Urine diversion, also called urine separation or source separation, refers to the separate collection of human urine and feces at the point of their production, i.e. at the toilet or urinal. 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 and a reuse or treatment and disposal system for the urine. Urine diversion toilets may, or may not, mix water and feces, or some water and urine. They never mix urine and feces. 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 urine-diversion flush toilet or UDFT. 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. If the collected feces are composted, it is called a urine-diverting composting toilet. Some technologies applied as part of an ecological sanitation concept use urine diversion. There are several commercially available urine diversion toilets and urine diversion dry toilets. Many look like a conventional sit-down or squat toilet and the bowl is divided into two sections, with the front section collecting urine and the rear section feces.
Design considerations
Purpose
Reasons for urine diversion which are relevant for all types of UD systems:
allow for the recovery of urine, which can be reused as fertilizer.
Principle
Urine diversion takes advantage of the anatomy of the human body, which excretes urine and feces separately. In a UDDT, the urine is drained via a basin with a small hole near the front of the user interface, while feces 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 need to be treated well before it can be safely used in agriculture. The main two treatment methods are composting and drying. When feces are used without composting, it is called night soil, and is very smelly. Ash and/or sawdust are usually added to the feces chamber of a UDDT to speed the composting process. Of the two, ash decreases microbial activity faster. 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 can also be used for composting toilets to reduce odor and reduce excessive moisture.
Types of urine diversion devices
Urinals
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 feces. When urinals do not use water for flushing, 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 (UDFTs)
Urine diversion flush toilets have been manufactured in two main countries: Germany and Sweden. 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. 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.
It is unclear whether urine diversion and on-site urine treatment can be made cost effective; nor whether required behavioral changes would be regarded as socially acceptable, as the largely successful trials performed in Sweden may not readily generalize to other industrialized societies. Disadvantages and challenges with urine diversion systems include:
Social acceptance amongst users
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 or disposal issues
Urine precipitation in the urine diversion equipment due to struvite and calcium phosphate precipitates and resulting encrustations : 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.
