The gardener's gold water - on the sustainable use of urine

Chemist Prof. Dr. Hans-Willi Kling on a very special fertilizer

We have known how important urine is since the days of the WDR-Ü-Wagen with Carmen Thomas, when the topic 'Urine, a very special juice` enthused the population in NRW in 1988. In the wake of the broadcast, a book was even written that became a bestseller. Since then, the body's own juice has been perceived differently in society, and science and research continue to discover new advantages of the humanoid body fluid to this day.

At Bergische Universität, chemist Prof. Dr. Hans-Willi Kling, who heads the Department of Management of Chemical Processes in Industry and Analytical Chemistry, is familiar with the advantages but also disadvantages of human excretion. Undisputed is the potential benefit of urine, because "what we excrete is basically nutrient for the rest, i.e. we enter a kind of cycle," says the scientist. "What we excrete primarily in urine is urea, carbonic diamide you can call it, and that's something that can be broken down via bacteria. These bacteria are in the soil. They release ammonium nitrogen, and the plant can take up the ammonium nitrogen again, can synthesize the proteins from it. So the cycle is closed again." The resulting high-quality food can be consumed or fed to livestock, he said. Meat products from livestock fed in this way would then be available to humans again.

The gardener's gold water is not always us able Urine was often used in earlier times. It was used for fertilizing, tanning leather, making gunpowder or gargling for sore throats. It is contained in ointments and is also a component of adhesives. Gardeners even speak of "gold water". This makes urine the predestined sustainability substance. "The urea is the actual thing we excrete," Kling explains, "such urine can certainly be used sustainably. People used to like to gargle because, if I'm healthy, the urine is actually germ-free." In wound treatment, people used it to wash out germs because it wasn't so taboo socially. "Today, people use what's called urea, and we find that in cosmetics under the Latin term urea. It soothes the skin." But our own bodily fluids can also carry disadvantages, because the excretion of urea also means the excretion of possible toxins that are not metabolized, i.e., broken down by our own body, and thus leave the body unfiltered, the chemist explains. These substances include, above all, drugs. "This is a problem at the moment when people have to take a relatively large number of drugs, or are permanently medicated. We then also find these drugs as such in their excretions, and they don't really belong in nature, especially if they are not easily degradable, because they disrupt the natural cycle."

Fertilizing ... but properly

Urine is used intensively in agriculture. Slurry or manure, also known as biological fertilizer, helps to produce good harvests if done correctly. "The thing you have to be careful of, of course, is that such large amounts of nitrogen, for example, are not washed by rain directly into the nearest bodies of water," Kling explains. "In the past, manure was simply spread directly on the ground, but today that urine is put directly into the ground through slot nozzles on agricultural machinery. That way, when the next downpour comes, it's not discharged into surface water, because there it does exactly the same thing it does in the field, it fertilizes." This unwanted addition of water nitrogen inevitably leads to eutrophication (accumulation of nutrients in an ecosystem, editor's note), the pond becomes overgrown, the oxygen is reduced and the water body tips over. This experience was made in the 60s and 70s of the last century.

The advantage of this natural fertilizer is obvious to Kling: "It is biological fertilizer. I'm not attacking other resources, but rather I'm returning what belongs back into the cycle in a concentrated way." On the island of Gotland in Sweden, which has major wastewater problems, there is an interesting project that collects up to 70,000 liters of urine from urinals over a three-year period during the peak tourist vacation period and uses a special process to produce dried pellets from it as fertilizer. The scientist sees the advantage of this project primarily in the consistency of the fertilizer. "These pellets are much easier to handle than large quantities of urine solution. When I dry something like this, it's not subject to decay. I can store and apply it better."

New wastewater treatment plants are what the country needs ...

A wastewater separation process of urine is already being done in some countries. In the Netherlands, there are waterless urinals connected to the sewage treatment plant in the basement, and in a Paris eco-district, they have already installed separation toilets. Biologists repeatedly highlight the importance of our excreta in terms of nutrient richness and industrial usability, even estimating that humans produce enough urine to replace a quarter of the world's current nitrogen and phosphorus fertilizers. And yet, despite such a clear sustainability argument, no one really picks it up. Kling knows why: "That would mean a complete redesign of our wastewater systems. Here in Wuppertal, we are already relatively far along with the Barmer separation system; we process rainwater and wastewater separately," he explains. "The rainwater is then fed to the surface waters and only my wastewater is treated and purified accordingly biologically in the wastewater treatment plant." Further separation of our excreta would then have to be installed directly at the consumer through a third pipe. "That's a huge expense and would mean that everything we have now as infrastructure would have to be rebuilt accordingly, because the input to the treatment plant now just changes completely. And that, in turn, would be an investment of somewhat greater expense, to say the very, very least."

How do you market a taboo subject?

Our excretions are a socially taboo subject, often associated with disgust. But in order to actually be able to use urine, a change in thinking about human hygiene is needed, biologists demand, because if consumers don't accept the product, you can't market it. "I think it's just related to the head," Kling says spontaneously, "we accept that I apply manure and slurry as biofertilizer. But where is the big difference between a cow's urine and humanoid urine? From my point of view as a chemist, it's marginal. It is simply an ethical head problem. One accepts that the plant has been fertilized with biofertilizer and even pays more for it. But the moment there's also human excrement in there, it starts to get disgusting or objectionable, and your appetite does start to wane."

Urine express in times of climate change?

Urine recycling methods are important because global resources are running out. The mineral phosphorus in the process is a component of fertilizer, and is ingested and excreted by humans with their food. Local wastewater treatment plants use a lot of water. In Switzerland, the Urine Express, a urine treatment plant on wheels, was developed. In the Urine Express, a biological process produces fertilizer for lawns, gardens, parks or vegetables. Fertilizer from pee thus makes a valuable contribution to the environment and, in the wake of climate change, could be an alternative for a sustainable industry. "That's where another element plays an important role now in addition to nitrogen, namely phosphorus," Kling explains. "Nitrogen is actually available to us in almost unlimited quantities. It's a very different story with phosphorus." He says agriculture is currently happy to work with artificial fertilizers, the essential component of which, in addition to nitrogen, is the element phosphorus, which humans urgently need. "Our bones and teeth need phosphates, but unfortunately the naturally occurring resources are very, very finite." He said that this has already put politicians on the map, and that research is already being actively conducted on topics such as phosphorus recycling from sewage treatment plants. Phosphorus is found in sewage sludge and processes are now needed to extract it again and make it available again biologically, the chemist knows. "This is still difficult, because sewage sludge is still treated as a waste product in the purification of water and is usually incinerated. The phosphorus is in the sludge, but not in a form that makes it available to the plant. Thus, I am pulling phosphorus out of that cycle." So the question is how to get the large amounts of phosphorus out of sewage sludge, he says. Kling knows of sewage treatment plants that are already storing their sludge because its phosphate content is so high that incineration would be tantamount to destroying urgently needed raw materials. "There are processes in place," he explains, "and we are also involved with an external partner. It's not all that simple; the devil is in the details, even with this research. These are new technologies, you have to develop them, test them and then be willing to introduce such technologies!" Global food production is directly dependent on phosphorus. But this important plant nutrient is increasingly being lost from soils. The main cause is soil erosion. Africa, Eastern Europe and South America cannot replace this loss with mineral fertilization. "Most of our wastewater is treated and so I would then have the opportunity to reintroduce phosphorus through the sewage sludge. I think the key is to look at what is waste right now as a valuable resource in the future and think about how to generate recyclables from that waste again to completely close those loops."

Fertilizer ordinance prohibits use of human excreta

In Germany, many things are regulated by law. Therefore, there is also a so-called Fertilizer Ordinance (DüMV), which prescribes how fertilizer is used on German fields. Human excrement and urine are prohibited there, even in compostable form. What stands in the way of the use of fertilizers of human origin is the problem that the excrement also contains germs, pathogens, drug residues and hormones, and these must not get into the soil. Although there is already a risk analysis by the German Institute for Standardization, Kling knows, according to which there are technically mature processes that eliminate possible pathogens, the road to implementation will be a long one. In any case, the ecological potential is high. Composting, which tends to close the material cycle again, seems to be more effective today than the route via the sewage treatment plant. A three-year field trial by the Brandenburg-based company finizio will present initial results this year.

Closing material cycles is the be-all and end-all

"As a rich industrialized country, we are certainly in a position to work with appropriate artificial fertilizers. We can afford it," Kling states, while pointing out that this strategy is finite, however. "The thing we can't afford in the long run is the way we do it. We have to become more sustainable and work up thoughts like closing material cycles more intensively." He said everything is always looked at from an economic perspective, but more weight needs to be given to the idea of sustainability. "If you look at the soils in our country or even in Europe today, we see that we naturally have to fertilize with intensive agriculture. The number of people who need to be fed is constantly growing, but our land is not increasing. Therefore, I have to generate more per hectare." Climate change is doing its part, he said, and we are experiencing that firsthand. Dry summers, forest dieback and our water resources are not endless here in the Bergisches, he said. "We do have our streams everywhere, after all that was the source of the Bergisch industry, but that won't remain permanently so in the future. There are large areas of land that will then erode and have problems."

In 1622, the playwright Jean-Baptiste Poquelin, alias Molière, was born in Paris. In his works, he always described people's weaknesses and vices in a humorous and critical way. One of his comments has lost none of its relevance even in times of climate change and the associated sustainability debate: "We are responsible not only for what we do, but also for what we don't do." Nothing has changed in this regard, even after 400 years.

Uwe Blass

Prof. Dr. Hans-Willi Kling studied at the Ruhr University in Bochum and earned his doctorate at Bergische University. He held various positions in the private sector, he taught at the Bergische Universität from 2003 in parallel to his industrial activities and in 2010 followed the call to the chair "Management of Chemical Processes in Industry". In 2012, the merger with "Analytical Chemistry" followed under his leadership.