Elimination efficiency of organic UV filters during ozonation and UV/H2O2 treatment of drinking water and wastewater effluent

Abstract

The efficiency of elimination of organic UV filters by ozonation and UV254nm/H2O2 processes was assessed and predicted in simulated treatments of sewage-impaired drinking water and wastewater effluent in bench-scale experiments. Second-order rate constants (k) for the reactions of the eight UV filters with ozone and [rad]OH were determined by quantum chemical calculations and competition kinetics methods, respectively. The UV filters containing phenolic (ethylhexyl-salicylate, homosalate, and benzophenone-3) and olefinic moieties (4-methylbenzylidene-camphor, benzyl-cinnamate, and 2-ethylhexyl-4-methoxycinnamate) showed high ozone reactivity (k ≥ 8 × 104 M−1s−1 at pH 7), while those without such electron-rich moieties (isoamyl-benzoate and benzophenone) were ozone-refractory. All the UV filters showed high [rad]OH reactivity (k ≥ 6.2 × 109 M−1s−1). In concordance with the rate constant information, the phenolic and olefinic UV filters were efficiently eliminated by ozone treatment, requiring specific ozone doses of <0.5 mgO3/mgDOC for ∼100% elimination. The UV filters were eliminated by ≤ 38% at a UV fluence of 1500 mJ/cm2 in the UV254nm-only treatment. Rapid photoisomerisation between the E and Z geometric isomers was observed for the olefinic UV filter, benzyl-cinnamate. The addition of H2O2 (10 mg/L) greatly enhanced the elimination of all UV filters, indicating that [rad]OH was the main contributor to their elimination in the UV254nm/H2O2 treatment. A chemical kinetics approach developed previously for ozonation and UV/H2O2 processes was shown to predict the elimination of the UV filters in the tested water matrices reasonably well, demonstrating that the chemical kinetics method can be used for a priori prediction of micropollutant elimination in oxidative treatment processes for potable reuse of municipal wastewater effluents. © 2019 Elsevier Ltd