Composting Toilet Process

Composting is the breakdown of organic matter in the presence of aerobic organisms. This is the same process that happens wherever organic matter is exposed to oxygen and moisture: in forests; garden compost piles; lawns; etc. The composting toilet system allows human waste to break down into simple, stable compounds that have value as plant nutrients (i.e., fertilizer).

Biological Aspects

In the Clivus system, the breakdown of waste is carried out by organisms that thrive within a temperature range of 20-45 °C. Chief among these are a wide range of bacteria and fungi. Also highly active within the compost system are many invertebrates, such as red worms that transport oxygen and moisture throughout the compost mass while they assist the physical and chemical breakdown.

Bulking material (typically, pine shavings or shredded bark mulch) is added to help maintain a porous texture that promotes aeration and good moisture content. Human pathogens are killed not by the heat within the composter but by predatory organisms and the long retention time in the system. Especially important in the composting process are the nitrifying bacteria (e.g., nitrobacter and nitrosomonas) which turn the nitrogen in human waste into nitrites and nitrates—forms of nitrogen plants need for growth.

Chemical Aspects

One of the most important processes taking place within the compost system is the chemical transformation of the nitrogen in human waste. Most of the nitrogen is contained in urine in the form of urea. In the composter, urea is readily broken down into ammonia and carbon dioxide by a variety of bacteria and fungi. As it passes through the compost mass, nearly all of the ammonia is converted, first to nitrites, and then to nitrates by nitrifying bacteria. Nitrate, incorporated in manufactured fertilizer at great cost and environmental damage, is a form of nitrogen readily taken up by plants.

Two other macro plant nutrients, phosphorous and potassium, along with a wide range of micro-nutrients, are also present in human waste in useful quantities and are captured by the composting process. Separated from the solid matter by the composter design, the compost liquid that results is a stable, high-strength fertilizer. Fecal matter in the compost system is reduced in volume by more than 90%, and breaks down over time. When fully composted, this material looks and smells like topsoil, and is an organically rich soil amendment.

Greywater System Process

Since greywater—water from sinks, showers, and washing machines—contains only about 10% as much nitrogen as does human waste, it’s far less of a pollution problem. When greywater is put into the aerobic environment of topsoil soon after it has been collected, plants and soil organisms use the nutrients it contains. The nitrogen in greywater is first converted into ammonia by aerobic organisms in the water. Once the greywater is put into topsoil, soil organisms quickly convert the ammonia to nitrate which can then be used by plants.

Conclusion

By use of the processes described above, the composting toilet and greywater irrigation technologies have the following benefits:

• Saving water that would otherwise be used to carry toilet waste.
• Protecting water sources from pollution by human waste.
• Creating fertilizer for use in plant growth.
• Providing irrigation water for plants.