Application of hybrid oxidative processes based on cavitation for the treatment of methyl blue solutions

Over the past few decades, the scientific community has developed an increasing interest in high-performance water treatment systems based on cavitational processes. Hydrodynamic cavitation (HC) is one of the promising technologies for wastewater treatment, especially for dyeing solutions, since it shows high efficiency in treating dyes, even at low concentrations. Both strategies have been shown to be efficient ways to get rid of pathogenic bacteria by disinfecting waters and achieving the mineralization of numerous organic pollutants. This makes cavitation-based techniques an attractive choice for use in water treatment facilities' post-treatment stages. Modern techniques have been presented that combine advanced oxidation processes (AOPs) with cavitation for increased oxidation capacity. When used together, cavitation and AOPs (such as O3, H2O2, and Fenton's process) can cause materials to decay much more quickly. This work aims to investigate the degradation of Methyl Blue (MB) with HC and evaluate the effectiveness of a hybrid process (O3 + HC). The experimental tests were conducted to determine the optimal operating conditions (pressure, pH, O3 dosage). Furthermore, the feasibility of MB mineralization at a high concentration range (10-100 mg/l) was performed. Cost estimation and energetic analysis were discussed. As a result, the optimal conditions were: P = 4.5 bar, pH 2, O3 = 7.5 mg/L. For the initial concentration of 10 mg/L, the MB decolorization yield of HC, O3, and HC + O3 were 10%, 99%, and 100%, respectively, after 30 min of treatment. The addition of O3 promoted the degradation efficiency above 95%, decreasing the treatment time. Increasing the O3 feed rate can reduce the treatment time. A flow rate of 8 L/min of ozone was adopted in the optimal flow value. The hybrid process has an important effect in improving the performance of wastewater treatment by reducing treatment time, causing saving in energy consumption and process cost.