By Amy Dindal
As per- and polyfluoroalkyl substances (PFAS) demand increasing attention due to health, environmental, and regulatory concerns, the pros and cons of available treatment options should be thoroughly evaluated.
Per- and polyfluoroalkyl substances (PFAS) are manmade chemicals that have been widely used for decades in various applications — from cookware and packaging to stain repellants and firefighting foam. As required by their applications, the chemicals are extremely durable and have been observed in the environment, exposing humans and animals around the globe, and earning the somewhat ominous nickname of “forever chemicals.”
Widespread use of PFAS chemicals over a long period of time has resulted in varying levels of impact to most environmental media worldwide, including sources of drinking water. As noted by the Interstate Technology and Regulatory Council’s Fact Sheet on the Occurrence of PFAS: “The concentrations of these human-caused ambient or ‘background’ PFAS concentrations may vary widely, based on proximity to industrial areas, patterns of air and water dispersion, and many other factors.”1
The Safe Drinking Water Act (SDWA) requires the U.S. EPA to evaluate unregulated contaminants for occurrence in our public drinking water systems every five years. As part of the EPA’s mission in protecting public health, occurrence data are collected through the Unregulated Contaminant Monitoring Rule (UCMR) to support the agency’s determination of whether to regulate new contaminants. The impact of PFAS to our drinking water supply has been under evaluation since the EPA began monitoring for six PFAS under the Third UCMR in 2013.2 Under the Fifth UCMR, the EPA intends to extend the list to monitor 29 PFAS in public drinking water systems, starting in 2023.3
In May 2016, the EPA announced a lifetime health advisory for PFOA and PFOS in drinking water, which was not an enforceable standard, but has been implemented as such in several states in the absence of a federal maximum contaminant level (MCL). In February 2021, the EPA announced proposed regulatory determinations for PFAS in drinking water, so an MCL for PFOA and PFOS could be in place by the end of the year.4 With growing public awareness and expected national standards, municipal water utilities will want to be prepared to address the MCL. Current treatment options are limited and expensive, but technologies that could lessen the cost and burden of PFAS treatment and removal for the water industry are emerging.
Options For Treating PFAS In Drinking Water
The EPA has identified several ways to remove PFAS from drinking water. These technologies can be used at water treatment facilities, hospital water systems, individual buildings, or even in homes. According to the EPA, each has financial and logistical considerations that need to be evaluated on a case-by-case scenario.5 Filtering water through tanks containing granular-activated carbon (GAC) is the most commonly used approach. Once PFAS are observed at the outlet of the GAC tanks, the GAC is considered spent and must be removed.6 This approach has the scale and capacity to effectively extract PFAS from drinking water, and there are GAC systems at water treatment facilities across the U.S. The drawback is that spent GAC must be heated to 1,300°F in an oxygen-free environment to be reactivated, which can be a costly and cumbersome process.7
Drinking water can also be treated with powdered activated carbon (PAC). While it is less effective at removing PFAS than GAC, and more expensive, it is useful in scenarios that require rapid removal of PFAS because the PAC can be added directly into the rapid mix tanks of a water treatment plant.8 Like GAC, the issue of what to do with the sludge that contains adsorbed PFAS remains.9
Ion-exchange resins are another option. Treatment with ion-exchange resins is typically more expensive than GAC, but it is possible to remove a high percentage of the PFAS for a window of time dictated by various factors, including the type of resin used, water quality, and which PFAS need to be removed.10 These ion-exchange resins are either single-use or require regeneration with solvents, which yields a concentrated waste stream that needs further treatment.
Nanofiltration and reverse osmosis filter water through membranes that are typically more than 90 percent effective at removing a wide range of PFAS. Approximately 80 percent of the water coming into the membrane passes through to the treated water, leaving roughly 20 percent as a high-strength concentrated waste.11 Both technologies can be costly and energy intensive.
Promising Destruction Technology Is Here
With all of the above treatment technologies, PFAS contamination is transferred from one media to another. An ideal solution would be one capable of destroying PFAS and preventing them from transferring elsewhere to avoid creating harmful byproducts. Fortunately, a technology that can destroy PFAS from environmental aqueous media and the concentrated waste streams generated from other treatment applications does exist — supercritical water oxidation (SCWO).12
SCWO powers an exciting new onsite destruction solution that is currently being scaled for treatment of waste materials. Unlike treatment technologies that transfer PFAS from water to another media, supercritical water oxidation can effectively destroy PFAS in contaminated water to non-detect levels in seconds, leaving only inert salts, carbon dioxide, and PFAS-free water behind. An added benefit of reducing PFAS to the lowest levels of detection is that it mitigates concerns about meeting unknown future regulatory limits.13 Once tested to confirm regulatory compliance, the treated water can be used or discharged back into the environment.14
Currently, SCWO is available for treating onsite finite volumes of contaminated water. However, it has the potential to be paired with other drinking water treatment techniques. Reverse osmosis can be used on the front end to reduce water volume, after which the resulting highly concentrated PFAS stream can be destroyed using SCWO. Similarly, SCWO can be used for onsite treatment of GAC and ion-exchange resin regenerant, enabling recycled GAC and ion-exchange resins to be used for multiple treatment cycles. This would also reduce operation and maintenance costs and lengthen the life of the GAC system.15
The addition of destruction technologies such as SCWO provides the most promising solution for PFAS removal in aqueous media. The technology also enables continued use of existing treatment systems, which could potentially save water utilities a lot of money. There is still more to learn about coupling PFAS treatment and destruction technologies, but the rigorous research that is underway is providing the solutions we need to address this challenge.
About The Author
Amy Dindal is currently leading Battelle’s PFAS program and is responsible for setting technical direction and oversight of a multidisciplinary team of more than 50 staff that includes scientists, engineers, chemists, biologists, toxicologists, and modelers. In this role, Dindal has applied her technical understanding of chemical processes and analytical chemistry to support development of innovative approaches and technologies to characterize, model, and remediate PFAS compounds in water and soil. Under Dindal’s technical leadership, the team has filed 10 provisional patents, three nonprovisional patents, and five trademarks in less than 2 years. Amy holds a B.S. in chemistry from Penn State University and has been a certified Project Management Professional (PMP) since 2006.