Ozone microbubble-aided intensification of degradation of naproxen in a plant prototype

Abstract

Naproxen (NPX), one of the best-selling nonsteroidal anti-inflammatory drugs, is found in surface and drinking water at concentrations up to 1 μg dm−3. It has been emerging as a water contaminant during the last two decades. Conventional removal techniques, i.e. sewage treatment, membrane separation, filtration, and adsorption have been found to be inefficient for complete removal of NPX. Intensification of the wastewater treatment processes is important in order to achieve higher degradation efficiencies. Advanced oxidation processes (i.e. ozonation, photolysis, and photo-Fenton) have the greater capability of NPX removal. In the present study, a combination of ozonated microbubbles and H2O2 was used for effective removal of NPX. The use of microbubbles increased the mass transfer into the aqueous phase. Use of H2O2 with ozone increased the degradation process significantly, which confirms the − the hydroxyl radicals generated in situ under the alkaline conditions. The ozone supply rates were 0.39, 0.41, 0.44, and 0.48 mg s−1 and the corresponding reaction times were 10000, 2400, 840, and 240 s, respectively for 98−99% conversion for pH 9. The pseudo first-order reaction constants or O3 alone and H2O2 + O3 were in the range of 2.89 × 10−3 − 6.44 × 10−3 and 3.39 × 10−3 − 13.6 × 10−3 min−1, respectively. The effects of ozone supply rate and pH of the reaction system were also studied. The by-products were identified and a mechanism of ozonation of NPX was proposed. The main intermediates were 2-methoxy-6-ethyl naphthalene, (2-methoxy-6-methyl naphthalene, and 1-(6-methoxynaphtalen-2-yl) ethyl-hydroperoxide.