Urine-diverting dry toilet

Double-vault UDDT, waterless urinal and shower integrated into a household's bathroom in non-sewered area of Lima, Peru

Double vault UDDT used in squatting position in Ouagadougou, Burkina Faso

Back view of UDDT toilet building at school in low-income aread of Lusaka, Uganda, showing access to faeces vaults

A urine-diverting dry toilet (UDDT) is a type of dry toilet with urine diversion. It can be configured as a sitting toilet (with a urine diverstion pedestal or bench) or as a squatting toilet (with a urine diversion squatting pan). The most important functional design elements of the UDDT are: source separation of urine and faeces (feces); waterless operation; and ventilated vaults or containers for faeces storage and treatment. UDDTs may be constructed with two dehydration vaults that are used alternately or one single vault with interchangeable containers. The UDDT is a dry excreta management system known since the late-1990s and can provide an alternative to pit latrines and flush toilets for certain contexts where they are particularly suitable.

An alternative name of it is urine diversion dehydration toilet (also abbreviated as UDDT), although with this term more emphasis is placed on the process of dehydration in the vault of the toilet and it should only be used for UDDTs with two vaults.

This type of toilet is also called by many people ecosan toilet, although this is not recommended as ecosan is not limited to this type of toilet.

UDDTs can also accommodate users who prefer anal cleansing with water by including a separate anal cleansing pan with a drain to divert wash water into a dedicated disposal or treatment system. In many cases, UDDTs are offered together with waterless urinals to prevent male users from standing over the UDDT and aiming by mistake for the wrong hole, i.e. the faeces hole.

Principle

Urine diversion takes advantage of the anatomy of the human body, which excretes urine and faeces separately. In a UDDT, the urine is drained via a basin with a small hole near the front of the user interface, while faeces fall through a larger drop-hole at the rear. This separate collection – or "source separation" – does not require the user to change positions between urinating and defecating, although some care is needed to ensure the right position over the user interface. Female users may find that some urine may enter the vault during normal operation. This is typically a small amount and does not significantly affect the function of the toilet.

A UDDT consists of eight basic functional elements:

1. Urine diversion toilet seat or squatting pan;
2. One or two vaults, usually above ground, or one shallow pit for faeces collection and storage;
3. Urine piping system leading from the user interface to an infiltration or collection system;
4. Ventilation pipe to exhaust moisture and odours from the vault or pit; 
5. If required: An anal cleansing area with mechanisms for the separate collection and drainage of anal wash water; 
6. Toilet super-structure, unless the toilet is installed inside an existing house;
7. Bucket with dry cover material; and
8. Hand washing facility with soap and water - like any other toilet should have. 

Various types of cover material, such as ash, sawdust, soil or lime is added to the faeces chamber of a UDDT to reduce odour and speed up the drying process (or to raise the pH in the case of lime).

Suitability

UDDTs are particularly suitable in situations where:

1. Water is scarce or costly, such as in arid or semi-arid climates; 
2. Sewerage infrastructure costs are prohibitive, such as instances of unfavourable terrain, sprawling settlement patterns or poverty;
3. Frequent flooding would impact pit latrines and septic tank systems, resulting in inoperable toilet systems and the contamination of water resources;
4. Unfavourable soil conditions, such as unstable or rocky soil and high water table, make pit-based sanitation difficult and expensive;
5. Groundwater is the primary source of drinking water and is likely to be contaminated by pit-based sanitation;
6. Limited land space restricts the excavation of new pits if full pit latrines are usually not emptied;
7. Indoor installations are preferred as they provide greater comfort and security at night thus making them more accessible for all;
8. Local agriculture and diminishing soil fertility create demand for affordable fertiliser and soil conditioner.

Challenges

Significant barriers to more universal acceptance of this technology remain. These include in the case of developing countries: lack of awareness, a limited supply of prefabricated UDDT components and a low interest in financing sanitation services for non-sewered areas of settlements.

Many users outside of rural areas do not have an interest in handling excreta to fertiliser their gardens. Therefore, service providers should set up a collection service, similar to the "bio bin" scheme in Germany which is a system to collect household organic waste from kitchen and gardens to transport this organic waste to a centralised composting or biogas facility.

UDDTs have been criticised for being out of reach for low-income families as their construction costs might be quite high compared to pit latrines. However, rather than looking only at the construction cost, the whole of life cost (or life-cycle cost) should be considered, as the regular emptying or re-building of pit latrines may add a significant expense to the households in the longer term. When a period of 10 years is considered in the analysis, UDDTs may well be the more economical alternative as emptying the faecas vaults is a very low-cost activity.

Comparison with pit latrine

The advantage of UDDTs compared to pit latrines is the conversion of faeces into a dry odourless material and therefore a complete avoidance of the issues surrounding faecal sludge management. A well-maintained UDDT is an odour and insect free toilet which is appreciated by users and allows simple removal and less offensive and safer handling of the faecal material once the faeces vault has filled up. Moreover, the risk of water pollution is minimised through the safe containment of faces in aboveground vaults and this allows the toilets to be constructed in locations where pit-based systems are not appropriate.

Reasons for keeping urine and feces separate in a UDDT compared to a pit latrine can be to:

1. reduce odour (a mix of urine and faeces causes substantial odour);
2. avoid production of wet, odorous faecal sludge, which has to be removed by someone when the pit latrine is full;
3. enable fast drying of faeces which makes handling of faeces more simple and hygienic;
4. reduce environmental impacts;
5. allow for the recovery of urine, which can be reused as fertiliser.

Reuse of dried faeces

The faeces are in almost all cases not entirely sanitised when removed from the vaults of the UDDT, so careful handling is obligatory. In scenarios with reuse of excreta in agriculture, a post-treatment of faecal matter and storage of urine is advisable to ensure adequate sanitisation. The World Health Organisation has issued in 2006 the “Guidelines for the safe use of wastewater, excreta and greywater in agriculture” containing guidelines for managing the health risks associated with the use of excreta, including excreta from UDDTs, in agriculture. The key concept of these guidelines is the multiple barrier approach which can also be applied to reuse activities in connection with UDDTs.

Design aspects

Bench design

UDDTs can also be built with a bench style user interface. This design has been standardised by the company Rotaria del Peru who have built by now 800 double vault bench UDDTs in and around Lima, Peru. This type of toilet has a wide, spaceous bench or box, covering both faeces chambers, into which two urine diverstion toilet seats are integrated.

Users with disabilities can benefit from this kind of design as it is very sturdy (compared to the option of a chair or commode over a pit latrine). The wide bench provides space for an assistan if needed, and handrails can easily be fixed next to the toilet. This type of UDDT is accessible directly from the ground level and does not require access steps or ramps unlike conventional raised UDDTs.

Source of bowl or squatting pan

The toilet bowls or squatting pans for UDDTs can be commercially manufactured from plastic or ceramic and transported to the user or built locally by local NGOs or artisans, for example made of concrete.

Historical development

The UDDTs with double dehydration vaults that we know today were originally designed around 1950 in Japan and further developed in Vietnam in the 1960s as a means of increasing the hygienic safety of excreta reused in agriculture.

Since the 1990s, modifications of this design such as addition of ventilation pipes to the faeces vault have been developed in many countries. Prefabricated ceramic or plastic urine diversion squatting pans and pedestals have become available on the market, generally increasing the durability and perceived prestige associated with the system.

UDDTs have also been commercially produced in Sweden since the mid-1990s for example by the company Separett who have sold approximately 200,000 UDDTs between 1994 and 2010. Such off-the shelf commercial products are now also available in Do-it-yourself shops and are used in locations where piped sewerage is not available, such as remote summer cottages in Sweden or for camping activities.

Examples of UDDT installations

The exact number of UDDT users worlwide is impossible to determine, but a rough estimate by GIZ in 2012 based on known projects in 84 countries put the number at approximately 2 million users worldwide (this list does not include commercially sold units).

Some examples are provided below:

• The NGO Women in Europe for a Common Future (WECF) and local partners have built built many urine-diverting dry toilets for schools in Eastern Europe, Caucasus and Central Asia (EECCA region).

• Haiti - SOIL has built urine-diversion toilets and composting waste treatment plants in Port-au-Prince as part of the 2010 Haiti earthquake emergency relief effort and in northern Haiti. There are currently 20,000 people using these units and more than 400,000 liters of compost have been produced as a result.

• Cambodia - Lien Aid has assisted with the development and implementation of floating toilets that utilize UDD in a project called “River of life”

• Boating - Chris Melo, sailboat resident and nautical engineer, cites 9 reasons to convert from conventional nautical toilets that store waste in black water tanks, or immediate discharge it overboard, to a UDD composting toilet Two competing manufactures for nautical use call their products Nature's Head and the Air Head Toilet.

• Camping - Leave no trace is not only a philosophy but a necessity in areas where human waste left behind would not decay naturally. There are now portable UDD toilets for example by the Swedish company Separett that allow feces to be collected and packed out. Only urine is left behind which is of less concern as urine is nearly pathogen free.

• NatSol, a UK company that specialises in urine diverting dry toilets, has developed a solution that avoids the usual problems of blockage and fouling of urine separating bowls. It uses the Coandă effect to divert and send urine to a soakaway, rather than rely on evaporation.
• Owing to limited water supplies in outer space, NASA started in May 2009 to utilize a UDD toilet to recycle urine into drinking water.
• In Namibia, UDDTs are known under the name of Otji toilets.
• More examples of installations of UDDTs in developing countries is available in 45 case studies of the Sustainable Sanitation Alliance that describe projects with UDDTs.

External links

• Documents on UDDTs in library of the Sustainable Sanitation Alliance
• UDDT photos in flickr photo database of the Sustainable Sanitation Alliance