Photocatalytic degradation of vancomycin using titanium dioxide and optimization by central composite design

Conventional wastewater treatment processes are not completely effective in removing vancomycin. In this study, affecting parameters on vancomycin degradation, such as pH, catalyst, initial vancomycin concentration, temperature, and reaction time were investigated simultaneously during a removal process based on titanium dioxide with ultraviolet irradiation in an aqueous solution. Titanium dioxide was synthesized and characterized using X-ray diffraction and scanning electron microscopy. The average size of the synthesized crystals was 4.7 (+/- 0.2) nm. Design of experiments was done by a central composite design based on the response surface methodology and multiple linear regression was implemented to construct the final model and evaluate the design. The total sum square values of the model were compared with the total sum squares of the error (residual) using Analysis of Variance. R-2 in the final model was 0.92, which was close to R-adj(2) (0.88). The optimal values of vancomycin degradation (pH = 5.1, initial concentration of vancomycin = 58.2 mg l(-1), titanium dioxide = 54.9 mg in 250 ml reactor, temperature = 39.6 degrees C, time = 36.3 min) were obtained. Vancomycin degradation efficiency with the ultraviolet application was 89.5% which reached 93% with aeration and 25% without ultraviolet. After twice catalyst reuse, it was decreased from 89.5 to 80% and 78%. According to the results, obtained optimal conditions during treatment by titanium dioxide is an acceptable way to eliminate vancomycin in pharmaceutical industries wastewater, in high concentrations and mild-acidic pH, which does not require high temperatures and much time.