Phosphorus recycling from human excreta in French agroecosystems and potential for food self-sufficiency

Phosphorus (P) is an essential constituent of life but large P losses from agroecosystems and sanitation systems are a major source of eutrophication in water bodies.These losses are doubly detrimental as P in human excretions can be used for crop fertilization.Through a unique dataset of 20,000 French WasteWater Treatment Plants (WWTPs) operational measurements over two decades and a P mass balance, we assess the fate of human excretions and their agricultural potential.Despite 75% of French WWTPs sludge being spread on crops, only 50% of the excreted P makes it back to agroecosystems. This is among the highest rate in Western countries where assessments have been made.Meanwhile, another 35% of the excreted P ends up in surface waters or the environment through WWTP discharge, individual autonomous systems diffuse losses, and sewers leaks.The remaining 15% is incinerated or sent to landfills.Moreover, while WWTP removal efficiency increased in the 2000s, reaching an 80% national average, it has been followed by a decade of stagnation in every French basin.The final removal efficiency for each basin, from 65% to 85%, closely matches whether the area was defined as P-sensitive in the European directive.Our results suggest that recycling all P in excretions could help supply 7 to 34% of French food supply without changing the current food system.Reshaping agricultural systems (shifting to more plant-based diets, decreasing P losses and food waste) would enable to go even further on the road to food sufficiency

The nutrition/excretion system of urban areas : socioecological regimes and transitions

L’alimentation et l’excrétion constituent deux besoins physiologiques fondamentaux de tout être humain. En analysant leur matérialisation depuis l’échelle cellulaire jusqu’à celle des grands cycles biogéochimiques planétaires, nous proposons de considérer que l’alimentation et l’excrétion humaines participent d’un système dont les modalités de réalisations dans les différentes sociétés humaines permettent de caractériser des régimes socio-écologiques. Nous avons plus particulièrement analysé les systèmes alimentation/excrétion des territoires urbains au regard de leur soutenabilité et proposons une méthodologie de caractérisation fondée principalement sur l’analyse du flux de la substance qui nous paraît la plus pertinente, à savoir l’azote, et sur les modalités de gestion des urines humaines qui représentent près des trois quarts de ce flux. Nous montrons que les systèmes alimentation/excrétion des différentes communautés humaines présentent une très grande variété selon les lieux et époques considérés et proposons de les distinguer entre autres en fonction de leur circularité, c’est-à-dire par le taux de retour sur des sols agricoles des excrétats. En prenant l’agglomération parisienne comme cas d’étude, nous montrons que son système alimentation/excrétion a été de plus en plus circulaire au cours du XIXe siècle, culminant au tout début du XXe siècle aux alentours de 50 % de circularité, avant de se linéariser progressivement au cours du XXe siècle. En ce début de XXIe siècle, nous caractérisons le système alimentation/excrétion de l’agglomération parisienne comme non soutenable car linéaire à plus de 95 %, intensif, inefficace et polluant aux échelles locales et globales. Ces caractéristiques sont généralisées au sein du monde occidental et interpellent sur la possibilité d’une transition socio-écologique vers des systèmes alimentation/excrétion soutenables. Or, depuis les années quatre-vingt-dix, une prise de conscience relative à l’urine a réémergé, principalement en Suède puis dans l’Europe germanique. Elle s’est traduite par de nombreuses réalisations et recherches autour de la séparation à la source des urines. Nous montrons que ce dispositif est actuellement le seul, dans le monde occidental, à avoir permis de nouveau la mise en œuvre de systèmes alimentation/excrétion circulaires. Pouvant être déclinée sous de multiples formes en fonction des contextes, la séparation à la source des urines bénéficie, malgré le verrouillage socio-technique de l’agglomération parisienne autour du tout-à-l’égout, d’un contexte favorable à son développement. Nous avons élaboré un scénario prospectif explorant ainsi la possibilité que l’agglomération parisienne dépasse, en quelques décennies, l’extremum de circularité qu’elle avait connu à la Belle Époque et que les acteurs de ce territoire réalisent, en cohérence avec une transition socio-écologique des autres systèmes énergétiques, hydrauliques et de transport, un régime socio-écologique soutenable de leur système alimentation/excrétion. Cette thèse fait partie du programme de recherche et action OCAPI (www.leesu.fr/OCAPI)Nutrition and excretion are fundamental physiological needs for all human beings. Analysis of their materiality, from the cellular scale up to the great planetary-scale biogeochemical cycles, shows that nutrition and excretion form a system. The focus of our study is the sustainability of the nutrition/excretion systems of urban areas, which we have sought to assess by analysing substance flows. The most relevant of these substances seems to be nitrogen, so by assessing urban nitrogen flows we can characterise the different possible socioecological regimes and their sustainability. We identify a wide diversity of nutrition/excretion systems depending on the places and eras considered. We propose to distinguish them in terms of their circularity, in other words by the rate at which nitrogen from excreta returns to agricultural land. Using the Paris urban area as our case study, we show that its nutrition/excretion system became increasingly circular in the 19th century, reaching maximum circularity right at the start of the 20th century, before becoming steadily more linear in the course of the 20th century. In these early years of the 21st century, the nutrition/excretion system of the Paris urban area is essentially linear, and still generates significant pollution at both local and global scales. Its environmental footprint is exacerbated by a diet that is very protein rich, mostly animal in origin, and by the non-consumption of a significant proportion of the food produced. All these factors make it unsustainable. These characteristics are found throughout the Western world and raise questions about the possibility of a socioecological transition to sustainable systems of nutrition and excretion. Since the 1990s, initially in Sweden, followed by Nordic and German-speaking Europe, awareness has been growing of the role of urine. Urine is responsible for three-quarters of urban nitrogenous excretions and is a safe substance: following a period of storage, it can be used as agricultural fertiliser. This new awareness has been followed by extensive experimentation and research on urine source separation. We show that this is currently the only method in the Western world to have accomplished a return to circular systems of nutrition/excretion. Urine source separation can be done in multiple ways, depending on circumstances, and conditions in France are favourable to its development, despite the sociotechnical lock-in to mixed sewage management systems. In a forward-looking scenario, we therefore explore the possibility that the Paris urban area could return to, and within a few decades even surpass, the heights of circularity that it attained during the Belle Époque. In that case, alongside a socioecological transition in the other systems – water, energy, transport – the people of this territory could establish a sustainable regime for their system of nutrition/excretion. This thesis is part of the OCAPI research and action programme (www.leesu.fr/OCAPI

Table ronde "Surexploitation des ressources"

National audienc

Le système alimentation/excrétion des territoires urbains : régimes et transitions socio-écologiques.

Nutrition and excretion are fundamental physiological needs for all human beings. Analysis of their materiality, from the cellular scale up to the great planetary-scale biogeochemical cycles, shows that nutrition and excretion form a system. The focus of our study is the sustainability of the nutrition/excretion systems of urban areas, which we have sought to assess by analysing substance flows.The most relevant of these substances seems to be nitrogen, so by assessing urban nitrogen flows we can characterise the different possible socioecological regimes and their sustainability. We identify a wide diversity of nutrition/excretion systems depending on the places and eras considered. We propose to distinguish them in terms of their circularity, in other words by the rate at which nitrogen from excreta returns to agricultural land.Using the Paris urban area as our case study, we show that its nutrition/excretion system became increasingly circular in the 19th century, reaching maximum circularity right at the start of the 20th century, before becoming steadily more linear in the course of the 20th century. In these early years of the 21st century, the nutrition/excretion system of the Paris urban area is essentially linear, and still generates significant pollution at both local and global scales. Its environmental footprint is exacerbated by a diet that is very protein rich, mostly animal in origin, and by the non-consumption of a significant proportion of the food produced. All these factors make it unsustainable. These characteristics are found throughout the Western world and raise questions about the possibility of a socioecological transition to sustainable systems of nutrition and excretion. Since the 1990s, initially in Sweden, followed by Nordic and German-speaking Europe, awareness has been growing of the role of urine. Urine is responsible for three-quarters of urban nitrogenous excretions and is a safe substance: following a period of storage, it can be used as agricultural fertiliser. This new awareness has been followed by extensive experimentation and research on urine source separation. We show that this is currently the only method in the Western world to have accomplished a return to circular systems of nutrition/excretion.Urine source separation can be done in multiple ways, depending on circumstances, and conditions in France are favourable to its development, despite the sociotechnical lock-in to mixed sewage management systems. In a forward-looking scenario, we therefore explore the possibility that the Paris urban area could return to, and within a few decades even surpass, the heights of circularity that it attained during the Belle Époque. In that case, alongside a socioecological transition in the other systems – water, energy, transport – the people of this territory could establish a sustainable regime for their system of nutrition/excretion. This thesis is part of the OCAPI research and action programme (www.leesu.fr/OCAPI).L’alimentation et l’excrétion constituent deux besoins physiologiques fondamentaux de tout être humain. L’analyse de leur matérialité, depuis l’échelle cellulaire jusqu’à celle des grands cycles biogéochimiques planétaires, montre que l’alimentation et l’excrétion font système. Nous avons centré notre étude sur les systèmes alimentation/excrétion dans les territoires urbains et avons cherché à évaluer leur soutenabilité par des analyses de flux de substances. À cet effet, l’azote apparaît comme la substance la plus pertinente. L’évaluation des flux d’azote urbains nous permet ainsi de caractériser les divers régimes socio-écologiques possibles et leur soutenabilité. Nous mettons en évidence une grande diversité de systèmes alimentation/excrétion selon les lieux et les époques considérés. Nous proposons de les distinguer selon leur circularité, c’est-à-dire par le taux de retour sur des sols agricoles de l’azote des excrétats. En prenant l’agglomération parisienne comme cas d’étude, nous montrons que son système alimentation/excrétion a été de plus en plus circulaire au cours du XIXe siècle, jusqu’à un maximum de circularité au tout début du XXe siècle, avant qu’il ne se linéarise progressivement au cours du XXe siècle. En ce début de XXIe siècle, le système alimentation/excrétion de l’agglomération parisienne est essentiellement linéaire et encore relativement polluant aux échelles locales et globales. Son empreinte environnementale est exacerbée par un régime alimentaire très riche en protéines, majoritairement d’origine animale, et la non-consommation d’une part importante de la nourriture produite. Il n’apparaît donc pas soutenable. En outre, ces caractéristiques se retrouvent dans l’ensemble du monde occidental et interpellent sur la possibilité d’une transition socio-écologique vers des systèmes alimentation/excrétion soutenables. Or, depuis les années quatre-vingt-dix, une prise de conscience relative à l’urine a réémergé, principalement en Suède puis dans l’Europe scandinave et germanique. L’urine contient en effet les trois quarts des excrétions azotées urbaines et elle est salubre : après un simple stockage, elle peut être utilisée comme engrais agricole. Cette prise de conscience s’est traduite par de nombreuses réalisations et recherches autour de la séparation à la source des urines. Nous montrons que ce dispositif est actuellement le seul, dans le monde occidental, à avoir permis de nouveau la mise en œuvre de systèmes alimentation/excrétion circulaires. Pouvant être déclinée sous de multiples formes en fonction des contextes, la séparation à la source des urines bénéficie de conditions favorables à son développement, en dépit du verrouillage socio-technique autour du tout-à-l’égout. Dans un scénario prospectif, nous explorons ainsi la possibilité pour l’agglomération parisienne de retrouver, et même de dépasser en quelques décennies, l’extremum de circularité qu’elle avait connu à la Belle Époque. Les acteurs de ce territoire pourraient alors parvenir, en cohérence avec une transition socio-écologique des autres systèmes énergie, eau et transport, à un régime soutenable de leur système alimentation/excrétion.Cette thèse fait partie du programme de recherche et action OCAPI (www.leesu.fr/OCAPI

Cycle de l'azote dans les systèmes alimentation/excrétion : potentiel des excréments humains utilisés comme engrais

International audienceNitrogen (N) in human excretions (urine and feces) is currently treated as a waste and a source of pollution. For the past decades, in the cities of the global North, the adopted solution has been to neutralize nitrogen in wastewater treatment plants (WWTP), especially through denitrification, and to release it in its inert form (N2) in the atmosphere. Yet from a nutrient cycling viewpoint, this is a loss of a valuable resource, especially in a context where N fertilizers are currently obtained through the Haber-Bosch process.Using WWTP operational data, we show that N abatement rate in French WWTP increased in the 2000s but has stagnated since the 2010s, releasing about 1/3 of the incoming pollution in the waters. Only about 10% is recycled as fertilizers in the form of sludge spread on crops. The remaining N is mostly denitrified to the air.L'azote (N) contenu dans les excrétions humaines (urine et fèces) est actuellement traité comme un déchet et une source de pollution. Au cours des dernières décennies, dans les villes Occidentales, la solution adoptée a été de neutraliser l'azote dans les stations d'épuration des eaux usées (STEP), notamment par dénitrification, et de le libérer sous sa forme inerte (N2) dans l'atmosphère. Pourtant, du point de vue du cycle des nutriments, il s'agit d'une perte d'une ressource précieuse, en particulier dans un contexte où les engrais azotés sont actuellement obtenus par le procédé Haber-Bosch.En utilisant des données opérationnelles de STEP, nous montrons que le taux d'abattement de l'azote dans les stations d'épuration françaises a augmenté dans les années 2000 mais stagne depuis les années 2010, rejetant environ 1/3 de la pollution entrante dans les eaux. Seuls 10% environ sont recyclés en engrais sous forme de boues épandues sur les cultures. épandues sur les cultures. L'azote restant est principalement dénitrifié vers l'air

Past and Future Trajectories of Human Excreta Management Systems: Paris in the Nineteenth to Twenty-First Centuries

International audienceThis chapter addresses the fate of nutrients in agro-food systems after their ingestion by humans. Depending on how human urine and faeces are managed, they can become a source of pollution to the environment, or they can be used as a resource, notably as fertilisers, thus contributing to closing the loop of nutrients. Taking the city of Paris as a case study from the nineteenth to the twenty-first century, we analyse the fate of human excreta through the evaluation of corresponding nitrogen and phosphorus mass flows. We put forward two major phases concerning the management of human excreta : 1. The circularisation phase (1800s to 1900s): human excreta management is characterised by increasing circularity which peaks in the 1900s with around 50% of human excreta nutrients being recycled. 2. The linearisation phase (1900s–today): human excreta management is characterised by increasing linearity, i.e. a decrease in recycling rates of nutrients. Generalisation and improvement of wastewater treatment have led to decreasing pollution but also confirm the linearisation process (e.g. 5% recycling of human excreta nitrogen). This increase in linearity came together with increased dependency of agro-systems on fossil resources. Ongoing climate change is also putting the current system under pressure since the dilution capacity of the Seine River is decreasing, while the population of Paris is increasing. We therefore analyse three scenarios of future human excreta management (incineration, end-of-pipe recycling and source separation) and show that source separation of human excreta may offer the perspective of a sustainable human excreta management system

Fate of nitrogen in French human excreta: current waste and agronomic opportunities for the future

International audienceNitrogen (N) is essential for plant growth and protein synthesis but global reactive N losses, mainly from food systems, induce strong environmental impacts. N losses after human excretion are often overlooked because, in Western societies, they partly occur as inert N2, following denitrification in wastewater treatment plants (WWTP), and losses in waters are often small compared to diffuse agricultural emissions. Yet N from human excretions could be used for crop fertilization, potentially with very high recycling rates via source separation. In this study we use unique operational data from the ∼20,000 French WWTPs to produce a N mass-balance of excretions in the French sanitation system. Even though 75 % of WWTPs' sludge is spread on crops, only 10 % of the excreted N is recycled and 50 % of N is lost to the atmosphere, mainly through WWTP nitrification-denitrification. The remaining 40 % ends up in water or in diffuse losses in the ground, of which about half is lost outside of the WWTPs' discharge system, through sewers storm water and individual autonomous systems. While WWTPs removal efficiency increased in the 2000s, it has been followed by a decade of stagnation, reaching 70 % at the national level. This national average hides regional discrepancies, from 60 to 85 % in the 6 French water agencies basins. These differences closely correlate with the classification as “N sensitive areas” and is mainly due to large WWTPs which handle most of the N load. Recycling all N in excretions could supply 10 % of domestic protein consumption in the current French food system, and up to 30 % if it is prioritized towards crop production for human consumption. Redesigning the food system (decrease of nutrient losses, more plant-based diets) could further increase this contribution

Phosphorus recycling from human excreta in French agroecosystems and potential for food self-sufficiency

Phosphorus (P) is an essential constituent of life but large P losses from agroecosystems and sanitation systems are a major source of eutrophication in water bodies.These losses are doubly detrimental as P in human excretions can be used for crop fertilization.Through a unique dataset of 20,000 French WasteWater Treatment Plants (WWTPs) operational measurements over two decades and a P mass balance, we assess the fate of human excretions and their agricultural potential.Despite 75% of French WWTPs sludge being spread on crops, only 50% of the excreted P makes it back to agroecosystems. This is among the highest rate in Western countries where assessments have been made.Meanwhile, another 35% of the excreted P ends up in surface waters or the environment through WWTP discharge, individual autonomous systems diffuse losses, and sewers leaks.The remaining 15% is incinerated or sent to landfills.Moreover, while WWTP removal efficiency increased in the 2000s, reaching an 80% national average, it has been followed by a decade of stagnation in every French basin.The final removal efficiency for each basin, from 65% to 85%, closely matches whether the area was defined as P-sensitive in the European directive.Our results suggest that recycling all P in excretions could help supply 7 to 34% of French food supply without changing the current food system.Reshaping agricultural systems (shifting to more plant-based diets, decreasing P losses and food waste) would enable to go even further on the road to food sufficiency

The Water Framework Directive’s “percentage of surface water bodies at good status” : unveiling the hidden side of a “hyperindicator”

International audienceThe Water Framework Directive (WFD) has provided the means of standardizing the way surface water bodies are monitored throughout the European Union (EU), using a common evaluation measure, the percentage of surface water bodies at good status, based largely on the structure and functioning of aquatic ecosystems. However, the evaluation of good status is based on the way the WFD is implemented, which differs in each country. In this article, we analyze how the WFD is implemented in France, how the water agencies divide up the water bodies, the areas covered by their monitoring networks, and the modalities of obtaining data to provide the EU with the percentage of water bodies at good status. This analysis reveals that it is this hyperindicator itself that is at stake, obtained by successively aggregating values measured in time and space, from the monitoring station to the River Basin District (RBD), reducing vast amounts of information to a single measure per RBD, while long-term monitoring of the major European rivers and their sedimentary budgets, which show improvements in certain quality aspects, are largely overlooked by the WFD. When drawing up the indicator, the agencies identify certain biases but not others. This raises the question of its use and relevance for managers and politicians, at both national and European level