Combination of photocatalysis with hydrodynamic cavitation for degradation of tetracycline

- Coupling photocatalysis with hydrodynamic cavitation shows synergistic effect.
- HCO3− improves degradation rate of tetracycline in combined process.
- Degradation pathway of tetracycline involved hydroxylation and loss of some groups.

Hydrodynamic cavitation is a promising technology for wastewater treatment. In this study, TiO2 (P25) photocatalytic degradation of tetracycline, an antibiotic compound extensively used and environmentally hazardous, was conducted with hydrodynamic cavitation employed simultaneously. Many factors, such as initial tetracycline concentration, solution pH and presence of inorganic anions, were explored. Kinetics were investigated at varied contaminant concentrations, and the pseudo-first-order rate constant for tetracycline photocatalysis coupled with hydrodynamic cavitation was 1.5-3.7 times of the sum of those for the individual processes. These results indicated that a synergistic effect occurred in the combined method. Tetracycline degradation was pH-dependent and favored at alkaline pH. The presence of HCO3− in the medium induces promotive effect on the photocatalytic degradation of tetracycline in the presence of hydrodynamic cavitation, while sulfate and chloride exhibit only minor effect. UV/Vis spectra, Fourier transform infrared (FTIR) adsorption spectra and liquid chromatography-mass spectra (LC-MS) were used to evaluate the degradation mechanism. Scanning electron microscopic (SEM) images of TiO2 confirmed that hydrodynamic cavitation can prevent photocatalytic particles from agglomeration.