Waste or resources? Another story of excrement

Source: French to English Tester   Published on: 2026-03-31

Source: The Conversation – France (in French)– By Fabien Esculier, Researcher, coordinator of the OCAPI action-research program at LEESU, National School of Bridges and Roads (ENPC)

Just a few decades ago, excrement – urine and fecal matter – was considered a vital source of fertilizer. They were replaced by fertilizers of fossil origin at the cost of significant environmental and health damage. Today, relegated to the rank of bulky waste, human excrement sees its precious nutrients mostly destroyed or discharged into rivers.

In thebook, which is published today by Actes Sud editions, researcher Fabien Esculier, from the École nationale des ponts et chaussées (ENPC), advocates for the rehabilitation of these materials and their reintegration into a form of circular economy. Below we reproduce an excerpt from his introduction.

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Human excretions have gradually been relegated to the rankcollective unthink. The main interaction we have with them is to hope to see them disappear as quickly as possible, to keep them as far away as possible from all our senses.

Almost no one talks about them or cares about what becomes of them… except for theyoung children, naturally very interested in these fascinating subjects! However, there are two major paradoxes here.

Firstly, we produce two precious resources daily, urine and feces, which are fundamentallyfood for the soil and for plantsFrom the point of view of the functioning of ecosystems, and therefore the support of human life on Earth, as well as from the perspective of prevention for human health, putting our excretions into water is probably among the worst options conceivable, deployed on a large scale only for a few decades.

Once exploited for their fertilizing power, today treated as waste

Humans must eat plants to live – or eat animals that have themselves eaten plants. Once it has been ingested, almost the entirety of the matter from our food ends up in our excretions (except mainly the carbon which is exhaled as carbon dioxide gas and then captured by plants in the atmosphere).

Soils and plants feed precisely on these excretions which, when used cautiously, can enable a true circular economy between the management of human excretions and the cultivation of food plants.

In recent human history, it seems rather difficult to find a society thathad not taken advantage of the fertilizing powerof our excretions. In doing so, the health risks associated with excretions are actually more likely to be better managed than if it is mainly about getting rid of them.

This is where the second major paradox appears. Although we stop thinking about it once the flush has been triggered,our excretions do not disappear for all that.

In fact, our society takes great care of it. From the people who change diapers, clean toilets, or unblock pipes, through the sewer workers, builders, and operators of treatment plants, up to thefarmers who spread sludge on their fields, the human waste management sector is a very important part of our economy. And yet very undervalued.

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Also to read:
Behind the contamination of the Seine waters, a global problem of fecal matter management

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Recreate a circular economy of excretions

It is not only about better managing our excretions but also about a shift in the way we value them.

Indeed, for several decades now, with the development ofsynthetic fertilizerderived from fossil resources and the gradual abandonment of the centuries-old practices of agricultural valorization of our excretions, the main result of this economy of human excretions mixed with water is a loss of food resilience.

It also leads to pollution of aquatic environments and a costly destruction of the natural fertilizer that is our excretions. Thus, in the sewage sludge spread on fields in France, there is not even 10% of the main fertilizing material of our excretions, namely nitrogen.

Yet France, as an agricultural nation, is almost the champion of the Western world in this area: other countries tend to hover around 5%, 2%, or often 0% of the valorization of thenitrogenous natural fertilizer from our excretions.

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Also to read:
How industrial agriculture disrupts the nitrogen cycle and jeopardizes the habitability of the Earth

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The largest “factory for the destruction of natural fertilizer” in France

It was by becoming interested in this second paradox that I gradually became passionate about our excretions. After a general engineering training at the École Polytechnique, I specialized in environmental engineering at the École Nationale des Ponts et Chaussées.

In 2007, my first engineering internship consisted of studying a phase of work on what I now call the largest “natural fertilizer destruction plant” in France, namely the Achères wastewater treatment plant (called Seine aval), which receives the excretions of about 5 million inhabitants of the Paris urban area.

Before this phase of work, the nitrogen from wastewater arriving at this station was mainly discharged into the Seine, which caused dramatic pollution of the river. It was then seen as a very great environmental progress to send the nitrogen from the wastewater into the atmosphere to protect the river.

For me, it was a major dissonant entry. The largest civil engineering project in Europe at the time, to which I contributed, was dedicated to building a plant that would use fossil resources to destroy natural nitrogen fertilizer.

The dilution rate of our excretions indeed prevents the implementation of recovery processes: 1.2 liters (l) of urine and 120 grams of fecal matter are mixed each day with approximately 25 l of flush water and 125 l of other domestic wastewater collected in the sewers.

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Also to read:
Recycled urine for future fertilizers

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Destroy the nitrogen in wastewater on one hand, import synthetic fertilizers on the other

At the scale of all of France, the solution that has been implemented over the past decades is therefore to destroy half of the nitrogen fertilizer in our wastewater, whilecontinuing to discharge about 40% of it into aquatic environments.

At the same time, France has long been completely dependent on imports of fossil resources to carry out the exact opposite reaction in nitrogen fertilizer synthesis plants. These reflections on my internship work led me to study how materials, molecules, and atoms circulate to meet our fundamental needs for food and waste elimination. Here is the journey.

We depend upstream on a petrochemical plant that synthesizes nitrogen fertilizers. In this plant, using a large amount of energy and fossil resources, atmospheric nitrogen is converted into nitrogen fertilizer available for plants.

These nitrogen atoms then travel from the factory to the field, from the field to the plant, from the plant to our mouth, from our mouth to our cells, and finally from our cells to our urine, which is the main way the human body excretes nitrogen. At this stage, the nitrogen is exactly in the same chemical form as it was when it left the nitrogen fertilizer synthesis factory, namely urea.

And its journey continues: from our urine to the toilet, from the toilet to the sewer, from the sewer to the treatment plant. And there, with roughly the same amount of energy consumed and the same amount of greenhouse gases emitted per unit of nitrogen, the nitrogen fertilizer from our excretions undergoes the exact opposite reaction of the petrochemical fertilizer plant: its dissipation into the atmosphere.

In 2007, while I was shocked by this linear, intensive, and polluting system, for most people I had spoken to, there was no problem. Fossil resources were unlimited, climate change was not very significant, pandemics were bad memories, peace in Europe was eternal, economic growth was going to resume, and water would always flow from the tap.

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Also to read:
The world is now in “water bankruptcy,” according to a UN report

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The Grand Paris project is incompatible with the current sanitation paradigm

For nearly twenty years, I have observed that these illusions have vanished one after another from the collective consciousness and from the reality of our lives. Tragically, of course, since this is a major upheaval of our societies that is underway. But there is still a (meager) consolation prize: more and more people are once again concerned with the material conditions of their existence. The air we breathe, the water we drink, the insects that pollinate our food plants… and our waste that could fertilize our fields!

At the end of my studies, I had the chance to enter the senior administration of the ministry in charge of sustainable development, becoming an engineer in the Corps des Ponts et Chaussées. The dream: the Grenelle Environment Forum was in full swing and I was going to be able to join the public service to implement this famous and much-needed ecological transition. The dream was short-lived: a few months after I started, our President of the Republic stated that the environment had “been enough already.”

After several professional experiences in administrations responsible for water and sanitation policies, the year 2013 marked a turning point in my career. The Île-de-France regional directorate of the Ministry in charge of Sustainable Development had just released a report explaining, in essence, that it was not possible to carry out the Grand Paris project while respecting the water quality objectives of the Seine downstream of the urban area.

Climate change was causing a gradual decrease in the flow of rivers, while the Grand Paris project was leading to a gradual increase in the population. The low flow of the Seine was already insufficient to dilute the treated wastewater of the urban area while ensuring good water quality. The situation was only going to get worse in the future.

An action-research program on the management of human urine and fecal matter

After I had contacted numerous organizations to find out how one could seriously respond to this deadlock, it was finally researchers who told me that, faced with a challenge of such complexity, the best method to approach the problem was to conduct research. After a year and a half of setup efforts, I finally succeeded, at the end of 2014, in launching theOCAPI action-research program, hosted at the Water, Environment and Urban Systems laboratory at the École Nationale des Ponts et Chaussées (ENPC).

I thus became a researcher, also adopting the stance of a “public policy intrapreneur,” trying as best I can from this position to empower the many collectives interested in this subject, primarily by sharing knowledge and trying to inspire atransformation of public and private action in the matter.

First French academic action-research program to focus on questioning the management methods of human urine and fecal matter from a systemic perspective, OCAPI experiencedfor ten yearsa development as significant as the growing awareness of the dead ends of this management approach, which involves extracting precious water only to pollute it with our waste, export it far from inhabited areas, and attempt to destroy these fertilizing materials that have become pollutants in aquatic environments and spreaders of health risks. The OCAPI program is particularly concerned with the so-called techniques ofsource separation, where urine and/or human fecal matter are collected separately to be used in agriculture, andwhich are currently being deployed in France. Onecall to action and proposals to change scalehave recently been written.

This book aims to share the story, often very little known, of the main stages that have brought us to this situation and to open up possibilities and imaginations towards sustainable futures.

The OCAPI program (www.leesu.fr/ocapi), coordinated by Fabien Esculier, receives public funding (Seine Normandy Water Agency, ADEME, ANR, FranceAgriMer, European Union, local authorities).

–ref. Waste or resources? Another history of excrement –https://theconversation.com/waste-or-resources-another-history-of-excrement-278218