Ozone-activated peroxymonosulfate (O3/PMS) process for the removal of model naphthenic acids compounds: Kinetics, reactivity, and contribution of oxidative species

Abstract

Due to their recalcitrance, naphthenic acids (NAs) are one of the constituents of interest in oil sands process water (OSPW). In this study, peroxymonosulfate (PMS) activated by ozone was employed to degrade NA model compounds in buffer solutions. At an ozone/PMS ratio of 2:1, a removal of 85 % was observed for a model diamondoid NA compound (1-adamantanecarboxylic acid; ACA) after 45 s of reaction. Compared with ozone alone, the degradation of ACA was accelerated in the presence of ozone/PMS, with an overall pseudo-first order rate constant (kobs) increasing from 8.02 × 10−4 s−1 during ozone treatment to 6.74 × 10−2 s−1 in the ozone/PMS system. Although ozone/hydrogen peroxide (H2O2) showed high degradation for ACA, the ozone/PMS system showed a higher kobs of 5.44 × 10−2 s−1at a PMS dose of 0.042 mM, while at the same dose of H2O2, kobs was equal to 3.62 × 10−2 s−1 for ozone/H2O2. This result showed the synergetic effect of ozone and PMS on the degradation of ACA. Relative kinetics studies using mixtures of model NA compounds showed better performance for ozone/PMS to degrade aromatic NAs compared to ozone/H2O2. Hydroxyl radicals and sulfate radicals were found to be responsible for the removal of ACA, with limited effect of molecular ozone. The proposed degradation pathways for ACA included hydroxylation, carboxylation, and polymerization under ozone/PMS, while hydroxylation and carboxylation were the main degradation pathways under ozone/H2O2. The results of this study emphasize the potential of ozone/PMS process to treat OSPW by accelerating the degradation of recalcitrant organic compounds.