Each day, about 20 million gallons of sewage flows into the city of Tacoma's wastewater treatment plants.
The water is separated, treated, and discharged into the Puget Sound, which leaves behind sludge — a mix of human excrement, industrial waste, and everything else that ends up in Tacoma's sewers. The plants further treat the product to reduce pathogens, bacteria, heavy metals, and odors, and convert it into a fertilizer called biosolids, which is high in phosphorus, nitrogen, and other nutrients that help plants grow.
Tacoma produces about 5,000 dry tons of biosolids annually and sells it in bags under the brand name TAGRO to about 9,000 customers at local hardware stores, as well as to urban gardeners and farmers in the Tacoma region.
"The focus here has been on recycling and the production of beneficial products — clean water, energy, and soil amendment fertilizer … including biosolids," said Dan Thompson, division manager of business operations for TAGRO.
Over 50 percent of the approximately 130 million wet tons of sludge produced nationally each year is treated and applied to cropland, which the U.S. Environmental Protection Agency (EPA) notes is less than 1 percent of U.S. farmland. As a fertilizer, it's popular with some farmers because most wastewater treatment plants give it away for free or sell it at prices that are below than the cost of synthetic fertilizers.
The use of biosolids in agriculture is increasingly coming under fire as a potential health and environmental threat, however. While some see it as an effective way to close the loop on recycling waste, some scientists, health professionals, and advocates say using biosolids in agriculture is poisoning the nation's farmland and compounding a number of health risks. Advocates argue that without stronger, comprehensive regulations that cover what types of waste can be used in biosolids — and what waste industries are allowed to send into public sewer systems — the nation is taking unknown risks with its food and water supplies, not to mention the health of farmers and people living in farm communities.
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The Sierra Club Washington's Darlene Schanfald calls biosolids a "witch's brew" of toxic substances.
"It can contain up to 90,000 man-made chemicals and we don't even know what new chemicals are made synergistically by combining them," she told Civil Eats. "No one can say if [biosolids are] safe."
Such concerns are driving some states to take a closer look at biosolids and sewage management programs as increased testing is consistently finding levels of per- and polyfluoroalkyl substances (PFAS) that are alarming health officials and the public.
Ultimately, the debate over biosolids comes down to two basic questions: Can anything be done to ensure they are safe? And if this waste can't be recycled as fertilizer, what can be done with it?
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One of the most controversial piece of the sewage puzzle is the fact that factories, slaughterhouses, and other industrial facilities are allowed to discharge their waste into the taxpayer-funded sewer system.
Thompson said the city of Tacoma's pretreats biosolids by closely monitoring upstream industry's discharge to reduce the amount of toxins that make it to its treatment plant and, ultimately, its biosolids. Fourteen staff members monitor nearby industries' discharges. Similarly, regulators in Michigan have successfully reduced the amount of PFAS in biosolids by identifying which businesses were sending the chemicals to the sewers and requiring those businesses to find another way to dispose of them.
Even with aggressive pretreatment programs in place and new awareness of PFAS, it's not clear that all water treatment plants know which chemicals could turn out to be harmful. And there's a general consensus among advocates that the nation's regulatory system should require companies to prove chemicals are safe before putting them in use.
While experts determine the safest way to use or dispose of biosolids, Laura Orlando, a Boston University civil engineer, believes a ban on land application is in order. "Everything we have that's being manufactured in our society ends up in our sewer and it's going to be in the sludge, so I think we should take land application out of the equation while we figure out what to do with it," she said.
Human waste is a nutrient-rich substance that farmers around the world have spread on cropland for centuries. The practice didn't rise to an industrial level in the U.S. until the passage of the 1972 Clean Water Act (CWA).
Prior to that, pollutants were often dumped in the nation's waterways, said David Lewis, a former EPA microbiologist who continues to study sludge. The CWA required communities to clean their water in treatment plants, but that left an ever-growing amount of sewage sludge.
At first, the waste industry largely burned it, but that often violates the Clean Air Act, Lewis said. Municipalities also tried dumping it in the ocean, but that created large dead zones. Then, in 1993, the EPA approved a proposal to spread it on land after it was treated and turned into biosolids.
Lewis said he opposed the rule change while at the EPA and linked two deaths around that time to biosolids: "That's what really brought public attention to the issue."
The EPA only requires nine pollutants — all heavy metals — to be removed from biosolids, as well as living pathogens such as E. coli and Salmonella. Sludge may be treated by air drying, pasteurization, or composting. Lime is often used to raise the pH level to eliminate odors, and about 95 percent of pathogens, viruses, and other organisms are killed in the process, according to waste management industry officials.
Composting has shown some potential in breaking down pathogens in human waste. A 2016 literature review of the existing science at the time found that composting biosolids can reduce pathogens, degrade organic contaminants and other emerging substance of concern, and reduce the bioavailability of heavy metals by converting some metals into stable organic forms.
The composting process can also significantly reduce the concentration of a number of pharmaceuticals, pesticides, polychlorinated biphenyls (PCBs), trinitrotoluene (TNT), perchlorate, some phthalates, and nonylphenol (NP), among others. In addition to PFAS, Brominated flame retardants and triclosan, the key ingredient in many antibacterial products, have both shown relative resistance to degradation in compost systems. In addition, the duration and method of composting both appear to be important factors.
Tacoma's Thompson said fears over contaminated biosolids are overblown because the department's pretreatment program eliminates many pollutants.
"There's a misperception that treatment starts at the treatment plant, but pretreatment is a huge part of what we do," he said. "We are in constant contact with industry, we are really trying to regulate at the source."
But he conceded that chemicals that some thought were to be safe have turned out to pose harm, such as PFAS and other "forever chemicals." "It seems like every five years we come up with something that everyone thought wasn't a problem, then we find out it could be a problem for humans," Thompson said.
Critics point to the EPA's Office of Inspector General's critical 2018 report, which found that the EPA couldn't properly regulate biosolids because it "lacked the data or risk assessment tools needed to make a determination on the safety of 352 pollutants found in biosolids." Among those pollutants were hormones, pesticides, plasticizers, and medications, and it labeled 61 of those "acutely hazardous, hazardous, or priority pollutants."
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The EPA is in the process of revising its biosolids rules, and an agency spokesperson told Civil Eats the agency is "working to complete a screening tool and risk assessment framework for biosolids land application scenarios," as well as undertaking a biennial regulation review.
Over the last decade, concern over these issues have have led companies such as Whole Foods and Del Monte to pledge to stop buying products grown with biosolids — but it's not clear what has been done to follow through on the pledges.
In 2003, Switzerland became the first country to ban biosolids, while Maine last year put restrictions on their use. Municipalities in Wisconsin, Michigan and Florida, among others, have stopped spreading sludge altogether.
In an ideal world, cycling through nutrients in a way that feeds the soil and cuts down on the use of synthetic fertilizer would be the ideal use for human waste. But some advocates say that because the system is so flawed, it may be time to put other alternative approaches in to place.
As of now, sludge that isn't turned into biosolids is landfilled or incinerated — both of which are expensive compared to spreading it on farmland.
Critics like Boston University's Orlando call for sewage sludge to be isolated in landfills with methane controls until an alternative is developed. The latter would partly involve reducing the amount of sludge produced through processes like anaerobic digestion and moving to a decentralized sewage system in which waste is treated in small quantities instead of large, unmanageable volumes.
Only a small amount of the nation's sludge is currently isolated in dedicated landfills, and none of those use methane controls. That sort of storage is costly, Orlando said, but opting to do it would "force us to think about sludge reduction."
"Who cares when you can put it in a truck and put it on Farmer John's field? Why put the effort into the research?" she asked.
Among the best available options for physically reducing existing sludge is anaerobic digestion (a technique also being used to control waste on some dairy operations). It's an expensive method only used at 1,200 of the nation's 16,000 treatment plants, but it can reduce volumes by up to 50 percent.
Orlando said sewage loads must be made more manageable by decentralizing what she characterized as an outdated sewage system. Instead of dealing with one very large stew of every type of waste that's in a sewage district, officials could manage smaller batches that have far less waste and are less volatile.
Separating as much human waste from industrial waste as possible and working with smaller loads makes the sludge "more stable, homogeneous, and compact," Orlando said. "You can manage it better, because it has uniform properties."
Decentralizing the system couldn't happen over night, but she adds that sewage officials could start by taking small steps. That could mean not hooking new and growing towns into already huge metropolitan systems, and redesigning configurations as aging treatment plants need replacing. Orlando likened it to redesigning and updating technologies in cars.
The government must also require industry to properly and safely deal with its own waste instead of simply discharging it into public sewers where it mixes with other industries' waste, said Steve Stevick, chair of Sierra Club's Wastewater Core Residuals team. Doing so "would go a long way to reducing sludge's toxicity," he added.
"Industry has to be held responsible for the degree that they contribute to the problem," he said. Sewers now represent "a subsidy to private industry" because the public pays to dispose of companies' waste, Stevick added.
Orlando believes that industry can profit off of a decentralized system, especially if it generates energy from methane. She pointed to the fact that zero waste efforts have found ways to reuse industrial byproducts as difficult as slag and sludge leftover from steel manufacturing.
"It can be a positive economic story," she said, while also pointing out that the federal government used to pay for about 75 percent of sewage costs. In recent decades, that burden slowly shifted to local governments shoulder the bill and spend billions annually dealing with sludge.
Advocates also call for strengthening the regulatory system, and pointed to the European Union's REACH legislation, which "places responsibility on industry to manage the risks from chemicals and to provide safety information on the substances."
Sally Brown, a research associate at the University of Washington who has studied biosolids for 30 years, argues that addressing industrial waste at the source is a "super effective way to reduce" toxicity in sludge, and the benefits of biosolids now outweigh the risks. She vehemently defended the use of and process behind biosolids, but agreed that reducing the number of harmful chemicals is the best way to get "the most bang for your buck."
"Who are the bad guys? Is it the people who treat the wastewater? No. It's the people who put these chemicals in every known product," she said. "We're going to have an enormous impact if we get rid of [chemicals] that have no real value."
Schanfald and Lewis also pointed to some successes with pyrolysis, or gasification, which destroys chemicals using high heat, and binds heavy metals to activated carbon. That leaves a residue that may be safer to use on crops because pathogens and most toxic substances are eliminated, Lewis said, though the process itself could pollute the air. A team of researchers from Florida A & M University and Cal Poly recently published research suggesting that microwaving could remove heavy metals from biosolids while retaining its useful nutrients.
Still, home and human waste loads remain a problem. Environmentalist Abby Rockefeller believes that the only waste that should go in the sewer is the water with which humans wash. She wants to see "source separation across the board." That not only means requiring industry to address its own waste, but separating human waste in composting toilets, and ensuring that residential food waste no longer goes down the drain.
No matter which approach — or approaches — wastewater treatment plants and policymakers take, the Sierra Club's Schanfeld emphasized that the current system cannot continue.
"We simply cannot keep spreading biosolids on farmland," she said. "It's deteriorating and poisoning our soils and our land."