Human urine may be a less polluting alternative to traditional fertilizers

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Researchers and NGOs consider human urine an alternative to chemical fertilizers, to reduce environmental pollution and feed a growing population.

Synthetic nitrogen fertilizers boost agricultural production. The problem is that, when used in excess, they pollute the environment, and their prices are on the rise — even more so with the war in Ukraine.

What to replace them with? With urine, answer the researchers, among them the coordinator of the French research program Ocapi (Optimization of the Cycles of Carbon, Nitrogen and Phosphorus in the City), Fabien Esculier, who reflects on a review of food systems to make them more sustainable.

To grow, explains Esculier, “plants need nutrients, nitrogen, phosphorus and potassium.”

“When we eat, we ingest these nutrients before excreting them, mainly through urine,” adds this engineer.

For a long time, urban excrement was used in agricultural fields, before being replaced by chemical fertilizers.

When these nutrients are released in large quantities into rivers, however, they favor, for example, the multiplication of green algae and represent “one of the main sources of pollution by nutrient substances”, observes Julia Cavicchi, from the Rich Earth Institute, based in the United States. United.

overcome preconceived ideas

Separating and collecting urine requires changing toilets and collection networks, as well as overcoming preconceived ideas.

Urine diversion in toilets was already tried in Swedish eco-cities in the early 1990s and later in Switzerland and Germany. Tests are also being carried out in the United States, South Africa, Mexico, India and Ethiopia.

“Introducing green innovations takes time, especially a radical innovation like urine diversion,” says Tove Larsen, a researcher at Eawag (Swiss Federal School of Water Science and Technology).

The first generations of toilets with urine diversion, considered impractical and not aesthetic, or the fear of bad odors may have been a brake, suggests the researcher, in the hope that a new model developed by the Swiss company Laufen with Eawag will be able to solve the problem. these difficulties.

“It is necessary to overcome certain obstacles”, comments Marine Legrand, anthropologist and member of the Ocapi network.

Another question is: are people prepared to eat food fertilized with urine?

One study shows marked differences between countries. The acceptance rate is very high in China, France, or Uganda, but low in Portugal or Jordan.

“This theme touches the heart,” says Ghislain Mercier of Métropole Aménagement, which is developing an eco-friendly neighborhood in Paris with 600 residences and shops. There, urine will be collected to fertilize Parisian green spaces.

reorganize

According to him, there is great potential in offices, homes not connected to the basic sanitation network and in suburban neighborhoods without sanitary facilities.

However, it is necessary to get the support of the residents, rethink the pipes and face inadequate legislation.

Once collected, the urine must be transported to the fields, which is expensive. Several techniques allow reducing its volume and concentrating, or even dehydrating, urea. The Rich Earth Institute is developing technical solutions to make the distribution of this fertilizer easy and affordable for farmers.

As urine is not a major vector of disease, it does not require heavy processing for use in agriculture. The WHO (World Health Organization) recommends letting it rest. It is also possible to pasteurize it.

Urine is still struggling to establish itself as an alternative to synthetic fertilizers. With gasoline prices on the rise and the desire of many countries to strengthen their food sovereignty, amid the war in Ukraine, “economic restrictions will reach us faster than we imagined and open up more space for the issue”, comments Ghislain Mercier. .

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