Urine diversion, also called "urine separation" or "source separation", refers to the separation of human urine from feces at the point source, i.e. at the toilet's user interface. Separation of urine from feces allows human waste to be treated separately and used as a potential resource. Applications are typically found where connection to a sewer based sanitation system is not available or areas where water supplies are limited.
To achieve urine diversion, the following technical components are used: waterless urinals, urine diversion toilets, urine piping to a urine storage tank (or to a sewer) and a reuse or treatment and dispoal system for the urine.
Urine diversion toilets may, or may not, mix water and faeces, or some water and urine, but they never mix urine and faeces.
A toilet used to facilitate the separation of human waste products is called a urine diversion toilet or UDT. The bowl usually has two separate receptacles which may or may not be flushed with water. If flushed, the toilet is usually referred to as a UD flush toilet or UDT. If not flushed, it is a dry toilet with either drying or composting for the feces. If the collected feces are dried, it is called a urine-diverting dry toilet or UDDT (also called urine diversion dehydration toilet). If the collected feces are composted. it is called a urine-diverting composting toilet.
Some technologies applied as part of an ecological sanitation concept are using urine diversion. There are several commercially available urine diversion toilets (UDT) and urine diversion dry toilets (UDDT). Many look like a conventional sit down or squat toilet and the bowl is divided into two sections. The front section collects urine and the rear section feces.
Reasons for urine diversion which are relevant for all types of UD systems:
- to reduce water consumption
- to be able to collect urine, pure and undiluted, so that it can – after sanitisation by storage – be safely used as fertiliser in agriculture.
- reduce odour (a mix of urine and faeces causes substantial odour);
- avoid production of wet, odorous faecal sludge, which has to be removed by someone when the pit latrine is full;
- enable fast drying of faeces which makes handling of faeces more simple and hygienic;
- reduce environmental impacts;
- allow for the recovery of urine, which can be reused as fertiliser.
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.
Separate treatment of the two types of waste is justified since urine is nearly sterile and low in pathogens, provided an individual is healthy. This means that urine can be readily utilized as a fertilizer or discharged with less risk to community.
Human feces, on the other hand are high in pathogens, including up to 120 viruses and should either be composted or dried and burned as a biofuel. When feces are used without composting for several months, it is called night soil, which is recognizably odiferous. Its use in some areas has been so ingrained that entire cultures will not eat any vegetables or fruits unless they are thoroughly cooked.
Whether the feces are handled on site or hauled to another location, the weight and volume of material is reduced by separating out urine. Additionally, treatment is simplified and faster. Urine diversion is the main reason one manufacturer of composting toilets claims their product is less problematic than toilets that do not feature diversion.
Types of urine diversion devices
Urine diversion toilet designs generally require men to sit or squat while urinating in order to avoid unhygienic splashing of urine. In cultures where men prefer to stand for urination, urinals are a good complementary solution. Urinals – widely used by men at public toilets, restaurants, schools, etc. – work as urine diversion devices because urine is collected separately from faeces. When urinals do not use water for flushing (called "waterless urinals"), they can collect the urine pure, meaning without dilution with water. Suppliers for waterless urinals can easily be found on the internet.
Urine diversion flush toilets
Urine diversion flush toilets have been manufactured in two main countries: Germany and Sweden (one company also manufactured them in China in sitting and squatting style but no information is available on whether this was a commercial success and if these toilets are still sold nowadays). In Germany, the company Roediger Vacuum sold the "NoMix" toilet between 2003 - 2011. However, this toilet did not become a commercial success, and manufacturing, sales and technical support ceased in about 2010 (the most prominent installation of Roediger toilets installed today is at the Swiss Federal Institute of Aquatic Sciences and Technology in Dübendorf near Zürich, Switzerland). Likewise, the Swedish company Gustavsberg stopped selling their urine diversion flush model in about 2011 which was regretted by many people because it was generally working well.
In Sweden, urine diversion flush toilets are nowadays supplied by two manufacturers, Dubbletten and Wostman, which continue to sell their urine diversion systems today primarily for installation in summer houses in rural and semi-rural areas. These two types of urine diversion flush toilets have been installed in both research projects and community scale installations in Australia.
The design difference between the various models is the shape and size of the two compartments and in the way the flush water is introduced for the two compartments. In addition, the Roederig NoMix toilet was the only toilet that was able to collect the urine pure - without any flush water - due to a valve on the urine compartment that was opened when the user sat down and closed when the user stood up and flushed the toilet. It was also this valve that caused a lot of maintenance issues due to struvite precipitation in this valve. In the other urine diversion flush toilet models, the urine is diluted with a small amount of flush water, usually about one litre per flush.
The urine diversion flush toilet of Dubbletten features separate flushing with water in each of the two compartments.
Urine-diverting dry toilets (UDDTs)
Disadvantages and challenges with urine diversion systems include:
- Social acceptance amongst users (detailed research on this aspect has been carried out by researchers in Sydney, Australia)
- User cooperation: urine diversion toilets need some upfront awareness raising to ensure correct usage and social acceptance.  Also, they are cleaned differently to conventional toilets.
- Urine reuse/disposal issues
- Urine precipitation in the urine diversion equipment due to struvite and calcium phosphate precipitates and resulting encrustations (also called "urine stone"): this can be overcome with certain engineering and maintenance solutions but it requires plumbers who have experience with urine diversion piping systems or who are following published recommendations.
- von Münch, E., Winker, M. (2011). Technology review of urine diversion components - Overview on urine diversion components such as waterless urinals, urine diversion toilets, urine storage and reuse systems. Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH
- Rieck, C., von Münch, E., Hoffmann, H. (2012). Technology review of urine-diverting dry toilets (UDDTs) - Overview on design, management, maintenance and costs. Deutsche Gesellschaft fuer Internationale Zusammenarbeit (GIZ) GmbH, Eschborn, Germany
- http://weblife.org/humanure/chapter7_2.html Web article on pathogens that in turn mainly came from book, Appropriate Technology for Water Supply and Sanitation, by Feachem et al., World Bank, 1980.
- http://www.ncbi.nlm.nih.gov/pubmed/18578152 Evaluation of human urine as a source of nutrients for selected vegetables and maize under tunnel house conditions in the Eastern Cape, South Africa, Lead author: Mnkeni PN, April 2008
- http://ecosanservices.org/pdf/UDD-ToiletsTraining%20material.pdf UDD-Toilets and urine management
- http://www.ncbi.nlm.nih.gov/pubmed/19303763 Comparing microbial die-off in separately collected faeces with ash and sawdust additives, Author Niwagaba C et al, 2009
- http://www.cdc.gov/haiticholera/sanitation.htm CDC Document Potential sanitation solutions for emergency response, February, 2011
- http://ecovita.net/news/ How to fix a leaking (other brand) composting toilet, by July 2009
- von Münch, E., Winker, M. (2011). Worldwide listing of suppliers for waterless urinals - Appendix 1 for technology review of urine diversion components. Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH
- von Münch, E., Winker, M. (2011). Worldwide listing of suppliers for urine diversion pedestals/seats (for UDDTs or for UD flush toilets) - Appendix 3 of technology review of urine diversion components. Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH
- Winker, M., Saadoun, A. (2011). Urine and brownwater separation at GTZ main office building Eschborn, Germany - Case study of sustainable sanitation projects. Sustainable Sanitation Alliance (SuSanA)
- Winker, M., Schröder, E., Saadoun, A., Kilian, F. (2012). Factsheets of the SANIRESCH project in Eschborn, Germany - Factsheets of the MAP (struvite) reactor, greywater and brownwater treatment plant. Deutsche Gesellschaft für Internationale Zusammenarbeit GmbH, Eschborn, Germany
- Mitchell, C., Fam, D., Abeysuriya, K. (2013). Transitioning to sustainable sanitation - A transdisciplinary project of urine diversion. Institute for Sustainable Futures, University of Technology Sydney, Australia
- Fam, D.M., Mitchell, C.A., Abeysuriya, K.R., Meek, T. (2013) Facilitating organisational learning to support decision making and planning for sustainability in the water sector, Water Policy, vol. 15, no. 1, pp. 1094-1108.
- Lopes, A., Fam, D.M., Williams, J. (2012) Designing sustainable sanitation: involving design in innovative, transdisciplinary research, Design Studies, vol. 33, no. 3, pp. 298-317.
- Additional photos in SuSanA photo database on flickr
- SuSanA Discussion Forum about urine diversion systems