Per- and Polyfluoroalkyl Substances (PFAS) are a class of potenitally thousands of sythetic chemicals. PFAS were used in thousands of common products such as fire fighting foams, non-stick pans, stain guards, and other manufacturing processes. Generally, PFAS remediation is either completed by concentration methods (adsorption or filtration) and destruction or by direct destruction. Because the carbon-fluorine bond is one of the strongest covalent bonds in nature, only high-energy destruction processes are believed to be effective on PFAS. Commonly analyzed for PFAS compounds are:
- Perfluorooctane sulfonate (PFOS)
- Perfluorooctanoic acid (PFOA)
- Perfluorohexane sulfanate (PFHxS)
- Perfluorononanoic acid (PFNA)
Other "emerging" PFAS compounds include:
- Perfluorobutanesulfonic acid (PFBS)
- GenX
It is important to remember that, while many of the remedial techniques outlined below are applicable, adsorption and filtration remedial techniques are generally less cost effective on shorter chain PFAS compounds.
Applicable Remediation Technologies for PFAS
Physical
Air Sparging: Poor – As the vapor pressure is lower than 1 mm Hg and the compounds are relatively soluble, air sparging is not an effective process for groundwater remediation of PFAS.
SVE: Poor – As the vapor pressure is lower than 1 mm Hg , soil vapor extraction is not effective process for PFAS contamination.
Thermal: Good– Thermally enhanced technologies such as ISCO and ISCR (see below) have shown some promise in treating PFAS in groundwater.
Chemical
In Situ Chemical Oxidation (ISCO): Poor to Good – There are some field and laboratory demonstrations that show that specialized or enhanced chemical oxidation processes can effectively treat PFAS compounds.
In Situ Chemical Reduction (ISCR): Poor to Good – There are some field and laboratory demonstrations that show that heat- or pressure-enhanced ISCR processes can effectively treat PFAS compounds.
Biological
Aerobic: Poor – PFAS are generally not biodegraded in aerobic groundwater.
Anaerobic: Poor – Generally, PFAS not fully saturated with fluorine (“polys” or precursors) can be anaerobically degraded. Anaerobic degradation will transform the “poly” PFAS compounds into fully fluorine saturated compounds or “pers”. Full fluorine saturated PFAS compounds are currently not believed to degrade biologically.
Absorption
Activated Carbon/Resins: Excellent – PFAS can readily adsorb to activated carbon and manufactured resins. The initial capital costs associated with resins can be higher, but total project cost may be lower due to higher capacity for adsorption than activated carbon.
Chemical/Physical Properties of PFOA and PFOS
| Property | PFOA | PFOS | Benzene |
| Chemical Formula | C8HF15O2 | C8HF17O3S | C6H6 |
| Molecular Weight(g/mol) | 414.09 | 500.13 | 78.11 |
| Boiling Point (oC) | 192.4 | 259 | 80 |
| Vapor Pressure (mm Hg at 25 oC) | 0.525 | ~0.002 | 86 |
| Henry’s Law Constant @ 25 oC (unitless) | Not measurable |
Not measurable |
0.225 |
| Koc | 115 | 371 | 79 |
| Solubility in Water (mg/L) | ~9,500 | 680 | 1,780 |
NM Not Measurable
PFOA Properties USEPA 2016
PFOS Properties USEPA 2016