Phosphate powers life as we know it; yet most of us flush it down the drain
Diammonium phosphate fertilizer contains rock that is mined in a limited number of places around the world. Shutterstock photo
Elemental phosphorus is too volatile to exist in nature.
Expose a pure sample to air, and it could easily burst into flames. But connect a few oxygen atoms in water, and phosphorus becomes phosphate, a substance so crucial to life on Earth that federal officials recently classified it as a critical mineral.
Phosphate helps grow strong bones and plant roots. It also is used in semiconductor manufacturing and as an additive in water, making it essential not only for food production, but the nation’s health and economic security.
The mineral’s production and distribution channels can also be disrupted, which is why the government now considers it a critical mineral.
“The designation means that this is a national priority,” said Matt Scholz, one of several Arizona State University scientists working to create a more sustainable domestic phosphorus supply.
Scholz manages the Sustainable Phosphorus Alliance, a unit of the Julie Ann Wrigley Global Futures Laboratory. The laboratory was created to work across disciplines and with industry partners to rapidly transform systems necessary for life.
Why is phosphate a critical mineral?
Sixty minerals are now designated as critical, including recognizable metals such as copper and lead, and lesser-known substances such as ytterbium (used in lighting and displays) and niobium (used to strengthen steel).
Many minerals on the list, including lithium, silicon and gallium, are used in energy production and advanced manufacturing.
Phosphate is one of the few primarily used in agriculture.
The mineral is a key ingredient in fertilizer, and it comes from a finite supply of rock that is only mined and refined in a handful of countries, some of which are in active trade disputes with the U.S.
Unlike some minerals on the list, phosphate is not particularly rare. There is enough in the ground to last hundreds of years or more, though the remaining supplies will be more difficult and expensive to mine.
Meanwhile, strong global demand and uncertain trade policies have increased fertilizer prices, straining American farmers that already rely on razor-thin profit margins to stay in business.
The U.S. Department of the Interior added phosphate to its critical minerals list in late November.
Too much phosphate can be bad
Scholz said the designation could streamline the process to mine domestic supplies in the short term. But he and his colleagues are looking for ways to recycle phosphate in the long term.
Scholz is a co-managing director of the Science and Technologies for Phosphorus Sustainability, or STEPS, Center, a National Science Foundation-funded effort that includes researchers from 11 institutions, including ASU.
The center wants to decrease reliance on mined phosphate and the environmental damage that occurs when phosphate is overapplied, running off fields and into lakes and rivers.
Excess phosphate can trigger explosive algae growth, which can suffocate fish and trigger toxic blooms. It also is a common pollutant in wastewater, expelled primarily in urine when we eat meats, beans, whole grains and other foods rich in phosphate.
Treatment facilities must remove this phosphate before water is discharged. It is collected in sludge, which is typically reapplied on farmland, burned or sent to a landfill for disposal.
Where should we capture this waste?
Treavor Boyer, a professor in the ASU School of Sustainable Engineering and the Built Environment, wonders if there is a better way. He is experimenting with ideas to capture the phosphate in urine, before it is mixed with other waste.
“It’s not necessarily realistic to do this waste recovery everywhere,” he said. “What you want to do is target high-density locations that would have some sort of payoff.”
He thinks offices, public buildings and high-rise apartments could be promising collection points.
Boyer, who also works with the Global Futures Laboratory’s Water Institute, is now modeling how much phosphate could be captured from bathrooms in schools across metro Phoenix and the kinds of fertilizer it could produce.
ASU is working to make this a reality
For now, profitability is a challenge because mined phosphate, despite recent price increases, is still relatively cheap.
“If you take a million people over a year, and you collect all of the phosphorus from their wastewater, it would still only be about $55,000 a year in revenue,” said Paul Westerhoff, a Regents Professor in the School of Sustainable Engineering and the Built Environment and co-deputy director of the STEPS Center.
There is more than $10 million of gold and silver in the same amount of wastewater, he added.
Westerhoff has spent years studying where phosphate accumulates locally as part of the Global Futures Laboratory’s Central Arizona-Phoenix Long-Term Ecological Research project. His findings underline why Boyer and others are developing technology that can capture multiple potentially valuable materials from waste.
Bruce Rittmann, director of the Biodesign Swette Center for Environmental Biotechnology and also a member of the Water Institute, works with bacteria that can digest farm animal waste, wastewater sludge and even food scraps to produce methane, which can be sold as natural gas.
In addition to capturing phosphate, he is working to pull carbon, nitrogen and even precious metals like gold from these streams.
“A lot of our research is making an economic appeal,” he said. “Not just that you are doing a good thing for the environment, but that there are enough complementary resources to generate revenue.”
Why this research matters
Research is the invisible hand that powers America’s progress. It unlocks discoveries and creates opportunity. It develops new technologies and new ways of doing things.
Learn more about ASU discoveries that are contributing to changing the world and making America the world’s leading economic power at researchmatters.asu.edu.
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