Peracetic Acid–Ruthenium(III) Oxidation Process for the Degradation of Micropollutants in Water

This paper presents an advanced oxidation process (AOP) of peracetic acid (PAA) and ruthenium(III) (Ru(III)) to oxidize micropollutants in water. Studies of PAA–Ru(III) oxidation of sulfamethoxazole (SMX), a sulfonamide antibiotic, in 0.5–20.0 mM phosphate solution at different pH values (5.0–9.0) showed an optimum pH of 7.0 with a complete transformation of SMX in 2.0 min. At pH 7.0, other metal ions (i.e., Fe(II), Fe(III), Mn(II), Mn(III), Co(II), Cu(II), and Ni(II)) in 10 mM phosphate could activate PAA to oxidize SMX only up to 20%. The PAA–Ru(III) oxidation process was also unaffected by the presence of chloride and carbonate ions in solution. Electron paramagnetic resonance (EPR) measurements and quenching experiments showed the dominant involvement of the acetyl(per)oxyl radicals (i.e., CH3C(O)O• and CH3C(O)OO•) for degrading SMX in the PAA–Ru(III) oxidation process. The transformation pathways of SMX by PAA–Ru(III) were proposed based on the identified intermediates. Tests with other pharmaceuticals demonstrated that the PAA–Ru(III) oxidation system could remove efficiently a wide range of pharmaceuticals (9 compounds) in the presence of phosphate ions in 2.0 min at neutral pH. The knowledge gained herein on the effective role of Ru(III) to activate PAA to oxidize micropollutants may aid in developing Ru(III)-containing catalysts for PAA-based AOPs.