Synergistic degradation and degradation pathways of methylene blue by plasma process combined with cavitation impinging stream reactor based on hydrodynamic cavitation

Abstract

The plasma process is an advanced oxidation technique that boasts high efficiency and low cost. A combination of the plasma process with a cavitation impinging stream (CIS) reactor has been developed to investigate the degradation characteristics of methylene blue dye wastewater. The results indicate that under a pressure of 1.40 MPa and an impinging distance of 40 mm, the CIS reactor achieved a degradation rate of 52.83%, which was twice as much as self-excited oscillation cavitation alone. Furthermore, it was found that the optimum solution concentration for this reaction was 5.70 mg/L. Combining a plasma apparatus with a CIS reactor resulted in a degradation rate of 94.06% within 60 min, with a synergy index of 3.13. Intermediate products generated during the HC+plasma treatment were analyzed using liquid chromatography-mass spectrometry. Based on experimental and theoretical analyses, two possible pathways for methylene blue degradation were proposed. This study presents novel insights into the degradation pathway of methylene blue. The CIS+Plasma technology exhibits superior efficiency, higher cavitation yield, and lower operational costs, rendering it a viable option for large-scale wastewater treatment applications.