Treatment and Mitigation of PFAS in Drinking Water | AAAS EPI Center
Figure 9. Membrane Skid (Left) and a Single High-Pressure Membrane Element (Right)
RO and NF are proven PFAS-removal technologies, with removal of short- and long-chain PFAS to below detection limits in a majority of studies, as expected given their proven ability to remove other organic constituents 7,11,12,17 . In addition to significant short- and long-chain PFAS reduction, RO and NF can provide additional benefits such as enhanced removal of other constituents in water, and PFAS do not compete for removal with these constituents, unlike in PAC, GAC, and IX applications. Additionally, RO and NF systems have relatively small footprints. Unlike IX and GAC processes, PFAS removal does not decrease over time in RO and NF applications; however, one challenge is that the membranes will clog over time and require cleaning. Wash water used for cleaning may need to be stored for additional PFAS treatment. Another challenge is that RO and NF processes require pretreatment to protect the membranes from damage and post-treatment to prevent corrosion in the distribution system 32 . Pretreatment and post-treatment options can be costly to implement and maintain. Disposal of the membrane concentrate stream is also a challenge. The concentrate stream typically contains two to six times the concentration of removed contaminants compared to the feed water, and requires disposal 17,34 . The presence of PFAS in the concentrate stream can make disposal challenging, although research evaluating concentrate treatment options has been performed 17,34 . Concentrate disposal options include discharge to the sanitary sewer or a groundwater injection well, or treatment at a concentrate treatment facility using a process like GAC or IX. It should be noted that if the wash water or concentrate is not treated to remove PFAS, it will recycle PFAS into the water system and not truly destroy PFAS. RO and NF require high capital and operating costs compared to other PFAS reduction alternatives. These processes are energy intensive, which increases operating costs, and require additional capital investments such as pretreatment and post-treatment. Established Drinking Water Treatment Methods Summary Each established drinking water treatment technology has benefits and limitations, and selecting the appropriate method depends on a multitude of variables including the type of PFAS present and the concentration of other constituents, PFAS removal goals, and cost considerations. Table 1 presents a summary of treatment technologies, PFAS removal methods, PFAS removal effectiveness, and relative cost. The capital and operating cost of these technologies is dependent on the size of the WTP. These
27
Made with FlippingBook Online document