Influence of co-existing cations and anions on removal of direct red 89 dye from synthetic wastewater by hydrodynamic cavitation process: An empirical modeling

Abstract

In the present study the evaluation of Direct Red 89 (DR89) dye removal from synthetic wastewater by a lab-scale hydrodynamic cavitation (HC) process has been investigated under different operational conditions; the influence of co-existing cations and anions was applied using synthetic wastewater to assess whether the DR89 removal was enhanced. To study the effect of operational parameters, an empirical approach was adopted for the modeling of the HC process. The results showed that the DR89 degradation rate was strongly influenced by solution pH, reaction time and initial DR89 concentration. The removal efficiencies of DR89 were enhanced remarkably with the reaction time increment. When the initial concentration of DR89 increased from 30 to 90 mg/L, the DR89 removal efficiency decreased from 36.3 +/- 3.8 to 17.5 +/- 2.5. In addition, the highest DR89 removal efficiency (75.4 +/- 3.4) was observed at a solution pH of 3. At a solution pH of 8, the DR89 removal efficiency was 18.4 +/- 1.1. An initial DR89 concentration of 80 mg/L was 75.4 +/- 5.1 degraded after 130 min at a solution pH of 3. The results indicated that a synergistic effect occurred due to the added ions except for HCO3-. The removal of DR89 by the HC process was extremely enhanced with NO3- ions with synergetic index higher than 2.5. Kinetic studies revealed that the decolorization of DR89 by HC followed a first order kinetic mechanism. The comparison between the predicted results of the empirical model and experimental data was also conducted. The empirical model described the DR89 removal efficiency under different conditions (R-2: 0.93) and the results showed the HC reaction to be a useful technology for the treatment of dye in the textile wastewater.