Composting Toilets

Toilet waste collecting system that composts solids using aerobic bacteria.

Treatment Level:  Primary
Relative Cost:
  medium – high
Amount of Maintenance Interaction:  medium
Beneficial Byproduct:  some – lots (compost)


  • Significantly reduces water use, which in turn protects well supply or lowers water bills
  • Produces “humus” so that nutrients can be reused safely


  • Must use waterless or foam flush toilets to minimize liquids.
  • Must have separate plumbing system for graywater.
  • Must be located on a basement level (below all toilets, but still accessible).

Operation & Maintenance

  • Add bulking agents such as sawdust, straw, shredded newspaper, etc. every 1-3 months.
  • Allow compost to age a minimum of 12 months before removing for use.

Blackwater vs Graywater?

  • Because aerobic treatment is sensitive to excess moisture, composting toilets are for blackwater only.

Secondary Treatment Options

  • No secondary treatment needed.

Additional Notes:

  • Can be self-contained units (individual) or a collection system leading to a central composter
  • Can be passive (composts unaided by mechanical means) or actively heated and mixed to decrease composting time
  • Must include ventilation fans to keep compost aerated and eliminate odors

Composting Toilet Diagram (