Don’t Let Your Food Waste Become Sewage Sludge

The solid waste industry is greenwashing food waste-to-sewer programs

Laura Orlando March 14, 2023

A version of this story was previously published by Just Zero, a national nonprofit advancing community-centered zero-waste solutions. 

Plenty of people understand what compost means to soil and plants. Gardener’s call it “black gold.” Writer and farmer Eliot Coleman started farming in Harborside, Maine, in 1968. He describes how two acres of what is now very productive land at Coleman and Barbara Damrosch’s Four Season Farm started out with only two inches of topsoil, which they were able to increase with “a lot of home-made compost,” cover crops, seaweed, and limestone.

“Compost is produced by managing the breakdown of organic material in a pile called a compost heap,” writes Coleman in his book Four-Season Harvest. “Compost enhances soil fertility because fertile soil and compost share a prolific population of organisms whose food is decaying organic matter. The life processes of these organisms help make nutrients from the organic matter and the minerals in the soil available to growing plants.”

Composting is pretty straight forward and has been for hundreds if not thousands of years. Until now, when the waste industry has concocted a bait-and-switch scheme to turn your food scraps into their profits.

The two largest waste management companies, Waste Management and Republic Services, are banking on signing contracts with urban cities to divert food scraps away from landfills (a good thing) to sewage treatment plants that do not help the climate fight but where they can make a buck (a bad thing). The market value of these two corporations is more than $100 billion.

Food scraps, too often referred to as “waste,” have become part of the waste management juggernaut because there is money to be made in hauling, grinding, and putting your leftover food in the sewer. To be clear, food scraps are not waste until they are wasted.

As a civil engineer, I was taught in college how to “manage waste,” including that which goes down the drain. After 30-plus years of research and organizing, I have come to view “waste management” as a monster in the shadows.

The benefits of composting

Food provides livelihoods for farmers, nutrients for humans and animals, and a sense of joy for many. But the food we don’t eat, the scraps left on our plates, spoiled, or just unwanted, often ends up in landfills. In fact, food is 24% of everything we bury in landfills. Burying all that food negatively impacts the climate. How? Well, as food breaks down in a landfill, it emits methane, a powerful greenhouse gas. In fact, landfills are the third largest source of methane emissions in the United States, after oil and natural gas systems and agriculture (especially cattle and dairy in concentrated animal feeding operations).

Food scraps should never be buried in landfills. They can be composted in backyards or collected by cities and towns for composting at small or large facilities. San Francisco has been collecting food scraps for composting since 1996. In 2022, the city estimated it collected and composted over 550 tons of food scraps per day.

The benefit of composting is that it speeds up the natural recycling process for organic (previously living) materials. This allows us to recover carbon and other nutrients from organic materials, like food scraps, more quickly. The result is a natural fertilizer (compost) that can restore soil fertility and offset carbon dioxide emissions. Through its composting program, San Francisco provides compost to local farms, vineyards, and ranches to spread over their fields and crops, helping to grow healthy plants and fight climate damage.

Why food scraps shouldn’t go in the sewers

Another method of processing food scraps is called anaerobic digestion. Anaerobic digesters are typically sealed containers that use bacteria to break down organic materials in the absence of oxygen. This process creates a mixture of gases – mainly methane – referred to as biogas, which can be burned to produce energy. The material leftover in the container after the anaerobic digestion process is called digestate. Digestate can sometimes be used as a fertilizer, though it is not the same as compost. It can only be safely used if the material that went into the anaerobic digester was free from toxic chemicals. This is where we find a problematic link between sewers and food waste.

Many sewage treatment plants use anaerobic digesters to reduce the volume of sewage sludge—or “biosolids,” a term invented by public relations consultants. Sludge is a byproduct of wastewater treatment. It is what’s leftover in the treatment process after the wastewater is treated, including leftover toxic chemicals. Adding food scraps to the digesters at wastewater treatment plants increases the volume this toxic byproduct and loses any potential value it has as a compost.

Some cities and towns have been convinced by states and the waste management industry to send their food waste to these digesters. This is a terrible mistake. Take Cambridge, Mass., which offers a curbside collection program for food scraps. The city calls it a “compost” program. But it is part of a shell game. Cambridge trucks its food scraps to a site owned by Waste Management a few miles outside the city where they are ground up and turned into a slop. That slop is then trucked 25 miles away to North Andover, Mass., where it is added to the anaerobic digesters at the municipal sewage treatment plant. Why is this problematic?

A lot of different kinds of waste go into the sewer. Industrial wastes, hospital wastes, commercial wastes, landfill leachate (rainwater that runs through the toxic dump), human waste, stuff that runs off the roads, and every other kind of hazardous, toxic, and biological waste material that goes down the drain. 

The largest landfill in New England, located in Rochester, N.H., and owned by Waste Management, trucks its PFAS-laden leachate to a municipal sewage treatment plant in Madison, Maine, a town of 5,000 people 150 miles away. PFAS, also known as “forever chemicals,” are used by industry and are found in consumer products such as nonstick cookware. They can cause cancer, birth defects, liver problems, damage to the immune systems, and other serious health problems. The Madison plant cannot process the PFAS – no sewage treatment plant can – so the chemicals end up in the Kennebec River or the leftover solids (sludge).

What goes into the sewer becomes simply sewage. Its toxic and otherwise problematic constituents blend into this reified term. Sewage is treated to meet certain federal water quality standards. Standards that do not take into consideration the thousands harmful chemicals that eventually end up in the sewer. 

After sewage treatment, the water-based component of the process – treated wastewater – is discharged into rivers, lakes, and oceans. The solids – sewage sludge – are put into landfills, incinerated, or spread on to farms, gardens, or other land. 

Sewage sludge is a mud-like material containing hundreds of known toxicants, including PFAS. And yet, the federal government encourages its use as a fertilizer. Most municipal sewage treatment plants contract private solid waste haulers, like Waste Management and Republic Services, to take their sludge away. Where that waste goes is up to the waste hauler, and if it is in a place next to you, you have little recourse to stop the dumping.

Greenwashing sewage sludge

Why is sludge so loaded with toxic chemicals? Sewage treatment is focused on so-called “conventional” pollutants, such as oil, grease, fecal coliform, pH, nutrients like nitrogen and phosphorous, total suspended solids (anything that floats), and settleable materials (eg., sand). The most advanced sewage treatment plants are not designed to remove toxic chemicals. The only way to do that is to stop them from being produced or going down the drain in the first place. Achievable goals that should be on the top of the EPA and other regulatory agency’s to-do lists.

EPA reported that in 2021 of the 4.9 million tons of sludge from 2,500 sewage treatment plants (the U.S. has more than 16,000) that was hauled away, 43 percent was used in agriculture, home gardens, golf courses and on other land. EPA calls this “land application.” Of the rest, 42 percent was put in landfills, 14 percent was incinerated, and the remining 1 percent went someplace else.  Land application means putting, for example, literally pounds of PFAS on our farmland each year. It doesn’t have to be this way. The nation could follow Maine’s lead and ban the land application of sewage sludge, as the state did in 2022.

I have met farmers who have lost their dairy herds and even their farms because of PFAS poisoning related to sludge spreading. It is a national problem and its growing. In 2021, the federal government spent $1.5 million to compensate farmers whose dairy cows were poisoned by PFAS. 

Remember, PFAS are called forever chemicals for a reason: They don’t go away. PFAS make their way to the roots and shoots of plants, hunker down in the soil, and move into ground or surface water. To top it off, they accumulate with every additional sludge application.

The solid waste industry and some city and town sewage authorities, like those in Cambridge, are greenwashing food waste-to-sewer programs by promoting them as “waste-to-energy.” Sure, adding food scraps to sewage digesters keeps those scraps out of landfills, but it’s a shell game that we cannot afford to play. Adding food waste to the sewage sludge in these digesters creates a toxic mixture that endangers the environment and public health.

We should never mix food waste with sewage sludge. Instead left-over food should be composted. Composting urban food waste is a solution that can help fight climate change and protect healthy soils. Composting the right way can help us grow more nutritious food, strengthen soil health, employ more people, create more businesses, and offset climate-damaging emissions. When composting is not possible, anaerobic digestion can be a solution—but only if food scraps are not mixed with sewage sludge.

Let’s keep urban food scraps away from sewage treatment plants and use them to build healthy soils or generate energy in a toxic-free environment. Doing the right thing with food waste is a good investment in our health, soil, and future. Someday, we might actually stop calling it “waste.”

Laura Orlando

Laura Orlando is a civil engineer, science advisor to Just Zero, and a contributing editor at Barn Raiser.

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