Sonolysis of ciprofloxacin in aqueous solution: Influence of operational parameters

Abstract

Ultrasonic irradiation is a promising technique for the degradation of persistent organic molecules such as pharmaceuticals in wastewater. This paper focuses on the sonolytic degradation of ciprofloxacin (CIP), a fluoroquinolone antibiotic. During a first experiment at 25°C and 544 kHz, the degradation of a 15 mg L(-1) CIP-solution showed a pseudo-first order degradation constant k(1) equal to 0.0067 ± 0.0001 min(-1) (n=3). Experiments with the addition of t-butanol as a radical scavenger showed that reaction with *OH radicals is the main degradation route for ciprofloxacin. Since the production of *OH radicals was the highest at 544 kHz, this was also the most favorable frequency for CIP degradation in comparison with 801 (k(1)=0.0055 min(-1)) and 1081 kHz (k(1)=0.0018 min(-1)). The degradation constant is also strongly dependent on the temperature of the bulk solution. The degradation constant increased significantly with increasing temperature from 0.0055 min(-1) at 15°C to 0.0105 min(-1) at 45°C. According to the Arrhenius law, the apparent activation energy was determined to be 17.5 kJ mol(-1). This suggests that the degradation of CIP is diffusion controlled, as is the case for most radical reactions. A Langmuir-type heterogeneous reaction kinetics model could be used to explain the increasing degradation constant with decreasing initial CIP concentration from 0.0204 min(-1) (C(0)=0.15 mg L(-1)) to 0.0009 min(-1) (C(0)=150 mg L(-1)). According to the model a local reaction zone exists at the interface region of the cavitation bubbles. During bubble oscillation, molecules accumulate in the reaction zone and when the bubble finally collapses, the molecules in the reaction zone can be oxidized by the formed *OH radicals. This means that degradation is limited by the available surface at the interface. The model agreed very well with the experimental data (R(2)=0.975). The pseudo rate constant for decomposition (k(d)) was estimated to be 0.40 μM min(-1) and the modeled equilibrium constant (K) was equal to 0.047 μM(-1).

Degradation of pharmaceuticals by ultrasound-based advanced oxidation process

“…When the concentration is 15 mg L -1 , the reported rate constant was 0.0067 min -1 , but when it is decreased to 1.5 and 0.15 mg L -1 the rate constant gets enhanced to 0.0141 and 0.024 min -1 , respectively (De Bel et al 2011). Similar results are reported for tetracycline, sulfadiazine, sulfamethazine, acetaminophen, levodopa and atenolol.…”

“…The degradation of carbamazepine, ciprofloxacin, sulfadiazine, acetaminophen, levodopa, diclofenac and atenolol was reported at various frequencies (De Bel et al 2011;Isariebel et al 2009;Lastre-Acosta et al 2015;Nejumal et al 2014;Rao et al 2016). The degradation of 15 mg L -1 is found to be maximum at 544 kHz with a rate constant of 0.0067 min -1 .…”

“…When the frequency is increased to 860 and 1134 kHz, the rate constant decreased to 0.0055 Environ Chem Lett and 0.0018 min -1 , respectively. The degradation rate got enhanced from 0.0055 to 0.0105 min -1 when increasing the temperature from 15 to 45°C (De Bel et al 2011). The degradation of 25 mg L -1 of sulfadiazine, acetaminophen and levodopa at three frequencies such as 574, 860 and 1134 kHz was reported.…”

Optimization of ciprofloxacin degradation in wastewater by homogeneous sono-Fenton process at high frequency

“…respectively, at the highest frequency 1,134 kHz. [30] De Bel et al [33] found that the lowest frequency, 544 kHz, proved to be the most favorable on CIP degradation. The ultrasonic frequency significantly affects sonolysis due to both the critical size and lifetime of cavitation bubbles, which consequently affects the number of cavitation bubbles, the violence of the bubble collapse and the OH• radical production.…”

“…The influence of operational parameters in the sonolysis on CIP degradation and CIP initial concentration was studied by De Bel and collaborators. [33] Xiao et al [11] studied the role of matrix organic compounds on the sonolysis of CIP in aqueous solutions. The effective destruction of CIP at the frequencies of 20 and 620 kHz has been proven.…”