Taking the fight to PFAS ‘forever chemicals’

Just when we thought we might have a solution to the problem of high global warming potential refrigerants, global action against the use of “forever chemicals” linked to a multitude of products including synthetic refrigerants new and old raises a question over the long-term future of products like R1234yf – but mounting pressure to address the problem has spurred the emergence of an entire industry dedicated to overcoming the challenge of breaking down these seemingly indestructible substances.

What is the problem?

PFAS, an acronym for per- and polyfluoroalkyl substances, are entirely human-made chemicals widely used for their resistance to heat, water, and oil. Referred to as “forever chemicals” because of their strong carbon-fluorine bonds that are highly resistant to degradation, they have been used for decades in many everyday products, including refrigerants, firefighting foam, non-stick cookware, food packaging, textiles and carpets, metal plating, electronics manufacturing, and in the production of certain plastics.

Like other PFAS, those originating from refrigerants are persistent and mobile, meaning they do not readily break down and can move through the biosphere, ending up almost everywhere: soil, water (both surface and groundwater), air, sediments, and within living organisms. 

Currently, the most practical and cost-effective method for managing PFAS in refrigerants is careful recovery and recycling, with destruction at end-of-life.

Results from epidemiological studies and animal testing have also linked PFAS exposure to low birth weight, high cholesterol, thyroid disease, ulcers, and an increased risk of certain cancers, so there is an increasingly urgent need for strategies to degrade them.

PFOA (perfluorooctanoic acid) and PFOS (perfluorooctanesulfonic acid) are two of the most well-known and studied types of PFAS, of which there are 15,000. They are considered the ‘legacy’ PFAS because they were used extensively in the past and are persistent in the environment, and although PFOA and PFOS are no longer used or produced in the US, many have found their way into landfills, wastewater, and sources of drinking water.

So we’re stuck with them?

Incineration is a common method for attempting to destroy PFAS, but its effectiveness is limited and highly variable. While high temperatures (above 1000°C) can break down some PFAS molecules, complete destruction is not guaranteed, and the process’s effectiveness depends heavily on factors such as the specific PFAS compounds present, the incinerator’s design and operating conditions, and the presence of other materials in the waste stream. 

Furthermore, incineration carries the risk of producing harmful byproducts, including dioxins and furans.

The difficulty in destroying PFAS arises from variations in their molecular structure, specifically chain length. Longer-chain PFAS are easier to break down because they have weaker carbon-fluorine bonds and a larger surface area, making them more susceptible to degradation. 

Shorter-chain PFAS, however, possesses stronger carbon-fluorine bonds and a more compact structure, resulting in significantly enhanced chemical stability and resistance to degradation methods, meaning that effective PFAS removal often requires multiple treatment methods targeting different chain lengths.

Research into more efficient, environmentally sound, and affordable PFAS destruction technologies is being driven by stricter regulations and increased liability for chemical producers, landfill operators, and wastewater treatment plants facing the challenge of managing PFAS-contaminated waste.

So far numerous players are coming up with innovative, cost-effective ways of breaking the previously indestructible carbon-fluorine bond.

Plasma

Plasma arc technology offers a promising, energy-efficient approach to PFAS destruction although, like incineration, requires precise control to prevent the formation of potentially harmful byproducts. That said, its cost and scalability remain key factors for broader implementation.

An example of the destructive power of plasma technology is demonstrated by Onvector’s pilot program. This visually striking plasma, resembling a column of fire and lightning, effectively destroys PFAS contaminants in water.

The system uses a cyclone-like reactor to generate a rotating plasma from ionised argon gas. PFAS-contaminated wastewater is introduced into this vortex where the high-energy electrons within the plasma break the strong carbon-fluorine bonds in PFAS molecules, effectively destroying them – and while long-chain PFAS (like PFOA and PFOS) are rapidly destroyed, short-chain PFAS degradation is slower.

Unreacted solids are then separated and collected for disposal, with any remaining PFAS in the argon gas removed using activated carbon filtration.

Onvector’s technology is being tested in conjunction with pre-concentration methods, which concentrate PFAS from the water before destruction. This reduces the volume needing treatment and improves efficiency, particularly for wastewater with lower PFAS concentrations.

UV Photocatalysis

Claros Technologies specialises in PFAS remediation using advanced oxidation processes (AOPs) with proprietary technology that activates the photocatalyst with UV light, generating highly reactive species (like hydroxyl radicals) that oxidise and decompose the PFAS molecules, breaking their strong carbon-fluorine bonds. Pre-treatment is often necessary to remove substances that could interfere with the UV photocatalytic reaction. 

The technology’s scalability is a key advantage, making it suitable for various applications, from small-scale projects to large-scale industrial wastewater treatment, and while its energy efficiency and complete PFAS destruction are advantageous over methods like granular activated carbon (GAC) adsorption, a full economic analysis comparing it to other advanced oxidation processes (AOPs) and evaluating its long-term reliability is required.

Supercritical Water Oxidation (SCWO):

Revive Environmental, a spin-off of global ‘greater good’ research and development organisation Battelle, has developed the ‘PFAS Annihilator’ that uses supercritical water oxidation (SCWO) to destroy PFAS.

It works by heating and pressurising PFAS-contaminated water to above its critical point (374°C and 22MPa). This supercritical state enables an oxidiser to break the strong carbon-fluorine bond that makes PFAS so persistent. The process effectively destroys PFAS without creating harmful byproducts like shorter-chain PFAS, although it does produce hydrofluoric acid, which has to be neutralised.

These Annihilator systems, which can be integrated into existing wastewater treatment plants or deployed in shipping containers, are being used to address various PFAS contamination issues.

Currently, a major market is the destruction of PFAS-containing firefighting aqueous film-forming foam (AFFF). 

Revive is also working with various state governments and organisations to eliminate stockpiles of AFFF, a process that is expected to take several years.

Future applications include treating contaminated groundwater and assisting chemical manufacturers that use PFAS in their processes.

Electrochemical Oxidation

Electrochemical oxidation (ECO) is a developing technology for removing PFAS from water that uses electricity to break down PFAS molecules, either directly by stripping electrons at an anode or indirectly using powerful oxidising agents created by the electric current.

A key advantage of ECO is its low energy requirements as unlike some PFAS destruction methods it does not need high temperatures or pressures.

ECO is effective on long-chain PFAS but shorter chains are more resistant, so Aclarity and OXbyEL are two companies looking to improve this technology.

Aclarity says has successfully destroyed both long- and short-chain PFAS as its ECO approach goes beyond the electrode materials themselves, with optimised electrode design, reactor geometry, water flow, and processing techniques that maximise PFAS contact with the anode to enhance efficiency.

OXbyEL Technologies, on the other hand, uses a unique divided electrochemical cell where instead of flowing between the anode and cathode, the contaminated water flows solely over the anode.

This design, using a cost-effective electrode (approximately one-seventh the price of traditional boron-doped diamond electrodes) with a special catalyst coating and 3D structure, maximises contact with the anode, increases oxidation potential, and minimises unwanted side reactions like water electrolysis (which OXbyEL points out is the main energy consumer in the process).

This system also avoids creating the shorter-chain PFAS byproducts usually associated with incomplete degradation.

Hydrothermal Alkaline Treatment

Hydrothermal alkaline treatment (HALT) is a technology initially developed to destroy chemical weapons, now repurposed for PFAS destruction.

Researchers at the Colorado School of Mines optimised HALT for this purpose, and the Washington-based company Aquagga holds the exclusive licence and is commercialising it. HALT operates at approximately 350°C, a lower temperature than supercritical water oxidation (SCWO), a similar technology.

This lower temperature, combined with the use of a catalyst, makes HALT more energy-efficient than SCWO and capable of handling high-salinity water without pretreatment. 

Aquagga has successfully tested its mobile HALT unit in Fairbanks, Alaska, treating PFAS-contaminated water from a firefighting training area.

Partnering with ECT2, specialists in PFAS concentration, Aquagga leveraged ECT2’s foam fractionation to pre-concentrate the PFAS, significantly reducing the treatment volume.

The test demonstrated HALT’s portability and efficiency, processing over 1000 litres of contaminated water daily using only a generator and producing significantly cleaner discharge water.

Sonolysis

New York startup RemWell is tackling PFAS groundwater contamination with an innovative in-situ remediation system.

Unlike traditional methods that require costly and energy-intensive groundwater extraction for above-ground treatment, RemWell’s system uses a sonolysis reactor placed directly in a horizontal well that minimises pre-treatment options like filtration, osmosis, ion exchange, and foam fractionation that can concentrate the chemicals and further improve efficiency.

The reactor uses high-frequency sound waves to create imploding bubbles that break down PFAS molecules through two primary mechanisms: heat-induced pyrolysis, directly breaking down the PFAS, and the creation of highly reactive free radicals that chemically degrade the contaminants.

This compact device, installed up to 90 metres deep, where contaminated groundwater takes 12 hours or more to slowly pass through the reactor slowly to effectively degrade the contaminants.

With ongoing testing at a U.S. Department of Defence facility and planned trials in Sweden, RemWell’s technology is an example of international PFAS de-contamination efforts.

A big problem that needs diverse solutions

Although the cost-effectiveness and scalability of various PFAS destruction technologies remains under evaluation for now, it is clear that a collaborative approach combining multiple successful methods will be crucial to address an environmental problem that, in the US alone, results in around 65,000 public water systems being impacted by PFAS leachate from almost 15,000 closed and operational landfills.