Learn More

The Theory behind Composting Toilets

Composting Toilets have 4 factors that influence their efficiency.


In ideal conditions, the composting material inside a composting toilet has the consistency of a well-wrung sponge – about 45% to 70% moisture. When below 45%, there is not sufficient moisture for the microorganisms that do the composting work to function, and above 70%, saturated conditions begin to develop, and oxygen depletion becomes a limiting factor.

Maintaining moisture
In composting toilets the moisture content is maintained by proper ventilation, addition of proper mulch, frequent mixing of the compost and adjustment of the thermostat when the model features electric heating controls. These heating controls help keep the moisture at the optimum levels.


The typical temperature range for most composting toilets is 68°F to 112°F. Lower temperatures result in a moldering process that takes a significantly longer period of time to compost and therefore requires a much larger composting chamber.The temperature of the room the composting toilet is within determines the effectiveness of the composting process. If a temperature is not at least 64°F, the bacteria that do the composting go dormant and don't do their job.

Maintaining temperature
BioLet composting toilets have a constant flow of air circulating through them and the ambient room temperature needs to be maintained above 64°F during periods while the unit is in use. If the ambient room temperature is below this level, heaters in the electric models are unable to maintain sufficient heat to evaporate the excess liquid and sustain the composting process. During periods of lower ambient temperatures (late autumn, early spring, and winter) you may find it necessary to increase the thermostat on these electric models to maintain the proper operating state of a moist, loamy material with no indication of liquid. Conversely, you may find it necessary to decrease the thermostat during higher ambient temperatures (late spring, summer, early autumn) to keep from drying out the material inside the toilet. The composting process requires balance to work effectively. The floor a composting toilet sits upon needs to be insulated to help keep the temperature at its correct level. Bare concrete and similar flooring leeches heat from the composting system, preventing it from working properly.

The aerobic organisms responsible for the composting process require free atmospheric or molecular oxygen to survive. Without oxygen, they will die and be replaced by anaerobic microorganisms that will slow the composting
process and generate odors. For composting toilets to work most effectively, the materials being composted should be unsaturated with liquids, and have a loose texture to allow air to circulate freely within the pile.

Maintaining aeration

Many composting toilets have fans that help with the flow of air through the ventilation pipe; however, this cannot be completely depended upon.

  1. Several other factors need to remain in balance for maxium aeration
  2. Keeping the material inside the composting chamber in a loamy consistency.
  3. Proper installation of the ventilation pipe. Keep in mind that the addition of any angles in the vent pipe will reduce the airflow.
  4. Ensure a good flow of air to the bathroom from the living area.
  5. Proper mixing of the product inside the composting chamber. For electric models this is usually automatic.

Carbon to Nitrogen ratio (C:N)

Microorganisms require digestible carbon as an energy source for growth, and nitrogen and other nutrients for protein synthesis. When measured on a dry weight basis, an optimum C:N ratio for aerobic bacteria is about 25:1.8.

Maintaining C:N

A small handful of a base mulch per person per day or approximately 1 quart per person every week is a good rule of thumb to maintain a helpful C:N ratio, absorb excess moisture, and maintain pores in the composting material. BioLet Compost Mix is specially designed to maintain the ideal C:N balance within composting toilets. 

Composting Toilets require balance among many factors in order to work properly. When all the factors are in balance, composting toilets work well and odorlessly. Odors are a sure sign that one of these factors are not in right balance. Typically, the cause of problems within composting toilets is incorrect ventilation and ambient temperature. Ventilation must be installed exactly as the toilet's installation instructions say or the toilet will not work properly.

BioLet Privacy Policy
Close Window

Please wait...

BioLet Return Policy
Close Window

Please wait...

Support Registration
Close Window

Please wait...