One in every three people has no access to a completely hygienic toilet. The result is intestinal diseases and polluted groundwater in less developed countries. Within the scope of an international
competition by the Bill & Melinda Gates Foundation, Eawag has developed a squat toilet that manages without a sewage system or external power. It is a self-contained, autonomous system in which water is reused and raw materials can be processed from human waste.

A squat toilet with a closed water circuit for slums – this is the goal of Eawag project manager Tove Larsen (photo: Michael Sieber, Langnau/Zürich).

There it is, the very first model in the Eawag foyer in Dübendorf, Zurich. It is a design piece, more than two metres high and made of blue coloured polyethylene. It was dubbed the “poor man’s privy” in a TV feature. Eawag opted for the characteristically scientific style in its own press release: “Swiss researchers invent a new toilet”. This innovation is a response to an appeal
launched by the American Bill & Melinda Gates Foundation under the slogan “Reinvent the Toilet!” In mid-2012, Eawag received a prize in recognition of its proposed solution.

Approximately 2.6 billion people, namely one in three of the world’s inhabitants, have no access to a hygienic toilet. The result is diarrhoea and infectious diseases as well as the constant risk of groundwater pollution. In order to help mitigate such degrading and illness-inducing conditions, the Microsoft founder and his wife wrote to 22 universities and research institutes in 2011 asking them to propose a solution. The competition requirements were challenging. The toilet to be developed should be usable in the poorest parts of the world, function without a sewage system or external power and cost no more than five US cents per day and person. Moreover, to enable valuable raw materials in urine and faecal matter to be processed, the toilet should be integrated into a material cycle.

A squat toilet as a status symbol
For project manager Tove Larsen it was clear that such a complex task could only be solved by an interdisciplinary team. She herself is a chemical engineer specialising in process engineering
in the waste water sector. She gathered together additional researchers from different Eawag departments. Among them, in the guise of Austrian Harald Gründl, came a highly respected
designer who usually works in furniture or shop design for clients such as Armani or Bulthaup. “A toilet with appealing looks is a status symbol in less developed countries,” says Tove Larsen, “and that is also why it is used.” And it was this aspect too that won Gründl’s Vienna design studio EOOS and Eawag the 40,000 US dollar prize. The Bill & Melinda Gates Foundation
certificate says: “Special recognition for outstanding design of a toilet user interface”.

Concealed behind the attractive façade of the squat toilet dubbed the “Diversion” is to be found ingenious science and the fruits of intensively researched process engineering. Water filtration tests in a closed circuit were conducted at the Eawag laboratory. In the research institute’s cellar there are test facilities for extracting manure from human waste. So that everything meshes together in this stand-alone, self-contained system, each individual part of the whole must be fully thought through and refined.

“The key to this is the separation of urine and faeces,” says Tove Larsen, “because only this enables the efficient recovery of raw materials while at the same time reclaiming clean water within a closed circuit.” The project manager explained how this works using the exhibited model. Approximately one to one and a half litres of water are available for each use. This has to suffice for cleaning the toilet and washing the user’s hands – for the latter there is a small wash hand basin. There is also a small hand-held shower for efficient anal hygiene. As such, this separating toilet can be used in all cultural circles throughout the world.

A water reclamation circuit
All this is made possible by compact engineering. At the same time as a user of either sex pumps clean water into the toilet’s water tank by means of a small foot pedal, soiled water is led
into a biological reactor on the reverse side. In this reactor, the water flows through a membrane filter under the force of gravity, cleaning it in the process. Additional electrolysis by a solar-powered electrode ensures that the end product really is sterile water and can thus be reused. “Perfectly hygienic water for washing hands is critical,” says Tove Larsen, “It also means that the separating toilet can be used by Muslims or Hindus who habitually use water for anal hygiene.”

But how can the cost of five US cents per day and person specified by the Gates Foundation be achieved? Here too, the team headed by Tove Larsen has come up with answers. The researchers developed ingenious transport logistics adapted to the booming hut settlements in developing countries. This involves a toilet, used by two families, being emptied twice a week by an employee. “The whole thing is a modular system comprising self-closing faeces containers and urine collection vessels capable of being efficiently collected by a vehicle. This makes collection just as safe hygienically as the toilet itself,” says Tove Larsen. “We have also tested processes enabling urine and faeces to be processed at decentralised installations into saleable products such as manure or biogas.” This therefore completes the economic cycle: indigenous entrepreneurs rent the toilets to local families. The purchase and maintenance of the toilet costing 500 US dollars are financed by the sale of the products derived from it.

The project is now entering the next round. The Gates Foundation has made more than one million US dollars available for further development. This money will enable production of a prototype to be tested in the slums of Kampala in Uganda in April 2014. “If this goes successfully then the next step will be a short production run,” says Tove Larsen.