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Composting toilet

A composting toilet is any system that converts human waste into an organic compost and usable soil, through the natural breakdown of organic matter into its essential minerals. Aerobic microbes do this in the presence of moisture and air, by oxidizing the carbon in the organic material to carbon dioxide gas, and converting hydrogen atoms to water vapour.




"Self-contained" composting toilets complete the composting "in-situ,", while "central unit" ones flush waste to a remote composting unit below the toilet. Vacuum-flush systems can flush horizontally or upward.

Composting toilets can be installed anywhere, such as a cabin, cottage, bunkie, yurt, RV, pool cabana, boat, shed, barn, or home.

Some composting toilets use electricity, and some electrical systems use fans to exhaust air and increase microbial activity. Others require the user to simply rotate a drum within the composting toilet to allow for an aerobic breakdown of waste.

  Some composting toilets have a large compartment below the toilet. Others are little larger than a traditional toilet.

  All composting toilets eventually need some end-product removal. A full-size composting toilet does not need to have solids removed for several decades if the active tank volume is at least three times the yearly addition. This is because the waste dramatically decreases in volume: after around 5 years only 1-2% of the original volume remains. It is then a mineralized soil, which will not decompose any further. Other smaller systems may need to remove solids several times a year.

A related device, though only by its stand-alone use and not for its sustainability, is the incinerating toilet, which uses natural gas or propane to reduce the waste material to ash, in a process similar to a self-cleaning oven. However, these systems are quite expensive to run and emit a foul odour.

Commercial systems

  In recent years, several commercial compost-toilet systems have begun to compete with and replace conventional water closets in high-use public facilities. There they have found a market because of their resilience and the environmental advantages of not discharging pollutants into the environment. Outstanding among these is the three-storey C.K. Choi Building, which contains 5 compost toilets (10 seats) for 300 full-time employees. The IslandWood School on Bainbridge Island, WA (USA), relies entirely on compost toilets. Facilities Manager Dean Newcomb says, “All of the comments about the compost-toilet systems have been favorable. We keep the bathrooms immaculate, and the fan in the vent system generally works well, so it really gets rid of the misconception that these are smelly systems.”

Composting toilets reduce the volume of humanure and other organic materials on site over months or years through predominantly mesophilic composting and yield a fertilizer that is, after the legally required period, able to be used in horticultural or agricultural applications. Composting toilets are also becoming more common as an accepted alternative in homes, where the odor-free operation of a properly functioning unit appeals more to some houseowners than conventional toilets, with their consumption of large quantities of clean water and discharge of large amounts of sewage.

  Composting toilets have entered the mainstream plumbing realm by being tested and, if approved, certified to the ANSI/NSF-41 Standard. They can be tested and certified for ANSI/NSF-41 by any ANSI accredited testing laboratories such as Canadian Standards Association, CSA International, National Sanitation Foundation and Underwriters Laboratories.

Waterless, odorless composting toilets ensure that houses can remain occupied in drought areas where water is shut off for periods of time. An example is southern Spain, where at least one composting toilet per house could provide acceptable sanitation for as long as the drought prevails and water is unavailable. Likewise it provides always-usable public toilet facilities under such circumstances. This is becoming a very important application for the technology in areas all over the world where there is only periodic availability of water.

'DIY' systems

Far simpler DIY systems can be constructed and maintained cheaply. Odors are controlled by ensuring adequate ventilation, sometimes simply by leaving a small gap between the top of the wall and the roof, or using a low-voltage extractor fan. Odor can also be controlled by separating urine and feces, or by adding sufficient high-carbon content 'soak' material (see below) to absorb excess liquid. The material should remain aerated to prevent the compost from becoming anaerobic, which causes unpleasant odor. It must also either heat the feces to the point that pathogens are destroyed (a thermophilic process), or allow time (up to a year) for such pathogens to break down and disappear naturally (a mesophilic process). The advantages are that they use little water and may produce fertilizer safe for small scale agricultural use.

Another variant is the tree bog—a type of compost toilet that never needs emptying. Nutrient-hungry trees, such as fast growing willows, are planted around the tree bog, and they take up the nutrients and convert them to biomass, which may then be harvested.



Composting process and products

The process of converting human excrement into safe and usable compost material can take 3 months to a few years depending on climate, temperature, and the composting system. In 4 to 6 years there will be highly mineralized soil. Some composting-toilet models concomitantly turn urine into an odor-free, pathogen-free organic liquid fertilizer. Some countries, for example Sweden, allow this liquid to be used in agriculture after it is stored for 6 months. In full-size composting toilets, urine goes through a process called nitrification, resulting in an odor-free and practically bacteria-free liquid fertilizer.

Typically, the waste breaks down to 10% of its original volume. Most toilet-composting systems are mouldering, or low-temperature, toilets, where the waste is left for long enough that pathogens break down naturally, but there are also hot, or thermophilic, toilets, which heat the waste material high enough that pathogens are destroyed.

Some composting toilets separate the urine and the feces. Others mix the two, with the process requiring either evaporation of the liquid or the addition of substances such as sawdust, leaf mould, straw, or grass clippings to soak up the liquid.

Urine, rather than feces, contains the major bulk of plant nutrients worth recovering for reuse, including 90% of the nitrogen and 70% of the phosphorus. One advantage of modern composting toilets over conventional outhouses is that the latter leaches most nutrients into the groundwater, instead of saving them to be reused in agriculture or spread on the land.

Possible health risks and aesthetic issues

It can be hazardous to come into contact with improperly or incompletely composted human feces, because it may contain bacteria and other pathogens associated with human disease. For this reason, human waste should not be used as fertilizer without ensuring that it is composted thoroughly. When composting, the pile may achieve temperatures of 40°-50° Celsius. The Centre for Alternative Technology (CAT) in Wales recommends that in a cool temperate climate such as that experienced in the United Kingdom, where true thermophilic decomposition cannot be guaranteed, humanure should be allowed to break down for at least one year. It also advises that humanure should not be used as a fertiliser on crops that are directly handled and eaten, such as vegetables or salad leaves, but instead applied as a mulch around bush or tree fruits. Joseph Jenkins, author and proponent of humanure composting, recommends using composted humanure on any and all agricultural products.

In some situations, the finished compost must be Pasteurized prior to disposal. Governments provide operational definitions of pasteurization, which requires heating to a certain temperature for a certain time. In other situations, the finished compost must be sterilized, which requires more aggressive treatment and higher temperatures.

Many in the developed world find the idea of a composting toilet to be unappealing, perhaps due to the health and hygiene issues raised above. However, as long as basic safety rules and common sense are used, the real risks associated with a composting toilet system should be no more significant than any other situation where there may be some level of fecal contamination (such as using a water-based toilet, changing baby diapers, taking a bath). Educating people about the safe use of composting toilets will be an important factor in their gaining acceptance in the developed world. Water-based toilets were originally viewed with similar suspicions when they replaced the chamber pot.

Some health departments do not approve composting toilets as an alternative to septic fields. A septic field may still be required for treatment of grey water even if a composting toilet is approved. But reputable manufacturers of composting toilets usually help their customers deal with regulatory concerns.

Properly designed and sized in relation to use, composting toilets neither need power for processing nor use water, and will eventually reduce the solids to a final 1-2% of the added organic materials (feces and toilet paper). True composting is a slow process and takes around 4-6 years and a variety of processes involving bacteria, fungi, worms and other micro- and macro-organisms.

Ecologically, in the case of some of the more complex smaller systems, it may be that the use of electricity should be weighed against the use of water. In arid areas water may be more valuable than electricity, while in wet areas the opposite may be the case.

See also


List of manufacturers:

  • Advanced Composting Systems LLC
  • Biolet
  • Biolytix
  • Biosun
  • Clivus Multrum
  • Envirolet
  • Envirolet (Canada)
  • Nature-loo
  • Nature's Head
  • Sunfrost
  • Sun-mar

Notes & References

  • [3]
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Composting_toilet". A list of authors is available in Wikipedia.
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