ABSTRACT
Ampicillin and nafcillin antibiotics were treated by high frequency ultrasound (at 375 kHz and 24.4 W). Degradations followed pseudo-first order kinetics, which constants were k: 0.0323 min-1 for AMP and k: 0.0550 min-1 for NAF. Accumulation of sonogenerated hydrogen peroxide and inhibition degree of sonochemical removal (IDS) in presence of a radical scavenger were also stablished. Afterwards, ultrasound was combined with UVC light (sono-photolysis), with ferrous ion (sono-Fenton), and with ferrous ion plus UVC light (sono-photo-Fenton) to degrade the antibiotics. Furthermore, treatment of the pollutants in a complex matrix and removal of antimicrobial activity (AA) were considered. The antibiotics evolution was followed by HPLC-DAD technique and the accumulation of sonogenerated H2O2 was measured by an iodometry-spectrophotometry methodology (77.6 and 57.3 µmol L-1 of H2O2 after 30 min of sonication were accumulated in presence of AMP and NAF, respectively). IDS was analyzed through treatment of the antibiotics in presence of 2-propanol (87.1% for AMP and 56 % for NAF) and considering the hydrophobic character of pollutants (i.e., Log P values). Antimicrobial activity evolution was assessed by the Kirby-Bauer method using Staphylococcus aureus as indicator microorganism (sono-photo-Fenton process removed 100% of AA after 60 and 20 min for AMP and NAF, respectively). Finally, for degradations in the complex matrix, a simulated effluent of municipal wastewater treatment plant was utilized (sono-photo-Fenton led to degradations higher than 90 % at 60 min of treatment for both antibiotics). The data from the present work can be valuable for people researching on treatment of wastewaters containing antibiotics, application of advanced oxidation technologies and combination of sonochemical process with photochemical systems.
ABSTRACT
This work presents the degradation of ampicillin (a highly consumed ß-lactam antibiotic) in aqueous media by sonochemical advanced oxidation processes. Initially, effects of frequency, power and operation mode (continuous vs. pulsed) on the antibiotic degradation by sonochemistry were analyzed. Then, under the suitable operational conditions, pollutant degradation and antimicrobial activity (AA) evolution were monitored. Afterwards, computational calculations were done to establish the possible attacks by the hydroxyl radical to the ampicillin structure. Additionally, the antibiotic degradation in synthetic hydrolyzed urine by ultrasound was performed. Finally, the combination of sonochemistry with Fenton (sono-Fenton) and photo-Fenton (sono-photo-Fenton) was evaluated. Our research showed that ampicillin removal was favored at low frequency, high power (i.e., 375 kHz, 24.4 W) and continuous mode (exhibiting an initial degradation rate of 0.78 µM min-1). Interestingly, ampicillin degradation in the hydrolyzed urine by sonochemistry alone was favored by matrix components (i.e., the pollutant showed a degradation rate in urine higher than in distilled water). The sonochemical process decreased the antimicrobial activity from the treated water (100% removal after 75 min of treatment), which was related to attacks of hydroxyl radical on active nucleus (the computational analysis showed high electron density on sulfur, oxygen and carbon atoms belonging to the penicillin core). Sono-photo-Fenton system achieved the fastest degradation and highest mineralization of the pollutant (40% of organic carbon removal at 180 min of treatment). All these aspects reveal the good possibility of sonochemical advanced oxidation technologies application for the treatment of antibiotics even in complex aqueous matrices such as hydrolyzed urine.
