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.

Links

• Open Source Biodigester