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.