Naproxen abatement by thermally activated persulfate in aqueous systems

• Naproxen is fully degraded in thermally activated persulfate systems.
• Naproxen degradation mechanism is highly dependent on SO4- rather than on OHOH radicals.
• Naproxen mineralization extent is proportional to persulfate concentration.
• Inorganic ions slightly affect naproxen degradation efficiency in TAP systems.
• TAP systems showed total mineralization of naproxen in highly charged hospital effluent.

In this work, we investigated the use of thermally activated persulfate (TAP) as one of the most powerful advanced oxidation processes for the treatment of pharmaceuticals present in effluents. Pilot experiments were carried out on naproxen (NAP) solutions, and the effect of experimental conditions (e.g. inorganic additives, matrix) was assessed so as to better evaluate TAP systems and improve the reaction stoichiometric efficiency. A comparative kinetics study was provided for the removal of NAP vs work previously published using however other classes of pharmaceuticals e.g. bisoprolol, ibuprofen. The activation energy (EA) calculated was found to be 155.03 (±26.4) kJ mol−1. The best degradation rate was observed at 70 °C and found to be equal to 1.286 × 10−4 mM min−1. Furthermore, experiments were performed on untreated hospital effluents collected from the largest hospital in Beirut and spiked with NAP solution (50 μM). Results showed full mineralization of the pharmaceutical effluent that was achieved and monitored via total organic carbon (TOC) analysis. Liquid and gas chromatography coupled with mass spectrometry were the techniques used for the identification of NAP and its transformation products. A NAP degradation mechanism was proposed and found to be mainly based on the action of sulfate radicals operating by electron abstraction. This study demonstrated once more that TAP systems are a valid and efficient method that can be used for the removal of dissolved pharmaceuticals in water and sewage water.