Per- and polyfluoroalkyl substances, better known as PFAS, have earned an unfortunate nickname: ‘forever chemicals.”
It sounds dramatic, but from a chemistry and engineering perspective, it is not far from the truth. PFAS resist heat, water, oil, sunlight, and biological degradation.
Those properties made them commercially valuable for decades. They are also the reason removing PFAS from water, soil, and waste streams is so difficult.
Communities worldwide are now grappling with contamination in drinking water supplies, firefighting training sites, industrial facilities, and landfills. As regulators tighten allowable limits, utilities and engineers face a complex reality: PFAS are unlike other contaminants. The same tools that work for metals, pathogens, or hydrocarbons often fall short here.
To understand why PFAS removal is so challenging, you have to start with the chemistry.
The bond that won’t break
PFAS are defined by chains of carbon atoms bonded to fluorine. The carbon–fluorine bond is one of the strongest in organic chemistry. It is short, highly stable, and extremely resistant to thermal, chemical, and biological attack.
In most organic molecules, carbon–hydrogen or carbon–carbon bonds can be broken by heat, sunlight, oxidants, or microbes. PFAS do not cooperate. The fluorine atoms create a kind of molecular armor around the carbon backbone.
That shield makes PFAS resistant to hydrolysis, oxidation, reduction, and biodegradation under typical environmental conditions.
From an engineering standpoint, this means that conventional treatment processes, such as biological wastewater treatment or simple oxidation, do almost nothing to break PFAS down. They persist.
That persistence is not accidental. It is exactly why these compounds were so widely used.
Designed to resist everything
PFAS have been used in firefighting foams, non-stick cookware coatings, stain-resistant fabrics, food packaging, semiconductor manufacturing, and industrial surfactants. Their appeal lies in their chemical stability and ability to repel both water and oil.
Two of the most studied PFAS are perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). Both were widely manufactured for decades before health and environmental concerns led to phase-outs in many countries. But thousands of other PFAS compounds exist, many with slightly different structures and behaviors.
That diversity adds another layer of difficulty. PFAS are not a single chemical; they are a large class of compounds with varying chain lengths, functional groups, and physical properties. A treatment method that works well for one compound may perform poorly for another.
Soluble, mobile, and hard to capture
Many problematic PFAS are highly soluble in water. Unlike oil-based contaminants that float or metals that can precipitate, PFAS often remain dissolved and mobile.
Short-chain PFAS, in particular, are smaller and more water-soluble than their long-chain counterparts. They travel easily through groundwater and are harder to adsorb onto traditional treatment media.
As manufacturers phased out longer-chain compounds, many shifted toward shorter-chain alternatives. From a treatment perspective, that trade-off often makes PFAS removal more challenging.
In groundwater systems, PFAS can migrate long distances from their original source. This mobility complicates remediation, especially in large plumes beneath industrial or military sites.
PFAS removal vs destruction: A critical distinction
Most widely used treatment systems are designed to separate PFAS from water rather than chemically break them down. In practice, that means the compounds are captured and concentrated so they can be managed in a controlled way.
Take granular activated carbon (GAC). It works through adsorption: PFAS molecules adhere to the surface of highly porous carbon particles. This approach has proven effective, particularly for longer-chain compounds. Over time, the carbon media is replaced or regenerated as part of routine system operation, allowing facilities to continue capturing PFAS reliably.
Ion exchange resins rely on a similar capture concept, but instead of porous carbon, they use engineered charged sites that attract and bind PFAS molecules. These materials can be tailored for selectivity and performance, and they are regenerated through established operational cycles that concentrate the captured compounds for downstream management.
Membrane systems, such as reverse osmosis, take a different route. They apply pressure to push water through a semi-permeable barrier, physically separating PFAS from the treated water stream. The result is very high removal efficiency, with the compounds collected into a smaller, concentrated stream that can then be handled appropriately.
Across these approaches, the core function is separation and containment. The engineering focus is on reliably capturing PFAS from water and consolidating them into manageable forms for further treatment or disposal.
Energy barriers to destruction
If PFAS are so stable, why not simply break them down with heat or advanced oxidation?
The challenge is the amount of energy required. Because the carbon–fluorine bond is so strong, destroying PFAS requires extreme conditions: very high temperatures, strong reducing environments, plasma systems, or advanced electrochemical processes.
High-temperature incineration is one option, but it must be carefully controlled to ensure complete destruction and prevent the formation of harmful byproducts. Supercritical water oxidation and plasma-based technologies are being studied as potential destruction methods.
These approaches can break down PFAS, but they are energy-intensive and not yet widely deployed at full municipal scale.
From a cost and infrastructure standpoint, scaling destruction technologies remains difficult.
The analytical challenge
Another reason PFAS removal is complicated is detection.
Regulatory limits are now set at extremely low concentrations — often in the parts-per-trillion range. Measuring PFAS accurately at those levels requires advanced analytical techniques such as liquid chromatography coupled with mass spectrometry.
If you cannot reliably measure a contaminant at regulatory thresholds, verifying treatment performance becomes complicated. Utilities must carefully monitor influent and effluent concentrations to ensure compliance, which often increases operational complexity and costs.
A problem of scale
PFAS contamination is rarely confined to a single, easily isolated source. Firefighting training areas, airports, industrial discharge sites, landfills, and wastewater treatment plants can all contribute.
Wastewater treatment facilities often receive PFAS from domestic and industrial inputs, but conventional treatment processes pass them through largely unchanged.
That means PFAS can accumulate in biosolids or be discharged into receiving waters. Even if drinking water plants remove PFAS effectively, upstream contamination may continue.
The scale of contamination requires both point-of-use solutions and broader source control measures. Without reducing emissions at the source, treatment systems are left managing a persistent influx.
The short-chain shift
Regulatory pressure led to phase-outs of certain long-chain PFAS in the early 2000s. In response, many manufacturers adopted shorter-chain alternatives.
Short-chain PFAS tend to bioaccumulate less than long-chain compounds, but they are often more mobile in water and harder to remove using traditional adsorption methods.
This shift illustrates a recurring theme in environmental engineering: replacing one problem sometimes creates another. Treatment systems designed around earlier PFAS profiles may require modification to address newer compounds effectively.
Why prevention matters
Given how difficult PFAS removal is, prevention becomes critical.
Source control, product reformulation, industrial pretreatment, and regulatory oversight can reduce the burden on downstream treatment systems. Designing chemicals that do not rely on ultra-stable fluorinated structures would ease future remediation challenges.
Engineering solutions can manage PFAS, but they are not simple, cheap, or universally scalable. When chemistry works this hard to resist degradation, it is always going to demand substantial energy, infrastructure, and cost to reverse it.
The core challenge
PFAS are hard to remove because they were engineered to be hard to break. The carbon–fluorine bond resists natural degradation.
Many PFAS dissolve easily in water and move freely through groundwater systems. Most current technologies separate them rather than destroy them, shifting the contamination from one place to another.
The challenge is not a failure of engineering. It is a reflection of chemistry.
As research continues into destruction technologies and more selective treatment methods, progress is being made. But the underlying lesson remains clear: when we design chemicals for extreme stability, we inherit the long-term responsibility of managing that stability in the environment.
That responsibility is now front and centre for utilities, regulators, engineers, and communities worldwide.
