Impact of replacement per- and polyfluoroalkyl substances on an indirect potable water reuse scheme

Abstract

Indirect potable reuse (IPR) is increasingly adopted as a sustainable strategy for augmenting urban water supplies while maintaining environmental flows. However, the behavior of persistent trace contaminants such as per- and polyfluoroalkyl substances (PFAS) across the complete IPR treatment train, including natural attenuation processes, remains insufficiently characterized, particularly for emerging replacement compounds. This study presents a comprehensive two-year investigation (2022–2024) of 31 PFAS across a surface water-based IPR scheme in the Llobregat River basin (Spain), tracing their presence from the discharge of reclaimed water to the production of drinking water. Eight PFAS were consistently detected, with 6 : 2 fluorotelomer sulfonate (6 : 2FTS), a replacement PFAS, exhibiting the highest concentrations in reclaimed water (46.6 ± 4.8 ng L⁻¹) and measurable propagation downstream in river water (22.1 ± 2.5 ng L⁻¹). Modest increases were observed for PFHxA and PFOA, while most other PFAS showed negligible contribution from reclaimed water discharges. Within the advanced drinking water treatment train, reverse osmosis demonstrated >99% removal efficiency for all detected PFAS. In contrast, ozonation and ultrafiltration were ineffective, while granular activated carbon exhibited variable removal performance (13–99%) dependent on compound chain length. PFAS levels in finished drinking water were consistently below European regulatory limits. Seasonal fluctuations in ∑PFAS, PFOS, and PFBS were observed in river water but not in treated drinking water, indicating effective barrier performance. This work provides novel insights into PFAS fate within full-scale IPR systems and underscores the relevance of monitoring replacement PFAS in Mediterranean contexts. The findings support the development of targeted regulatory strategies and treatment optimization for safe potable reuse.