Our directory of things of interest

University Directory

How human waste could power global agriculture

Urban wastewater treatment plants – a future source of fertilisers? Urban wastewater treatment plants – a future source of fertilisers? (Image: Plantic)
17 Oct
New research measures the ability of major cities to re-use critical nutrients found in wastewater

Keeping our supermarket shelves packed with food requires an industrial production process that is heavily dependent on a regular supply of nutrients such as phosphorous and potassium fertilisers, as well as energy-demanding nitrogen fixing.

At the same time the agriculture industry is spending money to ensure it is able to maintain sufficient fertility in soil, the world’s cities are disposing of vast quantities of these same nutrients every time they are flushed away as part of urban wastewater.

‘We grow our crops in the field, apply nutrient-rich fertilisers, eat the crops, excrete all of the nitrogen, phosphorus and potassium and then those nutrients end up at the wastewater treatment plant,’ says Jeremy Guest, an assistant professor in the Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign (UIUC). ‘It is a very linear, one-directional flow of resources. Engineering a more circular nutrient cycle would create opportunities that could benefit the environment, economies and agriculture.’

romeRome is being seen as the city best placed to recycle nutrients from wastewater into food production (Image: Catarina Belova)

Guest and fellow researchers at UIUC analysed 56 major cities around the world to determine the feasibility of recycling these nutrients back into food production, based on the proximity of agricultural land to the urban centres where the food is then consumed. Of those analysed, Rome emerged as the best placed city to benefit from human-derived nutrients, while Los Angeles, New York and Boston were the three where this strategy was deemed least effective given the sprawling distances that would need to be overcome.

They also calculated that, overall, Asian cities would be best prepared to recover nutrients from city wastewater than those on any other continent, followed by Europe and Africa. The vast distances in Oceania mean this is the part of the world where the technique would be most difficult to implement.

‘Because this was developed as a global analysis, the method does not allow us to examine specifics for each city, such as the driving routes that would be required to haul nutrients or the locations of wastewater plants,’ continues Guest. ‘The results of this exercise should be taken as estimates of nutrient transport distances and are useful for identifying broad trends and locations that may warrant further investigation into reuse strategies.’

guest trimmerJeremy Guest (left) and John Trimmer (right) evaluated the feasibility of using human-derived waste as a safe and valuable nutrient commodity (Image: L. Brian Stauffer)

Lead author of the study, UIUC’s John Trimmer, points to a few examples of the technology required for the safe extraction of nutrients from wastewater, such as Ostara, a company that recovers nitrogen and phosphorus as a compound called ‘struvite’, which is then sold as fertiliser.

‘Beyond the cities in which Ostara is currently operating, including Chicago and Madrid among others, and places where biosolids are already recovered, we are aware of several organisations working in countries such as Kenya, Uganda, Rwanda, and Ghana to recover resources from sanitation systems and develop successful business models,’ explains Trimmer. ‘These efforts can involve composting collected solids, growing black soldier fly larvae as animal feed, or other approaches.’

So, the next time you flush the toilet, think about where those nutrients might end up. They could be back with you before too long.

geo line break v3

Free eBooks - Geographical Newsletter

Get the best of Geographical delivered straight to your inbox by signing up to our weekly newsletter and get a free collection of eBooks!

geo line break v3

Related items

NEVER MISS A STORY - Follow Geographical on Social

Want to stay up to date with breaking Geographical stories? Join the thousands following us on Twitter, Facebook and Instagram and stay informed about the world.

More articles in PLACES...


While researching his main article on the world’s smallest countries,…


Vitali Vitaliev briefly meets the down-to-earth ruler of Liectenstein


In the third of his series on geopolitical oddities, Vitali…


Increased rainfall intensity, predicted to occur as the climate changes,…


Now in its fourth year, this annual lecture series highlights…


With Jakarta suffering from severe subsidence, pollution and congestion, Indonesia…


A revolution in digital mapmaking is underway and the implications…


India has pledged $120billion to make its cities ‘smart’. But…


Buildings made from wood are becoming increasingly common in cities…


The lead author of a scientific study, which claimed that…


A team of researchers in Australia are urging urban planners…


An artificial intelligence tool can predict where conflicts related to…


Hundreds of historic landfill sites are at risk from erosion…


London has officially become the first of a new kind…


A new model of the monsoon system, which dispenses with the Himalaya Mountains,…


In the second of his features on the world’s geopolitical…


The discovery a long ‘tongue’ of ice beneath a glacial…


Benjamin Hennig explains two cartograms which demonstrate the global water…


Get on your bike with this collection of stories to…