Urine-diverting dry toilet

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

A Urine-diverting Dry Toilet (UDDT) is a type of dry toilet with urine diversion that can be used to provide safe, affordable sanitation in a variety of contexts worldwide. Through the separate collection of faeces (feces) and urine without any flush water, many advantages can be realised, such as odour-free operation and pathogen reduction by drying. While dried faeces and urine harvested from UDDTs can be and are routinely used in agriculture (respectively as a soil amender and nutrient-rich fertilizer - this practice being known as resource recovery), many UDDTs installations do not make use of any sort of recovery scheme. UDDTs are a good example of sustainable sanitation.

A UDDT can be configured as a sitting toilet (with a urine diversion pedestal or bench) or as a squatting toilet (with a urine diversion squatting pan). The most important design elements of the UDDT are: source separation of urine and faeces; waterless operation; and ventilated vaults (also called "chambers") or removable containers for faeces storage and treatment. UDDTs may be constructed with two dehydration vaults that are used alternately or with a single vault into which interchangeable containers are placed. The UDDT is a dry excreta management system (or "dry sanitation" system) and can be an alternative to pit latrines and flush toilets, especially where water is scarce, wastewater treatment is not feasible, nutrients are needed for agriculture, or environmental contamination is not desired.

Dry material, such as ash, sawdust, soil, sand, dried leaves, mineral lime, compost, and even dried and decomposed faeces after prudent storage and treatment, are generally added immediately to cover the faeces. These act to improve aethetics, reduce odour, and speed up the drying process. If anal washing takes place with water (i.e., the users are "washers") rather than by using toilet paper (by "wipers"), then this anal washwater must be drained separately and not be allowed to enter the faeces vault.

UDDTs are often equated as being synonymous with the approach to sanitation known as ecosan (ecological sanitation) or with composting toilets. However, neither of these associations are accurate or acceptable due to the fact that not all UDDTs are used in conjunction with the practice of reusing excreta and many times any composting that takes place in conjunction with the use of UDDTs occurs outside of or separate from the structure of the toilet itself.

Terminology

Schematic of the dehydration vaults of a UDDT with two vaults

UDDT at Gebers collective housing estate near Stockholm, Sweden

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

3-hole urine diversion squatting pan to accommodate anal washing in Krishnagiri District, Tamil Nadu

Exchanging the faeces container of a low-cost single vault UDDT at a household in Addis Ababa, Ethiopia

Alternative names for UDDTs include "urine diversion dehydration toilet" and "urine diversion desiccation toilet", 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 to describe UDDTs that feature two vaults or for UDDTs that feature a built-in electrical fan.

This type of toilet is also called by many people an "ecosan toilet" as this name is quite easy to communicate at the local level with potential users. However, the term ecosan is in fact much broader and not limited to this type of toilet.

Urine-diverting composting toilets are similar to UDDTs as they collect urine and faeces separately. However, treatment is achieved through the composting process, which is a process quite different from pathogen removal by dehydration.

Appropriateness

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.

Furthermore, in the case of developed countries, UDDTs can also be suitable in situations where:

• An individual, family or community wants to increase the resilience of their existing sanitation system in the face of possible natural disasters (i.e. climate change, earth quakes) or possible rising energy prices; and
• Following approval by local building inspectors and health department authorities, an individual or family seeks to reduce or perhaps eliminate the need for a septic tank system to reduce their environmental footprint (particularly when the UDDT is used in conjunction with an on-site greywater treatment system).

UDDTs can also be built for schools (many examples exist for example in Kenya, Rwanda and Uganda). However, these school UDDTs suffer from the same issues as any other type of school toilets related to the maintenance of the school toilets: If clear responsibilities and a dedicated budget for school toilets' maintenance is lacking, then the toilets may easily fall into disrepair, e.g. with blocked urine pipes or faeces vaults that are not being emptied.

Design considerations

2-hole (pink) and 3-hole (blue) urine diversion ceramic squatting pan from Indian NGO EEDS

Fundamentals

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.

Designers and users of UDDTs should strive to keep the faeces pile as dry as possible as this is the key factor in prevention of odour and flies (flies are not attracted to dry faeces). During storage, the faeces’ natural moisture slowly evaporates and is exhausted through the vault’s ventilation system, or is absorbed by the dry cover material. This process is called dehydration.

A UDDT consists of eight basic functional elements:

1. Urine diversion toilet seat or squatting pan;
2. One or two faeces vaults (also called "chambers"; with or without removable containers), 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 or is of the standalone or portable variety;
7. Bucket with dry cover material (see below);
8. Hand washing facility with soap and water.

Storage and drying time for faeces in the vaults

The impact of the storage time on the dryness of the faeces varies with climatic conditions. A general recommendation that is applicable for all climates is that the storage duration for faeces in double dehydration vaults should be at least six months, as measured from the last addition of fresh faecal matter to the vault.

During the dehydration process moisture is evaporating from the faeces and microbes are degrading the organic material. It is the dry conditions and the storage time that lead to the decline of pathogens in the faeces.

Fresh faeces consist of about 80% water and the majority of this water will evaporate away if it is allowed to do so by the faeces not being enclosed in air-tight containers or vaults. The water content of dried faeces after six months of drying is usually less than 25%. Depending on the degree of drying and the intended reuse application an additional post-treatment step, such as composting, might be necessary for reuse of excreta in agriculture.

Bench design

UDDTs can also be built with a bench style toilet seat. 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, spacious bench or box, covering both faeces chambers, into which two urine diversion toilet seats are integrated.

Users with disabilities can benefit from this kind of design as it is very sturdy (compared to a pedestal-type toilet). The wide bench provides space for an assistant if needed, and handrails can easily be fixed to the walls next to the toilet. Most importantly, this type of UDDT is accessible directly from the ground level and does not require access steps or ramps which are common for many UDDT designs.

Waterless urinals

UDDTs are often installed alongside waterless urinals particularly in lavatories or bathrooms frequented by male users. This is done for the convenience of male users and to address the problem of male users standing over the UDDT to urinate and inadvertently directing urine into the faeces vault or faeces container. For this reason alone it is mandatory that all UDDT users sit or squat to urinate.

Accessibility

Superstructures associated with UDDTs are sometimes built with steep, narrow stairs and without handrails. This design is not recommended as it can prevent users with disabilities from accessing the toilet. The needs of people with disabilities should always be considered in the design of sanitation systems, and in the case of elevated structures less steep stairs or ramps should be used instead. The aforementioned “bench design” can alleviate the need for stairs.

If a squatting toilet is built, it can be useful to add handle bars for holding onto for people who need support while squatting. For people with disabilities who need physical support while squatting, particularly when cleaning afterwards, a portable seat can be placed on the squat toilet to allow people to sit. When not needed, it can be placed out of the way.

Designs for flood prone areas

In flood prone locations faeces containers or vaults should be located above the flood water levels. If this is not feasible, it is possible to use ferrocement walls to isolate the vault(s) from encroaching flood waters.

Source of UDDT components

The toilet bowls or squatting pans for UDDTs can be commercially manufactured from plastic or ceramic. Alternatively, they can be fabricated locally out of cement or other materials by residents, local companies, NGOs or contractors. Stand-alone UDDT toilets made of plastic with or without built-in electrical fans are also commercially available.

Urban multi-storey buildings

Faeces collection chutes in the basement below the UDDTs that are on the different floors of a multi-storey building in Erdos Eco-Town, China

UDDTs with combined ventilation and collection systems can also be installed in urban multi-storey buildings but only few successful examples of such a design exist. Perhaps the only one is in fact the Gebers collective housing estate in Orhem, Sweden.

A much larger-scale installation which portrays the need to adhere to minimum design and installation standards existed in a project called the "Erdos Eco-Town Project" in Erdos which is located in the Inner Mongolia Autonomous Region of China. The project was implemented during 2003-2009. This urban installation for 3000 residents in multi-storey buildings utilized UDDTs that shared ventilation and urine collection pipework and made use of chutes that extended down into basements for the collection of feces. The UDDT system was accompanied by greywater treatment facilities, solid waste composting and the reuse of these materials as a fertiliser in agriculture.

However, due to several problems related to improper design and installation, the lack of a cohesive plan to address these deficiencies and the resulting resident objections, the UDDTs were replaced by conventional flush toilets in 2009. The main reasons for why these UDDTs were replaced with flush toilets were:

• Technical problems: Odour problems in the appartments caused by air pressure differences that resulted from poorly considered factors like high winds, open bathroom windows and kitchen exhaust fans produced serious objections amongst residents. Frozen ventilation pipes during the extremely cold winters of 2007 and 2008 caused odours from the faeces bins to back up into the apartments contributing further to residents' displeasure.
• In such a large-scale UDDT system the plumbing pipework for the urine pipes and the ventilation system need a relatively high level of engineering and workers who follow the technical installation drawings accurately - this was not the case in this project.
• The standard of living in the Erdos area rose dramatically during the project time period. Also, water shortage (which had been a driver for dry toilets) was no longer regarded as a problem since a pipeline was built to the Yellow River and deeper fossil water resources were extracted. Many residents viewed flush-toilets as the “gold-standard” in sanitation and dry toilets were considered as backward in a modern urban setting.
• The odour problems and widespread system failures were exacerbated during the extreme cold winter of 2007 and together acted as a negative tipping point for the project.
• A stakeholder education approach among residents focused on early participation and learning about the use and maintenance of the UDDTs was not possible, since the residents arrived on the scene only after the apartments were already built. They also had no choice in deciding on the kind of toilet that they wanted to have.
• Lack of a dedicated owner who felt responsible for solving maintenance issues.
• Once the design problems were identified, residents balked at covering the costs necessary to correct the problems with the existing system, particularly given their distrust of it. So, needing to resolve the issue quickly, the District Governor responded by investing in flush toilets instead.

If these lessons are taken into consideration, future large-scale UDDT installations in urban areas could succeed.

Types

Single vault construction

UDDTs with a single vault have interchangeable containers to collect the faecal material. Depending on the size of the vault, two or more containers can be stored inside. Containers should be limited to a maximum volume of approximately 50 litres, so that they still can be manually moved when they fill up. Once a container is full, it can be left for further dehydration or removed for further treatment. Removal of the container requires care due to fresh, potentially pathogen-loaded faeces being on top of the pile in the container. Because of the limited ventilation within the container, single vaults cannot reduce the pathogen load as effectively as double vaults. Therefore, a post-treatment of the faecal material is usually required. This can be achieved through further dehydration, composting processes or heat treatments.

On the other hand, if the container is made from a material that has a high permeability with air, such as woven sacks or baskets, then the drying performance in single vault UDDTs may approach that of double vault UDDTs.

Double vault construction

In double vault UDDTs the faecal material dehydrates in situ. The two above-ground vaults are used alternately. While one vault is filling up, the other (full) one stores the faecal material under dry conditions for at least six months. During this resting period, no fresh faeces is allowed to enter the full vault. In order to switch from one vault to the other, the user interface can either be switched or both vaults can be equipped with fixed seats and a cover sufficient to prevent access to the full vault. When the second vault becomes full, the first one is emptied with a shovel and then the user interface is moved over accordingly. The vaults are commonly sized so that one vault fills up in six to 12 months.

Other (portable, mobile)

Other types of UDDTs exist which are essentially variations of the single vault type, but which are more self-contained, sometimes refereed to as portable, mobile or stand-alone units and identifiable by their one-piece molded plastic shells or, in the case of DIY versions, simple plywood box construction. Most users of self-contained UDDTs rely upon a post-treatment process to ensure pathogen reduction. This post-treatment may consist of long-term storage or addition to an existing or purpose-built compost pile or some combination thereof. A post-treatment step is unnecessary in the case of very modest seasonal use and for those users that dispose of the collected urine and faeces via conventional solid waste streams like into the garbage or, for sailors, into the open ocean.

Mobile UDDTs are typically either fabricated out of new materials in a factory or workshop using a mix of proprietary and off-the-shelf parts - and then sold to the public either directly or via distributors or retail outlets; or fabricated at home out of wood, using new and re-purposed parts and materials. They are typically compact and lightweight, allowing one person to easily lift, transport, and maneuver them into place. Likewise, installation is a relatively simple process given that everything needed for the proper functioning of the toilet, except a source of electrical power for those models that include a fan and some allowance for exterior ventilation, is contained within the molded or wooden carcass. One advantage to this type of UDDT is that they are portable, making them an interesting option for remote or temporary installations and for installations aboard moving vehicles or non-stationary residences like boats, recreational-vehicles (i.e. caravan, camper van, motor home) and tiny-houses.

Features common to this type of UDDT include:

• a smooth easy-to-clean exterior surface
• a molded seat with a cover (both or either sometimes fitted with a rubber or neoprene gasket to further assist in isolating the toilet's inner workings)
• a molded urine diversion bowl (or bucket and funnel assembly) to facilitate the separate collection and storage in separate containers of urine and faeces (the containers consisting of either a proprietary design or, in the case of DIY versions, readily-available or re-purposed buckets, bottles or jugs)
• some allowance for either passive or active mechanical ventilation either consisting of a screened or filtered air inlet and a screened or filtered exhaust outlet (the latter consisting of a standard fitting to allow hook-up to a length of piping or tubing that is connected to the outdoors).

Features unique to some designs include:

• cleats for fastening the toilet to the floor (particularly useful when the toilet is installed in a moving vehicle or non-stationary residence)
• spill-proof urine storage to aid in leak-prevention during stormy weather or when otherwise underway (as in a moving boat or RV)
• built-in agitator for mixing and aerating the contents of the feces container (which greatly aids in drying and odour prevention)
• automatically or manually deployed pivoting or hinged trap door for covering the faeces container when not in use.

Health aspects

During normal use, a UDDT is just as hygienic and safe to use as any other type of toilet. However, health aspects need to be considered during removal and emptying of the urine and faeces containers of a UDDT. The health risks during emptying of the faeces vault or container of a UDDT are significantly lower when compared to emptying the pit of a pit latrine or the buckets of some types of dry toilets without urine diversion. However, the health risks are somewhat higher when compared to a flush toilet where the user does not normally have to carry out any emptying tasks at the household level at all, unless the toilet gets blocked.

Given their waterless nature, UDDTs are free from the risks associated with the splash back that can result from the flushing of a flush toilet.

With regards to health risks associated with reuse activities, the World Health Organisation's guidelines' from 2006 titled “Guidelines for the safe use of wastewater, excreta and greywater in agriculture” explain how to manage the health risks associated with the use of excreta 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.

Dried faecal matter from UDDTs after external composting, now ready for reuse (Addis Ababa, Ethiopia)

Usage

Wiping

For wiping of the anal area UDDT users can avail themselves of the same materials that are utilized while using other types of toilets. Suitable biodegradable materials available in the surroundings can also be used, such as leaves, corn cobs or sticks. These materials are deposited along with faeces in the faeces portion of the toilet so that everything can eventually decompose together. For example in Ecuador the soft, perfumed leaves of Piper auritum, Piperaceae and Melastomataceae are being used. Users have also used stones, although this makes the vault fill up very fast and is therefore not practical for UDDTs.

Anal washing with water

UDDTs can accommodate users who prefer anal cleansing with water by utilising either a three-hole urine diversion squatting pan or an area and drain next to the urine diversion pedestal where washing can take place - away from the urine and faeces holes. This is essential so as not to contaminate the urine and to keep the faeces as dry as possible.

Due to the faecal content of anal cleansing water, it should be considered as blackwater and treated or disposed of accordingly. Anal cleansing water can be drained into a soak pit, planted mulch bed or an infiltration trench. The anal cleansing water should be discharged into coarse material below the ground, but well above the water table to avoid groundwater pollution.

In some designs, the users are advised to do their anal cleansing above the urine compartment for simplicity reasons in order to avoid the need for a third hole. This mixture of urine and anal cleansing water requires further treatment to remove pathogens before it can be safely utilized in agriculture.

Water for anal washing can be supplied via a hose or spigot fed by a pressurized water delivery system or a gravity fed system supplied by a rainwater tank located overhead or from a water bottle or jug that the user carries into the toilet cubicle.

Cover materials added

For most UDDT types, users are encouraged to add a handful or scoopful of cover material atop each deposit of fresh faeces. This cover material is added for the following purposes: to promote dry conditions in the faeces vault by absorbing moisture, to control odour, to prevent infestation of flies and to create a visual barrier for the next user. It is also important to ensure that enough air can flow through the pile of drying faeces. For this reason bulky or fibrous material that is dry and that decomposes slowly is recommended. A host of cover materials and combinations of these materials can be used, depending on what is readily available:

• Leaves are good, but intact they are too coarse to cover the faeces properly to keep flies from getting in and odour from getting out.
• Sawdust works and can smell nice, depending on the tree species.
• Rice hulls are suitable in areas where rice is grown.
• Soil is excellent, abundant and nearly universally available.
• Wood ash as a cover material is appropriate but might not be available in sufficient volumes.
• Dried mosses (sphagnum, peat etc.)
• Lime can be used but the environmental impacts associated with its mining, processing and transporting should be considered. Ash and lime both have the advantage of raising the pH value of the faeces pile, thus adding to pathogen kill.
• In cases where the faeces are treated further in a composting process, it can be beneficial to select the cover material carefully in order to not only cover the faeces but also to inoculate them with beneficial soil microbes. In that case, finished compost could be used as cover material, although it is important that the users either do not touch this cover material with their bare hands or that the composting process is sufficiently controlled such that no pathogens remain in the material.

No cover materials added

In some circumstances and for reasons of simplicity, it can be sufficient to not use cover materials at all or to use toilet paper itself as cover material. One example is the case where the UDDT has a mechanized ventilation system and a view guard, like the UDDT manufactured by Separett which has a removable bucket, built-in fan and blue plastic view guard which closes when weight is removed from the toilet seat after use. Also in the case of public toilets, it can be easier to let the caretaker perform the task of adding cover material, rather than the user. An example of this are the public single vault UDDTs operated by the not-for-profit company Sanergy in low-income urban areas in Kenya.

Sitting or squatting

UDDTs can be built as sitting or as squatting versions to accommodate the users' preference of defecation posture. Some people prefer squatting UDDTs in public places (thought to be more hygienic) but sitting UDDTs for households (thought to be more comfortable). It may be preferable to squat instead of sitting for colon health, although this is not specific for UDDTs but may refer to any type of toilet.

Resulting products (dried faeces and urine)

Dried faeces

Further treatment

The required degree of treatment for the collected dried faeces depends entirely on whether this product will be reused in agriculture or not. If it is not reused but only buried then no further treatment is required. The dried faeces are in almost all cases not entirely sanitised when removed from a vault of the UDDT, so careful handling is obligatory. In scenarios wherein excreta is to be reused in agriculture, a secondary treatment of faecal matter and storage of urine is advisable to ensure adequate sanitisation. Faecal material from single vault UDDTs must always be post-treated, even if just via prolonged storage. Faecal material from double vaults has typically passed a certain storage time and is therefore already more sanitized. However, a secondary form of treatment is optional but recommended for household systems and required for large-scale systems.

Secondary treatment is usually performed at community level rather than at household level and can include thermophilic composting where faecal material is composted at over 50 °C, prolonged storage with the duration of 1.5 to two years, chemical treatment with ammonia from urine to inactivate the pathogens, solar sanitation for further drying or heat treatment to eliminate pathogens.

Reuse in agriculture

Main article: Reuse of excreta

Reuse of treated faeces in agriculture - like reuse of excreta in agriculture in general - can result in increased crop production through fertilizing effects of nitrogen, phosphorus, potassium and improved soil fertility through organic carbon.

Burial of dried faeces

If the dried faeces are not reused in agriculture they can instead be buried at a minimum depth of 25 cm in which case they normally do not pose a public health risk. Several US states permit disposal in this manner with some mandating lesser minimum depths, as little as 6 inches, and others not specifying any minimum depth at all.

For UDDT users in the United States, an important distinction to keep in mind is the fact that the federal 503 rule, the EPA regulation that governs the management of sewage sludge (also known as "biosolids"), has no jurisdiction over the byproducts of a UDDT and that all oversight of these materials falls to the states.

Urine

Further treatment

The required degree of treatment for the collected urine depends entirely on whether this product will be reused in agriculture or not. If it is not reused but only infiltrated then no further treatment is required.

Urine that leaves the body of a healthy person is practically sterile and therefore would not require treatment for pathogen removal. However, a contamination of urine with faecal pathogens is possible if the UDDT is not used correctly, i.e. when some faecal matter finds its way into the urine compartment. Also, for a few specific diseases, the relevant pathogens may be found in the urine; for example: Leptospira interrogans, Salmonella typhi, Salmonella paratyphi, Schistosoma haematobium, BK virus or Simian virus. The Ebola virus may also be found in urine from an infected person. The exact survival time of this virus in human urine outside of the human body is unclear but probably "up to several days" like with other body fluids at room temperature.

For these reasons, urine should always be treated for pathogen removal if it is going to be reused, unless reuse occurs at the same household where the urine was collected and on crops that are only consumed by these household members (in which case an infection amongst family members is more likely to occur via handshakes and hugs than via urine reuse activities).

The simplest and most common method of urine treatment for pathogen removal is via storage in closed vessels. The decomposition of urea that is present in urine into ammonia and hydrocarbonate leads to an increase in ammonia concentration and an increase of pH value to above 9. These two processes, and simply "time" as the third process, are effective in killing of pathogens. They are more efficient in warm temperatures and with low dilution of the urine with water.

Storage of urine kills bacterial pathogens encountered in urine – including Salmonella typhi and paratyphi and Mycobacterium tuberculosis – in a relatively short time span: a storage time of five weeks at temperatures below 20°C or of two weeks at temperatures above 20°C has been recommended to prevent transmission of mycobacteria when recycling human urine.

Recommended storage times to kill pathogens in urine vary from one to six months depending on ambient temperatures, the scale of the urine collection system and which crops will be fertilised with the urine.

Reuse in agriculture

Main article: Reuse of excreta

Reuse of treated urine in agriculture - like reuse of excreta in agriculture in general - can result in increased crop production through fertilizing effects of nitrogen, phosphorus, potassium and improved soil fertility through organic carbon.

Urine from the UDDTs can safely be used as nitrogen-rich and phosphorus and potassium containing fertiliser after a recommended storage period for pathogen reduction (see above under treatment).

Infiltration of urine

In cases where no reuse is possible or desired, urine is usually infiltrated in the soil unless this would cause groundwater pollution. In eThekwini municipality in South Africa or in Lima, Peru, for example, urine from UDDTs is safely infiltrated into the soil because the groundwater level is very low there and the groundwater is not used for any particular purpose. Infiltration can be done by directing the urine to a soak pit or by running a perforated urine pipe from the toilet to an area outside, where the hose is sloping gently downhill (for rural areas). Clogging of the pipe's holes can be avoided by ensuring there are no T-junctions, no joints and that a plastic mesh is installed in the urine funnel of the toilet to keep everything other than urine out.

Advantages

Very simple home- made design for a UDDT with a funnel for urine collection and a bucket for faeces collection at a household in Addis Ababa, Ethiopia

Comparison with pit latrines

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

1. reduce odour (mixing urine and faeces together 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 far more simple and hygienic;
4. reduce environmental impacts;
5. allow for the recovery of urine, which can be reused as fertiliser; and
6. allow for the recovery of desiccated feces, which can be reused as a soil enhancement.

The advantage of UDDTs compared to pit latrines is the conversion of faeces into a dry odourless material and therefore an avoidance of the issues surrounding liquid faecal sludge management (e.g. odour, fly attraction, difficulties in pit emptying). 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 above-ground vaults and this allows the toilets to be constructed in locations where pit-based systems are not appropriate.

UDDTs with vaults are also more permanent structures than most pit latrines, the latter of which in rural areas are typically relocated when the pit is full rather than emptying the pit. Therefore, pit latrines need more space and people are less willing to invest in a higher quality super-structure as it will have to be dismantled and moved at some point.

Comparison with sewer- and septic tank-based sanitation

The comparison of UDDTs with sewer-based sanitation systems (sewerage and wastewater treatment plants) is not as straightforward as the comparison with pit latrines as a sewer does not only deal with excreta management like a UDDT does, but it also transports greywater, municipal wastewater, stormwater and industrial wastewater. It goes without saying, however, that the installation of UDDTs in all households connected to a common sewer would result in vastly reduced volumes of water, nutrients and organic matter arriving at the associated wastewater treatment plant.

Sewer-based excreta management is impractical in many regions due to limited water supplies and the high cost of sewer systems and wastewater treatment plants. Furthermore, water-based sanitation systems (flush toilets) dilute excreta and create vast wastewater streams, something that UDDTs do not.

Similarly, the comparison between UDDTs and septic tank-based sanitation systems is not as straightforward as the comparison with pit latrines as a septic system must also manage greywater. However, the high cost of septic systems, particularly mound-type septic systems can be partially mitigated or, if used in conjunction with an onsite greywater system, eliminated altogether by installing a UDDT(s) in place of flush toilets.

Decentralised sanitation systems which employ UDDTs (particularly portable varieties) offer the potential advantages of quick deployment (especially where there is no capable centralized institutional infrastructure in place or no financial ability to implement larger centralized systems) as well as greater local control.

Policies could encourage the widespread use of UDDTs through: financial support of research programmes, enactment of regulations that require the recovery of resources from wastewater and adequately account for the reduced contaminant loading and incentives for resource recovery.

The separate, waterless collection of urine and faeces in UDDTs would prevent hormones and pharmaceutical residues (micro-pollutants which are contained in human excreta but not fully removed by conventional wastewater treatment plants) from directly entering drinking water sources via household wastewater (sewage). With conventional sewer-based sanitation systems, micro-pollutants, hormones and pharmaceutical residues are not removed and are discharged into surface water and possibly reaching groundwater (detected concentrations of pharmaceutical residues in groundwater are in the order of 50 ng/L in several locations in Germany). If the excreta from UDDTs is treated further and used as fertiliser then the pharmaceutical residues in the excreta will be degraded better in terrestrial systems (soil) than in aquatic systems. Therefore, UDDTs (or in fact all urine diversion systems) have a certain advantage over sewer-based sanitation systems in this respect.

Disadvantages

School UDDT in rural areas of Western Kenya; the steep stairs are not recommended as they are a barrier for people with disabilities

General hurdles

Significant barriers to more universal acceptance of this technology include, in the case of developing countries: lack of awareness, a limited supply of prefabricated UDDT components and a lack of interest in financing sanitation services for the non-sewered portions of settlements. It is important that whatever sanitation system is selected fit into an existing legal framework and that it has support at the local policy level from amongst the various government departments affected.

Many users do not have an interest in handling their excreta. Therefore, provisions should be made for door-to-door/curbside collection of these materials, similar to how existing municipal or private schemes collect household organic waste (from kitchens and gardens, etc.) and transport it to a centralised facility for composting or biogas generation.

Operational problems

The most commonly encountered operational problems with UDDTs, which are all quite easy to resolve on a technical level, include:

• Urine has accumulated in the urine diversion section of the toilet due to blockages in the urine pipe.
• Foul odours are emitted from the faeces vault because the contents of the faeces vault have become too wet.
• Foul odours are emitted from the urine drainage or collection system because urine has become stagnant somewhere in the system with an open surface.
• The faeces vault is infested with flies, insects or rodents, usually because it has become too wet.
• There are fresh faeces in the inactive vault (this is only relevant for double dehydration vaults), which is a sign that the user is not using the UDDT as intended.

Each of these problems are relatively easy to solve technically with trouble-shooting advice being readily available. However, there needs to be a commitment and willingness by the users or caretakers to resolve such problems. Due to the absence of such commitment in some cases, as well as poor preparation of the users before installing the toilets as well as lack of a dedicated follow-up, such operational problems have on occasions led to the abandonment of UDDTs in several pilot projects.

Comparison with pit latrines

Disadvantages of UDDTs compared to pit latrines include: higher capital costs (although whole-of-life costs might be lower), more awareness required by the user who has to use it properly (for instance not urinating into faeces compartment, and reacting appropriately when the urine vessel is full, when there are problems with the urine soak pit, when the urine pipe is blocked or when the faeces vaults or containers are full).

Comparison with sewer-based sanitation

One disadvantage of a sanitation system with UDDTs - and perhaps even with resource recovery in agriculture - compared to a conventional sewer-based system is that it requires greater coordination and cooperation amongst stakeholders from different sectors.

Costs

UDDTs have been criticised for being too expensive 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. For example, when a period of 10 years is considered in the analysis, UDDTs may well be the more economical alternative as emptying the associated faeces vaults is very simple and relatively low cost, even when a household opts to enlist an external service provider for this activity (assuming a service provider exists).

Compared to flush toilets connected to a sewer system and wastewater treatment plants, UDDTs are often thought to be cheaper. However, this needs to be assessed on a case-by-case basis because the two systems provide a different level of service (the sewer system also treats greywater whereas the UDDT does not); an example calculation exists for the case of Lima, Peru.

History

The UDDTs with two 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. This means their development was originally closely linked to the ecosan (ecological sanitation) approach to optimizing resource recovery of nutrients and organic matter in agriculture. Beginning in the early part of the 2000s, UDDTs have been seen increasingly as a toilet type that can also be provide advantages, even without any reuse activities attached to it.

Since the 1990s, modifications of this design (such as the addition of ventilation piping 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 between 1994 and 2010 the Separett company sold approximately 200,000 UDDTs. Numerous off-the shelf commercial products are now available and are used in locations where piped sewerage is not available, permitted or desired such as in remote summer cottages or for camping activities. At all times, users have also been building their own low-cost UDDTs with simple materials such as a funnel connected to a hose, a bucket and a seat.

Society and culture

Floor and roof of a low-cost UDDT in Ecuador

Demonstrating the use of a low-cost UDDT in Pumpuentsa, Ecuador.

Number of users

The exact number of UDDT users worldwide is unknown, but a rough estimate by GIZ (German Development Cooperation) in 2012 based on known projects in 84 countries put the number at approximately 2 million users worldwide.

Examples

South Africa (eThekwini Municipality, Durban)

The highest number of UDDTs in one area have been installed by the eThekwini Municipality in the non-sewered peri-urban areas of Durban, South Africa. To date, about 80,000 UDDTs are in operation in that area, serving about 500,000 residents (reuse of urine or excreta is currently not taking place).

Haiti

The NGO SOIL in Haiti has built UDDTs and composting treatment plants in Port-au-Prince as part of the 2010 Haiti earthquake emergency relief effort in northern Haiti. Their current design for households includes a small portable single vault unit made out of wood fitted with individual containers for excreta collection. As of 2014, SOIL has transformed all of their old UDDT vault toilets to an open vault design with removable plastic drums improving the processes by which excreta is collected and transportated to their waste treatment facility, thus making their business a fully “container-based system”. This allows SOIL to respond to heavy use (their toilets were filling up too quickly) and ensures a safe final product for reuse.

SOIL "Poopmobile" delivering buckets of human extra from mobile household UDDTs to the SOIL composting facility in Port-au-Prince

SOIL continues to provide humanitarian relief in some of Haiti’s most vulnerable communities – notably those that have been particularly impacted by the cholera epidemic – by providing free access to public container-based UDDTs for over 3,500 people. In addition, over 2,500 people are currently accessing a SOIL "EcoSan toilet" through the "EkoLakay" business pilot, with another 500 waiting to join, thus demonstrating the market demand for affordable sanitation, even in the world’s most economically impoverished communities.

Since building the first waste treatment facility in Haiti in 2009, SOIL has become one of the largest waste treatment operations in the country: SOIL’s two composting waste treatment facilities currently transform over 20,000 gallons (75,708 liters) of human waste into safe, organic, agricultural-grade compost every month. The compost produced at these facilities is sold to farmers, organizations, businesses, and institutions around the country to subsidize the cost of SOIL’s waste treatment operations.

Ecuador

Hundreds of UDDTs have been built in Ecuador, with various models adapted to different conditions, preferences, and budgets. There is even a minimalist model that costs essentially nothing and could be implemented by the poorest people for example in rainforest regions of Ecuador and for people affected by natural disasters and other emergencies.

Boating, recreational vehicles and camping

• For the boating community, it can also be an interesting alternative to convert from conventional nautical toilets that store waste in black water tanks, or immediate discharge overboard, to a UDDT. Two such UDDTs designed for nautical and recreational vehicle (RV) use (but not limited to these uses) are marketed in North America under the names “Nature's Head Toilet” and “Air Head Toilet”.

• Camping - Leave no trace is not only a philosophy but a necessity in areas where human waste left behind will not decay naturally. There are now portable UDDTs available (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.

Other examples

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