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How forever chemicals (PFAS) are removed

Q: A question for science : what process, substance or organic material will capture forever chemicals?

K: Various substances and processes can capture "forever chemicals"—or per- and polyfluoroalkyl substances (PFAS)—by adsorbing them, but these methods must be followed by destruction or disposal to truly eliminate the compounds. The most effective methods used for water purification are activated carbon and ion exchange resins. Innovative materials like cyclodextrin-based polymers and natural substances like chitin are also being developed and tested.

Adsorption methods used

Adsorption is a process where a substance accumulates on the surface of another material. This is the most common method for removing PFAS from water.

Granular Activated Carbon (GAC): GAC is made from carbon-rich organic materials like coal, wood, or coconut shells that are processed to have millions of tiny pores.
- How it works: PFAS molecules stick to the porous surface of the carbon as contaminated water passes through a filter bed.
- Performance: While very effective at removing longer-chain PFAS like PFOA and PFOS, it is less efficient for smaller, shorter-chain PFAS.
- Drawbacks: The carbon can become saturated with other compounds, which reduces its capacity to capture PFAS over time.
Ion Exchange Resins: These are highly porous, polymer-based beads with a charged surface.
- How it works: Since most common PFAS are negatively charged, they are electrostatically attracted to and captured by positively charged "anion exchange" resins.
- Performance: This method is often more selective and effective than GAC for a wider range of PFAS compounds, including shorter-chain ones.
- Drawbacks: Ion exchange resins are generally more expensive than GAC.
Cyclodextrin-Based Polymers: This is an advanced technology using "cage-like" molecules derived from starch.
- How it works: Cross-linked cyclodextrin polymers have a hydrophobic (water-repelling) cavity that can trap PFAS molecules. Scientists have developed new variants that use both hydrophobic and electrostatic forces for more targeted capture.
- Performance: These materials can be specifically engineered to bind to a wider range of PFAS and can be regenerated and reused multiple times.
- Advantages: They are highly selective for PFAS and are resistant to fouling by other organic matter that can plague activated carbon filters.

Membrane filtration

High-pressure membrane systems physically separate PFAS from water based on molecular size.

Nanofiltration (NF) and Reverse Osmosis (RO): These systems force contaminated water through semi-permeable membranes with extremely small pores.
- How it works: The membrane pores are small enough to block and retain PFAS molecules while allowing water to pass through.
- Performance: This is one of the most effective removal methods, often achieving over 90% removal for a wide range of PFAS compounds.
- Drawbacks: This process is energy-intensive and produces a concentrated waste stream that still requires specialized treatment or disposal.

Emerging and natural adsorbents

Scientists are also exploring renewable, organic materials for capturing PFAS.

Chitin and Chitosan: Chitin is a natural biopolymer from the shells of crustaceans and insects, and chitosan is a derivative.

How it works: Research shows that chitosan can effectively adsorb PFAS from wastewater. Its charged amino groups can be engineered to electrostatically attract contaminants like PFAS.

Advantages: Chitin is abundant and derived from a renewable waste source, making it a potentially inexpensive and sustainable option.

What happens to the captured forever chemicals?

Capturing PFAS is only the first step. The contaminated material must then be properly destroyed or disposed of. Methods for addressing the waste include:

Thermal Treatment: Incinerating the contaminated filter material at extremely high temperatures to break down the carbon-fluorine bonds.
Specialized Disposal: Landfilling the spent filter media with long-term management to prevent chemicals from re-entering the environment.
Regeneration: In some cases, such as with certain ion exchange resins and cyclodextrin polymers, the filtering material can be cleaned and reused, but this creates a highly concentrated liquid waste stream.

How forever chemicals (PFAS) are removed

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