Q: What are PFAS and why are they “forever” chemicals?
Charlie Liu: PFAS are manmade chemicals in use for decades. There are too many applications of PFAS to mention them all, but nonstick cookware, waterproof clothing, stain-resistant fabrics, and firefighting foam are some of the big ones. The ”forever” relates to PFAS persistence in the environment. PFAS have been linked to a variety of health concerns. There are thousands of different PFAS. The EPA (maximum contaminant level) addresses six PFAS.
Q: I’ve heard about PFAS being a class of compounds… what about other PFAS?
Charlie Liu: Thousands of PFAS compounds exist. Laboratories can quantify and report concentrations from 18 to 40 PFAS compounds. Advanced analytical methods can detect (but not quantify) other PFAS, but these analytical methods are not a day-to-day common practice. Moreover, while PFAS are persistent, the vast majority of PFAS are considered “precursor PFAS” and can transform (e.g., oxidize) in the environment to the PFAS we commonly see listed in regulations like drinking water MCLs or PFAS limits set by different state regulatory agencies.
Q: Where are we seeing the most PFAS contamination?
Charlie Liu: PFAS treatment to date has focused on groundwaters contaminated by firefighting foams containing PFAS (i.e., Aqueous Film Forming Foams or AFFFs), near Department of Defense installations, refineries, airports, firefighting training areas, and generally places prone to fuel fires. The carbon-fluorine bond of PFAS helps with lowering the surface tension of water and forms an aqueous film on top of the fuel. This film prevents oxygen from getting to the fuel and smothers the fire.
However, PFAS have been around since the 1930s and they’re used in so many different applications – sometimes it’s hard to exactly fingerprint the contamination source. Studies have confirmed PFAS presence in water resources worldwide, and even in places you wouldn’t expect, such as the Arctic. There is increasingly more focus on PFAS detected in sources other than groundwater such as surface water, municipal wastewater effluents, biosolids, industrial wastewater effluents, and landfill leachates. Studies indicate that PFAS can occur in municipal wastewater with little or no industrial influence, suggesting that PFAS contamination can result from residential uses such as after washing waterproof or stain-resistant fabrics treated with PFAS.
Landfill leachate from PFAS-containing waste is another potential source. PFAS can be in personal care products (dental floss, shampoo, sunscreen, make-up), fast food wrappers and food packaging, cleaning products – things made to resist water and oil may contain PFAS. And these products may enter the landfill and contribute to PFAS contamination of landfill leachate, which can then contribute to contamination of other water resources.
Finally, PFAS in drinking water is just one route of exposure. PFAS are used in a variety of products that people may consume as well. The good news is that some industries have voluntarily phased out the use of PFAS in their products, and some states have, or are beginning to ban or limit the sale of products containing PFAS.
Q: How do we treat PFAS?
Charlie Liu: We have over 20 years of knowledge on PFAS treatment. The most common technologies for PFAS treatment are adsorbent technologies like granular activated carbon (GAC) and ion exchange resins (IX). While the EPA also recommends membranes like reverse osmosis (RO) as a best available technology, RO primarily makes sense if there’s an easy way to dispose of the brine. However, PFAS would still be present in the brine, so additional future treatment of the brine may be necessary.
What can make PFAS treatment challenging is the ‘soup’ of other water quality constituents that may be present in the water like organic carbon, anions like sulfate, nitrate, and chloride, and metals like iron and manganese that can interfere with PFAS treatment and reduce treatment capacity. At certain concentrations, pretreatment of these water quality constituents is critical for effective PFAS treatment. Groundwater matrices are often not very complex, and GAC and IX can be used with little to no pretreatment. However, PFAS treatment is increasingly being looked at for more complex water sources like surface waters and wastewaters. In these sources, there are often higher concentrations of water quality constituents that will need to be pretreated for.
Q: What about regulations around PFAS in wastewater discharges or biosolids?
Charlie Liu: With the EPA MCLs, I would say most of the focus is currently on drinking water, with an increasing focus on wastewater and biosolids. EPA is still performing risk assessments for biosolids and some states have either banned, limited, or are monitoring and evaluating the land application of biosolids. Similarly, PFAS are increasingly monitored in wastewater discharges, with the potential for PFAS to be included in future discharge permits. There’s been an uptick in work to look at different treatment technologies for PFAS in wastewater discharges to prepare for potential limits in the future.
Q: What would you say is the biggest challenge currently facing water systems regarding PFAS?
Charlie Liu: Cost of treatment is a major concern. GAC and IX adsorption vessels and media are not cheap in both capital and annual O&M costs. Some estimates show that implementing treatment can be upwards of $1,000,000 per MGD of treatment depending on the size of the system. Annual O&M costs vary primarily based on the pretreatment and concentrations of competing water quality constituents that reduce PFAS treatment efficacy.
Number two is how low the MCL concentration limits are right now. The detection limit for most PFAS by commercial labs is two nanograms per liter, whereas the MCL concentrations are four nanograms per liter for PFOA and PFOS. These concentrations allow for very little response time for operators. Systems need to be very fine-tuned to meet these MCLs. One solution is to monitor for shorter chain PFAS (with fewer linked carbon atoms) that are not included in the MCLs like PFHxA or PFBA. These compounds are commonly found in sites that have PFAS contamination, and are expected to be detected earlier in the treated water than PFAS included in the MCLs. These compounds can serve as indicator compounds for timing media changeouts. Additionally, a delay in PFAS lab results, which can range from two to four weeks, further complicates monitoring and compliance. These challenges mean that it is important for facilities to fine-tune operations to understand water quality impacts and PFAS treatment characteristics in the first few months and years of operation.
Q: The waste stream of these treatment options will include these “forever chemicals.” What happens to that waste?
Charlie Liu: That’s something that is currently a hot area for research, so we’ll see what solutions emerge in the next few years.
Right now, many facilities are going with incineration and landfilling of the adsorption media, often selecting ‘hazardous’ facilities to be safe with potential future RCRA hazardous constituent designation, or reactivation if GAC is used. Incineration is the most expensive, and the verdict is still out on whether PFAS byproducts still exist after incineration. Sending the waste to a hazardous landfill can be cheaper than incineration. Landfilling won’t destroy the PFAS but can contain the PFAS waste while other solutions are explored. GAC reactivation is promising, and studies have demonstrated that PFAS can be destroyed during this process, but additional research is still needed to confirm. There are utilities across the country looking into regional reactivation facilities as a means of centralizing GAC reactivation and reducing costs.
There has also been movement on PFAS destruction and there are some interesting startup companies looking at technologies like super critical water oxidation (SCWO), hydrothermal alkaline treatment (HALT), and electrochemical oxidation. These are effective for destroying PFAS but are energy intensive and need a concentrated stream of PFAS for these destructive technologies to make sense. These technologies are generally at the pilot-scale phase and are not expected to be a replacement for separation technologies like GAC and IX, at least for now. These technologies will likely be combined with separation/concentration technologies to be effective.
Q: What should a water system do if they discover their source water contains PFAS?
Charlie Liu: Step one is to complete initial monitoring. According to the MCL rule, systems have three years to complete initial monitoring of their system, so we recommend completing initial monitoring for PFAS and water quality constituents that could impact PFAS treatment by adsorbents. Seasonal monitoring may also be a good idea to see if there are seasonal PFAS fluctuations. For surface water treatment plants, it may be worth evaluating where PFAS may be entering a lake or river and evaluate if there are ways to catch the PFAS before entering the facility.
Once water quality is evaluated, an alternatives evaluation could be performed to select treatment media, strategies, and potential need for pretreatment. Is the organic carbon content high and would IX be a better treatment option for than GAC for this water? Are iron and manganese high and is pretreatment needed? Is there enough space to implement GAC? Is blending an option?
Finally, testing may be needed using bench-scale rapid small-scale column tests (RSSCTs) and/or pilot-scale testing. RSSCTs are inexpensive tests that provide results in a short period of time, but use modeling approaches to provide an approximation of full-scale performance. Pilot-scale tests are more expensive and time consuming, but directly predict full-scale performance. The initial investment in pilot-scale testing, especially for a large system where incremental improvements in media performance could provide significant returns, may be worthwhile. These options do take time and cost money so these choices will be unique to each agency or facility.
Q: On average, what does the timeline from identifying PFAS in a water system to getting a design evaluated, selected, designed and built look like?
Charlie Liu: Depending on how big and complex the system is, we are probably looking at about two years for relatively small and simple systems. It may take three to five years for more complex systems including testing, design, permitting, implementation, and startup. But since we have a good understanding of how PFAS are treated, we can move quite quickly once some key decisions are made in an alternatives evaluation and testing stage.
Kennedy Jenks has wide-ranging experience with PFAS that can help streamline your project. If you have any questions about PFAS or would like more information, please Contact Us.
Check out some of our previous PFAS projects:
Eastern Municipal: One of the first PFAS pilot studies for full-scale drinking water operations in the US.
Santa Clarita: One of the first IX PFAS treatment projects in CA.
Lakewood Water District: A large fast-track PFAS project in WA, from design to construction in 10 months.
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