Deliverable D4.1 – Performance and assessment of drinking water treatment trains for removal of PFAS and industrial chemicals

The aim of this deliverable is to enhance the understanding of competitive adsorption and ion exchange of per- and polyfluoroalkyl substances and other industrial persistent, mobile and toxic substances (iPMT) in the presence of dissolved organic matter (DOM) and to optimize their removal in fixed-bed filters. To achieve this, laboratory and pilot-scale experiments were combined with monitoring of a large-scale groundwater treatment plant with activated carbon at a legacy contaminated site.

In order to identify an optimal treatment train for PFAS removal, different high performance and tailored adsorbents were tested at laboratory scale and benchmarked against state-of-the-art granular activated carbon (GAC). Initially, a comprehensive adsorbent screening was conducted that involved a series of equilibrium jar tests using 18 different adsorbents and spiked drinking water (including 13 PFAS and 7 iPMT). These adsorbents were selected based on a literature research for high performance adsorbents for PFAS and iPMT removal and included several activated carbons, strong basic anion exchange resins as well as novel adsorbents such as surface modified clays, a cyclodextrin polymer and a zeolite.

The results of the jar tests revealed that strong-base anion exchange resins (IX) were the most effective at removing PFAS. However, these IX were particularly vulnerable to competition from non-targeted DOM components. Activated carbons were found to be the most effective adsorbents in removing a wide range of iPMT, but they were ineffective at removing short-chain PFAS. For the alternative adsorbents tested, there were significant variations in their ability to remove PFAS and iPMT, with the bentonite-based surface modified clays (SMC) showing considerable potential due to their high PFAS selectivity. In line with current literature, the results showed that PFAS removal increased with the length of the perfluorinated carbon chain. For compounds of the same chain length, those with a sulfonate group were removed more effectively than those with a carboxylate group.

Based on the results from the jar tests, three GAC products, two SMC, and two IX were selected for testing in laboratory scale rapid small-scale column tests with spiked drinking water, including 15 PFAS and 8 iPMT. The RSSCT dataset was used to determine the breakthrough curves of all investigated compounds and to shortlist the adsorbents for subsequent piloting. In addition, the data was analyzed to identify possible synergies between adsorbents in order to identify the most promising treatment train. Usage rates were quantified for all adsorbents based on the RSSCT data.

In the subsequent piloting, an IX and a SMC, which had excelled in the laboratory tests, were piloted alongside a large-scale activated carbon plant. In addition, the most promising treatment train was tested, consisting of a combination of activated carbon and ion exchange. All process variants were tested at the same site for their ability to remove PFAS from legacy contaminated groundwater.

The target analysis in the pilot tests was supplemented by additional sampling campaigns for TTR-TRβ CALUX (PFAS CALUX) tests and suspect screening. These results allow a more holistic evaluation of the adsorptive processes. All adsorbents tested were able to reduce the PFOA equivalents in the PFAS CALUX tests. In the suspect screening, a lower number of substances was found in the GAC effluent than in the effluent of the SMC adsorber and the IX. This may indicate less selective removal by the activated carbon filter or leaching from the other adsorbents; further studies may be of interest.

In the subsequent cost analysis, it became clear that the choice of a suitable adsorptive process is highly site-dependent and depends on the composition of the PFAS and iPMT, DOC concentration as well as targeted effluent values. UV₂₅₄ was found to be a potential surrogate parameter for real-time monitoring of PFAS removal by AC and IX.