Treatment and Mitigation of PFAS in Drinking Water | AAAS EPI Center
GAC Is Considered a Best Available Technology for PFAS Removal and Provides Secondary Water Quality Benefits GAC adsorption is an established water treatment process, often used for the removal of common contaminants such as TOC, color, taste and odor compounds, and constituents of emerging concern (CECs) 8 . GAC is similar to PAC in that they both remove constituents through adsorptive mechanisms and target contaminants must compete with other constituents for adsorption sites. GAC media is larger in particle size than PAC (~1.0 to 1.6 mm), so GAC is loaded into vessels or filter boxes that allow water to pass through it. GAC can also be used in point-of-use applications in the forms of filters attached to a faucet, refrigerator or pitcher, although results from different point-of-use applications vary significantly and not all in-home filters are certified to remove PFAS 9 . The NSF International website provides information about in-home filters. Figure 2 presents GAC filters used in WTP. Figure 7 - GAC Filters (Left: in vessels; Right: in filter boxes)
GAC has proven its ability to reduce PFAS concentrations 11–16 . Removal is highly dependent on PFAS properties, where GAC is more effective for long-chain PFAS removal when compared to short-chain PFAS 7,13,15 . The presence of additional adsorptive compounds such as TOC or taste and odor compounds can inhibit PFAS removal by competing for adsorption sites 11,13,15,17 . GAC has been reported to provide PFAS removal ranging from 66 percent to > 99 percent, depending on the type of PFAS 15,18,19 . Not all GACs are created equal; carbon manufacturers have worked to optimize GACs to target PFAS removal. As a result, GACs may vary in PFAS removal efficiencies and lifespan until replacement is required. Like all other PFAS treatment options, removal efficiency should be validated with small-scale testing (referred to as pilot testing), as water quality and factors like contact time can also impact PFAS removal. Major benefits of using GAC are its reliability from a process standpoint, relatively low energy requirements, and high PFAS removal. A challenge of GAC is that it can be less effective for short-chain PFAS removal; however, validation at each site is recommended to verify removals 20 . Another challenge with GAC is that as adsorption sites on GAC media become exhausted and PFAS removal decreases, GAC media must be replaced. GAC replacement may be driven by a number of factors, such as the targeted PFAS and other water quality constituents being treated and the targeted PFAS. To overcome this limitation, GAC is often added downstream of other
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