How to remediate forever chemicals

Chances are, you’ve heard of ‘forever chemicals’ – and have probably come across them in daily life. Just this year, researchers have found them in pregnant women’s blood, on organic kale, and even in toilet paper. This comes alongside a growing pile of epidemiological evidence that exposure to forever chemicals could be implicated in “a variety of health effects, including altered immune and thyroid function, liver disease, lipid and insulin dysregulation, kidney disease, adverse reproductive and developmental outcomes, and cancer”.

In chemistry terms, forever chemicals are known as per- and polyfluoroalkyl substances (PFAS). They are a group of synthetic chemicals with atoms of fluorine (the F bit), and other elements strung along a chain of carbon atoms. There are thousands of PFAS, some of which have been around since the 1940s.  

The strength of the carbon–fluorine bonds makes these chemicals very versatile – for example, they are oil- and water-repellent, and heat-resistant. Thanks to these properties, manufacturers have used them in many things, from foams for firefighting, to waterproof clothing, nonstick cookware, coatings inside pizza boxes, and cosmetics. They’re even essential to the semiconductor industry. However, the properties that make them so useful in their intended applications also make them persistent in the environment – and dangerous to wildlife and people.

As the carbon–fluorine bond in PFAS molecules does not occur in nature, there is no known biodegradation pathway. PFAS can find their way into the water that we drink and get into our bodies, and are also difficult to remove with conventional water or soil treatment technologies. With unsafe levels detected in drinking water in the US and Europe, the race is on to solve the PFAS problem. That means safely capturing and removing the molecules and then destroying or storing them.

Extracting PFAS in solids and with bubbles

Firefighting foams have caused some of the most significant environmental leaks of PFAS. Now largely phased out, perfluorooctane sulfonate (PFOS) was a component of aqueous film-forming foams (AFFFs), used extensively to put out fires in airfields.
UK- and Germany-based firm Cornelsen has been targeting PFOS for more than 10 years, starting out with airfield remediations of jet fuel fires. Now, the company offers AFFF decontamination of fire trucks and appliances, in-situ remediation, and industrial water treatment systems. 

“There was a lot of it [PFOS], and we tried treating it conventionally, with adsorbent material. We quickly realised that was unsuccessful, incredibly expensive, and not very effective. It also produced a huge secondary waste stream,” says Matt Ingram, general manager at Cornelsen. 

The team focused on separation approaches (see ‘How to extract forever chemicals from water’). Working with the German applied research institute, Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT, Cornelsen came up with PerFluorAd. When added to contaminated water, this cost-effective biodegradable agent causes dissolved PFAS (including PFOS) to separate out in tiny solid clumps (precipitate) that can be filtered out of the solution. 

In the past five years, the company has been rinsing out firefighting appliances contaminated with PFAS. Demand in Germany has been consistently high and is growing in the UK. Ingram says the approach removes over 99% of longer chain PFAS present, including PFOS. 
Later, the company came across a sustainable PFAS remediation technology developed by Australian company Epoc Enviro. Surface-active foam fractionation (SAFF) uses rising air bubbles to remove PFAS contaminants from contaminated water. PFAS molecules have both water-loving and water-hating components, making them a ‘surfactant’ (like soap). Because of this, the PFAS stick to the surface of bubbles before they rise to the surface.

“It foams PFAS out of the water, then concentrates that foam many times further. We end up with a very small amount of liquid waste, and the water passes through clean the other side,” says Ingram. 
According to Ingram, PerFluorAd and SAFF are the only technologies that don’t create a large secondary waste stream. “PerFluorAd is dosed into the water and removes the PFAS as a solid. We then filter that out. So, the waste stream is as small as the amount of PFAS in the water.”

However, a major challenge for Cornelsen has been getting regulators to approve the technology, resulting in significant delays. “Scaling up has also been hard, in terms of both finance and establishing constant stable treatment,” says Ingram.

Designer granules

In tackling forever chemicals, Puraffinity, a green tech company based in the UK, has developed smart granules that can selectively remove PFAS from a contaminated solution. Puraffinity’s CEO and Co-Founder, Henrik Hagemann, was in an Imperial College London team in 2014 that entered an MIT competition to find solutions to pressing environmental challenges. “The issue that came up again and again was contaminants in water,” says Hagemann. “We kept being asked about these fluorinated compounds, so we began looking into using activated carbon materials.”

Back then, “there wasn’t even a name for PFAS”, he says. “We learnt about them from customers with contamination issues, like an airport that needed to clean up run-off water from firefighting foam drills, and the oil and gas sector that used [PFAS such as PFOS] to inhibit fires on oil-drilling rigs.”

Having raised £20 million, the company has spent nearly £13 million developing this smart material for environmental remediation and decontaminating industrial manufacturing facilities, commercial airports and military bases. “At first, we focused on developing a membrane, but we found it got blocked up,” he says. “So, we switched to a granule … You can just dump it in, like a pellet into an industrial-sized media bed.” 

Unlike conventional ‘blanket’ approaches, Hagemann and his team tailored the granule to selectively remove different types of PFAS. To do this, they developed special peptides mimics – short chains of amino acids, the building blocks of proteins – that preferentially stick to different PFAS molecules. They then took these peptide mimics and coated the granules with them so that, in a contaminated solution, PFAS molecules would attach themselves to the coated granules. 

Additionally, when the granules are fully saturated with PFAS molecules, they can ‘regenerate’. This removes the PFAS molecules, so that the granules are ready for another round of decontamination. The successfully separated PFAS must then be stored or destroyed.

Finding peptide mimics that interact in the right way with both the granules and the pollutants has been no easy task. The team has generated enormous data sets with tens of thousands of data points to measure how well different materials stick to PFAS molecules of interest. They have patented one material that sticks to six of the most common PFAS.

Puraffinity has recently manufactured the granules at its largest scale yet, a batch of up to 50 kilograms. It is working with the German government to validate the product’s safety at TZW, a site run by DVGW, the German Technical and Scientific Association for Gas and Water. “It has been third-party validated at the German government-owned site, and their sites in the US – so we can roll that out for industrial installations.” 

In this pilot phase, the team anticipates being able to treat 25 tonnes of water a day. Beyond the pilot, Puraffinity would be able to roll out to high-flow installations, treating up to 500 cubic metres (approximately 500 tonnes) of water an hour, equivalent to a typical chemical manufacturing plant’s water use. Most of their sites are in the US or Europe, with more to be announced as they go live. “We want to keep the public onboard. Solutions are coming – it’s not just that we’re finding more [and more] PFAS!”

Destroying leftover PFAS

The final piece of the puzzle is what to do with the PFAS left after processing. In the past, researchers heated the waste to temperatures of up to 1400°C. However, this energy-intensive process can still release harmful chemicals.

As a result, many startups and researchers are searching for safer options. In October 2023, MIT Technology Review reported on several US-based PFAS destruction technologies, some established, others emerging. The Michigan-based company Revive Environmental uses an approach called supercritical water oxidation. Here, relatively high temperatures and pressures turn water to a supercritical state, where it has both liquid-like and gas-like properties. These conditions help to break the strong carbon–fluorine bonds, with inert salts its only byproducts. Other methods bombard PFAS with high-energy electrons, or use high pressures and temperatures coupled with alkaline catalysts.

According to Hagemann, the new destruction technologies are “exciting, but not [at a] commercial stage yet.” He adds that these next-generation destruction companies also need “next-gen capture steps”, such as Puraffinity.

Another destruction technology has emerged from Northwestern University in the US. The Northwestern team’s August 2022 study in Science showed PFAS can be destroyed at temperatures of up to 120°C in a solution of two relatively harmless chemicals: sodium hydroxide or lye, a chemical used to make soap, and dimethyl sulfoxide. Only safe byproducts were left at the end.

More innovations in remediation are coming, and one promising approach is with ultrasound. Dr Madeleine Bussemaker, a chemical engineer at the University of Surrey, has been studying how to turn forever chemicals into relatively harmless carbon dioxide and fluoride. She and her colleagues reported in 2020 that ultrasound can completely degrade all PFAS so far tested. Although ultrasonic degradation is still at an early stage, the team aspires to develop a large reactor capable of treating contaminated domestic water supplies or firefighting foams and adapting the process for soils.

Challenges remain

While Hagemann describes existing technology to be “incapable of removing PFAS contaminants to the level required to keep up with these changing regulations”, he agrees regulation is the way forward. 

Although there have been proposals to ban PFAS (in March 2023, the EU began a public consultation on this – now abandoned), Hagemann does not support a total ban. “I’m a biomedical engineer and I know a double-digit percentage of medical devices, say, are manufactured using PFAS. How are you going to phase them all out as a class?”

Yet, he has been contacted by people who have had stents inserted in the heart because of built-up cholesterol, and checks have found them to have very elevated PFAS levels. “It’s a sense of urgency that really centres us as a company. This is a once-in-a-generation chance for an engineer to have a real impact on people’s lives,” says Hagemann. He describes one way to lower the concentration of PFAS in your body: donating blood. A public study found that by giving blood, you donate a disproportionate amount of your PFAS.

Hagemann adds: “This space is one of the hardest problems being worked on in sustainable materials. You have the vast chemical design space, where brute force manual search isn’t enough; and you have the nonlinear behaviour of PFAS, which requires you to have a lab and run the analytics to get the different disciplines speaking. It’s not just money – it’s also time. But the more focus we put on PFAS, the more companies will be trying to develop new alternatives.” 

They already are. In October 2022, the highest-profile brand in the outerwear materials industry, Gore-Tex, replaced its world-famous formula for waterproof clothing with its new PFAS-free membrane, GORE-TEX® ePE (expanded polyethylene) membrane. Patagonia, a leading role model in sustainable clothing, calls ePE “the game changer”. 

More recently, global chemicals manufacturer 3M pledged to discontinue its PFAS manufacture by 2025. In August 2023, the company reached a $10.3 billion settlement with the US government after claims by public water providers that it polluted drinking water with PFAS.

It just goes to show – alongside all the concern and challenges, there is optimism in the search for safe, clean solutions to remediating PFAS.