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.”
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.”
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.
