According to the study published by the French Urban Planning Agency, 29 million baguettes of bread could be produced daily using wheat fertilized by human urine – roughly 10 times the current daily consumption – saving 703 tonnes of nitrogen used in artificial fertilizers.
Taking this illustration further, French engineer Louise Raguet baked ‘Boucle d’Or’ – Goldilocks bread – using wheat fertilized in urine gathered from female urinals in the 14th Arrondissement of Paris.
Raguet hopes to “break taboos over excrement” and create a more sustainable food and farming system that makes use of human refuse, while cutting farming costs and boosting crop yields.
“Urine is a great fertilizer,” Raguet told a conference on urban architecture recently.
“It’s a neglected liquid, usually dismissed as a waste product. But it is packed with nutrients and should be treated like a gold mine.”
Human urine is a rich source of nitrogen, phosphorous, potassium and other trace elements that plants can use to grow, and is also sterile when expelled from the body.
“When you pee in water, treatment plants remove the nutrients. They do not return to the earth. The system is not circular.
“It’s [also] ideal to replace chemical fertilizers and avoid the pollution they cause,” she said.
Huge and unrecognised threat
In the French study, scientists Manuel Pruvost-Bouvattier, Martial Vialleix, Aurélie Joveniaux and Fabien Esculier said nitrogen and phosphorus – which are necessary for agriculture – “massively depend” on imported fossil resources.
Apart from the impact it has on the environment and the climate, there is also a “a huge and unrecognised threat that hangs over the sustainability of our food”.
To feed the residents of Ile-de-France, for example, more than half of the nitrogen input comes from synthetic fertilizers. Their manufacture is energy-consuming and highly emissive of greenhouse gases. Phosphorus – extracted from fossil mines mainly located abroad – is forecast to run out soon, if practices continue as they do.
The scientists claim that urine recycled into fertilizer is likely to meet these challenges – depending on the evolution of the food and sanitation systems and, obviously, societal acceptability.
To overcome the challenge to collect urine as soon as it leaves the body, Raguet has designed a female urinal, nicknamed Marcelle. The decision to employ female urine is part of what Raguet calls ‘ecofeminism’, which advocates using eco-friendly products to empower women.
To further ensure the ingredient’s sterility, Raguet diluted it 20 times before being sprayed on the wheat crops, which eventually were used to make the Goldilocks bread.
According to Raguet, large volumes of human urine can be stored for three months in a closed tank as its high alkaline content and the ammonia destroy unwanted molecules like drug residues or germs.
There was no report on how the ingredient affects the bread’s taste.
Authors: Pruvost-Bouvattier, M, Vialleix, M, Jovéniaux, A and Exculier, F
L’Institut Paris Region N° 858, 2020