Sulfamethazine degradation by heterogeneous photocatalysis with ZnO immobilized on a glass plate using the heat attachment method and its impact on the biodegradability

In this paper, the degradation of sulfamethazine (SMT) was performed using of photocatalytic process in the presence of ZnO catalyst immobilized on glass plate (on ZnO/glass plate) under UV light. The ZnO/glass plate was characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra; the results of the characterization demonstrated that the properties of ZnO/glass plate were maintained unmodified. The adsorption and the photolysis tests revealed the absence of adsorption of SMT onto ZnO/glass plate and the absence of direct photolysis of SMT. The effect of the initial solution pH, the flow rate and the initial concentration of SMT on the photocatalytic process was studied and optimized by using central composite design (CCD). The model equation obtained led to a classification of these parameters based on their level of significance. The results suggested that the most influential factor was the initial concentration of SMT (x(2)), which had the strongest effect on the response (- 11.6) and the negative sign of the coefficient suggested that the degradation of SMT decreased for increasing initial SMT concentration. It was followed by the flow rate with positive effect on the yield of SMT degradation (+ 2.06). The model also demonstrated the absence of pH effect in the studied interval and that the strongest interaction was between the pH and the flow rate. The kinetic of degradation of the SMT can be described by a pseudo-first order kinetic model for 10 and 50 mg/L of SMT; while the kinetic of degradation was described by a pseudo-second-order kinetic model for the highest initial concentration, [SMT](0) = 100 mg/L. The optimal values of the solution pH, the flow rate and the initial concentration of SMT were 6, 0.56 L/min and 11 mg/L. Under these conditions the removal efficiency of SMT was 96% and the BOD5/COD ratio increased from 0 to 0.20 after 5 h of irradiation time.