Can human urine help solve the world’s food problems?
Researchers believe urine has potential to replace chemical fertilisers
‘Go pee on the rhubarb!” Engineer Fabien Esculier has never forgotten his grandmother’s unconventional approach to gardening — in fact, it has inspired his career.
Human urine may seem like a crude way of fertilising plants in the era of industrial agriculture, but as researchers look for ways to reduce reliance on chemicals and cut environmental pollution, some are growing increasingly interested in the potential of pee.
Plants need nutrients — nitrogen, phosphorus and potassium — and we ingest these through food, before “excreting them, mostly through urine”, said Esculier, who runs the OCAPI research programme in France looking at food systems and human waste management.
This presents an opportunity, scientists think.
Fertilisers using synthetic nitrogen, in use for around a century, have helped drive up yields and boost agricultural production to feed a growing human population. But when they are used in large quantities, they make their way into river systems and other waterways, causing choking blooms of algae that can kill fish and other aquatic life.
Harmful emissions
Meanwhile, emissions from this agricultural ammonia can combine with vehicle fumes to create dangerous air pollution, according to the United Nations.
Chemical fertilisers also create emissions of the potent greenhouse gas nitrous oxide, contributing to climate change. But the pollution does not just come directly from the fields. “Modern-day sanitation practices represent one of the primary sources of nutrient pollution,” said Julia Cavicchi, of the United States Rich Earth Institute, adding that urine is responsible for around 80 per cent of the nitrogen found in wastewater and more than half of the phosphorus.
To replace chemical fertilisers, you would need many times the weight in treated urine, she said. But she added: “Since the production of synthetic nitrogen is a significant source of greenhouse gases, and phosphorus is a limited and non-renewable resource, urine diverting systems offer a long-term resilient model for human waste management and agricultural production.”
Wastewater potential
One 2020 study by UN researchers found that global wastewater has the theoretical potential to offset 13 per cent of the world’s demand for nitrogen, phosphorus and potassium in agriculture.
But pee diversion is easier said than done. In the past, urban excrement was transported to agricultural fields to be used as fertiliser along with animal manure, before chemical alternatives began to displace them. But now if you want to collect urine at source, you need to rethink toilets and the sewage system itself.
A pilot project to do just that began in Sweden in the early 1990s in a selection of eco-villages. Now there are projects in Switzerland, Germany, the US, South Africa, Ethiopia, India, Mexico and France.
“It takes a long time to introduce ecological innovations and especially an innovation such as urine separation which is very radical,” said Tove Larsen, a researcher at Switzerland’s Eawag aquatic research institute.