Showcase ‘P-lab’: urban raw materials in a small-scale circular economy

Two to three carrots Manufacturer Laufen supplied two special toilets that separate the urine from the flushing water and the faeces. Conthe coupled these together with a waterless urinal to a bioreactor and a vacuum evaporator to recover various valuable nutrients plus high-quality water using a process of nitrification and distillation. Besides phosphorus, the plant also recovers nitrogen and small amounts of potassium and boron. Harmful substances such as drug residues and hormones are in principle removed during the process. “The plant can handle 30 litres of urine a day”, she explains, “that’s enough to deliver around 10g of phosphorus. Next to the container we have a small greenhouse where we use the recovered nutrients to feed various crops. This enables us to also study what effects different proportions of fertilisers have on different food crops.”  In this way the urine of city dwellers can be used right away and on location to grow fruit and vegetables that the same city dwellers eat and then re-excrete…. and with the least possible burden on the environment. The result: a safe, small-scale recycling system that helps make cities circular. According to Conthe’s calculations, one pee provides enough nutrients to grow two to three carrots. “Scaling up this demonstrated process will enable us to go some way to meeting urban food needs. For example using forms of urban farming.”

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