Efficiency Determination of Catalytic Processes of Ozone/Activated Carbon and Ozone/Persulfate for Degradation of Reactive Blue 194 Dye in Aquous Solutions

Abstract

Introduction: Reactive dyes are designed to covalently bond with cellulosic fibers, and are widely used in textile industries due to their wide colour ranges, and high degree of wash fastness. However, reactive dyeing is not eco-friendly because of the heavy discharge of chromatic alkaline wastewater with high concentrations of NaCl and high temperature. High solubility and recalcitrant properties of the reactive dyes make these wastewaters one of the most difficult dye-containing streams and resistant to conventional treatment. Therefore, in this study, we aim to investigate the degradation of a model dye (Reactive Blue 194) in simulated textile wastewater using advanced oxidation processes of activated carbon catalyzed ozonation (ACCO) and persulfate catalyzed ozonation (O3/PS). Methods: The O3/PS and ACCO reactors were fed with 2.5 and 1.2 liters of synthetic wastewater, respectively, and continuously fed by ozone gas at a constant flow rate of 1.5 L/min and ozone concentration of 178 mg/L. Each ozonation run lasted 40 min and samples were taken at fixed time intervals. Samples were then analyzed for color, UV254, COD and TOC. In order to identify the mechanism of RB194 reactions, some experiments were performed using tert-butanol and methanol as radical scavengers. Moreover, the effect of temperature was examined by introducing the entire columns into a thermostatic water bath at 25, 35 and 50 ℃. In the final trials, the contribution of activated carbon (GAC) adsorption, sole ozonation, and PS alone in dye removal was determined under similar experimental conditions. Results: The decolorization rate of O3/PS process was always higher than that of the ACCO process, removing the highest dye concentration (200 mg/L) within only 10 min. The dye removal rate in ACCO system accelerated with increasing chloride ion concentration, from 0.1125 min-1 in NaCl 5 g/L to 0.2957 min-1 in NaCl 50 g/L, but it did not have the same effect on O3/PS process (k=0.4633 min-1). In the saltrich environment, both the O3/PS and ACCO processes in acidic conditions improved the color and COD removal, while the UV254 was better removed at pH of 12. Under such conditions, more destruction of COD, TOC and UV254 (with 63,2 60 and 100% efficiency, respectively), were achieved in ACCO system. Increasing the temperature in ACCO process improved the removal efficiency via diffusing dye molecules into the GAC pores, but it did not favor the O3/PS process by a 25% growth in COD content. Conclusion: Based on the results of this study, the ACCO process, which was found as more capable process in color degradation, is more suitable option for the treatment of saline wastewater containing reactive dyes. This can be attributed to the role of chlorine radicals resulting from the radical scavenging of HO• by chloride ions. In this process, the enhancement of radical reactions with the contaminant in acidic conditions and low temperature improves the treatment mechanism. The main problem of ACCO is the GAC instability during continious operation of the system, which can be compensated by the regeneration and modification of chemical properties of GAC.