How Millennial Scientific is Tackling PFAS Challenges

Per- and polyfluorinated alkyl substances (PFAS) are synthetic chemicals widely used in industrial processes and consumer products. There may be as many as 14,000 different PFAS chemicals in existence. Industrial processes that utilize PFAS include their use in the manufacturing of plastics, semiconductors, paints and varnishes, pesticides, waterproof textiles, electrical wires, and other chemicals. They are also used in consumer products such as non-stick cookware, cosmetics, fast food packaging, and waterproof clothing, as well as firefighting foams.

PFAS, often referred to as “forever chemicals,” are a pressing environmental concern. These synthetic

Figure. Representative PFAS molecular structure illustration.

compounds, due to their non-biodegradable nature, can accumulate in the environment and the tissues of humans and animals. Even at very low levels (parts per billion), PFAS in food and water sources can pose significant health risks, from elevated cholesterol levels to certain types of cancer. This urgency has led to global efforts to limit their use and mitigate their environmental impact [1].

Why are PFAS so persistent? The answer lies in their unique properties. The carbon-fluorine bond, one of the strongest chemical bonds, is the key to their resilience, earning them the moniker “forever chemicals.” The varying length of their fluorinated carbon chains, from one (C1) to eighteen (C18) Carbon atoms, imparts hydrophobic properties. Meanwhile, the acidic (e.g., carboxylic acids, sulfonic acids) and other (e.g., ethers, alcohols, chlorides, sulfonamides) end groups give them a hydrophilic character, resulting in a vast and complex chemical composition.

How are PFAS monitored? The most common method for detecting the presence of PFAS in a sample uses a reversed‑phase high-performance liquid chromatography (HPLC) separation followed by tandem mass spectrometry (MS) detection. Mass spectrometry combines the need for quantitation and confirmation of PLAS at low detection limits under matrix interferences. HPLC columns, packed with alkyl phases chemically bonded to silica microspheres, are mainly used. The bonded phases that have been used include C8, C18, phenyl-hexyl, and pentafluorophenyl (F5). C18 is the most widely used phase. The sample preparation of PFAS environmental specimens before HPLC MS continues to evolve and be optimized.

How are PFAS removed and disposed of?

Current Approaches. PFAS waste after processing is a water-based suspension. The PFAS is then extracted from the water through filters that contain materials such as granular activated Carbon, ion-exchange resins, or membranes.

Incineration, landfills, and deep well injections are commonly used globally to dispose of isolated PFAS waste. However, each method has its drawbacks. Incineration, for instance, can release harmful byproducts, while landfills and deep well injections pose the risk of groundwater and soil pollution if not adequately contained.

Controlled incineration combined with flue gas scrubbing is a method that involves high-temperature heating in the presence of oxygen, which converts the hydrophobic carbon components of PFAS into CO2. The resultant gas, known as flue gas, is chemically treated to limit particulate pollution, carbon dioxide emissions, and other harmful byproducts.

Landfill involves disposing of PFAS-contaminated filters, or removing them as solids, and encapsulating them in solid structures, such as concrete.

Deep Well Injection involves underground transport and storage of waste liquids.

Landfill and deep well injections pose environmental risks. If PFAS is not adequately contained within the landfill or deep well, it can pollute the groundwater and soil. This impact on the surrounding environment could potentially threaten public health. Landfills require ongoing monitoring and maintenance even after they reach capacity, which can be a significant financial burden for communities. Local communities are increasingly resistant to these forms of disposal.

Countries and communities choose one approach over the other based on their specific needs.

Emerging Approaches. Due to the aforementioned drawbacks and challenges, recent efforts have focused on destroying PFAS at the source, rather than transporting it off-site for burial or incineration. Emerging technologies include electrochemical oxidation, supercritical water oxidation, subcritical process hydrothermal alkaline treatment, plasma, ultraviolet light combined with photocatalysts, and sonolysis. This Chemical and Engineering News (C&EN) article provides a nice overview of these methods [2].

The idea is to combine these technologies with approaches to concentrate PFAS upstream (using granular activated Carbon, ion Exchange resins, or membranes) to destroy them at the source rather than transporting them to an external facility for disposal or incineration. This strategy is more sustainable.

How is Millennial Scientific contributing to the efforts to monitor, remove, and destroy PFAS?

PFAS Monitoring. We are developing multimodal reverse-phase ion exchange HPLC media, specifically for short-chain (C4–C7) and ultra-short-chain (≤C3) PFAS, where current C18 methods may be suboptimal.

When the environmental impact and health hazards of legacy long-chain (≥C8) PFAS were realized, a shift in manufacturing occurred to substitute their use with short-chain (C4–C7) and ultra-short-chain (≤C3) PFAS. Initially, it was believed that these substituted short- and ultra-short-chain PFAS would have less environmental and health impacts. However, this has not been the case, and they still pose significant health concerns.

Additionally, ultra-short chain PFAS may not be included in routine PFAS HPLC MS methods due to difficulties in separating these small compounds using the most commonly used silica C18 reverse phases. The hydrophobic carbon chain on PFAS molecules enables the reverse-phase retention and separation mechanism to function. However, as the C-F chain length decreases, the ability for hydrophobic retention on the C18 chemistry decreases. For example, perfluorobutanoic acid (PFBA), a perfluoroalkyl carboxylic acid with the formula C3F7COOH, elutes close to the void volume of an HPLC column with typical C18-based methods, indicating that it is just barely retained.

Our strategy involves the development of multimodal graphitic carbon microbeads that can interact more effectively with short and ultra-short-chain per- and polyfluoroalkyl substances (PFAS). The design of these microbeads is such that their average diameter is 5 μm, making them suitable for high-performance liquid chromatography (HPLC). Their graphitic structure facilitates reverse-phase interactions with the hydrophobic carbon chains. Additionally, the chemical composition is tailored to impart a positive charge on the microbeads, allowing them to electrostatically interact with the negatively charged ionic head group present on the PFAS chain, which provides a secondary retention mechanism. Together, these multimodal interactions improve the separation performance of short and ultrashort PFAS.

PFAS removal and destruction. Our strategy involves developing multimodal graphitic microbeads with an average diameter of 40 μm that can be used for Electrochemically Modulated Liquid Chromatography (EMLC), also known as Digital Chromatography. We externally apply a voltage (≤ 2 volts) to modify the interfacial properties of the electrically conductive graphitic carbon microbeads' stationary phase material (e.g., surface charge and oxidation state). This voltage allows the stationary Phase's composition to be tuned before or during the separation procedure, changing the interactions between the stationary phase and PFAS in real time. Technical issues have prevented the commercial development of this technique for chromatography, including a lack of customizable media suitable for scale-up, high costs, and batch-to-batch variability of current media (synthetic graphite) options. We are solving these issues.

Additionally, once nuisance analytes such as PFAS have been selectively separated, the same setup allows their electrochemical breakdown by marginally increasing the external voltage.

The unique features of our approach include:

1. Capture, release, and degradation (if needed) of PFAS driven by applied voltage. This simplifies the workflow, reducing or eliminating the need for ionic buffers and minimizing the use of water to retain and release the analytes from the stationary phase material. If necessary, the same setup can be used for the electrochemical degradation of the analytes. These benefits lower operational and maintenance costs.

2. Ion exchange and reverse-phase separation mechanism. The surface charge retains the analytes even after the removal of the electric field. Additionally, the graphitic microbead's chemical composition facilitates non-covalent interactions with the carbon chain present on PFAS. This multimodal separation of PFAS improves separation efficiencies. This capability enables efficient, repetitive, selective separation of analytes.

Our technology and products, incorporating sustainability principles from cradle to grave, help PFAS removal and destruction operations work more sustainably. The selective electrochemical extraction and destruction of PFAS chemicals using the same setup eliminates the need for removal and storage of PFAS. Currently, two separate steps are used to remove and destroy PFAS: the first involves reverse osmosis (RO), granular activated carbon (GAC) filters, and ion exchange to extract PFAS, while the second step involves PFAS destruction techniques as outlined in the Emerging Approaches section above. Our approach combines these two steps into a single unit operation, significantly reducing the use of consumables, water, and energy. It controls and abates waste emissions, conserves water usage, destroys PFAS, and recycles functional consumable materials.

For more information on how our NanoPak-C All Carbon media or custom media services can address your PFAS challenges, or to request samples, please email us at inquiry@millennialscientific.com, call us at 855-388-2800, or complete our online form.

References

1. PFASs Listed Under the Stockholm Convention (UN Environment Program, 2019https://chm.pops.int/Implementation/IndustrialPOPs/PFAS/Overview/tabid/5221/Default.aspx).

   
   

2. Britt E. Erickson, Competition to destroy ‘forever chemicals’ heats up, C&EN, Volume 102, Issue 7, 2024. https://cen.acs.org/environment/persistent-pollutants/Competition-destroy-forever-chemicals-heats/102/i7