Open Source Biodigester Calculations

Number of People Served

Design goal for scalable systems is for a 16x16 foot room to handle the waste of 100 people [1], 100 chickens [2], or 25 pigs [3]. This is a design that can handle pigs if humans chose pork and beans as their protein staple.

With biodigester totes (1 cubic meter) stacked 2 high - a 16x16 foot room can accommodate 32 of such totes.

Chat says 1 cubic meter serves 4 people.

First Principle Calculation

• Limit is water volume handling from appliances, assuming that this water dilutes organic waste sufficiently
• Thus, must essentially design for toilet flow, as a dishwasher uses about 1 gallon per person per day [4] and average toilet flow is 12 gpppd (gallons per person per day) [5] and 8 gpppd for efficient toilets.
• In the Supertoilet case, we have a figure of 0.5 gpf or 1 gpf. - with most flushes at half - so an average 6 toilet flushes per day [6]. That is 4 gpd assuming 4 ppd and 2 spd.
• Thus, we must design for 5 gpd for toilet and kitchen sink loading per person.
• For 25 day retention time and 80% load derating - 32 biodigester totes serve 50 people in temperate climate zones. [7]

Cost

At the cost of insulated space and $1600 in totes assuming $50 per tote in surplus, the cost is attractive.

Septic tanks are $1/gal for comparison, while totes are 1/2-1/4 of this, minus the digging.

If gas and nutrient are a byproduct for a biodigester, that is where the win comes in. [8]

Internal Links

• Open Source Biodigester

Terms Relevant to Calculations

• Adsorbable Organic Halides / Total Organic Sulfur + Total Inorganic Sulfur / Total Sulfur Content or Total Sulfur
  • The former is mainly a concern in terms of Pollution, the latter may aid in estimating Hydrogen Sulfide Formation in Anaerobic Digestion Biogas / optimizing Feedstocks / Anaerobic Digestion Feedstock Pretreatment to reduce this
• Biomethane Potential
• Drain Fixture Unit
• Organic Load Rate
• Retention Time
  • Hydraulic Retention Time
  • Solids Retention Time
• Media Temperature
• PH

External Links

• A 2025 Paper Titled “ Dynamic Simulations of Anaerobic Digestion Plant” using Open Modelica.
  • Anaerobic Digestion Model No.1 (Aka ADM1 )
    • developed by the International Water Association ( IWA )
• A 2024 Open Access Paper Titled “ Open‐Source Anaerobic Digestion Modeling Platform, Anaerobic Digestion Model No. 1 Fast (ADM1F)”
• A 2024 Slide Deck from a PlanET Biogas Webinar Titled “Design Considerations for Anaerobic CSTR Digesters”
  • MIGHT not be Open Access, but the importance of Mixing, and the (at least MENTION OF) Design for Cleaning / cleanouts and such / Sand and Grit reduction/removal is nice
• [https://www.extension.iastate.edu/ageng/reflections-testing-strategy-anaerobic-digestion-using-right-tool-question-hand An Iowa State University Agricultural Extension Article Titled “ Reflections on Testing Strategy in Anaerobic Digestion: Using the Right Tool for the Question at Hand By Daniel Andersen, associate professor, Iowa State University”