The future connection between human waste, sanitary engineering and sustainable agriculture is becoming increasingly clear. According to a study by University of Illinois Urbana-Champaign professor of civil and environmental engineering, Jeremy Guest, countries could move closer to using human waste as fertilizer and closing the loop towards circular, sustainable economies.
A new study characterizes the spatial distribution of nutrients from human urine – nitrogen, phosphorus and potassium – and the need for agricultural fertilizers in order to define supply-demand location typologies, their worldwide distribution and the impact on resource reclamation. The results are published in the journal Environmental Science and Technology.
“The total amount of nitrogen, phosphorus and potassium in our bodies remains largely constant once we stop growing,” said Guest, who is also the deputy director of research at the US Institute for Sustainability, Energy and the Environment. by I. “Whatever comes in through food and drink, has to be excreted in our urine, feces and sweat. Knowing this, we can estimate how much of each of these nutrients is in a population’s excretions if we know their diet. “
Previous studies by Guest and others have assessed the potential for nutrient recovery from human waste around the world and identified locations with excess nutrients from human waste relative to local agricultural fertilizer needs.
“The new study is the first to describe the relationship between nutrient supply and demand from human waste using a single mathematical equation,” said Guest. “The quality of sanitary infrastructure varies widely around the world, as does the way people are fed and the availability of land that is suitable for agriculture. The ability to characterize and quantitatively compare the nutrient recovery potential of a site can do a lot to better inform decision-makers about future wastewater and agricultural policy. “
The team performed extensive numerical and geographic analyzes of nutrition, population, hygiene, and agricultural data from 107 countries to achieve this quantitative characterization on a global scale. The research revealed three different supply-demand typologies: countries with a common supply-demand; Countries with a displaced demand for supply; and countries with different supply-demand proximity.
The United States and Australia, for example, fall under the shifted supply-demand typology. They have intensive agriculture in areas far from major cities, so nutrient supplies from human waste are far from where they are needed, Guest said. Even with an advanced sanitary infrastructure, this means that nutrients would have to be transported long distances, either as heavy liquids or converted into concentrated crystalline products. In economic terms, says Guest, it makes sense to work with a concentrated product in order to implement a fertilizer made from human waste in these countries.
The study reports that in countries with similar supply-demand typologies such as India, Nigeria, and Uganda, the human population is significantly close to agricultural land, which enables local reuse. In many communities with simultaneous supply and demand, however, there is a need for improved sanitary infrastructure. Guest said implementing a human waste fertilization program for sanitation and agriculture in these locations could be of great benefit.
Countries like Brazil, Mexico, China and Russia show a continuum from co-location to displacement of nutrient supply and demand. The study reports that policymakers need to address the use of nutrients from human waste with more regionalized strategies and a range of local reuse and transport approaches. “Higher income countries in this group may have the infrastructure and economic support for various technologies, but those with limited financial resources need to prioritize some areas of resource recovery technology,” Guest said.
The team was surprised to find that the typologies closely matched the United Nations Human Development Index.
“Countries with a higher HDI value such as the USA, Western Europe and Australia tend to fall into the shifted supply-demand typology, and countries with a lower HDI value tend to fit the same-place supply-demand typology. Of course there are exceptions, but we didn’t expect to find such a strong correlation, ”said Guest.
The team hopes this research will help clarify the salient economic, sanitary, and agricultural characteristics of countries around the world so that decision-makers can prioritize investments, policies, and technologies that meet the goals of a circular economy and the provision of sanitation for bring everyone forward, guest said.
Relation: Echevarria D, Trimmer JT, Cusick RD, Guest JS. Define nutrient colocation typologies for human supply and harvest demand to drive resource extraction. Environment Sci Technol. 2021; 55 (15): 10704-10713. do: 10.1021 / acs.est.1c01389
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