Lowering PFAS concentrations in tap water is essential.
To achieve this, water treatment systems use technologies such as activated carbon adsorption.
If testing confirms that PFAS concentrations are below regulatory or advisory limits, the immediate safety of drinking water can be protected.
Yet one question remains:
Where does the PFAS removed from the water actually go?
PFAS adsorbs onto activated carbon.
It is separated by membranes and transferred into concentrated wastewater.
It can also be collected with foam.
Even when PFAS disappears from the water in front of us, the substances themselves have not necessarily disappeared.
From water to activated carbon.
From groundwater to concentrated liquid.
From widespread, low-level contamination to a smaller volume of highly concentrated pollution.
The fundamental difficulty of PFAS management is that removing PFAS is not the same as destroying it.
The third article in this series examines removal technologies such as activated carbon, as well as the challenges that arise afterward: spent carbon, concentrated wastewater, incineration, disposal, and the question of who pays for long-term treatment.
Water Treatment Does Not Make PFAS Disappear
Conventional water treatment plants typically use processes such as coagulation, in which chemicals are added to raw water to gather fine particles; sedimentation, in which those particles are allowed to settle; and filtration through sand or other materials.
These processes are effective for removing turbidity and particulate matter.
However, PFOS and PFOA dissolved in water are difficult to remove sufficiently through conventional coagulation, sedimentation, and sand filtration alone.
This is why the following technologies are being considered and deployed:
- Granular activated carbon
- Powdered activated carbon
- Ion-exchange resins
- Reverse osmosis membranes
- Nanofiltration membranes
- Foam fractionation
- Treatment systems combining multiple technologies
These technologies adsorb or separate PFAS from water, lowering the concentration remaining in treated water.
In many cases, however, they do not completely break down the exceptionally strong carbon–fluorine bonds that characterize PFAS.
They simply move PFAS from water to another location.
Why Can Activated Carbon Remove PFAS?
One of the best-known PFAS treatment methods is adsorption using activated carbon.
The surface of activated carbon contains countless microscopic pores. These give the material an extremely large surface area and allow it to adsorb organic compounds and other substances from water.
PFOS and PFOA can also be captured on this surface.
Water treatment plants may pass water through adsorption vessels filled with granular activated carbon or add powdered activated carbon directly to water before recovering it.
When properly managed, activated carbon can be an effective way to reduce PFAS concentrations in water.
Its performance, however, is not constant.
Removal efficiency varies depending on the type of activated carbon, water temperature, water chemistry, PFAS concentration, the amount of other organic matter present, and the contact time between the water and the carbon.
Adsorption also differs among PFAS compounds. In general, long-chain PFAS tend to adsorb more readily to activated carbon, while short-chain PFAS are more likely to pass through treatment.
Even if a system monitors only the combined concentration of PFOS and PFOA, other short-chain PFAS may still be passing into the treated water. Further research and monitoring will be needed to understand this risk.
Activated Carbon Has a Replacement Cycle
The amount of PFAS that activated carbon can adsorb is limited.
As it continues to be used, its surface gradually fills with PFAS and other organic compounds. Eventually, its adsorption capacity declines.
When the carbon approaches saturation, “breakthrough” may occur, allowing PFAS to pass into the treated water.
Installing activated carbon is therefore not the end of the process.
Water must be monitored continuously before and after treatment. Changes in concentration must be tracked, and the carbon must be replaced at the appropriate time.
If PFAS concentrations in the raw water are high, replacement will be required more frequently. Water containing large amounts of other organic substances may also exhaust activated carbon more quickly because those compounds compete for adsorption sites.
In addition to the initial cost of installing the equipment, the following operating expenses continue over time:
- Water-quality testing
- Purchasing activated carbon
- Maintaining adsorption vessels
- Replacing activated carbon
- Transporting spent carbon
- Regenerating or disposing of spent carbon
- Verifying treatment performance
PFAS treatment is not a public works project that ends once a facility has been built.
As long as contaminated raw water continues to be used, the costs and management responsibilities remain.
Spent Activated Carbon Becomes a Material That Has Collected Pollution
Activated carbon that has adsorbed PFAS contains the contaminants removed from the water.
Its characteristics are therefore different from those of unused carbon.
PFAS that was previously spread at low concentrations across a large volume of water has now been collected inside a single vessel, container, or adsorption system.
Japan’s Ministry of the Environment explains in its PFAS handbook that, if spent activated carbon is not managed properly, adsorbed substances such as PFOS may leach out and cause further environmental contamination.
When spent carbon must be stored for an extended period, it is important to keep it indoors, protect it from rainwater, and inspect its storage condition regularly.
If it is left exposed to the elements or stored at a poorly managed site, rainwater could carry the collected PFAS back into the environment.
A material used to clean water must not be allowed to become a new source of contamination.
Can Activated Carbon Be Reused After Regeneration?
Spent granular activated carbon can sometimes be regenerated and reused through processes such as thermal reactivation.
Regeneration removes substances adsorbed within the carbon’s pores and restores some of its adsorption capacity.
Compared with using new activated carbon every time, this may reduce resource consumption and waste generation. Technical demonstrations conducted by Japan’s Ministry of the Environment have also estimated potential reductions in carbon dioxide emissions through the circular use of regenerated activated carbon.
However, “the carbon has been regenerated” and “the PFAS has been completely destroyed” are two different claims that must be evaluated separately.
If the temperature, residence time, furnace design, or exhaust-gas treatment is inadequate, PFAS or partially decomposed substances could be transferred into exhaust gases or other waste streams.
How much PFAS remains in the regenerated carbon?
How completely was it destroyed by heat?
What remains in the exhaust gas and ash?
The entire process can only be evaluated by examining not merely the incoming spent carbon but also the regenerated carbon, exhaust gases, ash, and wastewater leaving the system.
Ion-Exchange Resins Also Create a Destination for PFAS
Ion exchange is a process in which specific ions dissolved in water are adsorbed onto a resin.
Depending on operating conditions, ion-exchange resins may provide greater adsorption capacity than activated carbon and allow treatment equipment to be made more compact.
Once a resin loses its adsorption capacity, however, it must be replaced or regenerated.
A disposable resin must be managed appropriately as PFAS-containing waste. If the resin is regenerated, the process produces a concentrated regeneration liquid containing PFAS washed out of the resin.
Again, the PFAS has not disappeared.
It has moved from the water to the resin and then into an even more concentrated waste liquid.
When evaluating a treatment technology, it is therefore necessary to consider not only the PFAS concentration in the treated water but also how the resin and regeneration waste will ultimately be managed.
Reverse Osmosis Produces Highly Concentrated Wastewater
Reverse osmosis applies pressure to water and forces it through an extremely fine membrane, separating water from dissolved substances.
It can potentially remove a high proportion of PFAS as well as many other contaminants.
On the opposite side of the membrane from the purified water, however, a concentrated waste stream remains.
Even when most of the incoming water is recovered as treated water, PFAS accumulates in the smaller volume left behind. The total volume becomes smaller, but the concentration becomes higher.
If this concentrate is discharged untreated into a river or sewer system, the PFAS may simply be transferred to another water system.
Reverse osmosis also presents several other challenges:
- Energy consumption required to maintain high pressure
- Membrane fouling
- Regular cleaning
- Membrane replacement
- Treatment of membrane-cleaning wastewater
- Management of PFAS concentrate
A high removal rate alone does not determine whether a technology is sustainable.
We must ask what was removed, where it accumulated, and how it will be treated afterward.
The entire water-treatment process must be followed.
Collecting PFAS in Foam
Some PFAS have surfactant properties and tend to accumulate at the boundary between water and air.
Foam fractionation uses this characteristic.
Air bubbles are introduced into the water, PFAS gathers on the bubble surfaces, and the resulting foam is collected.
If PFAS spread thinly through a large volume of water can be concentrated into a small amount of foam or liquid, the volume requiring further treatment may be significantly reduced.
Foam fractionation, however, does not destroy PFAS.
The collected foam and concentrate still contain PFAS and require additional treatment.
Rather than solving the problem on its own, foam fractionation is expected to serve as a pretreatment step before activated carbon adsorption, membrane filtration, or thermal destruction, reducing the volume that must undergo final treatment.
Combining Separation and Destruction
Attempting to apply high-temperature treatment directly to PFAS-contaminated water would require heating an enormous volume of water and consuming a great deal of energy.
Practical treatment therefore requires two main stages:
- Separate PFAS from a large volume of water and concentrate it into a smaller volume.
- Destroy or appropriately dispose of the concentrated PFAS.
Activated carbon, ion-exchange resins, membranes, and foam fractionation primarily perform the first stage.
Incineration, thermal decomposition, plasma, and other technologies are being examined for the second stage.
PFAS management therefore requires more than searching for a single universal technology. Multiple processes must be combined according to the contamination level, water volume, water chemistry, and physical form of the resulting waste.
Does Incineration Completely Destroy PFAS?
In Japan, technical guidance describes incineration and other treatment methods for waste containing PFOS and PFOA.
Such waste must be processed at facilities capable of maintaining appropriate temperatures and residence times while controlling exhaust gases.
PFAS contains extremely strong carbon–fluorine bonds.
If the temperature is too low or the waste remains inside the furnace for too short a time, complete destruction may not occur. Other PFAS compounds or fluorinated substances could potentially be produced.
The furnace’s set temperature is not the only important factor.
The treatment system must also be evaluated according to:
- The temperature actually experienced by the waste
- Residence time inside the furnace
- Combustion conditions, including oxygen availability
- The concentration and quantity of PFAS entering the system
- Exhaust-gas treatment equipment
- Management of ash and fly ash
- Measurement of exhaust gases, wastewater, and residues
Japan’s Ministry of the Environment has conducted technical demonstrations of thermal treatment for PFAS-contaminated soil and waste. These studies examine not only treated soil but also exhaust gases, fly ash, and other outputs.
We cannot simply conclude that PFAS has disappeared because it was burned.
We must determine how the fluorine originally contained in PFAS was ultimately recovered, transformed, or released.
Can Plasma and Other Destruction Technologies Become Practical?
Research and development are advancing on new methods for destroying PFAS, including plasma treatment, electrochemical oxidation, supercritical water oxidation, and photochemical treatment.
Plasma treatment uses a high-energy state to break the exceptionally strong bonds within PFAS molecules.
Some demonstrations are examining systems in which PFAS is first concentrated through foam fractionation or freeze concentration and then destroyed using plasma.
However, achieving a high destruction rate in a laboratory or small-scale demonstration does not mean that the same system can immediately be deployed at water treatment plants nationwide.
Several questions remain:
- Can the technology process large volumes of water?
- Is its energy consumption realistic?
- Can the equipment operate reliably over long periods?
- Will short-chain PFAS or decomposition products remain?
- Can a complete mass balance be confirmed using total fluorine measurements?
- Are the installation and operating costs affordable?
- Can the system remain safe during equipment failures or natural disasters?
There is a considerable distance between “PFAS was destroyed in a research trial” and “this system can be operated safely as public infrastructure.”
Demonstration reports from Japan’s Ministry of the Environment have also noted that commercial-scale applications of non-incineration PFAS destruction technologies remain limited in Japan.
Does Landfilling Merely Send the Problem into the Future?
When PFAS-containing waste is disposed of in a landfill, the PFAS itself is not destroyed.
Engineered landfills may have liners and leachate-treatment systems. Over the long term, however, it is still necessary to consider the possibility that PFAS-containing water could leach out of the waste.
If the leachate is treated with activated carbon, another stream of spent activated carbon is produced.
Will that carbon be incinerated?
Will it be regenerated?
Will it be stored somewhere else?
As PFAS moves from one facility to another, it creates a chain of management responsibilities.
Interim guidance updated by the U.S. Environmental Protection Agency in 2026 also addresses incineration, landfilling, and underground injection of PFAS-containing materials. It emphasizes minimizing environmental releases while acknowledging the uncertainties associated with different disposal methods.
Overseas regulations cannot simply be applied to Japan without considering differences in law and infrastructure.
Nevertheless, the underlying principle is shared: PFAS must continue to be tracked even after what is described as “final disposal.”
Removal Rates Alone Cannot Evaluate a Technology
PFAS treatment technologies are often introduced through a single figure: the percentage of PFAS they can remove.
The ability to reduce PFAS concentrations in treated water is, of course, important.
But a removal rate does not tell the entire story.
Even if a facility removes 99 percent of PFAS, the remaining one percent may still be discharged with a very large volume of treated water.
Conversely, even if PFAS can be concentrated effectively, the problem remains unresolved if the concentrate cannot be treated safely.
A comprehensive evaluation should consider:
- PFAS remaining in treated water
- Performance against short-chain PFAS
- PFAS transferred to activated carbon or resin
- Concentrated wastewater and cleaning water
- Exhaust gases from incineration
- Bottom ash and fly ash
- Intermediate decomposition products
- Energy consumption
- Carbon dioxide emissions
- Leakage risks during transportation
- Long-term operating costs
Rather than measuring only part of the input and output, treatment systems must establish a mass balance for PFAS and fluorine across the entire process.
Who Pays for PFAS Treatment?
PFAS management creates long-term costs.
When groundwater or rivers are contaminated, water utilities may be forced to stop using a water source, blend it with water from another source, or install additional treatment equipment.
Not every region, however, has access to an alternative water source.
If activated carbon treatment must continue, replacement and disposal costs will continue for as long as PFAS remains in the raw water.
When the source of contamination and the responsible party can be identified, it may be possible to discuss requiring that party to bear the costs.
As examined in the second article in this series, however, identifying the source of groundwater contamination can be extremely difficult.
The original operator may no longer exist.
Multiple sources may overlap.
Records of historical PFAS use may not remain.
The discharge may have occurred before regulations were established.
If no responsible party can be identified, local governments or water utilities may have to pay for countermeasures. Those costs may eventually be reflected in taxes or water charges.
Owners of private wells may also have to pay for household treatment systems, replacement filters, water testing, and alternative drinking water.
The people who created the contamination are not always the people who pay to address it.
This is one of the environmental justice issues at the heart of the PFAS problem.
Can Household Water Filters Solve the Problem?
As public concern about PFAS grows, interest in household water filters is also increasing.
Some products using activated carbon or reverse osmosis can reduce PFAS concentrations under specified conditions.
Not every water filter, however, has demonstrated PFAS removal performance. Effectiveness changes according to water quality and the length of use, and removal capacity declines if cartridges are not replaced appropriately.
Household systems also produce used cartridges containing adsorbed PFAS.
A home water filter can be one option for reducing an individual’s exposure.
It cannot resolve groundwater contamination across an entire community.
If the public responsibility of providing safe tap water is shifted entirely to individuals who can afford treatment equipment, access to safe water will become unequal according to economic circumstances.
What is needed is not only individual self-protection but an integrated social response combining source investigation, raw-water monitoring, water treatment, and waste management.
Preventing Pollution from Being Moved Somewhere Out of Sight
Keeping tap-water concentrations below health-based limits is essential for protecting residents.
Preventing exposure through drinking water must remain the first priority.
But the PFAS problem does not end the moment the number measured at the tap falls.
Where is the spent activated carbon stored?
Who transports it?
At which facilities is it regenerated or incinerated?
Are exhaust gases and ash being tested?
How is concentrated wastewater treated?
Who bears the cost?
This information should be made available to the public just as water-quality testing results are.
If the treatment pathway remains invisible, residents cannot determine whether the pollution was merely moved outside the water treatment plant or whether it was actually destroyed and responsibly managed.
PFAS Management Must Not End with “Removed”
PFAS can be removed from water.
But the PFAS that has been removed remains somewhere else.
If it is collected on activated carbon, the spent carbon must be treated.
If it is separated by a membrane, the concentrate must be treated.
If a resin is regenerated, the regeneration liquid must be treated.
If PFAS waste is incinerated, the exhaust gases and ash must be examined.
The output of one process becomes the input of the next.
This is why PFAS management must ask not only whether the water has become cleaner but whether the substances removed from it can be tracked to the very end.
Remove PFAS from water.
Concentrate it into a smaller volume.
Safely destroy or treat the collected PFAS.
Measure the exhaust gases, wastewater, and residues produced afterward.
Preserve the records and share them with society.
Only when this entire chain is connected can it truly be called PFAS treatment.
Water purification is not the end of the problem.
Where did the PFAS go after it disappeared from our sight?
Society has a responsibility to follow it all the way to its final destination.
References
- Ministry of the Environment, Japan: Information on Per- and Polyfluoroalkyl Substances (PFAS)
- Ministry of the Environment, Japan: PFAS Handbook
- Ministry of the Environment, Japan: Collection of Technologies for Reducing PFOS and Related Substances
- Ministry of the Environment, Japan: Guidelines for Responding to PFOS and PFOA, Third Edition
- Ministry of the Environment, Japan: Demonstration Report on PFAS Destruction and Treatment Technologies
- Ministry of the Environment, Japan: FY2024 Technology Demonstration for Reducing PFOS and Related Substances
- Ministry of the Environment, Japan: Questions and Answers on PFOS and PFOA
- U.S. Environmental Protection Agency: 2026 Interim Guidance on the Destruction and Disposal of PFAS and PFAS-Containing Materials
This article is based on information publicly available as of August 2026.
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