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Oct 30, 2023

Getting rid of the goo

Over the past decade, landfills across the U.S. have been fighting a sticky, polymer-like substance called “black goo” or “flubber,” which can clog vital equipment and impair leachate and gas

Over the past decade, landfills across the U.S. have been fighting a sticky, polymer-like substance called “black goo” or “flubber,” which can clog vital equipment and impair leachate and gas collection operations.

The anomaly, primarily found at wetter landfills or sites that accept sludge from wastewater treatment plants, has baffled scientists as they attempt to figure out what the black solid is and where it comes from.

At this year’s WasteExpo, taking place May 1-4 in New Orleans, panelists in the session, Leachate Management: An Update on “Flubber” and “Black Goo,” discuss the fouling material, its origins, tools for prevention and remediation and updates on current research.

Craig Benson, a panelist on the session and professor emeritus of civil, environmental and geological engineering at the University of Wisconsin, said he first ran into black goo about 10 years ago while working at a wet landfill in the Southeast.

The site, which had been receiving a lot of odor complaints, was struggling to keep leachate levels down because of frequently clogged pipes. “We could not keep the pipes running; constantly pumps [were] getting clogged up with this black, goopy stuff,” he said. “Essentially [the solids] were rebuilding every other day.”

Benson continued to find the presence of black goo at other sites, prompting him to investigate the phenomenon further.

“We would see it more and more, the presence of this black, goopy, sticky material—different from the historically black, biological matter that we’re all familiar with,” he said. “This was different stuff. It wasn’t just biofilm; it was a different material.”

What is it?

To find a solution to the problem, Benson said he first needed to understand how the substance moves through landfills and how it is entering leachate collection systems.

Using roughly 30 samples taken from municipal solid waste landfills in the U.S., Guam and Puerto Rico, Benson’s research found that, regardless of a landfill’s location or material composition, most samples have the same physical characteristics—a stretchy, rubbery material with a strong odor, which likely can be attributed to sulfide compounds affixed to the “sticky stuff.”

To identify the substance further, Benson used Fourier-transform infrared spectroscopy (FTIR) to look at the chemical bonding and chemical structure of black goo samples. With FTIR, an ultra-infrared beam is sent into the sample, where some wavelengths are absorbed and others aren’t. A sensor measures what is reflected off, thus creating a “fingerprint” of what the material’s composition.

When looking at black goo samples from 17 different U.S. landfills, Benson said they all “essentially had the same FTIR spectrum and … the same type of bond.”

He also noticed the bonds were similar to acrylate-based polymers, which he noted are ubiquitous in today’s world.

In addition to FTIR, Benson used thermal gravimetric analysis (TGA) to study the composition of black goo. “We did a very simple … TGA, thermal gravimetric analysis, [where] I take a sample, I put it in an oven, I ramp up the temperature and I measure the mass as it heats up. Essentially, I’m burning off parts of that sample over time.”

During this process, Benson said he recognized a key distinction that led him to believe the samples could be a commercial polymer.

“[The] weight of the sample [was] diminishing over time, … so this is water essentially being extracted, and then it just plummets. And then it continues to decrease more,” Benson said when describing a graph of the TGA analysis. “This plummeting is in the polymer decomposition range; that’s a synthetic polymer. It’s not a natural material.”

In most commercial polymers, such as polyacrylate, Benson said it should be possible to “take that hydrated, gooey stuff, dry it and make it solid, and then I can rewet it and it should reform itself just like it was before.”

In doing so, Benson found that the “black stuff” in the black goo peeled away, leaving behind a gelatin-like goo–a common occurrence when testing synthetic polymers.

When comparing the results to common polyacrylates, as well as some commercial products that contain the substance, Benson said FTIR results were almost identical. Household items that often contain polyacrylates are diapers, meat pads, hygienic pads, pet pads, and dewatering agents. Wastewater treatment plants also sometimes use soluble polymers to remove suspended solids and/or contaminants from water.

With a more confident idea of what black goo is, Benson now is trying to create a definition and key parameters for the substance.

“One thing we see for sure is that all the materials that have a similar chemical structure typically have at least 45 percent organic content,” he said. “If it’s less than 45 [percent], it’s unlikely to be this kind of black goo with that polyacrylate material.”

Remediation efforts

Progressive Environmental Services, based in Gaffney, South Carolina, entered the environmental services space in 2019 after primarily working with the U.S. Navy on chemical pipe cleaning services.

The company mostly worked on scaling issues in leachate pipes until presented with black goo-related issues by clients, says panelist Steve Carl, founder and president of Progressive Environmental.

After a few encounters with the substance, Carl said he concluded it is “completely water insoluble. It is a black tar material.” In learning that the goo floats in water, he said his company found a way to clean pipes clogged by the matter.

“I think because the goo floats and the ‘taffy’ floats, I don’t think the polymers are migrating their way down. I think as the leachate levels are moving up, they’re lifting the polymers and creating that layer to float on the top of the leachate that is perched inside the landfill,” he said.

Using a foam-based cleaning method, Carl said the foam reaction pushes black goo buildup vertically through the perforated pipes of a leachate collection system. How far the goo is pushed out horizontally is limited by the reaction generated, he added.

When working with a new landfill, Progressive Environmental first shuts off the leachate collection system entirely. Personnel then lets the system cycle to see how fast leachate is coming in versus how fast the system is pumping out.

“I will tell you, almost all of the time we will see your pumps pump down, and somewhere between 20 and 40 seconds, we turn [the system on] and then it takes them more than an hour, sometimes two hours to recharge,” Carl said. “That pump’s pumping 50 gallons a minute, it pumped down in 30 seconds for easy math, that means I just moved 25 gallons out of a 10-foot-by-18-inch pipe that’s moving 130 gallons.

“I moved 25 gallons out of it and it cycled the pump. And then it’s taken two hours to refill that 25 gallons—something is plugging those perforations. Scheduled maintenance for system integrity is better than a crisis fix.”