Fertiliser can be made from human urine in just a few simple steps

Urine is rich in nitrogen, which is important for plant growth, and now scientists have found an efficient way of utilising this to make human wastewater into fertiliser

By Alex Wilkins

20 January 2025

Human urine could be used to make fertiliser

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A more efficient way to extract fertiliser from human urine could help make better use of wastewater in cities and farms, without exacerbating global warming.

Human urine is rich in compounds useful for growing crops, such as nitrogen, but chemical processes to extract these compounds are less efficient than industrial methods of making fertiliser, such as the Haber-Bosch process, which converts nitrogen in the air to ammonia by adding hydrogen. However, these methods are often energy intensive and produce climate pollutants.

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Now, Xinjian Shi at Henan University in Kaifeng, China, and his colleagues have found that adding oxygen from air and a graphite catalyst to urine produces a nitrogen-rich chemical called percarbamide. The process only requires a few steps and produces no waste products.

“Prior to our method, the traditional method of separating [the nitrogen-rich compound] urea from urine was to concentrate urine to precipitate urea and inorganic salts, and then purify urea by exploiting the differences in solubility,” says Shi. “This process is cumbersome and the resulting purity is low.”

Shi and his team placed thin sheets of graphite, which had been modified to have defects in the way their atoms were joined, on an electrode. This was then put in a concentrated urea-rich solution.