From the field to the toilet and back again: The nutrient recovery revolution

The problem has dimensions like climate change – but hardly anyone talks about it: the nitrogen and phosphorus cycles are completely out of control. Science believes that the planetary limits have been exceeded as much as with global warming. (1) Nothing less than humanity's food resources are threatened. Nevertheless, the topic is in the blind spot. Maybe because it's about what we dispose of in the “quiet place”.

However, our excretions contain substances that are essential for survival and that every plant and animal needs. Nitrogen is essential to form proteins, hormones and enzymes. Without phosphorus there would be no seeds or bones; The passing on of genetic information also depends on it. However, toilets and sewage systems have interrupted the material cycles of fertilizing, harvesting, eating and excreting. This was only possible because chemical factories supply agriculture with artificial fertilizer. It's high time to shed light on the connections – and alternatives that have already been developed.

Whether salad, broccoli, steak or chocolate pudding from the bag: almost every food contains nitrogen and phosphorus. After passing through our bodies, these nutrients end up in the toilet and mix in the sewer system with industrial wastewater, microplastics from tire wear and other dirt. After many kilometers through the most expensive infrastructure in Germany, they reach a sewage treatment plant. Here the operators try to get the many substances out of the water again so that they can then be discharged safely into rivers.

Nitrogen and phosphorus cause the greatest effort. In the biological treatment stage, bacteria eliminate the two nutrients in a kind of whirlpool. This consumes an enormous amount of electricity and ultimately leads to nitrogen escaping into the air and the phosphorus being transported into the sewage sludge using metal shavings. However, because the modder also contains heavy metals and microplastics, it is hardly allowed into a field anymore and is mostly burned. The nutrients that came from the country to the city with the harvests no longer return there.

Dealing with our legacies in this way was only possible because factories have been producing artificial fertilizers for decades. But the production of nitrogen is extremely energy-intensive and, together with factory farming, has led to twice as much nitrogen today as there was a hundred years ago. Meadows, forests and rivers are over-fertilized and many animal and plant species have already become extinct as a result. Groundwater wells also had to be closed.

In contrast, the EU has now put phosphorus on the list of critical raw materials because it fears extreme supply bottlenecks. China and the USA are hoarding the material. A large proportion of the minerals obtained through mining that end up in German fields come from Western Sahara, which is occupied by Morocco. This is associated with human rights violations and environmental damage.

In order to reduce dependency on the world market, German sewage treatment plants will soon have to recover phosphorus. The Remondis group has maneuvered itself into pole position and is touting mono-incineration of sewage sludge as a solution. The process requires a lot of energy and chemicals, pollutes the climate and will further increase wastewater fees.

Drinking water to transport feces

In addition, there is another pressing problem. Every day, around 35 liters of our most important food – drinking water – rush through the toilet bowl per human bottom. In contrast, a person only needs around two liters to quench their thirst and cook. In Germany too, the days are over when people didn't have to worry about water supplies. As a result of the four drought summers since 2018, 500,000 hectares of forest have already died. In many places, especially in the east of the country, groundwater levels are falling and problems on farms are increasing.

However, instead of thinking about how we could save or reuse water, administrations are currently considering supplying Berlin with desalinated water from the Baltic Sea or tapping into the Elbe for this purpose. Again, an expensive and very energy-consuming technology is supposed to provide the solution. Questioning the toilet seems unthinkable: after all, it has the aura of being one of the outstanding achievements of modernity.

But things cannot continue like this in the long term. We have embarked on a path with water closets, sewers and artificial fertilizers that is creating an ever-growing tangle of problems. Humus content and the diversity of microorganisms in the soil are dwindling and with it their natural fertility and water-holding capacity – and at a time when droughts and floods are increasing due to climate change. To ensure that things continue to grow in the fields, artificial fertilizer is used. Both the production of nitrogen and its elimination in sewage treatment plants require an extremely large amount of electricity. In addition, drug residues from wastewater damage ecosystems worldwide. In addition, microplastics have long since returned to us via the food chain. The list could be continued, because global warming, water problems, disrupted nitrogen and phosphorus cycles and species extinction are closely linked and feed each other up.

The good news: Solutions can also reinforce each other if they don't concentrate on one point but rather approach the matter systemically. And there have actually been people working on a combined sanitation and nutrient transition for a long time. The movement is still under the radar of public perception.

Diverse solutions in the works

Pioneers build dry separation toilets and operate them at festivals and in public spaces, others research the soiling of faeces and their fertilizing power. They work on networked solutions, formulate legislative proposals and develop systems that also work in large residential complexes and settlements. The recently published book “Holy Shit – the value of our legacies” (the author of the article is the author of the book, editor's note) not only summarizes the current problems, but also introduces numerous people, projects and companies that work on fundamental changes.

Parallels to the early days of the renewable energy movement over 30 years ago are obvious: just like sun and wind, urine and feces are also available decentrally and free of charge. It is important to collect them, process them hygienically and put them back into circulation. The wastewater engineer Tove Larsen calculated decades ago that sewage treatment plants could be two-thirds smaller if the urine were discharged straight into the toilet. After all, it is our liquid excretions that carry most of the nitrogen and phosphorus into the sewage system. The idea that a good fertilizer could be made from it only came to her through discussions with other experts.

The Eawag Institute, which is responsible for water and wastewater in Switzerland, has been researching urine separation and treatment for over 25 years. The renowned sanitary company Laufen has now brought a toilet bowl onto the market that can hardly be distinguished from a toilet on the outside. It drains the urine undiluted at the front using the so-called teapot effect.

In Eawag's basement, a small company uses it to produce the urine fertilizer Aurin. A membrane filter ensures that medication residues are eliminated – a technology that will soon also be used in sewage treatment plants, but because of the volume of water generated there, it has to have huge dimensions and is correspondingly expensive. Aurin can be sold in Switzerland, but not yet in this country: human excretions are not yet on the list of permitted raw materials in German fertilizer law.

Eawag's goal is to develop solutions on a large scale. The necessary technologies exist and some new settlements are already being equipped with them. A research project is currently underway with the Indian metropolis of Bangalore, where there is already a lively trade in recycled water.

In Eberswalde, Brandenburg, Florian Augustin and his company Finizioden process feces from festival visitors into humus-rich soil. First, the excrement is sanitized using natural processes in a steel container at 75 degrees Celsius for a week, then composted together with straw and other additives for eight weeks. As part of a research project, the substrate then ends up in a grain field. Everything suggests that the depleted soil can be regenerated in this way in combination with urine fertilizer.

Ariane Krause, who was able to completely close the nutrient cycle between eating, excretion and fertilization in Tanzania, is also involved in the research project. She used all plant and kitchen waste as well as human excrement sanitized in an oven, processed some of it into biochar and was able to quadruple the harvest in the first year. The system closes the nitrogen and phosphorus cycles, revitalizes the soil and is able to keep yields permanently high.

Sanitation and nutrient transition belong together

However, the current infrastructure, economic interests, study and training courses, laws and control bodies are still stabilizing what has been established. Together they act like a concrete foundation for the development path once taken, which has become increasingly broader over time.

Without a doubt, a change in sanitation and nutrients will be even more difficult than the restructuring in the energy sector, because the social taboo also has to be overcome. But in the long term there is no way around it. After all, it's about nothing less than preserving the human food supply. That's why we have to start talking first – about urine and shit.(3)

About the author

Annette Jensen studied political science and German. She is a journalist, author of the book “Holy Shit” and one of the speakers for the Berlin Nutrition Council.