What Are They?
Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are both known contaminants of emerging concern (CECs) and have recently garnered a lot of coverage in the water industry because of the now known harm they cause to humans and wildlife as well as the magnitude of contamination across municipal water sources.
PFOS and PFOA were both widely applied chemicals used to make carpets, clothing, fabrics, paper packaging and other materials that are resistant to water, grease or stains. They were also used in fire retardants and in various industrial processes. Due to their resistance and “strengths” in certain environments that made them great for manufacturing applications, they now pose a hazard in part because of that resiliency and due to reasons, that were unknown during widespread use.
The Environmental Protection Agency (EPA) has established health advisories that seek to “provide drinking water system operators, and state, tribal and local officials who have the primary responsibility for overseeing these systems, with information on the health risks of these chemicals, so they can take the appropriate actions to protect their residents.”
The EPA has also committed to support states and public water systems in reducing exposure to PFOS and PFOA in drinking and has also established health advisory levels at 70 parts per trillion.
If water analysis results confirm that drinking water contains PFOS and PFOA at concentrations greater than 70 parts per trillion, EPA recommends that water systems quickly undertake additional sampling to identify the potential source and scope of the contamination.
PFOS and PFOA are resistant to many municipal technologies however, there are several groundwater treatment options:
Membrane Filtration: Membrane filtration, a technique that uses a porous membrane filter to separate particles in fluids, is an option. To be effective, this process may need the addition of other minerals, and waste or byproducts must be managed. Reverse Osmosis (RO) is a proven method that is widely applied in North America and can also work specifically as a catch all and preventative method to safeguard against the majority of other CECs that may not have been identified yet. With all membrane filtration methods, operators should seek to minimize the volume of reject in an effort to minimize the size (and costs!) of pretreatment equipment and brine disposal volumes. Municipalities are encouraged to seek out high recovery RO options as well as those RO processes (such as CCRO) that not only offer high recovery rates but very little maintenance and oversight.
Anion Exchange: Anion exchange is a form of ion exchange where a negatively charged biomolecule binds to a positively charged resin. This is a complex treatment option and competition with common ions for binding sites on resins can impact its effectiveness. Additionally, organics, total dissolved solids, and minerals can clog resins and reduce the efficiency of the treatment. Cost can also be a factor.Activated Carbon: Some testing has demonstrated activated carbon (specifically Granular Activated Carbon, or GAC) filters as an effective technology for reducing perfluorinated compounds such as PFOS and PFOA from water.