A Comparative Study to Analyse Efficacy of O3, O3/UV, O3/UV/PS for the Degradation of Reactive Dyes in Wastewater

Abstract

The aim of present work was to investigate the performance assessment of reactor configurations for mineralization of synthetic wastewater by ozonation and ozone based Advanced Oxidation Processes (AOPs), i.e., O3, O3/UV, O3/UV/PS. Preliminary studies were carried out in Bubble column reactor with RB5 dye and efforts have been made to determine effects of various operating parameters such as, ozone flowrate, pH, UV intensity and TOC: PS ratio on selected processes i.e. O3, O3/UV and O3/UV/PS at constant parameters such as, initial concentration of RB5 at 500 mg/L, 12 pH, 60 LPH flow of O3, UV intensity 66 W (if applicable) and TOC:PS ratio 1:40 (if applicable). It was observed that O3/UV/PS is more efficient in removal of TOC. Further, experiments were conducted in the bubble column with recirculation and in Venturi reactor, the result exhibited better performance of Venturi reactor in terms of %TOC removal. Further, the design of experiments was planned with parameters such as types of dye, water recirculation flow, pH, ozone flow, UV intensity, TOC:PS ratio and initial dye concentration, for both the reactor configuration. The study revealed that in Bubble column with recirculation reactor, water recirculation had a significant effect on overall treatment performance, i.e. %TOC removal, whereas, for Venturi reactor dye had a significant effect on overall treatment performance. In design of experiments excluding dye as parameter and remaining set of parameters as it is, with three different dyes, i.e., RB5, RY145 and RR 120 for both the reactor configuration, confirmed superior performance of Venturi reactor. The better performance of Venturi reactor may be attributed to proper contact of ozone, persulfate, and pollutant. Based on design of experiments best operating parameters were chosen to be 1.86 g hr-1 ozone flowrate, 12 pH, 66W UV intensity and 1:40 TOC:PS ratio. It was also investigated that %TOC removal of synthetic dye solution of selected reactive dyes follows pseudo first order kinetics with respect to the dye. Compared to Bubble column with recirculation, degradation rate was higher in Bubble column and Venturi reactor. In addition, kinetic studies were conducted for O3/UV/PS process in three different reactor configurations. The kinetic rate constants obtained were, 0.0122 min-1, 0.0115 min-1 and 0.0205 min-1 for Bubble column, Bubble column with recirculation and Venturi, respectively. Thus, O3/UV/PS was found to be a most efficient process with Venturi reactor amongst the above-mentioned processes. Further, studies were carried out with the optimized parameters for O3/UV/PS in Venturi reactor for an individual dye to identify some important parameters such as kinetic rate constant, EE/O and TOC/OCC. Studies revealed TOC removal 86.34%, 82.14% and 59.47% for RB5, RR120, and RY145 respectively. In addition, the result of EE/O which is used to analyze the effectiveness of selected AOPs on the basis of electrical energy consumption, was 125.35, 144.88 and 276.40 for RB5, RR120, and RY145 respectively, reflects higher energy consumption per order reaction for RY145. Similarly, TOC/OCC results were 0.053, 0.043 and 0.039 for RB5, RR120, and RY145 respectively, reflects recalcitrant nature of RY145. Thus, the research concluded that O3/UV/PS process provides efficient removal of TOC. However, its performance depends on reactor configuration. Venturi reactor is more efficient than bubble column reactor with recirculation.