Degradation of diclofenac through ultrasonic-based advanced oxidation processes at low frequency

Abstract

This work presents the results regarding the degradation of 1 mg L −1 DCF using the ultrasound (US) system and the US/photo-Fenton process at 40 kHz. The operating conditions of each advanced oxidation process (AOP) studied were optimized using the response surface methodology, specifically a central composite design of experiments, and the influences of the solution pH, US power and hydrogen peroxide and ferrous ion concentrations were evaluated. Additionally, the degradation kinetics of DCF were investigated and adjusted to the Okitsu and Serpone models. The Serpone model gave the best fit (R2 values equal to 0.966 and 0.972 for the US system and the US/photo-Fenton process, respectively), obtaining DCF kinetic constants of 0.034 µmol L−1 min−1 and 0.153 µmol L−1 min−1. A DCF removal of 70.30% was obtained through the US system in 120 min; however, by applying the US/photo-Fenton process, a removal of 94.42% was achieved in 45 min under optimal operating conditions. The degradation of DCF in surface water and the influence of the matrix on DCF elimination were also analyzed under optimal operating conditions. A decrease in the percentage of DCF removal was observed (18.71% and 35.32%, when the US and US/photo-Fenton processes were applied for 120 min and 45 min of treatment, respectively) in surface water, which was ascribed to the content of organic and inorganic species, limiting the oxidation and mineralization potential of the tested AOP.