Per- and polyfluoroalkyl substances, known as PFAS, have an unfortunate nickname: “Forever Chemicals.”
That sounds dramatic, but from a chemistry and engineering perspective, it’s not far from the truth. PFAS are resistant to heat, water, oil, sunlight, and biological degradation.
These properties have made it commercially valuable for decades. These are also the reasons why PFAS are so difficult to remove from water, soil, and waste streams.
Communities around the world are currently grappling with contamination of drinking water supplies, fire training areas, industrial facilities, and landfills. As regulators tighten tolerance limits, utilities and engineers are faced with the complex reality that PFAS are different from other pollutants. The same tools available for metals, pathogens, and hydrocarbons are often insufficient here.
To understand why PFAS removal is so difficult, we need to start with chemistry.
unbreakable bond
PFAS are defined by a chain of carbon atoms bonded to fluorine. The bond between carbon and fluorine is one of the strongest bonds in organic chemistry. It is short, stable, and highly resistant to thermal, chemical, and biological attacks.
In most organic molecules, carbon-hydrogen or carbon-carbon bonds can be broken by heat, sunlight, oxidants, and microorganisms. PFAS will not cooperate. Fluorine atoms create a kind of molecular armor around the carbon skeleton.
This shielding makes PFAS resistant to hydrolysis, oxidation, reduction, and biodegradation under common environmental conditions.
From an engineering perspective, this means that traditional treatment processes such as biological wastewater treatment and simple oxidation are largely ineffective at breaking down PFAS. they stick.
That tenacity is no accident. This is exactly why these compounds were so widely used.
Designed to resist everything
PFAS are used in firefighting foams, nonstick coatings on cookware, stain-resistant fabrics, food packaging, semiconductor manufacturing, and industrial surfactants. Its appeal lies in its 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 being phased out in many countries due to health and environmental concerns. But there are thousands of other PFAS compounds, many with slightly different structures and behaviors.
This diversity adds an additional layer of difficulty. PFAS are not a single chemical. These are a large class of compounds with varying chain lengths, functional groups, and physical properties. A treatment that works well for one compound may not work well for another.
Soluble, mobile, difficult to capture
Many problematic PFAS are highly soluble in water. Unlike airborne oil-based contaminants or metals that can precipitate, PFAS often remain mobile in a dissolved state.
In particular, short-chain PFAS are smaller and more water-soluble than long-chain PFAS. They move easily through groundwater and are less likely to be adsorbed by conventional treatment media.
As manufacturers phase out long-chain compounds, many have moved to shorter-chain alternatives. From a treatment perspective, that tradeoff often makes PFAS more difficult to remove.
In groundwater systems, PFAS can travel long distances from their original source. This fluidity makes remediation difficult, especially in large plumes beneath industrial or military sites.
PFAS Removal and Destruction: Key Differences
The most widely used treatment systems are designed to separate PFAS from water rather than chemically degrade them. In practice, this means that compounds can be captured and concentrated and managed in a controlled manner.
Consider granular activated carbon (GAC). This works by adsorption. PFAS molecules attach to the surface of highly porous carbon particles. This approach has proven particularly effective for long-chain compounds. Over time, the carbon media is replaced or regenerated as part of regular system operations, ensuring that the facility continues to capture PFAS.
Ion-exchange resins are based on a similar trapping 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 are regenerated through established operational cycles that concentrate captured compounds for downstream management.
Membrane systems such as reverse osmosis take a different route. Pressure is applied to force water through a semi-permeable barrier, physically separating PFAS from the process water stream. As a result, very high removal efficiencies are obtained, and compounds are collected in smaller concentrated streams that can be properly processed.
Across these approaches, the core features are separation and containment. The engineering focus is on ensuring that PFAS are captured from water and integrated into a manageable form for further treatment or disposal.
energy barrier to destruction
If PFAS are so stable, why not just break them down with heat or advanced oxidation?
The challenge is the amount of energy required. Because the bond between carbon and fluorine is so strong, extreme conditions are required to destroy PFAS, including very high temperatures, strongly reducing environments, plasma systems, and advanced electrochemical processes.
High-temperature incineration is also an option, but must be carefully controlled to ensure complete destruction and prevent the formation of harmful by-products. Supercritical water oxidation and plasma-based techniques are being investigated as potential destruction methods.
Although these approaches have the potential to destroy PFAS, they are energy intensive and have not yet been widely deployed at a full municipal scale.
Scaling destructive technology remains difficult from a cost and infrastructure perspective.
Analytical challenges
Another reason PFAS removal is complicated is detection.
Currently, regulatory limits are set at very low concentrations, often in the parts per trillion range. Accurately measuring PFAS at these levels requires advanced analytical techniques such as liquid chromatography combined with mass spectrometry.
Validation of treatment performance is complicated when contaminants cannot be reliably measured at regulatory thresholds. Utilities must carefully monitor influent and effluent concentrations to ensure compliance, which often increases operational complexity and costs.
A matter of scale
PFAS contamination is rarely confined to a single, easily isolated source. Fire training ranges, airports, industrial wastewater fields, landfills, and sewage treatment plants can all contribute.
Wastewater treatment facilities often receive PFAS from household and industrial inputs, but traditional treatment processes pass them through largely unchanged.
This means that PFAS can accumulate in biosolids or be discharged into receiving waters. Even if drinking water plants effectively remove PFAS, upstream contamination can persist.
The scale of contamination requires both point-of-use solutions and broader source control measures. If emissions are not reduced at the source, treatment systems will remain in control of a persistent influx.
short chain shift
Regulatory pressure led to the phase-out of certain long-chain PFAS in the early 2000s. In response, many manufacturers have adopted shorter chain alternatives.
Although short-chain PFAS tend to bioaccumulate less than long-chain compounds, they are often more mobile in water and difficult to remove using traditional adsorption methods.
This change illustrates a recurring theme in environmental engineering. That is, replacing one problem may introduce another. Treatment systems designed based on initial PFAS profiles may need modification to effectively address new compounds.
Why prevention is important
Given how difficult PFAS are to remove, prevention is key.
Source control, product reformulation, industrial pretreatment, and regulatory oversight can reduce the burden on downstream processing systems. Designing chemistries that do not rely on ultrastable fluorinated structures will alleviate 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 always takes a lot of energy, infrastructure, and cost to reverse it.
core issues
PFAS are difficult to remove because they are designed to be indestructible. The bond between carbon and fluorine prevents natural deterioration.
Many PFAS are readily soluble in water and move freely through groundwater systems. Most current technologies separate them rather than destroy them, moving contamination from one place to another.
This challenge is not an engineering failure. It’s a reflection of chemistry.
Research continues and progress is being made in destructive techniques and more selective treatment methods. But the underlying lesson remains clear. When we design a chemical for extreme stability, we inherit a long-term responsibility to manage its stability in the environment.
That responsibility is now top of mind for utilities, regulators, engineers, and communities around the world.
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