Human and livestock waste holds a wealth of untapped nutrients. Now, a team of researchers have analyzed precisely how much, finding that mining these nutrients from waste could meet all the nitrogen needs and half the phosphorus needs on US farms, amounting to billions in value and reducing the need for synthetic fertilizers.
To make use of this waste we’d have to grapple with “pronounced spatial misalignment” between where nutrients come from, and where they need to go—which is fixable through better coordination between farms, cities, and waste sectors, the researchers write in their Nature Sustainability study.
To explore the potential of this waste, they looked at the nutrient needs of 15 key crops that are farmed in the United States, and then paired this with data on the hotspots of human (feces and urine) and animal (manure) waste across the country. They also considered the nutrient levels that these waste products contained.
According to their results, we flush away and discard a surprising amount of nutrients: human and animal waste contains enough nutrients to meet 102% of nitrogen needs on US farms, and 50% of phosphorus demand. An economic evaluation of this wasted waste revealed that it is equivalent to $5.71 billion according to 2020 prices; adjusted for inflation that would be $7.19 billion today. Not only would this supply cut huge fertilizer costs for farmers, but it would also reduce reliance on the fossil fuel sources needed to make synthetic fertilizers.
As one study author noted, relying on existing nutrient supplies could in the future better insulate farming and protect food security from the effects of war, which can tighten the supply of fossil fuels and disrupt the trade routes required to make the synthetic versions.
But first the US—and other countries looking to follow suit—would need to resolve their own internal supply chain issues. Because as well as quantifying the abundance of nutrients contained within our waste, the study also exposed how disconnected this is from the need across the country.
For starters, a lot of the nutrient-rich waste is produced in cities, but it’s needed in rural places. What’s more, despite the abundance of nutrients available in waste, several places in the US are unable to access enough of the nutrients needed to farm: the researchers found that 26% of farming locations had less nutrient supply than demand.
Geographically, there could be some easy wins. The study found that roughly 37% and 46% of the waste-embodied nitrogen and phosphorus overall could be used locally. For instance, in parts of North Dakota, Iowa, Wisconsin, Indiana, and Montana a surplus of nutrients could easily be distributed to nearby farming regions, where there is actually a nutrient-deficit. About 61% and 56% of the nitrogen and phosphorus that’s left over after this allocation could also be redistributed in other parts of the country without too great a cost.
But this would still require coordination to get it where it’s needed—and it still leaves a chunk of the waste-embodied nutrients unused.
So what do the researchers suggest? They recommend starting locally, so that where it’s possible, waste gets processed close to its origin, and transported from there through distributed networks to local sites. Sharing out the nutrient-rich bounty across the country as a whole requires that farming, waste, and urban sectors be better connected with each other so they can distribute it more evenly.
In mapping out the problem and the potential, for now this study offers only the broadest of brush strokes. But considering the richness of our waste, the researchers say, “This is a coordination problem, not a resource problem.”
Liao et. al. “Realizing an equitable circular bionutrient economy in the United States.” Nature Sustainability. 2026.
Image: © Anthropocene Magazine
