An imminent application scenario is the cleaning of hanger fire-fighting pipelines and fire trucks that used PFAS-based AFFF in the past decades. This time, we used tap water for the 100-fold dilution of AFFF (Table ). The UV/S-EO treatment resulted in very similar evolution/degradation kinetics for all individual PFAS and F - release (Fig. ) to the DI water diluted AFFF (Fig. ). We also observed very similar reaction kinetics for all species at the dilution factors of 50 (Fig. ) and 500 (Fig. ), except that the more diluted (i.e., less concentrated) AFFF needed less time to achieve 100% defluorination. For the UV/S module, the chemical and energy consumption appeared proportional to the dilution factor (Fig. ). The treatment of 500-fold diluted AFFF needed 10 mM sulfite and 12 h to reach the maximum defluorination of 46%. For the 50-fold diluted AFFF, 100 mM sulfite and 120 h were needed to reach the maximum defluorination of 48%. In comparison, the EO module is less sensitive to the dilution factor. The time required to achieve the 100% overall defluorination for 50-and 500-fold diluted AFFF was 24 and 12 h, respectively. It is important to highlight that the 50-fold diluted AFFF had a record-high TOC > 4000 mg L -1 and TOF at 200 mg L -1 compared with those samples treated in the previous studies (Table ). Hence, the UV/S-EO has demonstrated great promise to destroy concentrated PFAS in wastewater, particularly for the major challenges in fire-fighting system cleaning and AFFF disposal (after adequate dilution).