Energy consumptions. We calculated the energy efficiency of UV/S and EO modules based on the slopes of the quasi-linear segments of the defluorination profiles (Figs.4d, S7d, S8d, and S9d) as the required energy input (kWh) to convert per gram of the organic fluorine to F -(Figs. and). The light-adsorbing water matrices are usually expected to limit the efficacy of photochemical systems, but the UV/S system exhibited a consistent energy efficiency for the 50-, 100-, and 500-fold diluted AFFF. In particular, the UV/S treatment further reduced the absorbance at 254 nm in the 50-fold diluted AFFF from 1.36 to 0.36 (Table ). This "self-sharpening" feature makes UV/S suitable for treating concentrated AFFF. The lowest dilution factor of 1:50 in this work is three orders of magnitude lower (i.e., three orders of magnitude more concentrated) than the previous UV/S demonstration, which diluted AFFF 60,000-fold and operated at pH 9.5. The limited dilution substantially reduced the water volume to be treated, thus substantially saving the electrical energy for UV irradiation.