- Waterless toilet systems
- Treat excreta by creating dry conditions, increasing pH, and ventilation and addition of dry absorbents
- Produce a material easy and safe to handle, that can be further processed to a valuable soil conditioner
- Most suitable in dry climatic conditions
AGeneral description
Nathasith Chiarawatchai, Florian KlingelLast update: 30/08/2004Page 1/9
ecosan Sector Project, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH, P.O. Box 5180, 65726 Eschborn
Fon: (++49) 6196 - 79 4220, Fax: (++49) 6196 - 79 7458, E-mail: , Internet:
A.1Basic principles
In a dehydration toilet, the excreta inside the processing vault are dried with the help of sun, natural evaporation, ventilation and the addition of dry materials. The toilet requires no water. This technology is increasingly popular in the developing world, especially in arid climates where water is scarce and faeces can be effectively dried. The faeces are collected in a chamber below the toilet seat (or hole) and are dried. High temperature in the chamber, together with ventilation are the most important mechanisms in the drying process. The ventilation also reduces bad odours. A moisture content below 25% facilitates rapid pathogen destruction.
Absorbents such as lime, ash, sawdust, or dry soil should be added to the chamber after each defecation to absorb excess moisture, make the pile less compact and make it less unsightly for the next user. Addition of absorbents is also reported to reduce flies and eliminate bad odours. Moreover, pH will also be increased due to this addition, and hence enhance bacterial pathogen die-off.
As breakdown of organic material in dehydrating conditions is slow, toilet paper or similar objects placed in the chamber will not disintegrate quickly. Toilet paper can therefore either be handled separately, or be composted in a secondary treatment process.
Once the chamber is becoming full, the content needs to be moved out. The contents are further stored or composted (by home composting or at a local composting centre), before they can be used as a soil conditioner.
Sanitation tests have shown that the hygienisation of faeces through dehydration process is satisfactory after six months. Nonetheless, it has been reported that the eggs of the parasite Ascaris lumbricoides have been viable for years in a dry environment (Del Porto, 2000), therefore further storage, sun drying, or high-temperature composting may be recommended. The product from the dehydration process, crumbly cake, is not compost but rather a kind of mulch which is rich in humus, carbon, and fibrous material, phosphorous and potassium. Nutrients will be available to plants after further decomposition of the dehydrated material.
A.2Available technologies
Many alternative ways of constructing dehydration toilets exist. Generally it appears that double-vault toilets with urine diversion show the most successful results and the highest popularity. Several modifications can been applied to enhance the process and to suit each region’s condition. The main distinguishing features are listed in the following.
Urine diversion or non-urine diversion
Most dehydrating toilets require prior separation of urine to allow sufficient drying of faeces. Systems where urine and faeces are mixed do only work properly in very dry climates. Some installations provide a drainage system for the chamber to improve dehydration of the solids.
Single vault or double vault
Dehydration toilets can be built with a single or a double chamber for collection of faeces. By using a double-vault, handling of fresh excreta can be excluded. Most of the dehydration toilets hence derive this double-vault technology. Single-vault systems, require less building cost, but need more labour work for guaranteeing equal hygienic safety as double-vault systems.
Squatting or sitting toilets
Dehydration toilets can be built for squatters or sitters, both in combination with urine diversion or without.
Dry anal cleansing or wet
Dehydration toilets can easily receive dry cleaning materials such as toilet paper. Dehydration toilets can also be used for wet cleaning cultures, water from anal cleaning then has to be drained in a separate pipe so that no liquid is led into the vault.
Self-constructed or prefabricated
Most of the system can be self-constructed by the users totally or partially by using commercially available squatting pans or toilet seats. In some areas, complete systems including the toilet cabin are available on the market.
A.3Applicability
Dehydration toilets have been applied in various, mostly developing countries, including China, Vietnam, India, Nepal, Mexico, Ecuador, El Salvador, South Africa, Zimbabwe, and many and others. Currently
Dry climates
Dehydration toilets are most suitable for regions with high average temperatures, long dry, and short rainy seasons, or arid climatic conditions. Nevertheless, with simple solar heaters, they can also work in a more humid climate.
Dehydration toilets are waterless systems that are particularly suitable for conditions where water is scarce.
Rural and urban areas
Dehydration toilets can be placed in outside the house, attached or even inside to house. Dehydration toilets are therefore suitable both for rural and densely populated urban areas.
Different cultural setting
Dehydration toilets are suitable for different cultural settings: they can be designed to suit both sitting and squatting cultures, and both dry or wet anal cleansing habits.
Compare favourable to pit latrines
Dehydration toilets are built with a permanent structure, the collection chambers normally is situated above the ground. This avoids several severe problems that typically occur with pit latrines, which require a deep hole, dug in the ground: contamination of ground water through infiltration does not happen; nutrients in urine and faeces can be recovered; construction is possible even where underground is rocky or where high groundwater levels are present; pits fill up and need to be replaced after a certain time, dehydration toilets are permanent.
Some advantages compared to composting toilets
Compared to composting toilets, another dry toilet type suitable for ecosan concepts, dehydration toilets can have come advantages. The main advantage is that the dehydration process is less sensitive than the composting process, resulting in lower maintenance needs. This, of course, is only valid if design and climate allow a good functioning of the drying process. In cool and humid climates, a composting process might be easier to maintain than dehydration.
The product of a dehydration toilet is drier than from a composting toilet and therefore easier to handle. Post-treatment of removed solids is recommended for both, composting and dehydration toilets.
In a dehydration toilet, the required additive can be anything from ashes, lime, sawdust and other dry organic materials, whereas in a composting toilet, the additive needs to be more specifically chosen to enhance the decomposing process. Ashes, particularly suitable for dehydrating toilets, are often available in households.
Careful handling required
An important condition for the succes of dehydration toilet is that sufficient user comittment ot operation and maintaince can be provided.
Cleaning of a dehydration toilet seat or squatting pan has to be done careful without too much water, to avoid introduction of water in the collection chamber. A bulking agent has to added regularly to the faeces. The collection chamber has to be checked and emptied in regular intervals. In non-urine-diverting versions, wetness of the chamber content has to be observed and drainage function corrected if necessary.
All those tasks require a certain level of responsibility and care from the users. Neglected maintenance can quickly lead to malfunctioning of the process and may impair severely the appearance and hygiene of the toilet.
User acceptance
Dehydration toilets are only an option if they are accepted by users. Especially handling and reuse of dry faeces and separated urine might be difficult to accept by users in certain cultural or socio-economic settings.
User acceptation often depends on the perception of status connected to the new facility. Compared to situations with open defecation, communal toilets or pit latrines, dehydrating toilets generally compare favourably. If flush toilets are already established, dehydration toilets often are connected with lower status. In such cases, strong other advantages are needed to lead to acceptance of the dehydration toilets.
The fact that men need to sit for proper urine separation may lead to acceptance problems that generally can be overcome by providing simple urinals for men.
Reuse
Regular reuse of urine and dry faeces is important for sustainable operation of dehydration toilets. Reuse provides incentives for proper operation and maintenance of the facility.
Therefore, dehydration toilets are most usefully operated in rural and peri-urban areas, where the toilet users can directly use products from toilets in their gardens.
This direct reuse cycle is often not possible in urban areas, where no space for cultivation exits in close vicinity of the toilets. In such situations, management systems for collection, marketing and use of products from toilets, are very important for sustainable operation of dehydration toilets.
A.4Further Reading
Austin, A. and Duncker, L., 2002, Urine-diversion: ecological sanitation systems in South Africa, CSIR Building and Construction Technology, South Africa.: Report concerning urine-diversion toilet s based on the dehydration process in South Africa, including the associated social aspects.
Esrey, St. A., et. al., 1998, Ecological sanitation. Department for Natural Resources and the Environment, Sida, Stockholm, Sweden.: Well-illustrated book concerning different types of ecological sanitation toilet as well as performance and health issues.
Morgan, P., 1999, Ecological sanitation in Zimbabwe: A compilation of manuals and experiences.: technical manual in term of latrine design.
Peasey, A., 2000, Health aspects of dry sanitation with waste reuse. Task No. 324, WELL.: Report concerning several types of dehydration toilets and their associated health aspects.
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Nathasith Chiarawatchai, Florian KlingelLast update: 30/08/2004Page 1/9
ecosan Sector Project, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH, P.O. Box 5180, 65726 Eschborn
Fon: (++49) 6196 - 79 4220, Fax: (++49) 6196 - 79 7458, E-mail: , Internet:
BDetailed information on different types of dehydration toilets
B.1Double-vault dehydration toilet with urine-diversion
Nathasith Chiarawatchai, Florian KlingelLast update: 30/08/2004Page 1/9
ecosan Sector Project, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH, P.O. Box 5180, 65726 Eschborn
Fon: (++49) 6196 - 79 4220, Fax: (++49) 6196 - 79 7458, E-mail: , Internet:
B.1.1Functional principles
Two alternating vaults
Faeces are collected in two vaults beneath the toilet seat or squatting pan, where they are dried. A ventilation pipe connected to the vaults is reducing odours and enhancing the drying process. The urine is diverted by designed a funnel or specially designed squatting pans or toilet seats. Anal cleansing water may be diverted through a separate funnel.
Always one vault at a time is active and receives the faeces. A pile of organic material forms to which ashes, lime or a bulking agent should be added to maintain high alkalinity and absorb humidity. When this first vault is filled, the opening is sealed and the toilet bowl is transferred to the other vault.
The second vault is now active while the first is passive or “for maturation”. When the second vault fills up, the dried material can be removed from the first. The product has a sandy appearance and in general is perfectly smell-free.
Hygienisation through heat and high pH
Within the chamber, water content is reduced to about 25% and temperature can rise to up to 50 °C. This enhances pathogen destruction. Pathogen destruction is further enhanced by addition of alkaline material, such as lime or ashes.
B.1.2Handling and maintenance
Addition of adsorbents
One of the chambers is in use, the other is to be sealed. After each use, dry absorbents (sawdust, peat moss, dry soil, ashes, etc.) are sprinkled over the faeces to absorb moisture, increase pH, curtail bad odours and insects. Generally, after each use, people sprinkle one to two bowls of ashes over the faeces, but the exact amount depends primarily on users experience with their own system. The floor of the chamber can be sprinkled with powdered earth before first time use in order to absorb moisture from the faeces and to prevent them from sticking to the floor.
Removal of dry solids
The first vault can be used for about 2 to 6 months by a household of 5 to 10 persons, depending on the volume. When it is two-thirds full, someone in the household levels the content with a stick. He or she then fills the vault to the brim with dried, powdered earth, and seals the vault. All openings are tightly closed, e.g. with lime mortar or clay. The other vault now comes into use instead. When the second vault is nearly full, he or she opens and empties the first vault. The dehydrated faeces, now odourless, and can be reused as soil conditioner. Further storage or co-composting with other organic materials is strongly recommended to increase hygienic safety.
Urine drains away through the groove in the slab and collects in a jar or plastic container behind the toilet, or in a larger storage tank. Paper used for anal cleaning can be dropped in the hole for excreta or collected separately in box or jar and burnt.
B.1.3Extent of application
The urine-diversion double-vault toilet originated from the model of the Vietnamese dry toilet, constituting two chambers built above the ground with a drop hole for squatting while defecating (see Fig. 2). This toilet type has been developed in the 1960s to increase hygienic safety of the traditional use of excreta in agriculture.
Modifications of this design have been adapted in several countries, such as vent pipes to reduce odour and facilitate dry conditions, or toilet seats within the house.
A modified version of the Vietnamese double-vault dry toilet with toilet seats instead of squatting pans is promoted by the Mexican NGO, Espacio de Salud AC (ESAC). Furthermore, the design has also been adapted for use within houses (see Fig. 4). It has been reported from ESAC that this toilet has been successfully built in communities in a variety of climates from humid and temperate to dry and tropical.
Another adaptation of Vietnamese model was found in Guatemala, in which the design is similar to the one in Mexico. The so-called double vault dry alkaline fertilizer family (DAFF) latrine was introduced by the Centro Mesoamericano de Estudios sobre Tecnologia Apropiada (CEMAT) in Guatemala.
In China, prefabricated squatting pans for dry toilet systems with urine diversion have been developed and are produced at a very low price. These pans replace the drop holes normally used in squatting slab. The squatting pan will increase the durability of the system since it can prevent a collapse of the structure. It also enhances prestige status of the system. The design in China is also applied within houses.
In Kerala, India, water used for anal cleaning is diverted into an evapotranspiration bed next to the toilet. The bed requires little maintenance, only cutting the excessive growth plant. Urine is diverted separately (see Fig.4).
B.1.4Strengths and weaknesses
Health and environmental impact
A double-vault dehydration toilet can transform infectious faeces into a perfectly safe product, if following conditions are met:
- Faeces remain at least 6 months in the chamber before being removed
- Sufficient ashes or lime is added after each use
- Climate and chamber design cause temperature above >50°C during various days of the storage period.
Of particular importance for hygienical safety is the alternating system of the double vault toilet, as it allows avoiding any direct contact of users with fresh faeces and provides for a 6 month period, during which the effects of time, temperature and pH can act on pathogen organisms. Therefore, a double vault dehydration toilet is considerably safer than any single-vault system.
Due to the urine diversion, drainage of liquids can be avoided and pathogens be confined in the chambers. Systems where urine or washing water is mixed with faeces always produce contaminated liquids which are difficult to retain. Dehydration toilets with urine diversion therefore are generally safer than dehydration or composting toilets without urine and washing water diversion, and much better even than pit and VIP latrines.
The main health risks from a double vault dehydration toilet with urine diversion result from lacking maintenance, if its main principles are not respected: If the alternating rhythm of chamber use is not respected, safety of content cannot be guaranteed and people may manipulate infectious matter; if liquids enter the chamber, the drying process will be impaired and germs may be spread through leakage of liquids. Poor design and neglect of adding dry and alkaline adsorbents also decreases safety.
Costs and benefits
Construction of a dehydration toilet can in most cases be done with locally available materials and labour. Prefabricated parts may include toilet seats or squatting pans. If those parts don’t need to be imported from abroad, they are usually cheap and can be even cheaper than self constructed squatting pans made from cement.
Double-vault dehydration toilets have similar construction cost as a VIP or pit latrine, in the long term they are even cheaper because its life-time is considerably longer. Dehydration toilets with one chamber and without urine diversion also have similar costs, as savings for the omission of the urine diversion and a second chamber are compensated by systems for drainage of the chamber.