By Peter Chawaga, Associate Editor, Water Online
It’s always worthwhile to examine the most challenging drinking water problems through the lens of small systems. After all, systems serving fewer than 3,300 people account for 77 percent of all systems across the country, according to the Congressional Research Service.
So when it comes to perfluorinated chemicals (PFCs), which are affecting the drinking water in communities across the country, it is perhaps most critical to address the problem at systems serving minor towns and rural communities. To do so, the U.S. EPA dedicated its monthly webinar for small water systems in September to the problem.
“EPA works with the states to help determine which webinar topics would be of the most interest for states and water utilities,” said an agency spokesperson. “As a part of this ongoing series, EPA presented information pertaining to its analytical method for PFCs, source water issues for PFCs, and a discussion on the literature regarding PFOA and PFOS [perfluorooctanoic acid and perfluorooctanesulfonic acid] treatment for the technologies commonly employed by drinking water facilities.”
Attendees to the webinar, “Challenges And Treatment Solutions for Small Drinking Water and Wastewater Systems,” heard EPA researchers and engineers Drs. Jody Shoemaker, Marc Mills, and Thomas Speth discuss the PFC problem and how it pertains specifically to small systems. With such a complicated contaminant, they may need all the help they can get.
“PFC molecules are held together by extremely strong bonds,” the spokesperson said. “This renders ineffective technologies such as disinfection, biotreatment, and oxidation technologies.”
Making things worse are the conditions often faced by smaller systems.
“The removal of PFCs will require advanced treatment technologies that are relatively expensive,” said the spokesperson. “This often poses challenges for small systems, such as their lack of financial resources and declining rate bases, lack of technical expertise to operate and maintain these advanced technologies, workforce shortages with high turnover for experienced operators, lack of infrastructure to handle additional technologies, and the residuals that come with them.”
But the webinar was assembled to offer a silver lining to attendees. While PFCs are notoriously difficult to treat, they are still relatively rare. The EPA found that, based on Third Unregulated Contaminant Monitoring data it has received, only 1.3 percent of public water systems that sampled their water had at least one result with combined PFOA and PFOS levels above 70 ppt. To provide a method for detecting the occurrence of perfluoroalkyl acids (PFAAs), the webinar covered EPA Method 537, which can be adopted by systems that want to know their own status.
“EPA Method 537 uses solid phase extraction to isolate select PFAAs from tap water by passing the water sample through a solid sorbent that retains the analytes,” the spokesperson said. “If a drinking water utility or a commercial laboratory is going to implement Method 537, the major piece of equipment necessary is a liquid chromatograph/tandem mass spectrometer. The utility or laboratory personnel must also have the technical expertise necessary to operate the equipment.”
While treating PFCs is a challenge, the EPA shared some indications that they are susceptible to certain approaches.
“PFCs are negatively charged, raising the possibility of treating them with anionic exchange resins,” said the agency spokesperson. “Additionally, many PFCs such as PFOA and PFOS have high molecular weights which suggests that high pressure membranes such as reverse osmosis will be an effective treatment approach. Finally, the higher chain PFCs like PFOA and PFOS have moderate solubilities which allow for moderate adsorbability into activated carbons.”
Although there’s nothing that the EPA can do about the high price of treatment technology, it did lend some advice on how to go about choosing a solution and implementing it if it can be acquired.
“Each treatment system should be carefully tested, designed, and maintained to ensure that they are effective for treating PFOA and PFOS in that particular system,” the spokesperson said. “This should be completed at the pilot scale at the minimum, so that the utility can be completely confident of the treatment effectiveness for their water, and whether there are any unintended consequences of the chosen technology, such as residual handling and disposal, or water quality changed that may impact other aspects, such as distribution system corrosion rates.”
PFCs will likely remain a burden on all treatment plants, and like the presence of any contaminant, they will have a magnified effect on small systems. As more research is done, and more information shared, hopefully a more affordable solution will emerge.
“Additional pilot- and full-scale data for the following technologies would be useful: granular activated carbon, high-pressure membranes, and anionic exchange resins,” said the spokesperson. “This will allow for better information on what technologies should be considered for any given water quality. This would also allow EPA to better understand the limitations that small systems may have.”
Image credit: "miniature town" Cathy Llagas © 2013 used under an Attribution 2.0 Generic license: https://creativecommons.org/licenses/by-nc-nd/2.0/