Separating at source human faeces and urine and avoiding their mixture with other household waste (grey) water. The urine may be used as fertilizer and the faeces composted in dry closets. The separation toilet is not just seen as a technical solution in the absence of sewerage, but also as a more environmentally friendly toilet system because it enables appropriate reuse of the three waste streams of households which in wet-closet systems are mixed together.
Use of human excreta as fertilizer has hardly been utilized at all. The modern water-based sanitation systems flush it out into fresh or marine waters with consequent growth of algae, resulting in lack of oxygen and dead sea bottoms. This is hardly a system worthy of an advanced society and could be replaced by a closed system, with no pollution from bacteria or viruses and where the fertilizers in the wastes are harvested and used to feed crops.
Urine accounts for as much as 90% of the fertilizer each person excretes; annually this is sufficient to grow the 250 kilograms of crops consumed each year. Moreover the nutrients in the urine have ideal chemical forms for plant use: nitrogen is in the form of urea, phosphorus as superphosphate and potassium as an ion. Urine is free from heavy metals, because they are bound up into inert forms by the liver and kidneys. Unlike urine, faeces mainly consist of food parts that have limited use as fertilizer, i.e. mostly plant fibres with little nutrient value. And whereas urine is in most cases sterile, whereas faeces may contain as much as 100 million bacteria per gram. In the separation toilet, these problems are solved by separate treatment of urine and faeces.
In 1989, the first functioning separation toilet was developed by a Swedish doctor, who established his own small commercial enterprise.
The Nordic Environmental Institute has an exhibition of various alternative toilets in Tanum, Norway, including dry and wet separation toilets. Because hard rock subsoil conditions in much of Scandinavia make sewerage work difficult and costly, there is great demand for well-functioning "stand-alone" toilet systems.
Munkesogaard Ecovillage in Denmark has fitted separating toilets in its 20 terrace houses and apartments.