Abstract
The removal of per- and polyfluoroalkyl substances (PFASs) presents a challenge for drinking water providers. Guidelines for PFAS concentrations in final drinking water are regularly updated to ever-decreasing values, and conventional drinking water treatment plants are not designed to remove PFASs. Currently, the most frequently used removal technique, adsorption to granular activated carbon (GAC), is often considered challenging. High-pressure membranes, such as nanofiltration (NF), have been shown to remove PFASs efficiently. However, the creation of a waste stream comprised of at least 10% of the feedwater volume is recognized as a major drawback of this technique. In this study, a NF pilot plant was operated at a drinking water treatment plant in the city of Uppsala, Sweden, for six months. NF removed up to >98% of PFASs and fulfilled other water quality targets, such as the removal of uranium-238, dissolved organic carbon (DOC), and mineral hardness from the raw water. The concentrate from the pilot plant was treated with two different GAC materials and two different anion exchange (AIX) resins in column tests, where the superior performance of AIX over GAC was observed in terms of PFAS removal. PFAS adsorption curves for GAC were found to superimpose each other for the two water types if normalized to the specific throughput of DOC. The application of the freely available PHREEQC model revealed improvement possibilities in terms of resin properties. A cost analysis using the column test results compared GAC filtration to the combination of NF with adsorption materials. Treatment costs were found to be largely dependent on the PFAS drinking water treatment goals and concentrate discharge requirements, which highlight the economic consequences of prevailing guidelines for drinking water and discharge to the environment. The results of this study provide both the scientific community as well as drinking water providers with important insights into the application of NF for PFAS removal during drinking water treatment as well as that mechanistic and economic aspects of NF treatment and the management of the resulting concentrate.
Highlights
The group of per- and polyfluoroalkyl substances (PFASs) is a diverse family of more than 4700 different chemical compounds with a large range of physicochemical properties.[1]
Using anion exchange (AIX) resins for the removal of PFASs from the NF concentrate was shown to be more efficient than the use of granular activated carbon (GAC) based on the total amount of bed volumes the materials could treat before reaching a range of discharge goals
In a comparison of GAC materials treating both raw water and the NF concentrate, it was shown that, with the exception of PFBS, differences in the PFAS breakthrough could be explained by the specific breakthrough of dissolved organic carbon (DOC)
Summary
The group of per- and polyfluoroalkyl substances (PFASs) is a diverse family of more than 4700 different chemical compounds with a large range of physicochemical properties.[1]. PFASs have been produced since the 1950s, and their applications seem endless, covering a wide range of industrial and consumer products in both essential and nonessential applications.[7−9] While exposure via PFAScontaining products such as dental floss, water repellent textiles, or ski waxes presents an undisguised route of exposure
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