Response Surface Methodology Optimization for Photodegradation of Methylene Blue in a ZnO Coated Flat Plate Continuous Photoreactor

Abstract

Abstract In this paper, a continuous flat plate photoreactor with ZnO coating was studied in the photodegradation of methylene blue. The structural properties of catalyst were characterized by means of X-ray diffraction, Field emission scanning electron microscopy (FESEM), and energy dispersive X-ray (EDX). The XRD results indicate that high crystalline ZnO particles with average size of 13.5 nm were coated on the glass plate. The thickness of ZnO layer was 39.67 μm and the coating was uniform and crack free. The EDX showed clear border between glass and ZnO layer which confirmed no material transfer between glass and ZnO layer during thermal treatment. The influence of reactor parameters such as the slope of the glass plate, number of UV lamps, distance between lamp and ZnO coated glass plate and flow rate of wastewater was investigated using optimal custom design which is a subset of response surface methodology (RSM). The results indicated that the maximum photodegradation of methylene blue was achieved under the following conditions: plate slope of 9, 3 UVA lamps, 12 ml/s wastewater flow rate and 10 cm distance between lamp and glass plate. The response of surface methodology at optimum conditions was 65.05% while experimental value was 64.66%, showing good agreement between the experimental values and those predicted by the models, with relatively small errors which were only 0.64. The kinetic study was also performed for methylene blue photodegradation at optimum conditions.