Investigation of the Effect of Ultrasonic Waves on the Enhancement of Efficiency of Direct Photolysis and Photooxidation Processes on the Removal of a Model Contaminant from Textile Industry

The effect of ultrasonic waves (US) was studied on the degradation of Malachite Green (MG) as a model contaminant from textile industry by direct photolysis with ultraviolet (UV) radiation and UV/H2O2 processes. The US (35 kHz) and UV (253.7 nm) radiations were carried out with an ultrasonic bath and a 15 W low-pressure mercury lamp, respectively. Degradation of MG follows pseudo-first order kinetics in all cases. The apparent reaction rate constant (kap) for UV/US process is greater than sum of the UV and US processes but it is relatively low for practical uses. However UV/H2O2 treatment more efficiently decomposes this organic contaminant and combining this process with US can improve its efficiency. kap is influenced by variation of operational parameters such as power density, temperature, initial concentration of MG and H2O2 for US/UV/H2O2 process and activation energy was 9 kJ mol in the range of 294-307 K for this process. UV-vis spectral change of MG showed hypsochromic shift occurred with increasing sonication time, suggested N-demethylation process of MG.