Synergistic activation of persulfate by ultrasound/PbO2 anodic oxidation system for effective degradation of naproxen, a toxic and bio-recalcitrant pollutant: Process optimization and application for pharmaceutical wastewater

Abstract

Naproxen (NPX) is a widely used pain reliever that conventional treatment systems are unable to fully mineralize its residues in wastewater. The aim of this study is to develop a synergistic persulfate activation system based on ultrasound/PbO2 anodic oxidation process (US/PS/AO) for effective degradation of NPX and improving the biodegradability of pharmaceutical wastewater. PbO2 electrocatalyst was prepared by anodic deposition and then its characteristics were determined by FESEM, EDX and XRD techniques. Optimizing the effect of independent variables on NPX removal was done using an CCD method. The performance of the optimized US/PS/AO process for NPX degradation and TOC mineralization after 60 min of reaction was 98.5 % and 73.6 %, respectively. The reusability of the PbO2 electrocatalyst was maintained above 97 % in ten continuous oxidation cycles for NPX degradation. Also, the cumulative concentration of leaked lead (53 μg L−1) was within the permitted standard for discharging wastewater into the river. Using HPLC-mass spectrometer data, possible pathways for NPX mineralization were suggested. The biodegradability of pharmaceutical wastewater with the optimized US/PS/AO and PS/AO processes increased to above 0.4 after 100 and 150 min of treatment, respectively. However, the total energy consumption in the PS/AO process (US power = 0, EC = 83 kWh kg−1 COD) is significantly lower than the US/PS/AO (US power = 100 W, EC = 982 kWh kg−1 COD). The findings of the present study can contribute to the development of a cheap, safe, and effective integrated AOP for the treatment of pharmaceutical wastewater containing non-biodegradable compounds.