Urine shows promise as a fertilizer

Rich in nutrients, urine represents an interesting source of renewable fertilizer with a weak energy impact. Irstea researchers specializing in reusing wastewater in agriculture are working with Ecosec to better evaluate the risks and benefits of using urine as a fertilizer and to lay some scientific foundations for this currently underexploited field.

Urine contains a significant quantity of nitrogen: 80% of the total nitrogen we reject as human beings. This mineral element - or more precisely, its elimination - is one of the biggest items of energy consumption in wastewater treatment plants. Faced with this fact, a team from Ecosec (a company specializing in designing urine diverting toilets), in partnership with Irstea scientists from the G-EAU unit, had the idea of recovering urine collected in its toilets and using it as fertilizer. "Given the fact that recycling all the nitrogen found in human effluent would meet 30% of our global nitrogen fertilizer requirements1 and that manufacturing a ton of fertilizer currently requires an equivalent ton of oil, the idea of recovering nitrogen directly at the source from the output of diverting toilets and homes that could be equipped with them seems to be an obvious and relevant research avenue," explains Bruno Molle, researcher from the G-EAU unit.

A promising concept requiring further investigation

The next step was to confirm the feasibility of the approach and evaluate its effectiveness from a sanitary and agricultural perspective. To this end, Irstea researchers and Ecosec carried out two experiments2:

  • The first aims to evaluate and reduce the risk of contamination as much as possible. Although urine is naturally sterile and therefore contains no pathogens, the urine diverting system designed by Ecosec contains a phase in which there is contact between urine and fecal matter, which can lead to bacterial contamination.
  • The second aims to evaluate the fertilizing value of urine and the ground’s capacity to transfer nutrients found in urine to plants.

By the end of the study, the partners were able to confirm the relevance of the concept. The research revealed that storing the effluent for six months at room temperature was a suitable way of eliminating most pathogens. The results were also positive in terms of fertilizer assimilation in the ground and by plants as well as in terms of crop yields for lettuce fertilized with the urine.

 

Buoyed by these encouraging results, a new experiment has been launched in an organic vineyard near Montpellier. Its aim is to use various urine-based products (raw urine, precipitated urine) to fertilize the vines and compare the sanitary and agronomic impact in relation to traditional fertilizers. The challenge is to study more closely the speed of pathogen elimination with different effluent storage times, compare vine growth with different fertilizers, and assess the transfer of certain micropollutants (particularly pharmaceutical residues). Results are expected by the end of 2019 and the study will continue until the grapes are made into wine.

Could this concept be rolled out city-wide?

To evaluate the relevance of this concept within a more global context of recycling and the circular economy, Irstea researchers have joined the international Enlarge project3. Funded as part of the Sustainable Urbanization Global Initiative (SUGI) call for projects by the Belmont Forum4, this project aims to produce a decision support tool by analyzing production, storage, supply and consumption loops for the main resources: water, nutrients, energy. "Specifically, we need to create an equation to compare the quantity of urine potentially recoverable at the source using urine diverting toilets, with the water requirements of plants within the city and surrounding areas, such as green spaces and suburban agricultural areas. Our final aim is to evaluate the conditions in which this collection/recovery loop can be efficiently incorporated into a circular economy context across a city," concludes Bruno Molle.

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1- Source: FAO (Food and Agriculture Organization).
2- Funding: BPI France.
3- Enabling large-scale integration of technology hubs to enhance community resiliency via DDS in various urban food-water-energy nexuses. Partners: Delft University of Technology, Amsterdam Institute for Advanced Metropolitan Solutions, University of Central Florida, Institute for Sustainable Communities, Irstea, Ecosec, Ecofilae.
4- International group of funding agencies, focusing on research into the key challenges linked to global environmental changes.