Propranolol Degradation Products after Non-thermal Plasma Treatment using Coaxial DBD Reactor

Pharmaceuticals represent a considerable threat when they reach the environment. Propranolol (PRP), designed to be a biologically active compound, is a widely used beta-blocker prescribed for heart-related diseases. Due to its frequent use, PRP is detected in numerous aquatic environments and organisms. To completely remove pharmaceuticals such as PRP, advanced oxidation processes (AOPs) are often employed, like ozone, or electrochemical oxidation. Recently, the non-thermal plasma treatment has gained interest for water purification, due to in situ production of reactive oxygen species, such as hydroxyl radicals and superoxide anion radicals. The aim of this paper was to investigate plasma treatment for PRP removal from water. To achieve that, the dielectric barrier discharge (DBD) non-thermal reactor was used. This DBD reactor was already tested for degradation of different organic compounds. In this study, PRO solution (100 mg/dm3) was recirculated through the DBD reactor, while plasma was generated using ambient air and argon. The PRP degradation rate was monitored on HPLC-DAD, and the specific energy density (SED) was used to compare plasma effects on PRP degradation. SED was calculated by dividing the power (kept at 35 W and multiplied by the number of cycles of treatment) by the flow rate (held constant at 7.5 dm3/h). The single most striking observation is that pure argon contributes to faster PRP degradation. Namely, at 75 kJ/dm3, there was less than 5% of PRP left when treated with Ar non-thermal plasma, while only around 35% was achieved at the same point with ambient air. As for the degradation products, several compounds were identified (P326, P308, P292, P266, and P134). Interestingly, all compounds were spotted in air-treated PRP solution, but P326 and P308 were not found in samples treated by Ar-generated plasma. In summary, both decomposition rate experiments and detected degradation compounds imply that Ar may be a better plasma gas for PRP treatmen