Periodic Reporting for period 1 - CAFE (Circular Agri-Food Ecosystems: bringing nutrients back to the soil)
Période du rapport: 2022-10-01 au 2025-03-31
Agriculture requires a steady supply of fertilizers that notably contain nitrogen (N) and phosphorus (P), two elements that are necessary for the plants to grow. However, the fertilizer supply-chain is far from secured for France and Europe that synthesize half or more of its fertilizer from imported "natural" gas (meaning "fossil") and phosphate rocks. These notably come from Russia, the US, or Algeria, for the gas, and Morroco for the mined phosphate rocks. Beyond the geostrategic risks, phosphate is a finite resource which cannot be mined forever. Unfortunately, after we eat our food, the phosphorus we ingest is excreted in urine and feces, and half or more if it is eventually lost at sea after being flushed in toilets and leaving the sanitation system.
This linear and extractive system, together with current fertilizer application methods, has incurred great social and environmental costs around the world, leading to significant biodiversity loss, as well as a degradation of water and soil quality.
Source separation of organic matter and its recovery are likely to be critical for the long-term sustainability of the agri-food and waste-management systems in an increasingly urban world. Indeed, the transformation of kitchen or green waste and human excreta can provide invaluable resources such as compost, fertilizers, or energy and eventually remove the need for synthetic fertilizers entirely.
The aim of the project was thus to develop tools and scenarios to assess how, for any given territory, source-separation and fertilizer made from human excreta could bring the agri-food and sanitation systems on the path to circularity.
This linear and extractive system, together with current fertilizer application methods, has incurred great social and environmental costs around the world, leading to significant biodiversity loss, as well as a degradation of water and soil quality.
Source separation of organic matter and its recovery are likely to be critical for the long-term sustainability of the agri-food and waste-management systems in an increasingly urban world. Indeed, the transformation of kitchen or green waste and human excreta can provide invaluable resources such as compost, fertilizers, or energy and eventually remove the need for synthetic fertilizers entirely.
The aim of the project was thus to develop tools and scenarios to assess how, for any given territory, source-separation and fertilizer made from human excreta could bring the agri-food and sanitation systems on the path to circularity.
During this work, we showed that French sanitation leads to around 40 % loss of reactive nitrogen and phosphorus to the environment, with only 10 % of the nitrogen being recycled in agriculture and up to 50 % of the phosphorus, though in a polluted form, via wastewater sludge spreading. We also estimated what fraction of the fertilizer demand could be met by recovering human urine and feces. For France, we showed (manuscript, section 6.1.3) that almost all regions would be able to bring the nutrients back to agricultural parcels within less than 100 km. Given these distances, we confirmed that low-tech and resilient processes using stored urine and composted feces would have significantly lower environmental impacts compared to current sanitation and fertilizer production systems.
We also developed tools to assess the amount of nutrients excreted by human populations. We then coupled these results with new methods to assess the population that is present in an area over a given time period. This enabled us to assess the part of "urban metabolisms" associated to nutrients : how nutrients flow between rural areas and cities in food and sanitation systems. More precisely, we can analyze where nutrients are excreted (between residential, work, or touristic areas, for instance) and identify specific buildings that host many people and would thus be interesting to renovate to recover large amounts of nutrients to convert into fertilizer.
All these results were integrated into a decision-support tool that will be made publicly available online. The tool enables not only to run a diagnostic of a given area but also to explore scenarios for source separation and nutrient reuse in agriculture.
We also developed tools to assess the amount of nutrients excreted by human populations. We then coupled these results with new methods to assess the population that is present in an area over a given time period. This enabled us to assess the part of "urban metabolisms" associated to nutrients : how nutrients flow between rural areas and cities in food and sanitation systems. More precisely, we can analyze where nutrients are excreted (between residential, work, or touristic areas, for instance) and identify specific buildings that host many people and would thus be interesting to renovate to recover large amounts of nutrients to convert into fertilizer.
All these results were integrated into a decision-support tool that will be made publicly available online. The tool enables not only to run a diagnostic of a given area but also to explore scenarios for source separation and nutrient reuse in agriculture.
The calculation of deposits and potential benefits were instrumental to help municipalities and stakeholders work on exploratory projects (notably the Angers and Bordeaux metropolises). It also enabled us to supervise similar work on the Île-de-France region, for the Seine–Normandie water agency and at the scale of metropolitan France for the ADEME (French environmental agency). During the secondment, to make sure that these results and data are broadly available, I started working on a document directed at municipalities with the Institut Paris Region (formerly IAU). This document will summarize and add some additional references to the work that was presented during an event in the institute (replay available on the institute’s podcast), showing how source-separation can be integrated into and support existing territorial policies.
The project has shown that several value-chains for urine and feces-based fertilizer are clearly beneficial from an environmental perspective. To show that large-scale implementation can be successfully appropriated by the general public and the technical stakeholders in the long run, however, there is a need for institutional support to create several demonstrators at the neighborhood scale, and facilitate the reuse of the fertilizers. This step is necessary to bring about the supportive regulatory and standardization frameworks that can enable these new sanitation systems to become mainstream.
The project has shown that several value-chains for urine and feces-based fertilizer are clearly beneficial from an environmental perspective. To show that large-scale implementation can be successfully appropriated by the general public and the technical stakeholders in the long run, however, there is a need for institutional support to create several demonstrators at the neighborhood scale, and facilitate the reuse of the fertilizers. This step is necessary to bring about the supportive regulatory and standardization frameworks that can enable these new sanitation systems to become mainstream.