Pee and Poo

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130 gallons of pee and 360 lb of poo.

Energetics of Incineration

8.33 lb in 1 gallon

1 BTU = 1 lb water raised 1 F

160F raise to boil from 60.

1300 BTU till boiling.

3400 BTU per kWh

[1] - 2300 kJ to vaporize one kg

~10MJ for one gallon.

1/3 kWh for one gallon to get it to temperature, then about 3 kW hr per gallon to vaporize.

If have 500W of panels, that could do one person if you have 6 hours of sunlight per day.

Moisture of Poo is 75% - [2]

Thus, Poo itself would require 50W of solar panels to incinerate if liquids are separated.

30MJ - charcoal enervy per kg. 1/3 kg charcoal per day to do the job.

Proposed Solution

Advanced biofilter is required. If separate urine, handling liquid is not much more effort.

Heavy waste loading means that the energy content must be extracted in some form. The question is what form. Options:

  1. Safe powder from shit fryer.
  2. Liquids are used to grow algae.
  3. Aerobic biofilter processes all waste, generates worms. Requires high inputs of carbon.
  4. Biogas digester - anaerobic, and final product is fertilizer + cooking gas. This gets into volumes required. Tank under toilet is a good idea. Top oil film for smells is a good idea. Allows flushing capacity.
  5. Baseline is 1 cubic meter per person to handle waste, and fertilizer comes out the other side.


Simple, Highly Engineered System Concept

Separate pee and poo. Use 1-2 sq meter of duckweed/azolla in an aquaponic greenhouse to treat urine while producing high protein fish food - see Azo

Inclusion of Biogas

There is no better alternative for waste processing than biogas digesters - on grounds of net positive energy output as well as fertilizer production.

One issue is materials handling - so the optimal system would have to have a garden attached to use the fertilizer, or be part of a composting operation where a lot of carbon is applied.

Principles to apply:

  1. Separate pee and poo.
  2. Must be part of an integrated system with Aquaponics and garden.
  3. Must integrate with cooking gas infrastructure - an extra bonus.
  4. To be acceptable publicly, must use existing interfaces (such as toilet and septic tank concept). Can meet reticulation as septic tank plus flush toilet.
  5. Water purification is the most advanced aspect of this. This would require redworm towers plus algae bioreactor plus Aquaponics to strip nutrients, carbon filter for final purification step.

Implementation Phases for a Closed Loop Water System

  1. Biogas digester. Definition of done - practical system that provides 100% cooking fuel. Can have grass clippings etc assist for more power.
  2. Addition of redworm towers to digester effluent. Adds a collectable worm product. Definition of done: Closed loop system on fish food production, and water is reclaimed up to irrigation standards. Most nutrients removed, water is clear at this point. Turbidity at 50 NTU
  3. Addition of algae bioreactor for additional nutrient reclamation. Optional.
  4. Addition of multiple phase charcoal scrubbers for final water reclamation to potable standards, and sand, rock filter with aeration for final mineralization. Definition of done: turbidity down to 5 NTU after charcoal phase. 1 NTU after sand filter - [3].

Technical Challenges

  • Biogas digester temperature - 90-100F
  • Worm tower - worm collection mechanism
  • charcoal filter - production of charcoal source. Filter recharging.
  • Algae bioreactor - container wall algae growth. CO2 presence.
  • Macerator integration to toilet at low cost.


  • Flush toilet to maceration to work tower. Issue: requires significant harvesting of product, and injection of high carbon biomass into system. Challenge: good design for worm tower. Growing bed integration of this system with duckweed and azolla could get the nitrogen out.
  • Digester-only : good proven solution. Refinements for storage and maintenance are required.
  • Azolla could replace the algal route, and appears to be easier.
  • Direct worm tower after maceration, with effluent going to septic tank. Disadvantage: wastes nitrogen fertilizer.
  • To utilize all fertilizer - must use a production greenhouse. Assume low flush toilet of 1 gallon. 10 gallons of water per person, or 20 gallons per day. This would require 1 cu meter of growing bed, times a safety factor of five - or 5 growing beds. Assume 10:1 urine dilution for acceptability to plants. Minimum here is 5 gallons per person per day based on average per per day.


  • Pee fertilizer; Swedes are masters of separation - [4]
  • Separating toilets - [5]