Pure Methane Yield (V_CH_4) = Volatile Solids (kg VS) × BMP (Nm^3 CH_4/kg VS)

Daily Raw Biogas Volume = V_CH_4CH_4 Concentration (%)

Daily Thermal Energy (kWh) = V_CH_4 (Nm^3) × 9.97 kWh/Nm^3

CHP Electrical Power (kW) = Daily Thermal Energy (kWh) × η_CHP24 Hours

Annual Generation (MWh) = CHP (kW) × 8.760 × Availability (92%)

Worked Example

For example, digesting (12.0% TS, 80.0% VS, 60.0% CH_4 content) in a mesophilic digester with a 38.0% efficient CHP unit: Volatile solids loading is . Methane yield is producing *. The CHP generates 189.4 kW continuous baseload power, powering 145 homes and yielding 46.0 tons/day of organic biofertilizer digestate*.

Understanding Your Result

US EPA fuel economy benchmarks (2024): Compact cars 28–35 MPG combined; midsize SUVs 22–28 MPG; pickup trucks 16–22 MPG; hybrid vehicles 40–55 MPG; EVs equivalent 90–120 MPGe. At 3.50/gallon, every 1 MPG improvement saves approximately 35–50/year over 10,000–15,000 annual miles. Real-world fuel economy typically runs 15–20% below EPA ratings in stop-and-go traffic, cold weather (reduces efficiency 15–25%), or with heavy loads.