Treatment and Mitigation of PFAS in Drinking Water | AAAS EPI Center
PFAS reduction to below laboratory detection limits has been reported using IX , but removal is highly dependent on the presence and level of other contaminants in the water to be treated, the pH of the water, the contact time between water and resin, and the resin used 25–29 . IX has been shown to provide long-chain PFAS removal and short-chain PFAS removal 15,17 . In some studies, IX outperformed GAC for short-chain PFAS removal 30,31 . There are several benefits to using IX, an efficient PFAS removal of both long and short-chain compounds with relatively low energy costs to operate. However, IX resins, like GAC, may have limitations when PFAS competes with other compounds for exchange on the resin. To overcome this limitation, IX is often added downstream of other processes in PFAS applications to reduce the load of other compounds on the resin, improving PFAS removal capabilities. There are some additional challenges with using IX for PFAS reduction. Removal will decrease over time as PFAS consumes resin sites, prompting resin replacement 29 . Another major challenge with IX is that resin will contain appreciable levels of PFAS and will require disposal once it has reached the end of its useful life. Resin is typically landfilled or incinerated to destroy PFAS, but this can result in PFAS transferring from the resin to air emissions, which could recycle into the environment if not managed. Additional research is needed to develop test methods for PFAS in air emissions. Compared to other PFAS treatment methods, IX has a moderate capital and operating cost . IX resin is more expensive than GAC media, but less resin volume is required compared to GAC media at the same flow rate. IX can be a cost-effective solution to reduce PFAS, especially if short-chain PFAS removal is needed. The feasibility of ion exchange for PFAS removal should be evaluated at a pilot scale prior to full- scale implementation to ensure PFAS removal goals can be achieved. Membrane Separation Provides the Greatest PFAS Removal but Comes with Additional Considerations and Cost NF and RO are membrane filtration technologies that are established processes in the water industry. NF and RO filters are housed in membrane skids (i.e., a piece of equipment that can be rolled or moved). There can be several skids in use at a WTP for drinking water production. Figure 4 presents both a membrane skid, containing several hundred membrane elements, and a single membrane element. NF and RO technologies remove constituents by applying high pressures to push water through semipermeable membranes 32 . Water that passes through the membranes is known as the “permeate” stream, and water that does not pass through is known as the “concentrate” stream 33 . RO membranes are less permeable compared to NF and, therefore operate at higher pressures and remove more constituents. RO membranes are most often used to remove smaller, dissolved constituents such as sodium, chloride, and other total dissolved solids (TDS). NF is often employed to reduce larger compounds, including calcium and magnesium hardness, TOC, and color 32 . Therefore, RO membranes are typically selected over NF for applications where dissolved constituent removal is an additional objective. In addition to WTPs, membrane systems can also be installed in the home as point-of-use technologies.
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