The idea of someone sprinkling urine on building rooftops sounds like a major health hazard, but that’s just what Amsterdam’s water utility, Waternet, recently proposed. Though it sounds like a cruel prank, the project is actually part of an effort to find cheap, natural alternatives to traditional fertilizer. In order to flourish, Amsterdam’s many green roof tops need lots of nitrogen, potassium, and phosphorus, substances that some say could become scarce by 2030. Knowing that human urine contains a lot of all three of these nutrients, Waternet recently set up a demonstration project to harvest pee from public urinals. It hopes to process what it gleans into an upcycled fertilizer for public gardens and vegetated rooftops around the city.

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Recycling’s all well and good, but peecycling? The city of Amsterdam didn’t arrive at this decision lightly. The truth is, the world is likely running out of nitrogen, potassium, and especially phosphorus–all essential ingredients for healthy plant life.

“…there is a debate raging between scientists who claim that phosphorus resources in the natural world could run out within 50-100 years; and those who say they won’t,” writes Rich Heap for UBM Future Cities. “Phosphate fertilizer is an organic fertilizer that has been used since the mid-19th century. If the doom-mongers are right, then a shortage could hamper our ability to grow enough food.”

To test its hypothesis that the urine we typically flush down the drain is the key to greener cities, Waternet set up a series of temporary urinals (like the ones pictured above) in La Place de la Bourse. The plan is to process the urine in such a way that struvite, a powdery substance, is produced. This can then be applied to fields, gardens, and green roofs to help plants grow.

Even if the planet doesn’t run out of phosphorus the way some predict, there’s pretty much no downside to turning a waste product (pee) into a marketable product (fertilizer). Doing so could save Amsterdam, and other cities if they copy the idea, a lot of money.

“Construction started in September on a processing plant that is due to open in 2014, including a collection point for pure urine,” explains Heap. “It [Waternet] says wastewater from one million people in Amsterdam could enable it to produce 1,000 tonnes of fertilizer each year.

Via Treehugger