Cambridge has virtually eliminated the risky, widespread and long-lasting group of chemicals known as per- and polyfluoroalkyl substances, or PFAS, from its drinking water supply, for now. But there’s a new worry about the level and impact of PFAS in compost derived from sewage sludge, which could affect how the city disposes of food waste from households and small businesses.
Though it isn’t obvious how sewage treatment and food waste disposal are connected, they are when it comes to the city’s food scrap collection program, which reduces the amount of city garbage sent to landfills. This is how the program works: Discarded food from Cambridge and other communities goes to a tank in Charlestown, where the giant waste services company Waste Management Inc. mixes it into an oatmeal-like slurry. The material ends up at the Greater Lawrence Sanitary District’s sewage treatment plant in North Andover. There, the slurry gets processed with household, business and industrial sewage.
This treatment of food waste creates enough methane gas to produce ample electricity to run the sewage treatment plant and dry and purify sludge that settles after treatment. The dried sludge becomes compost that can be used by anyone from backyard gardeners to commercial farmers to enrich soil.
The circuitous process makes compost out of Cambridge food scraps. And some samples of the dried sludge that produces that compost contain measurable levels of PFAS.
PFAS, a family that includes more than 1,000 chemicals, have been linked to harmful effects on the liver, heart, growth and immune system, among other health problems, but the strength of the evidence varies and not all people are equally at risk. Known as “forever chemicals” because they don’t break down in the environment, PFAS have been used for decades in a wide variety of applications including nonstick cookware, firefighting foam, textile protectants and food wraps.
The Environmental Protection Agency last year set drinking water limits for six PFAS chemicals near zero, effective in 2029. Cambridge met those limits in its most recent quarterly drinking water tests for April through June, but the city must change water filters regularly at its treatment plant to keep within the standard.
Standards not set
Despite the links between PFAS and health problems, neither Massachusetts nor the U.S. Environmental Protection Agency have set standards for levels in sewage sludge or compost derived from sludge. Both the state Department of Environmental Protection and EPA are working to develop standards; the state DEP expected to report on a study of the issue by the end of this year. In 2021, the state began requiring plants that produce sewage-derived compost to perform quarterly tests of the dried sludge for 16 PFAS chemicals. (Inputs to the treatment plants, such as the Waste Management slurry, don’t have to be tested for PFAS.)
Asked whether Waste Management has tested the slurry for the chemicals, spokesperson Garrett Trierweiler said the process removes more than 99 percent of “physical contaminants such as packaging” and does not add additives or chemicals. The slurry isn’t “subject to regulatory or environmental testing requirements, including for PFAS,” he said. The state convened meetings in 2020 and 2021 with “stakeholders” and technical experts seeking to come up with a way to set PFAS limits for biosolids, the term for treated sludge that will become compost.
Cheri Cousens, executive director of the Greater Lawrence Sanitary District, said federal and state officials “are still determining what is safe” and the district was waiting for its decision. Meanwhile, the dried sludge must meet stringent limits for harmful substances such as heavy metals and cannot contain pathogens, she said. Greater Lawrence is the only sewage treatment plant that accepts citywide food waste, the DEP said.
Methane gas produced when the food waste slurry is processed with sewage offsets the plant’s need for electricity, Cousens said, and is “an environmental positive.” In addition, reusing the sludge as compost avoids burning it or sending it to a landfill; according to a report from Cambridge on PFAS in waste, in 2021, 14 percent of biosolids were incinerated and 42 percent landfilled.
Report to the council
Some in Cambridge are concerned about the city’s food waste disposal program and its possible connection to PFAS. “We need to make sure our food waste isn’t contributing to PFAS-contaminated sludge which has no place in our agriculture system,” Cambridge councillor Patty Nolan said Friday. A report from the city at the June 24 meeting of the City Council, requested by Nolan, implied that food waste is not a major source of the chemicals. It said that “the most significant sources of PFAS tend to come” from industrial facilities and consumer products such as textiles. “Even with new EPA and DEP rules for PFAS testing and reduction from drinking water and waste, the complete removal of all PFAS compounds in our waste is not expected,” the report said. It also said: “Regardless of how biosolids are disposed, a key priority is to reduce PFAS by addressing PFAS at the source before they get to the treatment plants.”
Nolan agreed but said that “while we need to address upstream contaminants that bring PFAS into our lives, we also need to identify and take responsibility for PFAS contamination in our downstream products. Our food waste program in Lawrence does report on PFAS levels although it is not as frequent as it should be. And we should continually monitor.” She also called for a broader examination of PFAS in city operations, saying that said there have been “isolated” discussions about the material in firefighting foam – Cambridge has discontinued it – and artificial turf and drinking water.
Widespread concern
The presence of the chemicals in sludge-derived compost is beginning to worry farmers and other citizens.
Residents of the Central Massachusetts town of Westminster say there were devastating effects when a local organic compost producer that used sludge from several wastewater treatment facilities, including paper waste processing plants, contaminated wells and soil with PFAS. The Boston Globe reported on the situation in 2022.
In March, landowners in Grandview, Texas, sued Synagro, one of the nation’s largest producers of compost from sewage sludge, claiming that the company’s product had contaminated drinking water wells and their land with high levels of PFAS. Synagro has denied the allegations.
A New York Times article on Aug. 31 said PFAS was being found on farmland in several states, including Maine, which has banned application of biosolids on farmland. Farmers have started to worry about their own health as well as suspected contamination of produce and the health of their livestock, the report said.
This post was updated Sept. 13, 2024, with comment from Waste Management Inc.
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Sewage should not be used as fertilizer, period. That’s the real problem.
Even if the city’s food scraps are pristine and pure, mixing it with sewage makes a dangerous mess out of it.
I won’t call this product compost because it’s not.
The city should redirect its efforts to actual composting. We could do a lot better by promoting backyard composting, and neighborhood composting for people without yards.
I think you may have missed that we have a huge rat problem and backyard composting can contribute, especially as most people are really careless about their waste.