Treatment of acid violet 7 dye containing effluent using the hybrid approach based on hydrodynamic cavitation

Abstract

The present work investigates the degradation of the azo dye, Acid violet-7 using hydrodynamic cavitation (HC) in combination with advanced oxidation processes (AOPs). The recalcitrant nature of the dye makes the conventional methods of degradation less effective and hence it is important to explore advanced methods. The development of treatment scheme for AV-7 using HC involved the optimization of initial dye concentration (10–200 ppm) and operating pH (3–10) to maximize decolorization using the approach of HC alone. At the optimum initial dye concentration of 20 ppm, operating pH of 3 and selected inlet pressure of 4 bar, the maximum decolorization was 39.1 % and mineralization was 25.2 % obtained using individual HC process without the addition of any chemical oxidants. The combined process of HC coupled with oxidants evaluated in the work were HC+H2O2, HC + KPS and HC + Fenton which resulted in the extent of decolorization as 70.49, 77.72 and 94.02 % respectively and the extent of mineralization as 38, 48.8 and 70.4 % respectively. The dye decolorization followed first order kinetics in all the approaches and obtained rate constants were used to evaluate the effectiveness of combinations in terms of the synergistic index. Additionally, comparison of efficacy of each treatment scheme was established with the aid of cavitational yield and the treatment costs. Overall, the combination of HC and Fenton oxidation was demonstrated to be the best approach for the degradation of AC-7 dye compared to the other combined oxidation processes.