A team of entrepreneurs and researchers in Kisumu, Kenya is converting human excrement into biochar and creating a low-cost, local fertilizer. Through their work they hope to keep excess nutrients out of Lake Victoria, address food insecurity, and improve quality of life. In this recording of our Spring 2026 webinar, Cornell University Professor Rebecca Nelson, an expert on the Circular Bionutrient Economy, describes the project.
The town of Kisumu, Kenya lies at the northeastern edge of Lake Victoria, the biggest lake in Africa and home of the earth’s largest freshwater fishing industry. The lake also provides water for agriculture, but high fertilizer costs and depleted soils prevent farmers from maximizing production. Meanwhile, excessive nutrients from informal settlements—communities without running water or sanitation—contribute to the harmful algal blooms in Lake Victoria that regularly kill thousands of fish.
To solve the three-pronged problem of runaway nutrients, food insecurity and poor quality of life, local enterprises are partnering with nonprofits and scientists to find solutions.
At the heart of the partnership is a farmers’ group called Kisumu Young Agripreneurs (KIYA) that has supported 500 farms and trained and mentored over 3500 youths. Roy Odawa, who heads up KIYA, works closely with an enterprise called Fresh Life, which provides and maintains 2,000 waterless, pee-and-poop-separating toilets in Nyalenda.
One of Fresh Life’s 2,000 waterless toilets, which separate urine from feces. Photo: Rebecca Nelson
Professors Nelson and Charles Midega, executive director at Poverty and Health Integrated Solutions in Kenya, are central to the project. Nelson teaches and conducts research at Cornell University that dovetails with this partnership in Kenya. “This is a dream come true for me,” she says. “Nyalenda is the most favorable place to do this work; every day we’re making progress.”
Roy Odawa and Rebecca Nelson add human urine to biochar made from human excrement. Their goals? Locally made fertilizer and a cleaner Lake Victoria. Photo: Jon Miller
To make the fertilizer, the team dries the feces on flat mats in a greenhouse. They mix these with wood chips and corn stalks or other crop waste, and heat the mixture to extremely high temperatures in a closed metal container to kill pathogens. The result is a porous, carbon-rich soil builder (similar to charcoal) that can absorb urine. Fresh Life has provided literally tons of human urine for the project and the team has figured out that adding magnesium to the urine will cause the phosphorus to precipitate. Now their partners can produce a beautiful granular fertilizer for crops that rivals commercial products.
Human feces are dried on mats in the greenhouse prior to being converted to biochar. Photo: Rebecca Nelson.
“I think we’re onto something important, building on Fresh Life’s big network of source-separating toilets here,” says Nelson. “With the fertilizer crisis, we can really do something for farmers as well as for the unsewered majority. If we gather materials from the Fresh life toilets, instead of the company taking them to the wastewater treatment plant, we can make fertilizer, and thus it’s cheaper for the toilet company. They can expand the number of toilets, and it’s a positive feedback loop.”
For his senior thesis work at Princeton, Jack Lohmann spent a month on Nauru, a Pacific island once rich in phosphate rock and now a decrepit relic. Nauru’s history of destructive mining is a cautionary tale to which Lohmann devotes an immense swath of his new book — White Light: The Elemental Role of Phosphorus in Our Cells, in Our Food, and in Our World (Pantheon Books, 2025).
The book unfolds the relationship between humanity and phosphorus rather than describing practical ways that societies can recycle human nutrients now. A few solutions are mentioned in passing, almost as a teaser (“In Japan, half of all human sewage is still made into fertilizer.”). Lohmann concludes: “Putting waste at the center of farming—where it always, until recently, had been—is a democratic action…. Waste is universally emitted and individually controlled.” You can’t argue with that. But how do we get out of the fix we’re in? White Light doesn’t answer this question, yet it’s still an important read for people who are seeking to understand the role of phosphorus in modern agricultural settings.
Partly lyrical and sometimes journalistic, White Light explores how phosphorus is central to life, growth, and rebirth. The black and white illustrations that begin each chapter, created by Alice Maiden, resemble block prints and gently remind us of nature’s cycles:
“In the moments that follow the death of a whale, when the light disappears and is swallowed by dark, the body’s weight draws to the base of the sea and compresses. It settles in mud. It forms an environment known as a whale fall, a world that will last for decades.”
Lohmann reminds us that rocks containing phosphorus — a rare element that’s critical for life —lend it to plants, which relinquish it to an herbivore’s bones, which ultimately find their way back to the sea. The author is critical of how industrial agriculture doesn’t foster soils containing organic matter, bacteria, and fungi. These are needed to make phosphorus-containing fertilizers fully available to crops. “On the whole,” he writes, “crops generally absorb one-fifth of the phosphate that is applied to the soil…. Around the world today, 70 percent of cropland contains more phosphate than it needs—although many of those soils, depleted of life, do not provide their phosphate to the crops that grow within them.”
In describing modern industrial agricultural practices, Lohmann pivots to those being studied since 1843 at England’s Rothamsted Research, the world’s oldest experimental station. “Each year,” he writes, “the amount of phosphorus that slips away through…wasted sewage, unused manure, food waste, and erosion—totals more than the amount that is mined. If phosphorus were reused as it once was—and as it still is in some communities around the world—mined sources would be all but unnecessary.” Rothamsted, so rooted in the past, is looking toward that future, and so must all of us.
1. Toilet Rewind. Monday, April 27th, 12-1 pm PST, 3-4 pm EST
Get ready to peek into the fascinating and little-known past when city dwellers kept their local waters clean by recycling and reusing poop. We’ll visit sand toilets of ancient Egypt, earthen-plaster toilets of the Mali empire, nutrient recycling systems of the Aztec’s lake-side city of Tenochtitlan, and the 19th century toilets that rivaled the water-flushing variety of today.
Presenters: Laura Allen, co-founder of Greywater Action, educator and author, will present with Martin Medina, a circular economy and waste management expert who works in Latin America, Africa and Asia. As an academic, he’s worked in universities in Mexico, Japan and the US, and he’s consulted for the World Bank, multiple UN programs and more.
2. From poop and pee to biochar-based fertilizer: Redirecting nutrients from Lake Victoria to Kenyan farms. Monday, May 11th, 12-1 pm PST,3-4 pm EST
A team working in an informal settlement in Kisumu, Kenya, is turning human excreta into clean, granular fertilizer to improve sanitation, agriculture, and the health of Lake Victoria. Learn from Cornell University professor Rebecca Nelson how the team is finding safe, low-tech, affordable products that help address the interwoven global challenges of food security, environmental sustainability and inequality.
Presenter: Dr. Nelson is a former MacArthur Fellow and expert on the Circular Bionutrient Economy. She teaches and conducts research in Cornell’s School of Integrative Plant Science and also the Ashley School of Global Development and the Environment. Both webinars are free and sponsored in partnership with OnThisEarth.blog, Greywater Action and the Rich Earth Institute.
Stories propel the phosphorus dilemma to an unfinished climax
The Devil’s Element: Phosphorus and a World Out of Balance (2023, W. W. Norton & Co, 228 pp.), bursts with stories, some of which you may not want to hear. Exploitation. Greed. Pollution. But insight, bravery, ingenuity and persistence, too.
In the riveting style of a newspaper reporter, Dan Egan draws us into one of the biggest environmental dramas of our time: the discovery of phosphorus as a soil amendment, the worldwide quest for it, the profligate use of it in the US, and the ways phosphorus is poisoning our fresh water, from Lake Erie to Lake Okeechobee.
His clear, fast-moving prose can tempt the curious, whether that be teen or adult, scientist or nonscientist:
Simanski was alone on the shoreline that day as he ambled, eyes down, over the sweep of rocks squeezed between the tongues of the lazy, glassy Baltic waves and a thirty-foot-high bluff when he spotted what he thought was a piece of fossilized oyster shell about the size of a US quarter. He didn’t consider the orangish stone a prize find, but he thought it was worth bringing home to show his wife. So the sixty-eight-year-old stooped over, picked it up and dropped it in his pants pocket….
After about ten minutes, Simanski heard a pop and felt a sharp pain near his hip, and when he looked down he saw yellow flames flaring from his left leg. “It was like lightning coming out of my jeans. Like a flash,” said Simanski, who was initially more baffled than frightened….
Bewilderment turned to terror after Simanski shoved his hand into this pocket to snuff out whatever it was that caused the fire and he felt nothing but a viscous substance that had the consistency of melted chocolate. When he jerked his hand out of his pocket each fingertip was covered in the goo and ablaze like its own candle.
Egan explains that those orange nuggets in the Baltic region aren’t gemstones but fragments of “some of the most dangerous stuff you can find on the periodic table—elemental phosphorus.” When bonded with oxygen, phosphorus becomes the stable phosphate that is essential to life, the “P” in our fertilizers that, along with nitrogen and potassium, spurs plant growth.
With a degree in history and a graduate degree from the Columbia School of Journalism, Egan gravitates to the long view of how we ended up where we’re heading. And where we’re heading is dire. We’re raiding dwindling phosphorus reserves and pouring it on crops. As phosphate drains to lakes and oceans, it’s feeding algae that choke waterways, suck out the oxygen, and disrupt the balance of life itself.
The phosphorus boom bedevils us still
The Devil’s Element is divided into two main parts. In the first, The Race for Phosphorus, the author takes us back several centuries to a time when guano, crushed bones, and pulverized rocks were discovered to boost crop growth, and the intense competition over who could mine them.
If his wince-inducing details don’t lure you onward, the predictions from some of his sources will. In the “War of the Sands” chapter, Egan writes, “Unlike manure, which is manufactured daily…the phosphorus rock deposits that sustain the world’s modern agriculture system do not regenerate on a human time scale. This will, eventually, likely pose a problem for every person on the planet….” Then he describes billionaire Jeremy Grantham’s ability to predict bad times ahead, like the tech bubble in 2000 and the 2008 housing crash. Regarding phosphorus fertilizers, Grantham says, “’There seems to be only one conclusion: their use must be drastically reduced in the next 20-40 years or we will begin to starve.’” While scientists disagree about exactly how long our reserves will last, there’s consensus that Morocco and Western Sahara have about 70-80% of the planet’s phosphorus reserves—and those are destined to be more valuable than oil.
In the second section, The Cost of Phosphorus, Egan unfurls several environmental sagas. After goliathian Procter and Gamble hooks American households on phosphate detergents, one scientist living in the wilds of Canada gathers the data and a photograph that turns the Tide (so to speak). Due to state bans and voluntary reformulations by manufacturers, U.S. household laundry and dishwasher detergents are phosphate-free today, but agriculture is a different story. The phosphates in fertilizers not absorbed by crops, in combination with those in livestock manure, continue to pour into the Great Lakes and other U.S. waterways. “The number of animals in the…[Lake Erie] watershed more than doubled to twenty million between 2005 and 2018,” writes Egan, “while the amount of manure-based phosphorus added to the watershed grew by 67 percent, to 10,600 tons annually. Those farming operations collectively produce as much excreta as a city of at least several million people. And…it eventually winds up in Lake Erie.”
As a journalist in residence at the University of Wisconsin-Milwaukee’s School of Freshwater Sciences and the author of The Death and Life of the Great Lakes (2018), Egan knows this dilemma well. But he admits to not being prescriptive. Heends the book with only a few ways we might be able to get ourselves out of the harmful algal-blooming mess we’ve created. The brief chapter called “Waste Not”—in the equally short Future section—explains the need to better manage manure in agricultural settings and sewage in cities. He delivers a quick overview of the immense potential benefit of upscaling urine-recovery technology by describing the University of Michigan’s bathrooms, the Rich Earth Institute’s urine diversion projects, and the sewage treatment plant in Hamburg, Germany—powered by captured methane and deriving phosphorus atoms from its biosolids. The overarching message isn’t lost on the reader: people are trying, but there’s no easy fix.
Summertime on Cape Cod, Massachusetts, is usually bursting with swimmers and boaters. Falmouth is no exception, drawing tourists to its finger-shaped ponds that open to the Nantucket Sound. But in July 2012, residents of Falmouth noticed green cloudy water and a foul smell coming from Little Pond. Seventeen striped bass and other dead marine animals washed onto the shore. The likely cause? An abundance of nitrogen from septic systems spurring algal blooms that depleted the oxygen in the water.
Estuaries on the heavily developed south shore of Falmouth, Massachusetts, where fresh-water ponds connect to the salty Vineyard Sound. Map: Falmouth Local Comprehensive Plan
For decades, construction of housing developments in Falmouth has outpaced wastewater management, leading to seriously impaired water in 14 estuaries. A year before the fish kill, the town formed the Water Quality Management Committee to weigh various solutions, including sewers, I/A (innovative/alternative septic systems), and household urine diversion. That’s when committee member Ron Zweig, an aquatic resources and fisheries management specialist, suggested that a lowly bivalve might help: the oyster.
Meet Eastern oysters
A reef of eastern oysters, the only oyster native to the Atlantic seaboard. Photo: Ron Zweig
Whether they’re served fresh on the half shell, fried, stewed or baked, oysters are popular and packed with protein, minerals, and even Vitamin B12. The eastern oyster (Crassostrea virginica) thrives in warm estuaries — where fresh water meets salty —and can form dense colonies that are home to other creatures. Although this bivalve was once prevalent in natural reefs, today it’s more frequently farmed in large mesh bags that hang from horizontal lines. These bags protect the oysters from green crabs, starfish, and other predators.
Nitrogen harvesters
Oysters are full of surprises. Born male, baby oysters — or “seed” — attach to a surface and after about a year of growing, become female. During the warmer months of the year, a fully grown 3-inch oyster can filter about 50 gallons of water daily as it feeds on tiny floating plants (phytoplankton). “In the process,” explains Zweig, “they harvest nitrogen for flesh and shell growth because phytoplankton grow on dissolved nitrogen. That oyster growth thus removes nitrogen from the aquatic ecosystem.”
While connected bags full of oysters float in a Falmouth estuary, they are removing nitrogen. Photo: Ron Zweig
Oysters decrease nitrogen in at least one other way. Their feces, or “biodeposits” containing nitrogen, settle to the pond bottom where they eventually decompose. Through a series of microbial processes, the nitrogen is finally released to the atmosphere as gas. This nitrogen is harmless and makes up to 78 percent of the air we breathe.
Oysters grow well in saltwater bays, but before 2011 no one on Falmouth’s south shore was growing them in bags. “People wondered whether we could even grow oysters in estuaries,” admitted Zweig, “so we decided to find out.” They conducted a trial to test the concept in some of Falmouth’s poor-quality estuaries. Growers donated seed, which was put into donated bags, “and we had more than 95 percent survival,” says Zweig. “They grew beautifully. Then we were able to get the town of Falmouth to commit $250,000 to conduct a pilot project.”
That pilot project led to others, and by 2021, the town had enough confidence and experience to set up a shellfish aquaculture program. Three growers rented and farmed an acre and a half of oysters in an estuary degraded from septic effluent. They put 1.43 million oysters in mesh bags on 1.5 acres (.6 ha) of estuary and confirmed that a 3-inch adult can remove roughly 0.26 gram (.009 ounce) of nitrogen from the water. That might sound trivial, but after Falmouth’s 2023 harvest, the oysters had removed at least 882 pounds (400 kg) of nitrogen from the estuary. That’s roughly equivalent to the amount of nitrogen that 89 Cape Cod homes with leaky septic systems release to the groundwater each year (10 pounds—or 4.5 kg—per household). These results don’t even account for the denitrification happening in the muck beneath the bags. If that could be measured, it might add nearly 50% more nitrogen being removed.
Two Falmouth environmental advocates, Hilda Maingay and Earle Barnhart, estimate that 10 acres of oysters would reduce planned sewering by 800 homes, saving Falmouth more than $64 million. They cite other advantages, too: oyster farming doesn’t involve massive infrastructure disruptions (such as digging up streets and landscapes) required by the installation of sewers and innovative/alternative septic systems. Additionally, the construction and operation of those systems emits greenhouse gases, whereas oysters farming does not. In fact, oysters pull carbon dioxide from the water and sequester it in their shells, which is another plus.
As oysters filter water, they ingest nitrogen-rich phytoplankton and assimilate that nitrogen into their shells and tissues. In addition, their biodeposits are transformed into nitrogen gas by bacteria in the sediments. Image: M. Lisa Kellogg
Oyster investment pays off
Growers can sell one oyster for about $0.30 to $0.70 (sometimes even as high as $1.00), depending on the season and supply. The 1.43 million oysters that Falmouth and the oyster farmers grew had an estimated market value of $650,000-$750,000. Growers are eager for more acreage to farm, and other coastal towns have begun to see oyster farming as one of the more cost-effective solutions to nitrogen pollution.
These public-private partnerships in Falmouth now account for 15 acres of oyster farming in several estuaries. The town will probably continue to provide seed for multiple growers who farm the estuaries and pay back a percentage. Stephen Rafferty, chair of the Falmouth Water Quality Management Committee, says that in 2024, fees amounted to about $55,000, which the town put toward more seed, equipment, and other expenses. They’re working with the state on permits for up to 200 more acres that would be suitable for rent. “Oysters are absolutely part of the long-range plan for reducing nitrogen,” says Rafferty. That plan will feature land-based solutions like stormwater improvements, sewers, reducing fertilizers, and innovative septic systems, in addition to oyster farming.
What’s not to like?
If oyster farming is a win-win for the environment, growers, and municipalities, what’s the catch? First, oysters are productive in the summer months, but during Northeast winters they need to be transported in their bags to cold storage so they don’t freeze. This translates to extra handling and the reality of seasonal — not year-round — nitrogen capture. In addition, oyster bags must be flipped weekly to expose different portions of the shells to sunlight, a practice that dries out algal growth and barnacles and improves the oysters’ size and shape.
Bags filled with oyster seed will be hung and must be flipped weekly to shake off sediment and algae. Photo: Westcott Bay Shellfish Farm
Oyster farms also affect nearby residents, some of whom don’t like the look of floating bags. Educating and engaging the community about the benefits is time-consuming and requires compromises. For example, residents who dig quahogs, a type of clam, need access to areas without oyster bags.
Finally, when an area’s shellfish industry is temporarily closed due to pollution, toxins, or storms, the harvest is disrupted. Some growers diversify by farming other shellfish, but none are as superb at removing excess nitrogen as the oyster. Challenges aside, the end result, Rafferty points out, speaks for itself: “The fact that we took the worst estuary in town, and now it doesn’t stink — people can go paddleboarding on it — shows that if you focus your efforts, it can be done.”
When you live 250 miles above the earth on the International Space Station (ISS), how do you get water? It can’t be brought in daily, nor is there room to store large quantities. Yet each astronaut living in the ISS needs about a gallon of water per day for drinking, food preparation, and hygiene. So they have to recycle urine, sweat, and even the water in their breath. “Yesterday’s coffee is tomorrow’s coffee,” is how astronaut Douglas Wheelock described it to the New York Times in 2015.
Not Lost in Space
November 2025 marks 25 years of continuous crews aboard the International Space Station. The largest structure ever built in space, the ISS is the length of a football field and has a mass of nearly a million pounds. But because it’s orbiting the earth at more than 17,000 miles an hour, inhabitants have that falling-roller-coaster sense of microgravity — near weightlessness. Up to six astronauts at a time from the U.S., Russia, Canada, Japan, and Europe live aboard this solar-powered structure, conducting experiments, forecasting weather, and testing technologies.
The solar-powered International Space Station spans the length of a football field and is the largest structure ever built in space. Image: European Space Agency
From pee to tea and back again
The technology for urine recycling on the ISS has developed over the past 50 years. Here’s an overview of how it works: Astronauts pee into a funnel connected to a hose that sucks up urine before it floats away. The collected urine is treated with chemicals to disinfect it and prevent precipitation. Then it’s sent to a urine processor to turn it back into clean water. Urine is 95% water and 5% “other”— urea, uric acid, salts, and waste products — so the processor’s job is to separate the water from the brine. Urine is heated to form steam, which condenses and is collected with the processor’s centrifuge. This cycle takes about 18 hours and recovers 85% of the wastewater it starts with.
Astronaut Suni Williams removes a urine collection hose from the bathroom wall of the International Space Stations. Image: NASA
Turning pee into drinking water in space may remind you of the science fiction movie Dune. The Fremen of the desert planet wore stillsuits — wearable filtration systems powered by movement — that captured and turned urine, sweat, and breath into drinking water. Though filtration on the space station isn’t as portable as a stillsuit, it gets the job done in real life.
Aboard the ISS, water made in the urine processor is sent to a water processor where it’s further purified and sanitized with iodine. The entire process takes about 8 days, and NASA claims that the resulting water is superior to that of many municipal water systems. At that production rate, however, you certainly wouldn’t want to spill your coffee. If you did, you’d scoop it up and reclaim it before it floats away. In fact, the astronauts even collect and recycle human tears.
Water on Earth is recycled too, but the scale is so much bigger than on a spaceship we might forget that our own drinking water has been recycled countless times. After we drink and urinate, wastewater is (we hope) cleaned, then mixes with groundwater or surface water. From there it evaporates, condenses, and falls as rain. Our planet is its own space ship, relying on a finite amount of water to be shared and cared for by all.
There’s no easy answer to Cape Cod’s sanitation conundrum. Some solutions are expensive and invasive while other — cheaper — options haven’t yet been perfected for community-sized applications.
Cape Cod is a beautiful and fragile place. When the glaciers retreated thousands of years ago, they left a sandy peninsula shaped like a bent arm off the coast of our continent that is reshaped each day by wind and water. Ocean breezes float from sand dunes and grasslands to the broom crowberries on the heath lands and through pitch pine forests. Nearly 900 freshwater ponds are deep enough to connect to the groundwater, which is the only source of drinking water for Cape Cod residents.
With a footprint just slightly larger than that of New York City, the Cape is small but popular. From 2019 to 2024, 20,000 people moved to Cape Cod. More than 232,000 residents live there year-round, and many seasonal residents are staying longer than in the past. Each year a whopping 5.5 million tourists visit.
On a Wednesday evening in France, Nicolas nestles two jugs of yellow liquid into his bike panniers and rides to a small warehouse where he’ll get produce from a local farmer. After he picks up carrots, greens and potatoes, Nicolas leaves something for the farmer: his urine.
