The miraculous virtues of urine

When scientists and eco-entrepreneurs join forces to revisit the miracle of water turned into wine, the result is a very special cuvée called "J'irai pisser sur vos vignes" ("I'll pee on your vines"). Or how the nutrients in our urine can be turned into fertilizer for the vines. Gospel of the Valurine project according to Marc Héran, researcher at theEuropean Membrane Institute (IEM).

Ecosec

The French consume drinking water, a lot of it, 20% of it just for flushing the toilet. Water that must then be transported to our wastewater treatment plants, treated and returned to our natural environment. It's not a virtuous circle, and the financial, energy and environmental costs are staggering.

With water, we've only just begun to think about it in the same way we did with waste twenty years ago, when we set up recycling channels," compares Marc Héran, a researcher at the French National Institute for Environmental Research.IEM. However, the question is similar for wastewater: can't we recover the nutrients it contains for irrigation, for example?

This water treatment specialist has been working on this experiment since last year with the Montpellier-based company Ecosec, and the La Jasse winegrowing estate in Combaillaux. For two years, two plots of vines will be irrigated with fertilizer made from urine collected in dry toilets installed in the village and specially designed by Ecosec to separate urine and faeces. The project is called Valurine.

From urine to fertilizer

"Without a doubt, the ecological transition is coming and will be accomplished. This awareness of our consumption patterns and their dependence on fossil fuels and raw materials is a major current issue", stresses the researcher.

" Our urine contains most of the nutrients used as plant fertilizers: nitrogen, phosphorus, potassium..." explains Marc Héran. Phosphorus, essential for plants, is "a fertilizer that enables high agricultural yields. We get it from phosphate mines, and we're getting more and more of it. A limited resource whose depletion could lead to a global agricultural crisis in the coming decades.

Nitrogen, on the other hand, is an unlimited resource," explains the researcher, "because it is present in the atmosphere. On the other hand, its cycle is extremely energy-intensive. Wastewater treatment plants are obliged to treat nitrogen before discharging it into the natural environment, in order to limit eutrophication (see box below). Transformed into a gas, the nitrogen is released back into the atmosphere before being captured again and transformed back into liquid nitrogen for use as fertilizer.

Strict controls

The question is how to use this urine properly. Urine can contain micropollutants and pathogens, so hygienization and control are essential throughout the transformation process. " We have not seen any internalization of pathogens in plants, and as for micropollutants, we are below detection thresholds," assures Marc Héran.

Another aim is to optimize the management of urine volumes, which are costly to store and transport. To limit these costs, the Valurine project is experimenting with several processes. The production of struvite, a powdered urine extract, and the concentration of urine by nitrification/distillation. "Struvite is extracted using a simple precipitation process, which recovers over 90% of the phosphate and some nitrogen in powder form, thanks to the addition of magnesium to the urine, which produces a precipitate.

Concentrating urine requires a little more know-how, as it must first be nitrified, as Marc Héran explains: "This consists in stabilizing the nitrogen present in the urine in the form of ammonium, by transforming it into nitrate". The urine is then distilled "to retain all the nutrients in just 5-10% of the initial volume".

The end of the sewer system

Once concentrated in solution or powder form, or simply used as it is, the urine is ready for drip irrigation in open fields. A small miracle that has led to the production of the very first bottles of wine from this fertilization process. The aptly named cuvée: "J'irai pisser sur vos vignes" (I'll piss on your vines ) is the story of an eternal restart, where nothing is lost, nothing is created, everything is valorized. " Urine can change the face of agriculture, but also that of our planet. The 21st century will be the end of the sewer," concludes the researcher.