Short-chain PFAS, more difficult to remove from drinking water

Michael Bartlett

By Michael Bartlett

Posted on August 07th, 2023

While short-chain PFAS show more hydrophilicity, long-chain PFAS show more hydrophobicity. This means that the former are more soluble in water, making these highly toxic chemicals very challenging to remove by using the technology for the latter. Nevertheless, exposure to both types of PFAS is dangerous to human health.

As the most well-known emerging contaminants, PFAS have become a major environmental issue over recent years. Based on their carbon chain number, these substances can be divided into short-chain compounds and long-chain compounds. Short-chain PFAS are significantly more soluble in water than long-chain PFAS, which makes the process of removal very difficult. Being surfactants, all of these chemicals have a hydrophobic tail and a hydrophilic function head. Short-chain PFAS show more hydrophilicity, whereas long-chain PFAS show more hydrophobicity. Consequently:

  • a higher solubility is often seen for a compound with high hydrophilicity, and solubility usually increases when the carbon chain number decreases
  • sorption efficacy is high for a compound with high hydrophobicity, and sorption generally increases when the carbon chain number increases
  • surfactants can create foam when gas is applied to the water, and the ability to form foam increases when the carbon chain number increases

Removing PFAS from drinking water sources is challenging due to the physical and chemical nature of these substances. Furthermore, all treatment technologies available are generally less effective for short-chain PFAS. It is worth noting that none of the current technologies can readily achieve the recently recommended levels from the national regulatory progress. This is how the characteristics of PFAS impact drinking water treatment:

  • Sorption: The common sorption media includes activated carbon, ion-exchange resin, and organoclay. All sorption media can sequester PFAS through hydrophobic sorption. The sorption of short-chain PFAS is less efficient, as they generally show less hydrophobicity. Ion-exchange resin and organoclay can also sorb PFAS via electrostatic charges. Therefore, ion-exchange resin and organoclay exhibit higher sorption efficiency for short-chain PFAS than activated carbon.
  • Reverse osmosis: This method filters water through a semi-impermeable membrane under high pressure. Larger molecules can be more readily filtered, and long-chain PFAS are larger molecules than short-chain PFAS. Even though reverse osmosis can thoroughly filter all PFAS, the filtration efficacy of the short-chain is generally less than the long-chain.
  • Precipitation: PFAS can be precipitated through coagulation and flocculation, the conventional wastewater treatment technology. The chemicals generally show negative electrostatic charges at circumneutral pH conditions, so cationic flocculant is more suitable for PFAS precipitation in drinking water with a circumneutral pH range. PFAS precipitate through electrostatic charge sorption with cationic flocculant and also co-precipitate with flocs. Higher hydrophobicity of PFAS results in more removal efficiency via co-precipitation, which means short-chain PFAS are less effective for precipitation.
  • Foam fractionation: This technology removes PFAS using the ability of the chemicals to form foam. It requires minimal pre-treatment. Although the foamability of PFAS can be reduced by various factors, foam can be formed and recovered as a waste concentrate. Nevertheless, the foamability of short-chain PFAS is significantly less than that of long-chain PFAS, which also makes this method less effective.
  • Oxidation: Oxidation methods first break down long-chain PFAS into short-chain PFAS, which can be seen as transient oxidation daughter products. Consequently, short-chain PFAS can be the most persistent PFAS in the oxidation treatment process. Many innovative methods using oxidation can be highly interfered with by the high organic contents in the drinking water.

According to a study from Applied Sciences, so far, low carbon treatment techniques of short-chain PFAS have included adsorption, membrane separation, bioremediation, and degradation techniques relating to advanced oxidation, plasma, thermolytic, and sonochemical degradation. These technologies could remove short-chain PFAS to a certain extent. Adsorption is the utmost widely applied technique for short-chain PFAS. The removal mechanisms of short-chain PFAS were mainly electrostatic action, hydrophobic effect, and ion exchange.

Finally, advanced oxidation techniques involving electrochemical oxidation and photocatalytic degradation degraded short-chain PFASs mainly relying on active free radicals. However, these techniques were not suitable for trace levels of short-chain PFAS. Therefore, the following removal technologies could be suitable for removing short-chain PFAS from drinking water sources:

  • adsorption
  • membrane separation
  • bioremediation
  • degradation techniques

If your drinking water supply is contaminated with PFAS, your community might be entitled to financial compensation from the PFAS water contamination lawsuit. The money you might obtain will cover the cost of water testing, remediation, and treatment. Our attorneys will gladly help you determine whether you qualify to join the PFAS water contamination lawsuit with minimal involvement from you.

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