Will human urine soon replace chemical fertilizers?

Several researchers and NGOs are seriously asking the question.

According to them, it would reduce environmental pollution and feed a growing population.

Synthetic nitrogen fertilizers boost agricultural production.

But used in excess, they pollute the environment.

Their prices are soaring, even more with the war in Ukraine, weighing on farmers.

What to replace them with?

Urine, answer researchers including Fabien Esculier, who is considering an overhaul of more sustainable food systems.

To grow, "plants need nutrients, nitrogen, phosphorus and potassium", explains the engineer and coordinator of the Ocapi research program (Optimization of carbon, nitrogen and phosphorus cycles in the city) in France.

When we eat, we ingest these nutrients before “excrete them, mostly through urine,” he continues.

Go beyond preconceptions

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

But when these nutrients are released in too large quantities into rivers, they promote the explosion of green algae, for example, and represent "one of the main sources of pollution by nutrient substances", underlines Julia Cavicchi, of the Rich Earth Institute, based in the United States.

Separating and collecting urine at the source requires rethinking the toilets, the collection network and overcoming certain preconceptions.

The separation of urine from the toilets was tested in Swedish eco-villages in the early 1990s, then in Switzerland or Germany.

Experiments are being carried out in the United States, South Africa, Ethiopia, India and Mexico.

In France, projects are emerging.

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

“We are beginning to understand how precious water is”

First generations of toilets with a urine separator, considered impractical and unsightly, or the fear of bad odors could have been a brake, she explains.

A new model developed by the Swiss company Laufen with Eawag should solve these difficulties, hopes the researcher.

Fabien Gandossi owns the 211 restaurant in Paris, equipped with dry toilets where urine is collected.

"We have rather positive feedback, people a little surprised, but (..) they see little difference compared to a traditional system".

"There are obstacles to overcome", comments Marine Legrand, anthropologist and member of the Ocapi network.

But “we begin to understand how precious water is” and “it becomes inadmissible to defecate in it”.

Are people still ready to eat foods fertilized with urine?

A study shows marked differences between countries.

The acceptance rate is very high in China, France or Uganda, but low in Portugal or Jordan.

“This subject touches on the intimate”, analyzes Ghislain Mercier, of Paris and Métropole Aménagement which is developing an eco-district in Paris with 600 housing units, shops… The urine will be collected there and will fertilize the Parisian green spaces.

According to him, there is significant potential in offices, houses not connected to mains drainage, or slums without sanitary facilities.

However, it is necessary to make the inhabitants adhere, to rethink the piping, to face unsuitable legislation... Once harvested, the urine must be transported to the fields, which is expensive.

Various techniques make it possible to reduce its volume and to concentrate, or even dehydrate, the urea.

The Rich Earth Institute is developing technical solutions to make spreading this fertilizer easy and inexpensive for farmers.

Since urine is not normally a major vector of disease, it does not require heavy processing for use in agriculture.

The World Health Organization (WHO) recommends letting it rest.

It is also possible to pasteurize it.

Urine is still struggling to establish itself as an alternative to synthetic fertilizers.

But with soaring gas prices and the desire of many countries to strengthen their food sovereignty, in connection with the war in Ukraine, "economic constraints will catch up with us faster than we would have thought and make the subject more audible,” comments Ghislain Mercier.

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