Composting toilet
From Wikipedia, the free encyclopedia
Composting toilets use biological processes to deal with the disposal and processing of human excrement into organic compost material.
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[edit] Types of toilet
A composting toilet can be defined as "...a system that provides an environment within a container for predominantly aerobic (in the presence of oxygen) decomposition and stabilization of waste."
There are two basic types of compost toilet, those that complete the composting process 'in situ' and those that are emptied to a separate compost pile remote from the toilet itself. The latter arrangement is sometimes referred to colloquially as a ‘bucket and chuck it’ system, like a "humanure bucket system"[3]. This means that faeces are deposited into a plastic container to which soak material such as straw, sawdust, dry grass, etc, is added in order to absorb excess liquid, cover human waste materials, exclude flies, reduce smells and balance Carbon:Nitrogen ratios. When full, the bucket is removed and emptied onto a composting pile that is kept separate from other composting materials such as kitchen or garden waste.
Some composting toilets use electricity, while others do not. Some electrical systems use fans to exhaust air and increase microbial activity. Other systems require the user to rotate a composting drum or otherwise stir the composting humanure from time to time.
Some composting toilets are large with a significant space requirement in the room below the toilet. Others are not significantly larger than a traditional toilet. Those small systems generally do not claim to finish the composting on-site, but are preparing the human waste materials for secondary composting in another location (like a compost pile).
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 due to the dramatic reduction in volume over time -- after around 5 years only 1-2% of the original volume remains. It is then a mineralized soil which will not decompose any further See [4] Other smaller type systems 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.
[edit] Commercial systems
In recent years several commercial compost toilet systems have begun to compete with and replace conventional WCs 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 of time, able to be utilized 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.
Composting toilets have entered the mainstream plumbing realm by being tested and, if approved, certified to the ANSI/NSF-41 Standard. Composting Toilets can tested and certified to ANSI/NSF-41 by any ANSI accredited testing laboratories such as CSA, CSA International, NSF and UL.
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.
[edit] 'DIY' compost toilet systems
Far more simple and basic DIY systems can also be constructed that require very little cost or maintenance, provided that attention is paid to a number of important factors. The toilet must control odors. This is achieved by ensuring adequate ventilation (sometimes simply by leaving a small gap between the top of the wall and the roof, more sophisticated systems may incorporate some kind of low voltage extractor fan). Odors can also be controlled by either ensuring that urine and faeces are kept separate or by adding sufficient high carbon content 'soak' material (see below) to absorb excess liquid. The design of the composting toilet should allow the material to remain aerated to prevent the compost from becoming anaerobic, which can result in unpleasant odors. It must also either heat the faeces to the point that pathogens are destroyed (a thermophilic process), or else allow sufficient time (up to a year) for such pathogens to break down and disappear naturally (a mesophilic process). The upside however is that they do not use any significant amount of water and they may produce fertilizer safe for small scale agricultural use.
Another variant is the Tree bog - a type of compost toilet which never needs emptying. Nutrient-hungry trees such as fast growing willows are planted around the Tree bog, which take up the nutrients and convert them to biomass which may then be harvested.
![A compost toilet facility viewed from outside. This structure was built entirely from recycled materials[1]](../../../upload/thumb/8/86/Finished.jpg/180px-Finished.jpg)
![A DIY compost toilet at Dial House, Essex, England, created at very low cost utilising an old school desk as the toilet unit [2]](../../../upload/thumb/7/74/Composttoilet.jpg/180px-Composttoilet.jpg)
[edit] Composting process and products
The process of converting human excrement into safe and usable compost material can take between 3 months to a few years depending on factors such as climate, temperature and the particular system being employed; and in 4-6 years will become highly mineralized soil. Some composting toilet models are concomitantly turning urine into an odor-free, pathogen-free organic liquid fertilizer. Some countries, for example Sweden, allow this liquid to be used in agriculture after a storage period of 6 months. In the full-size composting toilets, urine goes through a process called nitrification, resulting in an odor-free and practically bacteria-free liquid fertilizer.
The objective with a composting toilet is to destroy all the harmful pathogens, and turn the waste nutrients into fertile soil. 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 faeces. 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 faeces, 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.
[edit] Possible health risks and aesthetic issues
It can be hazardous to come into contact with improperly or incompletely composted human faeces, because it can 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 temperature may achieve temperaturees of 40°-50° Celsius, thus killing pathogenic bacteria such as E.coli. The Centre for Alternative Technology (CAT) in Wales recommends that in a cool temperate climate such as that experienced in the UK, where true thermophilic decomposition cannot be guaranteed, humanure should be allowed to break down for at least one year. They also advise 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 temperaure 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 (eg, using a WC style toilet, changing baby diapers, taking a bath, etc). Educating people about the safe use of composting toilets will be an important factor in their gaining acceptance in the developed world. It may also be worth noting that water-based toilets were originally viewed with the same type of suspicions when they replaced the chamber pot.
Some health departments will 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. Before making a significant investment, check with your local health department. Reputable manufacturers of composting toilets can, and usually will, help you 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 (faeces 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 within the context of a situation. In arid areas, water is probably more valuable than electricity while in wet areas, the opposite may be the case.
[edit] See also
[edit] External links
- 'The Humanure Handbook' (Webbook)
- Alternative Sanitation Technologies chapter from "An Alaskan Challenge: Native Village Sanitation"
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