Instant Genius - Why human urine may be our most untapped natural resource

Episode Date: July 19, 2026

While largely viewed as a toxic waste product with no practical use, our urine is actually rich in all manner of valuable nutrients that, with a little effort, can be extracted, recycled and converted into fertiliser for use on food crops, used to make building materials or even used to generate electricity. In this episode, we’re joined by Kai Udert, a researcher based at the Swiss Federal Institute for Aquatic Science and Technology, to talk about the many ways we could be putting our pee to better use. He tells us how our current systems of dealing with wastewater came into being, what happens to our urine once we flush it down the toilet, and talks us through some ways in which we may be able to make more use of this common, overlooked resource. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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Today, I'm talking to Kai Udett, a research from the Swiss Federal Institute of Aquatic Science and Technology, talking about something that most people keep private, urine, specifically how we can recycle it. Every time you go to the toilet, you could be flushing away a valuable resource. Historically, urine has been a highly valued commodity, used in everything from dyeing cloth and tanning leather to making gunpowder, and the Romans even used it to whiten their teeth,

though I really wouldn't advise trying that one at home. Today, though, urine is more often seen as a hazardous waste product that needs to be got rid of. Kai, however, is encouraging people to look at urine in a different way and recycle it into something more useful. Welcome to the show, Kai. Thank you for having me. Perhaps you could tell me what actually is urine recycling.

So urine contains a lot of nutrients that we actually need in agriculture. So it's nitrogen, it's potassium, it's phosphorus and sulfur and sulfur and subandar nutrients. And we excrete those nutrients because we took them up with the food and then we don't need them anymore and actually discharged them. And today we discharge them to the toilet, to the sewer system. But actually, they can be reused. They can be reused to produce food again. And why are people so interested in it? What can it be made into?

So we can produce a fertilizer. There are different kinds of fertilizer that can be produced. And there's actually quite a lot of research. And there are also some startup companies working on those different technologies. You could also make bricks, for example, out of urine. There were also some research studies on producing electricity from urine. So urine has a lot of possible applications actually some time ago. Before we had this really elaborated biotechnology of today, urine was also used to extract hormones

and to produce actually pharmaceuticals from human urine. So that's not something we really do anymore, though. No. It's probably not the easiest way to do things on scale, I've got to be honest. So one of the first things there you mentioned was fertilize. Where does our fertilizer at the moment actually come from? So we get the fertilizer. I mean, on one hand, for example, nitrogen.

Fertilizer is produced by the Harbour Bosch process. So we actually capture nitrogen from the air. So it's N2. N2 is actually transformed into ammonia and urea. And this is basically something which is produced with a lot of energy in large factories and then it's actually transported from other countries or maybe also produced in the own country.

In some way, it's a type of recycling, but it's a recycling over the atmosphere. So we actually capture the nitrogen from the atmosphere, produce a fertilizer from it, and then use it as a fertilizer, and then it actually goes back into the waters. Another nutrient is phosphorus, and phosphorus is actually mined today. So there are large resources, for example, in Morocco, also in the U.S., in China. There were some resources actually also be discovered in Norway. but it's a limited resource. So there were some estimates how long they will last.

Maybe it's not really the big issue about how long they last. It's more about what those minerals also contain. So quite often they also contain some heavy metals like cadmium and so on, which we really don't want to spread on our fields. And also there's some kind of dependency of foreign countries because we don't produce the phosphorus here, let's say in the UK or in the EU, we have to import them. And this is also on a global scale, this can also be an issue.

It certainly sounds like finding some kind of alternative way of getting these fertilizers is a great idea. How do you actually go about taking human waste and turning it into this fertilizer? So in the old times, I mean, the excreter were used as a fertilizer anyway. I mean, people might not really have understood, you know, what are the basics about fertilization? We know that since maybe 1850 that we have nitrogen phosphorus, but they knew, okay, the plants grow better if we recycle our excreter or animals excreter.

So this is something which has been done all over the world everywhere. And maybe about, let's say, 170 years ago, we installed on a large-scale sewer systems. And there it was about comfort and hygiene. In the beginning, it was really about comfort. Let's just wash away our excreter. let's not think about that they could also be used as fertiliser. So we actually forgot about that. And it was more about the comfort of having water-flushing toilets.

And then actually those nutrients were imported from South America, for example, ammonium nitrate, but also guano, which is a phosphorus mineral. And they were used, and this was actually cheaper than really established the nutrient recycling technologies based on human excretem. You've mentioned there that the sort of modern methods of, fertilizer took over because they are cheaper to run. Is that still the case? It's still the case. I mean, it's still cheaper. And I don't really understand completely how it works, but there are also some subsidies. I mean, it's also the whole supply chains. I mean, this is all actually established for

these modern fertilizers, as we know there. It's not done for human excreter or wastewater. So this is what we need to do. We use to recycle sewage sludge. There are some countries where sewage sluts is still recycled France, for example. Switzerland is forbidden. We are not allowed to do that anymore because there are some concerns about pollutants. It could be heavy metals. It could also be micropollutants, which we don't want to spread on our fields. Now we also know that PFAS, for example, were spread on the fields by recycling sewage sludge. But this also has to do with the fact that wastewater today, this is a mixture. of a lot of different waste.

So actually the valuable fertilizers that we have, that we excrete with urine and partly also with feces, I mean, this is now mixed with a lot of pollutants, and this makes it difficult to extract those nutrients, actually from the wastewater. And, you know, this is actually the beginning of the whole story why we really focus on urine. We think, hey, let's not mix urine with the remaining wastewater.

Let's capture it as early as possible, as close to the source, that we can actually extract of the nutrients. of the nutrients and produce a fertilizer. That's actually a really good question. How, if we were to do, you know, sort of some kind of large-scale urine recycling, how would you collect it?

Because at the moment, we're just flushing it down the drain with all the other things we flush down the drain. Yeah. So, I mean, we started the user interface how it's called or we can also call it the front end, you know, when it comes to sanitation technologies. Basically, it's the urinal, it's a special, urine, so separating toilets. So we can separate the urine already at the toilet. And I mean,

there are waterless urinals. There you don't even have the dilution. We have the urine separating toilets where we have some toilets with no flushing water, some other toilets with flushing water, and the toilets with flushing water also provide the same comfort as we are used to. But this is the easiest way, as close as possible to the source. And that means to the human beings, we actually collect and separate the urine from the remaining wastewater. And I can imagine there's some places in the world where making those kinds of changes is a lot easier. You know, sort of here in the UK, the idea of trying to install those toilets everywhere is

a bit mind-boggling. But is there places where you're targeting where this is a bit more of a sort of viable option? I think we can also do it here in Europe. I mean, there are new buildings which are constructed. You can install this, for example, additional drainage lines. that we need to collect the urine, those piping systems. But, you know, on the other hand, when I think about when the water-flushed sanitation system,

as we know it today, was installed, I mean, London was already a major city with a lot of buildings, Paris as well. A lot of cities worldwide were already built to a large extent. It was still possible to actually introduce water-flushing systems. I think this was even a bigger change than what we would have to do today. So I think on one hand, I mean, the easiest way is to really install it in new buildings, also here, but also maybe in low and middle income countries. But I also think there are technologies, there will be technologies to retrofit existing buildings as well. You've covered this a bit, but is there any reason why your recycling isn't involved at the moment?

What's the main sort of resistances that people have to this? There are a lot of different resistances. You know, maybe one of the first points the people mention is that, you know, maybe the population doesn't want to have urine-derived fertilizers. And there are actually quite a lot of studies on that. And they say, most of the people say, why not? But I want to make sure that this fertilizer is safe. So I don't want to have any pathogens in there. And I also don't want to have any pharmaceutical residues in it.

And it shouldn't smell. You know, I mean, these are the things. So if you can make sure it doesn't smell, there are no pharmaceuticals, no pathogens in there. people are actually happy with it. And if we are, on the other hand, it's also animal waste is also used. And in the end, it can also be smelly. It definitely can also contain pathogens and pharmaceuticals. So it's not such a big difference.

Maybe the real reasons why it's hard to introduce urine separation on a large scale is that the current sanitation system as we know it, so the wastewater management, as we know it, it's a really established technology. So we have the sewers, we have the industries, we also have the administrative setups to actually manage the wastewater as we know it. And I think one of the big issues is that wastewater management, so that means the sanitation system of today starts at the house. And now then we get to the street, we get to the sewers, we have the wastewater treatment plants,

and actually an architect doesn't care at all about wastewater. Now when it comes to urine separation, we have to enter the house with sanitation. So it's a new, totally new approach to sanitation. So suddenly the architect doesn't have to think only about piping, but also, hey, where do I actually install the system to recover the nutrients from urine? Or maybe the tanks to collect the urine. So this is like a new approach of constructing buildings. Then we need the fertilizer industry, which can actually deal with urine-derived fertilizers.

And then on the other hand, it's also the money that we need, to actually build those reactors. Think about photovoltaic. Photovoltaic was super expensive 10, 20, 30 years ago. Now it's actually cheap. And the same will be true for the urine treatment reactors as well. But in the beginning, the systems might still be expensive. So we need this learning curve so that the systems get cheaper.

And we also need the people, the companies, maybe also the funding agencies, and the investors that believe in the system and support the development of it. One thing I will say as someone who grew up in a rural area, fertiliser smells, regardless of where it's come from, I tend to find. Exactly true. In Toronto, every arrival is a statement, and nothing says it better than this. Cadillac Optic was the number one selling luxury EV in Canada for 2025.

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This sounds like a great thing that we could be doing with our urine and our wastewater. What currently happens to it? So the current wastewater system, in the beginning it was a lot about, aesthetics and hygiene. So actually the beginning was that we supplied water to the cities. There were actually issues about hygiene, aesthetics, and one of the reasons was the people, especially poor people were drinking the groundwater in the cities which was polluted. And there were cholera and some other really big issues with hygiene issues in the cities. And a lot of fresh water was provided to the cities. Now this water could

also be used to flush away the waste. So the waste would not be in the streets anymore, would not be collected, would not smell in the cities anymore. So let's just flush it away. And that was the beginning. And there were some researchers who said, you know, the buffer,

the carrying capacity of the receiving waters, of the rivers, of the lakes, of the ocean, this is high enough and strong enough actually to deal with this waste. And this was not true. So very soon, actually, those rivers were polluters, the lakes were polluted and for a really long time now we have been working on

reducing this pollution by actually building wastewater treatment plants at the end of those sewers before actually the water is discharged to the rivers and actually taking out the organic materials, the solids, the nitrogen, the phosphorus, today the pharmaceuticals, heavy metals, all those different compounds which are actually in the wastewater. And we want to prevent actually the pollution of the aquatic environment. But I think it's important to keep in mind the system was not installed in the beginning to really treat this waste,

but actually to convey it somewhere else, to put it into nature. It does sound like there's a lot of effort and presumably time and money being put into cleaning up the urine from our wastewater. So could this, in turn, if we recycled it more, would that help improve the environment as well? Definitely, because those nutrients are a problem in the receiving waters,

because we use them actually to fertilize and to produce food. But those nutrients can also fertilize algae in the ocean, in rivers, in lakes, and those algae shouldn't grow there. So we over-fertilize. It's the eutrification, as we know it. And eutrification is a big issue, because when those algae actually settle, they can consume oxygen. There will not be enough oxygen for fish and other animals in the water. Actually, the lakes and the ocean, they die. So there might be that zone. So we have to make sure that those nutrients are not actually reaching the receiving waters.

So by actually recovering nitrogen and phosphorus from the wastewater are actually not discharging nitrogen and phosphorus to the wastewater. We already helped the environment. And actually, this was at the beginning of the research that we do. So that's maybe 30 years ago. Some researchers here, Villeguya, Tovelas, and then some others, they thought about how can we further improve wastewater treatment. And there was one example like phosphate in laundry detergions, and that's even longer ago, where phosphate was banned in laundry detergents. And by this already, the quality, the water quality could be improved a lot.

So what's special about bending phosphatitis? in laundry detergents. It's a measure at the source. So we don't clean at the end of the pipe, but it's a measured source. And motivated by this success story, actually, there were some more thoughts about what other measures at the source could we take. And then the idea was, okay, let's take out the urine from the wastewater. And by this, we can already improve wastewater treatment. It sounds like there are potentially problematic things that are coming out in our urine. You've mentioned pharmaceuticals and heavy metals. Why are those such a danger to be then using those contaminants as fertilizer?

So heavy metals are actually not excreted with urine. So heavy metals might get into the wastewater by other sources, but actually urine doesn't contain a lot of heavy metals, except if they're, I don't know, dissolved from pipes or something else. But it can contain pharmaceuticals. So about two-thirds of the active ingredients, from pharmaceuticals are excreted with the urine. This can have some effects.

I mean, those are really potent chemicals, and we might not really understand all the possible effects those pharmaceuticals might actually have. So it is a danger. We know from artificial hormones that they have effects on fish. So this is one example of pharmaceuticals, but there are a lot of other pharmaceuticals. So there are some countries, including Switzerland,

that already started to remove pharmaceuticals from wastewater. So large wastewater treatment plants in Switzerland have to remove 80% of the pharmaceuticals. So there are 12 substances which they have to measure and they have to show that they remove 80% of those. Now, by actually removing urine from the wastewater, we already can make sure that those pharmaceuticals never end up in the aquatic environment. So they're already captured at the source. And then at the source, there can be some treatment. For example, we can absorb the pharmaceuticals and activate carbon. And then actually we are taking them out and they will not enter the environment.

They will not enter the fields with the fertilizer. So is the predominant problem there? It's the pharmaceuticals that are infecting the environment. Or is there also a problem with it, the fact that we've been using it on crops that are going to be used by humans? Yeah. So those pharmaceuticals are human pharmaceuticals, basically. and they might end up in our drinking water as well, or they might have some effects in the environment on animals, on plants.

Then we have the pesticides which are actually used in agriculture. But this is something else, which might also end up in the drinking water, but this doesn't have anything to do with the urine. One of the biggest reasons people are a bit reticent to do this, you mentioned, was hygiene concerns. How hygienic is this process and how do you make sure that everything's disinfected? So there are some people who claim that urine is sterile, which is not true. I mean, urine itself contains bacteria.

And then we should also think about how urine is collected. It's collected in urinals, it's collected in urine-separating toilets, and there's always some cross-contamination. So urine contains microorganisms, and those might be pathogens as well. So when we treat the urine, we have to make sure that those potential pathogens are actually killed or removed. in some way. There are different ways. One way, for example, is you can concentrate all those nutrients with distillation, and during distillation, the urine is actually heated to 80 to 90 degrees Celsius, and 80, 90 degrees Celsius is enough to actually kill those pathogens as well. So this is one way.

There are chemical methods. You can increase or really lower the pH value to kill microorganisms. you could also use some oxidative processes like ozone or something else. Although they're challenged because there are a lot of other organic substances in urine as well which consume those oxidants. It certainly sounds like this could potentially be a really important thing that we could be doing. But how much fertilizer can actually be produced in this way if we started converting all of our urine into fertilizer? I'm not completely sure because to make the exact calculation is not that easy. On one hand, we also use too much nutrients in agriculture as well.

So the question is, rather, how can we ensure that we actually reduce the fertilizer use in general? And then also how can we replace the remaining fertilizer with something which we produce anyway because we produce the nitrogen and phosphorus with the urine. And we don't have to produce nitrogen and phosphorus fertilizers by mining or with the Haber Bosch process. So, I mean, there's a bigger picture about replacing nutrients with urine. So fertilizer sounds like it's the sort of main focus of urine recycling at the moment. But there are other things that people are looking into potentially getting out of urine. What are some of those things?

So there were some studies on producing bricks. So urine can have a high pH value after urea. This is one of the components in urine is actually hydrolyzed and then you actually have bricks. urine has been used. You mentioned that, you know, by the Romans also, and not only by the Romans, also in the leather production, in some other. Also to produce soap as well, there are a lot of different ways how to do that. I think in the end, it's still the main focus I would stay are still the nutrients. And the reason for that is that we also have a huge nutrient problem.

world-wide. So when you think about the Earth boundaries, so we all talk about CO2 and climate change, but there are not so many people, but we should. We should talk also about the overload of the oceans with nitrogen and phosphorus. So this is one of the major points. And I think wastewater and agriculture, I mean, those are the sources for nitrogen and phosphorus. So we have to come up with some new approaches, how to manage those nutrients. Thank you for listening to this episode of Instant Genius, brought to you by the team behind BBC Science Focus. That was Kai Uded. If you like what you just heard, then please consider subscribing to Instant Genius on your preferred podcast platform.

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