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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. Micro and macro organisms do this over time, working through various stages of oxidation and sometimes localized pockets of anaerobic breakdown.
[edit] Types
"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. Some composting toilets have a large compartment below the toilet (in another living space). A composting toilet with this feature and sloped composting room for the compartment is called a "Clivus Multrum" composting toilet. Most of these separate sloped compartments require a great deal of space (more than a traditional toilet). "In situ" and "central unit toilets" however can be little larger than a traditional toilet. Finally, a special type of DIY-composting toilet is the double alternating pit compost toilet. Double alternating pit composting toilets or "fossa alterna" as they are sometimes called work similarly to regular composting toilets with separated compartment. However, the faeces compartment is just a pit (thus not contained in a bucket, ...) and after the pit is full, another one is used and the contents of the first one are used for fertilisation purposes.[1] It is important to note that composting is a biological process; systems that divert urine and use the addition of lime or significant volumes of wood ash to stabilize pathogens in the feces are called "drying toilets." This is due to the drying and high-alkaline additives that aim to destroy pathogens. A debate in the ecological sanitation field is whether drying or composting is preferable for more thorough pathogen destruction. A study out of Africa suggest that dehydrated feces can rehydrate with some pathogens intact. Urine diversion (sometimes called "urine separation"), whereby urine is drained via a separate drain in the toilet bowl or squat plate, is increasingly favored for some installations. The advantages: (1) urine and feces kept separate are less malodorous than when mixed and (2) aerobic processing (composting) occurs faster when moisture is controlled (up to a point; too dry, and the mass composts slowly). A third key advantage is that urine contains as much as 90 percent of the nitrogen and 50 percent of the phosphorus present in human excreta and yet is commonly pathogen free. Keeping it separate allows it to be used as a fertilizer with lower pathogen risk.[2] The arborloo does not make use of containers nor effective/optimal nutrient recycling. Instead, faeces falls into a pit until it becomes full. At that moment, a new pit is dug and the old pit with faeces (nutrients) is foreseen with a tree. The tree gathers the nutrients and converts it to wood mass (and/or fruit if it's a fruit tree). This wood mass and/or fruit can then be again used to supplement in the people's food requirements and/or energy requirements.[3] This might be more accurately called a "pit latrine." Some composting toilets use electricity, and some electrical systems use fans to exhaust air and increase microbial activity. Others require the user to rotate a drum or rotate tines within the composting toilet to allow for a predominantly aerobic breakdown of waste. In order to decrease smell, a composting toilet needs quick drying of its contents. In order to speed up this process, several special composting toilets have been made. The UDD toilet (urine-diversion dehydrating) is one such special type. This type of toilet has 2 containers: 1 waterproof container for urine and another for faeces.[4] UDD toilets can be bought or made DIY (see below for plans). UDD toilets have hardly any odour, because faeces can dry out better if not mixed with urine and water. Additional advantages are that urine collected pure can easily be reused as a fertiliser and faeces collected pure can (after drying) also be reused without much further processing in agriculture (see WHO guidelines from 2006 on reuse of excreta). They are reportedly also easier to operate and easier to build DIY than composting toilets, especially as much less knowledge is required. Solar toilets are another special type of composting toilet. They are made as regular composting toilets where the faeces chamber is painted black so that one gets faster drying. Usually though, painting the faeces chamber black is not necessary because with a good vent pipe it dries quickly enough anyway. 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 a few times a year. [edit] 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. One of these is the three-storey C.K. Choi Building at the University of British Columbia,[5] 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. 
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] Self made systems
Far simpler DIY systems can be constructed and maintained cheaply. Lately, through the Internet, good practical information and plans have become available. In particular, Practical Action[7] and EcoSanRes are now providing good approaches to recycling human waste to regain the nutrients and provide good DIY-toilet schematics. Other plans and schematics can be obtained from the Humanure Composting System Handbook (see below), Ecowaters, Composting Toilet World[8] , VillageEarth[9] Weblife,[10] and to some extent National Parks Board[11] Vela creations,[12] Freecycle.org,[12] and Jouneytoforever.[13] 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. [edit] Composting process and products
The process of converting human excrement is done through adding "cover materials" (see below) to the feces and letting it age. Additionally, kitchen (food) scraps may be added to the pile (eg meats, bones, fats, vegetable peels, liquids such as spoiled milk or stale beer, tea bags, egg shells, hair, ...), as well as animal manure and garden and yard materials.[14] Compostation into safe and usable compost material can take 3 months to a few years depending on climate, temperature, and the composting system. The composting of the human feces is usually done by letting it age in containers or open boxes. Several separate spaces are required to accommodate feces from different age as it composts. Generally, 3 spaces are used to accommodate a pile of feces of 1 year and a pile of feces from 2 years age. The third space is used to place feces which is soon to be dispersed on the land.[15] 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 "cover materials" such as sawdust, or alternatively, another organic material such as peat moss, coco coir, rotted leaves, leaf mould, straw, or grass clippings to soak up the liquid. The organic material also eliminates (a great deal of) the odour and prepares the feces for compostation. The type of material best used depends on its local availability, the make-up of the composting loo itself, personal preference, and so on.[16] 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. [edit] Possible health risks and aesthetic issuesComing into contact with improperly or incompletely composted human feces can be hazardous, 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 (104°-122° Fahrenheit). 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[citation needed], 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 may 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, the use of electricity might need to 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. [edit] ManufacturersList of manufacturers:
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