## 3 Decentralized Treatment Systems
### Surface, Open Water Systems and Groundwater Treatment
Sorption is the most widely used method, and filtration through GAC is commonly applied in drinking water treatment plants. With the aim to optimize the drinking water PEAS removal efficiency, filter service life and operational costs, [PERSON] et al. carried out a study in a full-scale drinking water treatment plant over a period of two years. The GAC filter removal efficiency was found higher for long-chained PFASs than for short-chained ones, and PFSAs were removed better than PFCAs. The removal efficiency decreased for GAC filters of a long operational age, and it was increased substantially by decreasing the flow. Estimations based on a six-month dataset suggested that GAC service life could be prolonged by almost half if the flow-rate was decreased from the conventionally applied 39 to 18 L s\({}^{-1}\) after having reached the treatment goal of \(\Sigma_{11}\) PFAS < 50 \(\mathrm{ng}\) L\({}^{-1}\) in the outgoing water. The adjustment to low flow-rates at the end of service life could then decrease the operations costs [162]. In a pilot-scale experiment, the PFAS absorbance capacity of fourteen commercially available adsorbents, eight granular activated carbons (GACs), four anion exchange (IX) resins and two alternative adsorbents (AAs) was tested at a groundwater source used for drinking water. Preliminary analysis of groundwater detected 11 different PFAS compounds at low (\(\mathrm{ng}\)/L) concentrations. The pilot system consisted of three adsorbent media skids as well as a pre-filtration skid, which included two 30-micron cartridge filters. The authors presented the results as \"time to reach a specific treatment goal\", because all adsorbent empty bed contact times (EBCTs) were the same EBCTs used in full-scale treatment systems. The time to reach a specific treatment goal in the pilot system would be the same in a full-scale system, facilitating the assessment of overall performance, media replacement time and costs. GACs were confirmed to be more effective at removing long-chained compounds than short-chained compounds. Bituminous activated carbons tested in this study had a better performance (longer media life) and were more efficient at removing long- and short-chain PFASs. The F600 carbon showed an exhaustion point of 80% by the end of the study (16 months), while all other products had been fully exhausted. Of the four tested IX resins, PSR2 + showed better performance for removing both short- and long-chain PFAS. Of the two AAs tested, FS200 had a significantly better adsorption of PFAS when compared with the ESA. However, the authors underlined that the relative performance of individual adsorbents within and across adsorbent types may be site-specific, owing to the conditions and groundwater quality [163]. In a phytoremediation pilot plant, the removal of PFAAs, mainly PFOA (1.5 to 2.4 \(\upmu\)g L\({}^{-1}\)) and PFBA (up to 1.2 \(\upmu\)g L\({}^{-1}\)), from groundwater affecting both public waterworks and private wells was carried out in a tank (1 m \(\times\) 3 m) containing three layers of gravel with different granulometry. The fraction of soil was only 1% of the volume, to isolate the performance of reed grass in PFAA extraction. The HRT was estimated to be 5.1 days. PFAS concentration in exposed reed grasses increased with exposure time, ranging from 2.5 ng g\({}^{-1}\) WW in plants harvested in October to 12.9 ng g\({}^{-1}\) WW in those collected in August of the following year. Phytoremediation in the pilot plant was able to reduce from 30 to 50% of PFASs in terms of mass flow, and most PFAA pollution was generally detected in leaves. The main problem of this system is the disposal of the contaminated plants, since the moved plants should be thermally treated in incinerators at a high temperature, 900-1000 \({}^{\circ}\)C, for the total defluorination [164]. The remediation of sulfolane-contaminated groundwater by Fenton and Fenton-like processes and optimal operational conditions were evaluated at batch and pilot scale in the study by [PERSON] et al.