Scientists see pee as possible fertiliser option

Paris – “Go pee on the rhubarb!” Engineer Fabien Esculier has never forgotten his grandmother’s unconventional approach to gardening – in fact, it inspired his career.

Human urine may seem like a crude way of fertilising plants, but as researchers look for ways to reduce reliance on chemicals and cut environmental pollution, some are becoming 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 a research programme in France looking at human waste management.

This presents an opportunity, scientists think. Fertilisers using synthetic nitrogen have helped drive up yields. 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.

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 was responsible for 8% of the nitrogen found in waste water and more than half of the phosphorus.

To replace chemical fertilisers, you would need many times the weight in treated urine, she said.

“Urine diverting systems offer a long-term resilient model for human waste management and agricultural production.”

One 2020 study by UN researchers found global waste water has the theoretical potential to offset 13% of the world’s demand for nitrogen, phosphorus and potassium in agriculture. But pee diversion is easier said than done. Toilets and the sewage system itself have to be rethought.

A pilot project to do that began in Sweden in the early 1990s in eco-villages. Now, there are projects in Switzerland, Germany, the US, South Africa, Ethiopia, India, Mexico and France. –