In nature, the concept of waste does not exist. Human excrement itself contain important elements, to the point that in ancient China it was usual, after a lavish meal at a friend’s house, to thank by defecating, that is, symbolically returning the nutrients received.

Today, thanks to increasingly circular sewage plants, it is possible to use sludge - containing a large part of human excrement - to produce biogas, materials and also to use water filled with elements such as nitrogen and phosphorus in irrigation.

Less used instead is urine, the final product of the excretion of the kidneys, which helps the function of maintaining the hydromineral and acid-base balance of the blood. In fact, 15 grams of nitrogen, a few grams of phosphorus and potassium, useful for fertilization, can be derived for every liter of liquid, while the mineral components, such as sodium, uric acid, calcium, magnesium, creatinine can be used as chemical building blocks. Many will already be turning up their noses at the thought of using pee because of the taboo we have created against a "waste" lived as disgusting but in reality, very valuable and abundant (and with the growing population there is guaranteed supply). Just think that in the past it was commonly used to fertilize crops, to tan skins, whiten clothes (contains ammonia) and produce gunpowder.

How to collect it

In a French study by the Institut Paris Region, the planning institute of the Paris region, in 2020, the methods of collecting and recovering urine (separately from faeces) are identified. Unlike faeces, urine has a very low risk of pathogen transmission, is easily controlled and offers the possibility of filtering pharmaceutical residues. Therefore, the collection is carried out through dry urinals, without or with very little water. At that point, treatments of any kind can be applied, from storage for local use to more complex industrial transformations or purification, in order to obtain different products.

There is no lack of experimentation. In Île-de-France, a large deposit of urine used as a low-impact fertilizer has been created in peri-urban cultures (an estimated saving of about 500 thousand tons of CO2 per year). Just think that over 700 tons of nitrogen and phosphorus are used to fuel 12 million Parisians, which will be partly replaced by nutrients derived from urine. In Sweden, which has been experimenting with the reuse of urine since the 1980s, several separate toilets have recently been installed in Gotland and various eco-villages. The urine, collected through differentiated pipes, is stored in tanks, then used to fertilize the nearby fields or even to produce neo materials.

On the campus of the Swiss Federal Institute of Aquatic Science and Technology (Eawag), in Dübendorf, urine is collected separately via a dry toilet and treated on site. Here was born Aurin, the first urine-based fertilizer concentrate approved in the world. Through an innovative technique, the Institute is able to produce 100 liters of liquid fertilizer from a thousand liters of urine.

Innovative processes

One of the most innovative experiments, recently told by the magazine Nature, is the Swedish Gotland, an enchanting island in the Baltic close to Finland. Since 2021 a team of researchers from the Swedish University of Agricultural Sciences, in Uppsala, in collaboration with a service company, Sanitation360, collected more than 70,000 liters of urine from urinals without water and specialized toilets scattered in different locations during the summer tourist season. The Swedish team created a process that dries urine in blocks of material with a consistency similar to that of cement, which if crushed produce a base and get a powder that, pressed, can be transformed into pellets and used as fertilizer for local crops.

One of the technological challenges is the preservation of urine: in fact, urea is hydrolyzed under the action of urease, resulting in the production of odorous emissions, due to precipitation and loss of ammonia, a challenge to overcome in the process of recycling urine. A 2021 study in the journal Frontier analyzes various methods of stabilizing existing urine, such as acidification, alkalinization, electrochemistry, inhibitory systems. The conclusion, however, is uncertain: while for example the use of electrochemical systems is suitable for decentralized sanitary installations, the duration of inhibition is short. Acidification and alkalinization processes are easy to use but have high raw material dosing requirements and can also have potential environmental impacts. Finally, inhibitors are the least effective and are usually used to regulate urease activity in the soil environment rather than for urine stabilization. But the study concludes: research is advancing rapidly, and the collection and reuse of urine will be increasingly efficient and effective. This desire for innovation can no longer be held back.


An article written by Emanuele Bonpan