RENTON — You wouldn’t expect something that began in your toilet to sparkle.
That’s the struvite, or phosphate minerals from the digestive tract of thousands of people across the Seattle metropolitan area, catching the light just so as an auger churns the mixture at King County’s wastewater treatment plant in Renton.
“Like little diamonds,” said Erika Kinno, the county’s policy and research supervisor.
Those little diamonds, alongside a slew of other nutrients, are precisely what make the human waste — processed at facilities like this — such a valuable commodity for forests and farms across the state, local officials say.
Humans have used their own waste as fertilizer for thousands of years, with varying degrees of success.
In King County, it’s a growing business. The program, called Loop, is one of the largest and most successful in the country, sending out thousands of tons of the stuff every year, and they’re looking to expand operations into neighborhood gardens near you.
County officials hold a grand vision for their work. Where others see waste, they see opportunity, particularly in the era of worsening climate change.
But the practice may face some headwinds. Scientists and federal officials warn against a slate of toxic forever chemicals, known as per- and polyfluoroalkyl substances, or PFAS, which can cause cancer and other health problems.
Farms across the country have been contaminated with sewer sludge rife with these hazardous compounds, leaving a trail of health issues for families and concerns for similar plots.
The risk is high and environmental regulators have no consistent way of understanding the full scope of contamination, skeptics say. Neither Washington nor federal officials have any testing requirements or legal limitations for PFAS found in sewage sludge.
Even proponents of the practice acknowledge they need more data. Here in King County, officials await the results of a yearlong PFAS analysis before determining their next steps.
How King County transforms wastewater into fertilizer
King County’s South Plant generates about 60,000 tons of recycled fertilizer every year, or six truckloads a day, and sends it out to farms and forest across the state. Naturally occurring bacteria play an important role in breaking down the organic matter.
How it works
Every day, millions of gallons of wastewater flow into King County’s treatment plants from obvious sources, like toilets, kitchen sinks and washing machines. But it also flows from stormwater drains, industrial businesses, retail stores and parking lots.
The end result is a milky type of liquid with a sharp and distinctive odor.
First, plants must remove the trash, said Rebecca Singer, wastewater operations manager for the county’s Renton plant.
Singer holds up a clear plastic cube about a foot wide. Inside is everything that’s been flushed down the drain or washed into street gutters. KitKat wrappers, tin foil, bottle tops, indiscernible bits of plastic and sanitary wipes.
The plant removes one of these cubes worth of trash every minute, sending it to the landfill, Singer said.
The wastewater heads on to open-air sedimentary pools where the solids sink to the bottom. Sprinklers mist surface waters to prevent foam from developing.
In the summer months, the smell turns a little ripe, Singer said, unfazed.
You get used to it.
The liquid flows through aeration, clarification, disinfection and filtration processes, leaving behind recycled water, which can be used or pumped into Puget Sound.
Solids, however, will be blended, digested (part of a process to kill remaining pathogens) in massive tanks and spun in centrifuges to remove additional liquid before the final product is dropped into specialized semitrailers to haul Loop across the state.
Singer shakes a small glass vial of the brown stuff, saying it’s similar to the tiny piles worms leave behind.
King County has been producing Loop Biosolids for decades, Singer said. But now they’re looking to expand into new territories.
Where it goes
You might have seen the Loop trucks heading back and forth over Snoqualmie Pass. About 15 leave King County a day, Singer said. The majority come out of Renton.
The product will be spread on the ground covering the Snoqualmie Tree Farm northeast of Seattle. The Department of Natural Resources uses it, too, as does Natural Selection Farms in Yakima County.
Another loyal customer is Boulder Park Inc., a farming cooperative in Douglas County, said Dave Ruud, who manages the operation. Farmers there began using Loop in the mid-’90s and noticed an almost immediate return. They mostly grow wheat and noticed it was growing taller and more robust.
Yields increased by as much as a fifth, Ruud said. Word spread quickly.
“As the neighbors saw the results, they said, ‘I’ve gotta have some of that poop,’ ” Ruud said.
They couldn’t get enough. At the outset, Ruud said farmers used up maybe 40,000 tons of biosolids. Now, they need about 120,000 tons a year. That’s more than King County can provide, so they’ve sought product from Pierce County and Lynden, Whatcom County, too.
Anytime there’s a shortage, Ruud jokes about gathering up his crew and throwing a chili fest in Seattle to boost production.
Around 110 waste treatment facilities across the state produce biosolids allowed to be spread on farms or gardens, said Emily Kijowski, the statewide biosolids coordinator for the Department of Ecology.
Personally, Sally Brown, a research professor of environmental and forest sciences at the University of Washington, orders hers from Pierce County. That’s sold under the name Tagro. And the results speak for themselves. She’ll brag about her 2-foot-long carrots.
“Well, I mean, maybe they’re only 18 inches, but you get the picture,” Brown said with a laugh.
Nitrogen fertilizers offer soils and plants only some of what they need, Brown said. Like having a refrigerator full of condiments but none of the actual substance. Biosolids offer a balanced and high-quality diet.
Not to mention the climate applications, Singer said. High-moisture content in the biosolids offers water to regions parched with drought. Using the waste captures carbon, too — the equivalent of taking some 9,000 cars off the road each year, she estimated. Because if the biosolids weren’t applied to farms and forests, the county would have to either dump them into a landfill or incinerate them. Both of those options generate massive quantities of carbon emissions and carry additional environmental implications.
Some treatment plants — like the South Plant in Renton — can also capture the gases produced during the digestion process and burn that to make electricity or pipe it back into the natural gas grid, Singer added.
Is it safe?
Decades ago, Seattle’s waste flowed into Lake Washington or Lake Union, clouding the waters with unsafe levels of nutrients.
But over the years the process has been refined, Brown said. The treated waste is now much cleaner (and so are the lakes).
Biosolids for agricultural lands are broken into two categories. Class B biosolids are treated to kill 99% of pathogens, like giardia or salmonella. It’s better suited for aboveground crops like wheat or corn.
Class A biosolids are treated even more — perhaps by heat or composting — to kill all detectable traces of these pathogens. This is suitable for backyard gardens.
King County in November launched a five-year pilot program to generate a Class A stream, and the first piles of the stuff sit on their lot, steaming in the winter air. That means the bacteria is still active and consuming pathogens in the mix, Singer said. Once they cool, the product is ready.
Biosolids are also tested for other contaminants, like arsenic, lead and mercury. Singer said King County tracks its shipments, too, so they can pinpoint precisely where in a field their truckloads were spread.
Waste treatment plants in Washington aren’t required to test for PFAS, used in everything from cosmetics and clothing to furniture and firefighting foams.
Even if they do test for PFAS, neither the state nor the U.S. Environmental Protection Agency has set any sort of limits to their concentrations, Kijowski said.
Adam Nordell and his wife have seen the devastation of PFAS in sewage sludge firsthand. The first-generation farmers ran an organic farm in Maine for years, growing wheat, rye, oats and corn, only to learn years after the fact that previous owners spread biosolids across their land.
Testing showed extremely high PFAS levels in the soil and water. Nordell’s family, of course, had been eating the produce, drinking the water, working with the soils. The land was contaminated.
Their business collapsed. He declined to discuss his medical history but acknowledged he has much anxiety about the risk, given their long-term exposure.
“We went from being 12 years into running our own business and building out this farm to moving into a friend’s guest apartment that following spring,” Nordell said.
In January the EPA warned that these forever chemicals found in sewage could exceed safety limits several times over.
While regulators scramble to find out just how far the contamination has spread across the country, companies producing the chemicals have known about the risks for years, said Jared Hayes, research analyst with the nonprofit Environmental Working Group.
“This is a long time coming,” Hayes said.
And now states are catching on. Maine and Connecticut have even banned the use of biosolids on agricultural lands, Hayes said. Much more testing is needed to understand the scope of the problem, but until then, he argued, biosolids shouldn’t be spread across agricultural lands or gardens. Better to err on the side of caution.
State and local officials here are all in favor of testing. King County has already conducted a yearlong survey, and spokesperson Akiko Oda said the results should be released in the months to come.
Shirlee Tan, public health toxicologist for King County, noted that they can’t just stop using biosolids. State law requires treatment plants to find a “beneficial use” for waste before they can consider incinerating or landfilling the stuff.
Tan said she’s far less concerned about PFAS in King County than she would be in places like Maine because we have no major manufacturers of the compounds in the area, discharging their chemicals into our municipal waste streams.
Some bigger companies in the area can contribute to PFAS contamination in King County but nothing on such an industrial scale, Tan said.
More testing would certainly help local officials understand our risk profile, Brown and Tan agreed. And if levels are spiking in certain places they can track down the source of PFAS so it no longer enters the waste stream.
For the moment, Kijowski said, she’s unaware of any specific pushes to require testing at the state level.
Brown said she’s not too worried. PFAS will be there in detectable levels almost certainly. These compounds are so common now they’re even in rain water. But they’re unlikely to be at incredibly high levels.
The biosolids industry is rife with branding issues. Some call the product “biosolids,” “night soil” or “sludge.” Singer said she requires Loop trucks to be washed before they leave the treatment plant and before they come back. No need for a dirty truck to remind people where their product comes from.
Some folks just don’t want to use a product that began as human waste, Brown said. But the farmers who know the benefits don’t mind. More for them, she said.
