PARIS-“Go pee on the rhubarb!”
Engineer Fabien Esculier never forgot his grandmother’s unconventional approach to gardening – in fact, it inspired his career.
Human urine may seem like a crude way to fertilize plants in the age of industrial agriculture, but as researchers search for ways to reduce reliance on chemicals and reduce environmental pollution, some s are increasingly interested in the potential of urine.
Plants need nutrients – nitrogen, phosphorus and potassium – and we ingest them through food, before “excrete them, mainly through urine”, said Esculier, who leads France’s OCAPI research program on plant systems. food and human waste management.
This presents an opportunity, scientists think.
Synthetic nitrogen fertilizers, which have been used for about a century, have increased yields and boosted agricultural production to feed a growing human population.
But when used in large quantities, they find their way into river systems and other waterways, causing smothering algal blooms that can kill fish and other aquatic life.
Meanwhile, emissions of this agricultural ammonia can combine with fumes from vehicles to create dangerous air pollution, according to the United Nations.
Chemical fertilizers also create emissions of nitrous oxide, a potent greenhouse gas, which contributes to climate change.
But the pollution does not only come directly from the fields.
“Modern sanitation practices represent one of the main sources of nutrient pollution,” said Julia Cavicchi, from the Rich Earth Institute in the United States, adding that urine is responsible for about 80% of the nitrogen present in wastewater and more than half of the phosphorus.
To replace chemical fertilizers, you would need several times the weight of treated urine, she said.
But she added: “Because synthetic nitrogen production is a significant source of greenhouse gases and phosphorus is a finite and non-renewable resource, urine diversion systems offer a resilient model over the long term. term for human waste management and agricultural production.
A 2020 study by UN researchers found that global wastewater has the theoretical potential to offset 13% of global nitrogen, phosphorus and potassium demand in agriculture.
But pee diversion is easier said than done.
In the past, urban dung was transported to agricultural fields to be used as fertilizer along with animal manure, before chemical alternatives began to displace it.
But now, if you want to collect urine at the source, you have to redesign the toilets and the sewage system itself.
A pilot project to do just that started in Sweden in the early 1990s in selected eco-villages.
There are now projects in Switzerland, Germany, USA, South Africa, Ethiopia, India, Mexico and France.
“It takes a long time to introduce ecological innovations and especially an innovation like urine separation which is very radical,” said Tove Larsen, a researcher at the Eawag Aquatic Research Institute in Switzerland.
She said early urine-diverting toilets were considered unsightly and impractical, or raised concerns about unpleasant odors.
But she hopes a new model – developed by Swiss company Laufen and Eawag – will solve these difficulties, with a design that channels urine into a separate container.
Once the pee is collected, it needs to be dealt with.
Urine is not normally a major carrier of disease, so the World Health Organization recommends leaving it for a while, although it is also possible to pasteurize it.
There are then various techniques for concentrating or even dehydrating the liquid, reducing its volume and the cost of transporting it to the fields.
Another challenge is overcoming public sensitivity.
“This subject touches on the intimate”, declared Ghislain Mercier, of the public management of Paris and Métropole Aménagement.
It is developing an eco-district in the French capital with shops and 600 homes, which will use urine collection to fertilize the city’s green spaces.
He sees great potential in large buildings such as offices, as well as houses not connected to mains drainage.
Even restaurants. Also in Paris is the restaurant 211, equipped with waterless toilets that collect urine.
“We’ve had quite positive feedback,” said owner Fabien Gandossi.
“People are a little surprised, but they see little difference from a traditional system.”
But are people ready to take it to the next level and eat urine-fertilized foods?
A study on the subject has highlighted the differences noted from one country to another. The acceptance rate is very high in China, France and Uganda for example, but low in Portugal and Jordan.
Synthetic fertilizer prices are currently skyrocketing due to shortages caused by Russia’s invasion of Ukraine, which has also prompted countries to consider boosting their food security.
This could be an opportunity to help “make the subject more visible,” Mercier said.
Marine Legrand, an anthropologist working with Esculier at the OCAPI network, said there were still “hurdles to overcome”.
But she thinks water shortages and increased awareness of the cost of pollution will help change attitudes.
“We are beginning to understand how precious water is,” she told AFP.
“It therefore becomes unacceptable to defecate there.”
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