What technologies are effective for PFAS removal?

There are three different treatment alternatives most commonly considered effective in the removal of PFAS from drinking water: adsorption using activated carbon, ion exchange using resins, and reverse osmosis using permeable membranes.

Granular Activated Carbon (GAC)

GAC contactor vessels are the most common units on the market for PFAS removal for both surface water and groundwater sources. The pressure vessels remove PFAS via adsorption to the GAC media and require backwashing of the vessels once they reach a certain differential pressure. GAC has been found to have greater efficacy removing of long-chain PFAS compounds than short-chain PFAS compounds. According to the USEPA, GAC has a maximum demonstrated removal rate of between 90% and 98% of the PFAS6 compounds regulated by the new MCL. 

Ion Exchange (IX)

Similar to GAC vessels, IX resins are typically installed in pressurized, contactor vessels in a lead-lag configuration. The positively charged resin attracts the negatively charged PFAS particles, removing them from the water. In many applications, IX has been found to have greater removal of short-chain PFAS compounds than long-chain PFAS compounds. According to the USEPA, IX has a maximum demonstrated removal rate of between 94% and 99% of the PFAS6 compounds regulated by the new MCL. Unlike GAC, IX resins have a finite capacity, and typically cannot be reactivated and reused, requiring an ultimate off-site disposal location. Additionally, IX resins require pre-filtration using bag filters to capture any solids in the raw water, adding to the capital, operations, and maintenance costs; however, IX resins typically have a longer lifespan before reaching this ultimate capacity when compared to GAC. 

Reverse Osmosis (RO)

RO utilizes high-pressure, small pore size, permeable membranes to separate PFAS compounds from feed water. The concentrated waste water is continually recirculated into the feed water or fed through secondary and tertiary RO systems, resulting in high recovery rates and non-detect PFAS levels. The remaining waste water is flushed out of the system, requiring a separate GAC or IX treatment system before the waste water can be disposed of. Additionally, the RO-treated water requires remineralization prior to entering the distribution system. RO membranes can provide removal over a typical lifespan of 10 years before requiring replacement. RO has been found to remove both short- and long-chain PFAS compounds. According to the USEPA, RO has a maximum demonstrated removal rate of 99% of the PFAS6 compounds regulated by the new MCL.

Show All Answers

1. What is “PFAS6”?
2. What are the current federal PFAS regulations?
3. What are the current PFAS regulations in Massachusetts?
4. What other PFAS requirements are coming? Is there a test currently available?
5. More than 4700 PFAS compounds exist. Are others likely in our water too?
6. What are the possible sources of the PFAS contamination?
7. Does the fire (or other) departments have any remaining fire retardant foam that contains PFAS?
8. What level of effort would be needed to investigate potential sources?
9. What technologies are effective for PFAS removal?
10. If we implement GAC, why can't we skip the interim filter and install.
11. Why is Wellesley considering GAC over IX? Should we use both?
12. I have heard reverse osmosis is more effective. Why not use that?
13. Of the more than 4700 PFAS compounds how many can GAC remove?
14. Is expended GAC media for PFAS removal considered hazardous waste?
15. Are there broader pollutant tests that we can execute to determine presence of contaminants beyond USEPA requirements? Would GAC filter improve the results?
16. What is the GAC disposal process?
17. Natick is implementing the granulated activated carbon filter system and is expected to go online at the end of December 2021. Could Wellesley piggy-back off of that solution in the interim?
18. What will interim PFAS treatment at the Morses Pond WTP include?
19. Why IX for interim and not solely GAC?
20. Is the interim treatment lifespan driven by time or gallons? If gallons, why not maximize the MWRA capacity to extend the lifespan of the interim system treatment media?
21. If we are able to minimize the use of the container filter, can we re-deploy the interim container filter to our other wells after Morses has been resolved?
22. Any idea on the expected life of the GAC media before replacement/regeneration is needed?
23. Could we simply use MWRA water during that time period?
24. What is the cost difference between using the MWRA water during this 15-18 month time period versus the ion exchange interim solution?
25. Would we own the $1.5 million interim ion exchange solution, or is this a rental or lease?
26. If we own this solution, could it be repurposed to treat water from the other wells if they test over the acceptable limit?
27. Could we share or resell this solution to another municipality once our granulated carbon solution is online?
28. What is the level of confidence in the MWRA connection improvement requiring 3-5 years?
29. What is the minimum Wellesley water sourcing at which our total life cycle is cost competitive with MWRA?
30. Is there a risk that other communities tap into MWRA that Wellesley will lose that option?
31. Can you explain the physical limitations of the current MWRA connection?
32. Please describe the risks of relying solely on our MWRA connection.
33. Should the physical limitations of the current MWRA connection be remedied?