Hydrated electrons (e^-_aq,E= -2.9 V) generated by advanced reduction processes (ARPs) have been proved to be a promising approach to eliminate various per- and polyfluoroalkyl substances (PFASs) in water. In this study, the decomposition of perfluorooctanoic acid (PFOA) in a complex water matrix by e^-_aq generated from the UV/sulfite process was investigated. The effect of pH (9-12) and co-existing compounds (chloride, nitrate, phosphate, carbonate and humic acid) on PFOA degradation efficiency was studied. In addition, the intermediates and possible degradation pathways were analyzed by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS). The results showed that the concentration of PFOA was below the detection limit (10 μg/L) after 1 h (conditions: C₀ 10 mg/L, initial pH = 10, sulfite 10 mM) while 89% defluorination was achieved after 24 h. Using a higher initial pH (pH = 12) greatly enhanced the PFOA degradation as 100% degradation and 98% defluorination were achieved after 24 h. The presence of carbonate (> 5 mM), nitrate (> 2 mM) and humic acid (> 25 mg/L) showed a significant negative effect on PFOA degradation via a UV blocking effect or quenching of hydrated electrons while the presence of chloride and phosphate had a smaller effect on PFOA degradation. Even at extremely high concentrations of chloride (1.709 M, pH = 11.25), the defluorination ratio reached 97% after 24 h of reaction time. During the process, short-chain perfluorinated carboxylic acids (PFCAs, C < 7) and hydrogen substituted compounds were detected, which implies that chain-shortening and H/F change reactions had occurred. Moreover, this confirmed the generation of sulfonated and unsaturated intermediates during the process, which disclosed valuable new mechanistic insights into PFOA degradation.

Nickel and vanadium were removed from real ammoniacal industrial wastewater (Ni 2–4, V 40–50 mg/L) obtained from a synthesis gas scrubber. The aim of the study was to develop an industrial application for simultaneous removal of nickel and vanadium. The studied methods were adsorption (activated carbon (AC), AquaSorb® 2000), anion exchange (Amberjet™ 4200 Cl) and cation exchange (Amberjet™ 1200 H). AC removed > 95% of nickel at pH 5.5–9 (dose > 2 g/L) but the vanadium uptake remained poor. In batch cation exchange, all nickel was removed (optimum pH 4–7) and 70–75% of vanadium was removed at pH 7 (5–10 g/L). All nickel was removed in batch anion exchange (optimum pH 5.5–9, 2–10 g/L). Over 89% of vanadium was removed in batch anion exchange at pH 7 (1–10 g/L). Adsorption capacities of 4.36 and 48.9 mg/g were obtained for nickel and vanadium in anion exchange at pH 7. In column anion exchange, all nickel and 92–98% of vanadium were removed in all three ion exchange cycles at pH 7–9. In regeneration, 72–96% of vanadium was eluted from the resin with 2.5 M NaOH. However, the elution of nickel with 2.5 M NaOH was not successful. An acid rinse (1 M H₂SO₄) enhanced nickel recovery up to 94%. Anion exchange proved to be the most effective method for simultaneous removal of nickel and vanadium from industrial wastewater.