Methyl orange decolourization through hydrodynamic cavitation in high salinity solutions

This paper presents the experimental results obtained on the decolourization of methyl orange (MO) in saline solutions, carried out through hydrodynamic cavitation (HC), used as a stand-alone technique, and in a hybrid configuration coupling with hydrogen peroxide. Experiments were carried out by adding NaCl in a solution in the range of 1.5 to 5 g/L to study the effect of salt on dye degradation by simulating the composition of a real tannery liquid waste. The results showed that the maximum efficiency was about 30% using a Venturi tube at an operating pressure of 0.55 MPa. The presence of hydrogen peroxide allowed the degradation process to be slightly below 70%; the presence of sodium chloride (5.0 mg/L) increased the decolourization efficiency up to about 70% as well, while the combined presence of NaCl and H2O2 had a negative outcome. The experiments on synthetic waste allowed to gain a MO degradation slightly below 90%. Process analysis was carried out to evaluate the possible integration of the HC within a real wastewater treatment plant by comparing the traditional treatment train with a new plant configuration, in which HC takes the place of a conventional coagulation tank.