Degradation of Direct Red 16 using hybrid treatment strategies based on hydrodynamic cavitation, and advanced oxidation processes

In the present study, the applicability of hydrodynamic cavitation (HC) and its combination with other oxidizing agents including sodium hypochlorite (NaOCl) and UV irradiation for the degradation of Direct Red 16 (DR16) was investigated. The effects of different operating parameters like initial pH (3.0-9.0), different DR16/NaOCl molar ratio (1:20, 1:17, 1:15 and 1:10), initial concentration (20-40 mg/L), and pressure (1.0-5.0 bar) on DR16 degradation were also studied. The combined approaches of HC + UV, NaOCl + UV, HC + NaOCl, and HC + NaOCl + UV were surveyed (under conditions of pH = 6.8, DR16 dosage = 20 ppm, NaOCl/DR16 molar ratio of 20:1, and P = 5.0 bar). The degradation efficiency obtained by the individual processes of HC, UV, and NaOCl were 20%, 17%, and 66%, respectively; while in combined processes of HC + UV, NaOCl + UV, HC + NaOCl, and HC + UV + NaOCl, 42%, 73%, 77% and 88% of DR16 degradation was achieved in tap water, respectively in 30 min of treatment time. Also, for HC + UV + NaOCl process 99% of DR16 degradation was obtained in deionized water. In order to evaluate the kinetics of DR16 degradation, two kinetics models including first order kinetics and fractal like kinetics equations were used. Among the studied kinetics models, fractal like kinetics model showed the best correlation with the experimental data. The obtained data showed that several mechanisms (paths) are involved in DR16 degradation. Based on the obtained results HC + NaOCl + UV can be served as a potential treatment method to degrade dyes and other organic pollutants from aqueous solutions.