UDDT

The UDDT is built such that urine is collected and drained from the front area of the toilet, while faeces fall through a large chute (hole) in the back. The liquids are diverted from the faeces in order to keep the processing chamber contents dry. Depending on the Collection and Storage/Treatment technology that follows, drying material such as lime, ash or earth should be added into the same hole after defecating. This helps in lowering the moisture content and raise the pH. The system thus creates conditions of dryness, raised pH and time for pathogen die-off (WINBLAD et al. 2004). If wet anal cleansing habits prevail in a community, anal cleansing water must be diverted (e.g. by providing a separate washbowl or by building 3-hole separating toilets).

Urine is collected in containers for direct use, storage, further processing (desiccation, struvite production, etc.). Hygienised urine can be used at small or at large scale, or locally discharged by infiltration into the soil (e.g. evapotranspiration bed). Faeces collected in UDDTs can either be dehydrated (storage and dehydration) or composted (co-composting  small-scale or large scale) before they are used as soil amendment.

There are two distinct types of UDDTs: double-vault UDDTs and single-vault UDDTs. In order to facilitate collection of the finished compost-like material (desiccated faeces and cover material), the former ones are designed to operate in batches whilst the latter ones provide only one collection cum storage compartment for containment of faeces. Therefore, off-site storage and drying or secondary treatment (e.g. co-composting  small-scale or large scale, etc.) have to be planned for. In general, UDDTs are built entirely above ground to provide for easy access to the processing chambers, which are placed on a solid floor of concrete, bricks or clay and the floor is built up to at least 10 cm above ground so that heavy rains do not flood it (WINBLAD et al. 2004).

Note that in some countries UDDTs are also referred to as composting toilets. This is sometimes misleading as urine-diversion dehydration toilets and composting toilets operate in slightly different ways.

Double-Vault Urine Diverting Dehydration Toilets

Present-day designs of double-vault UDDTs are based on the Vietnamese double-vault dry toilet, which was developed in the 1960s by local authorities (WINBLAD et al. 2004). Adapted to local needs and climatic conditions (e.g. toilet seats, anal cleansing water diversion, etc.), double-vault UDDTs have been introduced, amongst other countries, in Bangladesh, China, Ecuador, El Salvador, Guatemala, India, Kenya, Mexico, the Philippines, South Africa, Sweden, Vietnam, Yemen, but also cold-climate countries such as Mongolia, Nepal and Romania as cost-effective sanitation component in rural, peri-urban and urban settings.

With double-vault UDDTs, faecal matter is collected and stored in twin-pit compartments, which are used alternately. Daily deposits are made into one of the compartments. After each use, a handful of cover material (wood ash, sawdust, soil, lime, etc.) is sprinkled over the faeces to absorb moisture and help in speeding up the dehydration process. When one vault is full (which should take roughly one year), the respective compartment is sealed while the other compartment is put in use. The storage time is counted from the date of the last faecal matter contribution to a compartment, and should be at least one year to provide sufficient time for desiccation and hygienisation.

Urine and anal cleansing water must be diverted for practical reasons; urine may be collected separately and be applied as nitrogen-rich liquid fertiliser to agricultural land, and water used for anal cleansing may be infiltrated locally into the soil. The compost-like material (desiccated faeces and cover material, also called compost) can be applied to agricultural land as a soil amendment in order to increase the organic matter content, improve the water-holding capacity and increase the availability of nutrients.

Another popular model, mainly used in Africa and disseminated by the CREPA (Centre Régional de l’Eau Potable et l’Assainissement à faible couts) is the ”Tecpan” UDDT. These UDDTs have metal sheets as vault chamber doors, which are exposed to the sun, in order to absorb heat, transfer it into the vaults and speed up the drying process.

Single-Vault Urine Diverting Dehydration Toilets

Single-vault UDDTs, unlike double-vault UDDTs, provide only one collection cum storage compartment for the containment of faeces. Therefore, secondary storage and drying or other types of treatment (e.g. co-composting, etc.) are necessary. Urine and anal cleansing water diversion is equally important for double-vault UDDTS in order to maintain the dehydration process. The most practical design of single-vault UDDTs is to provide moveable containers. Movable containers allow removing the faeces easily once the container is full without disrupting the functionality of the toilet.

It is recommended to fill the bottom of the movable containers with some dry adding material in order to absorb leaking liquid and increase the stability of the bucket when it is still empty. An empty rice bag can serve as additional confinement for the faeces. It can be easily sealed with a piece of cord once it is full and stored for further drying and hygienisation without transferring the faeces or coming in contact with them. Once the hygienisation period is over, the compost bags can be directly transported for reuse in agriculture, similar to compost bags. “Hanging UDDTs” are specifically adapted to meet the needs of people living in coastal areas. Developed and implemented by the “Water, Agroforestry, Nutrition and Development (WAND) Foundation” in Initao and Libertad, Misamis Oriental, Philippines, hanging UDDTs provide for on-site sanitation in coastal areas that are influenced by tide and/or along river sides that are frequently flooded.

It is important that the two sections of the toilet are well separated to ensure that a) faeces do not fall into and clog the urine collection area in the front, and that b) urine does not splash down into the dry area of the toilet. There are also 3-hole separating toilets that allow anal cleansing water to go into a third, dedicated basin separate from the urine drain and faeces collection. Both a pedestal and a squat slab can be used to separate urine from faeces depending on user preference. For a worldwide listing of suppliers please see MUENCH et al. 2011 (Appendix 1-3).

Urine tends to rust most metals; therefore, metals should be avoided in the construction and piping of the UDDT. To limit scaling, all connections (pipes) to storage tanks should be kept as short as possible; whenever they exist, pipes should be installed with at least a 1% slope, and sharp angles (90°) should be avoided. A pipe diameter of 50 mm is sufficient for steep slopes and where maintenance is easy. Larger diameter pipes (> 75 mm) should be used elsewhere, especially for minimum slopes, and where access is difficult. To prevent odours from coming back up the pipe, an odour seal should be installed at the urine drain.

The UDDT is not intuitive or immediately obvious to some users. At first, users may be hesitant about using it, and mistakes made (e.g., faeces in the urine bowl) may deter others from accepting this type of toilet as well. Demonstration projects and training are essential to achieve good acceptance with users. For better acceptance of the system and to avoid urine in the faeces collection bowl, the toilet can be combined with a urinal, allowing men to stand and urinate.

A UDDT is slightly more difficult to keep clean compared to other toilets because of both the lack of water and the need to separate the solid faeces and liquid urine. No design will work for everyone and, therefore, some users may have difficulty separating both streams perfectly, which may result in extra cleaning and maintenance. Faeces can be accidentally deposited in the urine section, causing blockages and cleaning problems.

All of the surfaces should be cleaned regularly to prevent odours and to minimize the formation of stains. Water should not be poured in the toilet for cleaning. Instead, a damp cloth may be used to wipe down the seat and the inner bowls. Some toilets are easily removable and can be cleaned more thoroughly. It is important that the faeces remain separate and dry. When the toilet is cleaned with water, care should be taken to ensure that the faeces are not mixed with water.

Because urine is collected separately, calcium- and magnesium-based minerals and salts can precipitate and build up in pipes and on surfaces where urine is constantly present. Washing the bowl with a mild acid (e.g., vinegar) and/or hot water can prevent the build-up of mineral deposits and scaling. Stronger (> 24% acetic) acid or a caustic soda solution (2 parts water to 1 part soda) can be used for removing blockages. However, in some cases manual removal may be required.

An odour seal also requires occasional maintenance. It is critical to regularly check its functioning.
A detailed “To-do list for operation and maintenance” is compiled in RIECK et al. (2012).

Greywater from kitchen, bathrooms, laundry areas, etc. must not be disposed of in the UDDT, but be taken care of individually (e.g. applied to greywater towers, vertical gardens or surface, horizontal or [1851 vertical] flow constructed wetlands, etc.). (TILLEY et al. 2008)

(adapted from RIECK et al. 2012)

The construction of a UDDT can usually be done with locally available materials and labour. Prefabricated parts may include toilet seats or squatting pans. If those parts do not need to be imported from abroad, they are usually cheap and can be even cheaper than self-constructed squatting pans made from cement. Squatting pans made of ceramics which are not very costly and easy to maintain, are also available. The construction costs of a double-vault UDDT are slightly higher than the construction costs for a VIP or pit latrine. Single-vault UDDTs can be constructed very cheaply, depending on the creativity of the constructors and the locally available materials.

Plant ash, lime, dried soil or sawdust can be added after each defecation as a bulking agent to enhance the drying process (JOENSSON et al. 2004). The immediate coverage of the fresh faeces with an additive material can considerably lower nuisances caused by odour or flies. Faster drying also means that the biological degradation is small if sufficient additive is used and thus, the losses of organic matter and N from the faeces to the air are small (JOENSSON et al. 2004). Ash and lime have the additional beneficial effects of raising pH, which leads to improved pathogen die-off (JOENSSON et al. 2004). The addition of ash and lime should therefore be preferred (SCHOENNING & STENSTROEM 2004).