Taking the P on King’s Day in Amsterdam

WATERNET, a water company in the Netherlands, is today collecting urine from urinals in three locations in Amsterdam, as the Dutch people celebrate Koningsdag, or King’s Day, to make sustainable phosphate fertiliser.

Up to 1.5m people, dressed in orange, the colour of the Dutch royal house, are expected to take to the streets of Amsterdam for a day-long festival to celebrate the birthday of King Willem-Alexander. The consumption of large quantities of beer inevitably leads to the production of large quantities of urine. Urine is naturally quite high in phosphate, a vital crop fertiliser, and Waternet has been invited by Amsterdam’s regional public water authority to collect the urine to extract the valuable mineral.

Phosphate is generally produced from mined minerals, but it is estimated that natural sources are likely to run out within 30 years. Waternet has been producing the phosphate-rich mineral struvite from sewage at a specialist plant to the west of Amsterdam since 2013, but this is the first time it has set up specialist collection points at King’s Day. Pure urine yields 1.4 g/L of struvite compared to 0.015 g/L from raw sewage. The purer the urine, the better, so the urinals at events are an ideal source.

The liquid is first aerated, then magnesium chloride is added to the tank. This causes struvite (magnesium ammonium phosphate), to precipitate out of the mixture. The struvite crystals are extracted and rinsed ready for use directly. When raw sewage is used, the sludge is first used to produce biogas, before the mixture goes on to the struvite production process. The Waternet plant can produce enough fertiliser for the equivalent of 10,000 football fields every year.

Waternet says that removing struvite from sewage not only produces a sustainable fertiliser, but can also lower plant maintenance costs. Struvite build-ups can cause blockages and excess wear of equipment, so removing it prevents these problems.