Record-high prices for synthetic fertilizers are making manure a hot commodity.

With global food supplies under extreme pressure, fertilizer of any kind is critical to boosting yields and averting food scarcity. Animal manure is part of the solution, and its value has soared in recent weeks.

But as farmers seek additional ways to secure nutrients for crops, it’s time to consider an even more plentiful option outside of the pigsty: human waste.

For millennia, farmers utilized its potential. Now there’s so much more to be had. According to one recent study, human urine could meet 13.4% of the global demand for key agricultural nutrients. Extracting that nutrition will require changes in attitudes, infrastructure and even toilets. As synthetic fertilizer prices surge beyond the means of many farmers, it’s time to invest in the shift.

Humans realized that manure could boost crop yields at least 8,000 years ago. As human settlements evolved into villages and cities, sewage systems emerged to transport those nutrients back to fields. Diseases such as cholera were often transported with the untreated sludge.

Flush toilets and modern treatment systems eliminated most of the risk, but also deprived farmers of the nutrients they valued. Synthetic fertilizers filled the gap. By 2012, commercially produced synthetic fertilizers were responsible for between 40% and 60% of global food production, and were a key means of alleviating global hunger.

But nitrogen-based synthetic fertilizers are also responsible for 2.4% of global greenhouse gas emissions, according to one recent study. Those emissions are, in part, a consequence of the natural gas used in their production. When natural gas prices spike, as they have in the wake of the war in Ukraine, nitrogen fertilizer prices spike, too. That’s a problem for farmers; but for entrepreneurs and wastewater treatment specialists, it’s an historic investing opportunity.

Animal manure is the obvious substitute. But there are only so many pigs, chickens and cows available to supply it. Human waste presents a bigger opportunity. According to a 2020 study in a United Nations-sponsored journal, humanity produces five times more wastewater than the total volume of water flowing over Niagara Falls. Of that, perhaps 48% remains untreated as it’s released into the environment. In poorer countries, it’s still often used as fertilizer.

For the developed world, modern sewage treatment plants are one alternative. In New York City, expensive wastewater treatment systems produce over 1,000 tons of biosolids — the solids remaining after water is drained from waste — from 1.3 billion gallons of wastewater daily. Most is sent to landfills (some via an infamous “poop train”), while some is further treated so that it can be used safely as fertilizer.

It’s not just New York. Affluent local governments around the world are producing similar, human excrement-based products that, thanks to surging demand for alternatives to synthetic fertilizers, are in increasingly short supply. By one accounting, this global biosolids market could be worth around $2 billion by 2025.

Unfortunately, few cities are in a position to pay for New York-style wastewater treatment. In 2011, the Gates Foundation recognized the problem and initiated what it called the Reinvent the Toilet Challenge to develop low-cost sanitation independent of water and sewer systems. Field testing is underway for a Gates-sponsored toilet that accomplishes these goals and produces a compostable cake from dried urine and excrement. Similar projects are underway elsewhere. In Sweden, for example, researchers are pressing nutrient-containing cakes from urine recovered from specially designed toilets.

Nonetheless, as investment flows into the excrement recovery niche, doubts linger as to how owners and users will feel about extracting their wastes instead of flushing them away. The better bet is probably wastewater plant technology that recovers valuable nutrients from the traditional stream.

“The municipal waste facility is potentially the new mine,” Jason Trembly, a professor of mechanical engineering at Ohio University, said in a phone interview. “Instead of extracting ore from the ground, we can do that more successfully through wastewater.”

In 2021, Trembly and a colleague, Damilola Daramola, were awarded a $2.1 million grant by the US Department of Energy to research the use of electrochemical methods to convert wastewater into fertilizer. The goal is to produce a low-cost and renewable energy technology that can be incorporated into new and existing systems in developed and emerging markets. A successful system would provide a low-emission competitor to synthetic fertilizers, potentially contributing to lower costs globally. The next step, Trembly told me, is to secure funding for a pilot scale demonstration.

As fertilizer and food costs continue to spiral upward, the cost of additional grants shouldn’t stand in the way of expanding and furthering experiments into new toilets and waste-management systems. The energy and agriculture departments should seek to expand targeted grants to this overlooked niche. Likewise, private investors seeking new twists on old technology could do worse than taking a look at toilets and sewers.

Human waste won’t replace synthetic fertilizers on a large scale this planting season. But with a little help, they’ll soon be an affordable, clean alternative for farmers worldwide.  

• Fertilizer Shortages Finally Give Dung a Chance: Amanda Little

• Higher Food Prices Aren’t Making Farmers Richer: Adam Minter

• The World’s Food System Is Too Dependent on Wheat: Jessica Fanzo

(Corrects first name of Professor Jason Trembly in 13th paragraph.)

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Adam Minter is a Bloomberg Opinion columnist covering Asia, technology and the environment. He is author, most recently, of “Secondhand: Travels in the New Global Garage Sale.”

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