Human Urine Could Be Used As a Sustainable Fertilizer, Say Researchers

The global demand for fertilizers in agriculture is growing every day, making it necessary to reduce dependence on non-renewable sources. According to the Food and Agriculture Organization (FAO), the global demand for nitrogen as a fertilizer grows annually by 1%, which amounts to an increase of 1.074 million tons each year.

The production of these fertilizers relies heavily on non-renewable energy sources such as natural gas, oil, and coal, representing significant energy consumption and CO2 emissions.

This new study, led by the Sostenipra group of ICTA-UAB in collaboration with the GENOCOV group of the Department of Chemical, Biological, and Environmental Engineering, presents human urine nutrient recovery as a solution to transforming urban agriculture. The article, published in the scientific journal Resources, Conservation and Recycling, explains that the use of urine allows exploiting local resources and minimizes the use of external inputs, contributing to the sustainability of the agricultural process. Furthermore, it reduces dependence on limited resources and supports a more environmentally responsible cycle.

In this context, human urine or "yellow water" is a rich source of nutrients, particularly nitrogen, essential for agricultural production. In addition to its benefits as a fertilizer, it helps reduce greenhouse gas emissions and pollution from water sources such as rivers and aquifers.

To assess its feasibility, researchers tested the process in the bioclimatic building of ICTA-UAB, which houses a pilot plant for nitrogen recovery and a greenhouse integrated into the roof, where the impact of the recovered nitrogen on tomato crops is tested. The process begins in the underground plant, where urine from waterless male urinals is stored and directed to a specialized reactor. In this reactor, the urine is mixed with a base to regulate its acidity, while microorganisms transform the urea in the urine into nitrate, a form of nitrogen that plants can absorb more easily.

The nitrate produced in the reactor is then used to irrigate the hydroponic tomato crops in the greenhouse located on the building's rooftop. According to the study, one cubic meter of treated yellow water yields 7.5 kg of nitrogen, which would allow the cultivation of 2.4 tons of tomatoes outdoors.

Although this is still a laboratory-scale study, the results show that the environmental and economic impact would be reduced if urine recovery were carried out on a larger scale, by connecting all the urinals in the building to the nitrogen recovery reactor. Experimental work is still being conducted, such as the analysis of pharmaceutical compounds consumed by people and their potential appearance in crop tissues.

Reference: Maiza MV, Muñoz-Liesa J., Petit-Boix A, et al. Urine luck: Environmental assessment of yellow water management in buildings for urban agriculture. Res Cons Recy. 2025. doi: 10.1016/j.resconrec.2024.107985

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