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

A more efficient way of extracting fertilizer from human urine could help cities and farms make better use of wastewater, without increasing global warming.

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

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

“Prior to our method, the traditional method of separating urea (nitrogen-containing compounds) from urine was to concentrate the urine to precipitate the urea and inorganic salts, and then take advantage of the difference in solubility to purify the urea,” Xi says. “This process is cumbersome and the resulting accuracy is low.”

Shi and his team placed thin sheets of graphite on an electrode that had been modified to contain defects in the way their atoms connect. After this it was put in a solution containing concentrated urea.

When they passed electricity through the solution, solid crystals of percarbamide were formed, which were formed from oxygen in the air, hydrogen from water, and urea from urine. These crystals can then be easily separated from the liquid solution.

Next, the team tested how percarbamide worked as a fertilizer and found that it helped wheat, peanut and lettuce plants grow taller than those grown with just water or normal urea fertilizer. Shi says this may be because percarbamide can continuously release oxygen and help control nitrogen levels in the soil.

james mcgregor The University of Sheffield, UK, says this approach could be used for other chemical processes, but it may be difficult to scale up to city-wide wastewater treatment.

He says, “I would be surprised if we were sitting here in 10 years’ time and this was a major industrial process, but it potentially has applications for decentralized, local, small-scale production, perhaps especially in agricultural settings.” In.”