Ozonation Of Azo Dye Research Articles

Ozonation of azo dye in a semi-batch reactor: A determination of the molecular and radical contributions

Azo dye ozonation was carried in a semi-batch reactor to evaluate both the molecular and radical contributions of ozone on the dye decay. From two mass balance equations, the simultaneous determination of mass transfer, self-decomposition and solubility parameters of ozone were determinated; thus establishing the steady state conditions in the experimental system. The results of kinetic studies showed that the decay of azo dye was a pseudo-first-order reaction with respect to dye concentration and the overall rate constant increased with an increase in the pH, however declined with an increase in the dye concentration. Furthermore, from the overall rate constants obtained at various pH values a mathematical analysis of dye decay was performed, which provides a practical new method to quantify the radical and molecular contributions in the ozonation of azo dyes.

Enhancement of biodegradability by continuous ozonation in Acid Red-151 solutions and kinetic modeling

Abstract In this work, continuous ozonation of aqueous Acid Red-151 was performed in a stirred tank reactor at neutral pH and 25 °C. The results show that ozonation is capable of a rapid conversion of the Acid Red-151 dye molecule to more biodegradable intermediates up to the ozonation time of 120 min at which the optimum BOD5/COD ratio is obtained. The peak BOD5/COD ratios were found to be in the range of 0.028–0.35 for the initial dye concentrations being in the range of 1000–100 mg/L, respectively. The proposed kinetic modeling by Liakou et al. [S. Liakou, S. Pavlou, G. Lyberatos, Ozonation of azo dyes, Water Sci. Technol. 35 (4) (1997) 279–286; S. Liakou, M. Kornaros, G. Lyberatos, Pretreatment of azo dyes using ozone, Water Sci. Technol. 36 (2–3) (1997) 155–163] for another azo dye, namely Orange II, could be satisfactorily applied here, to the continuous ozonation of Acid Red-151, which allowed the prediction of the key variables measured experimentally, regardless of the particular intermediate compounds generated during ozonation.

Influence of mass transfer and chemical reaction on ozonation of azo dyes

Azo dyes can be only mineralised by chemical oxidation. In this paper the oxidation of Reactive Black 5 (RB 5) and Reactive Orange 96 (RO 96) with concentrations between 35 and 5,700 mgL(-1) (RB 5) and between 20 and 2,050 mgL(-1) (RO 96) was investigated in a lab-scale bubble column. The reactor was modelled for two cases, a completely mixed and a plug flow gas phase. The oxidation rate was influenced by mass transfer for all dye concentrations used. For low dye concentrations mass transfer alone was decisive for the reaction rate showing no enhancement due to chemical reaction, E approximately equal to 1. However, in the region of high dye concentrations, the slope of the ozone concentration profile inside the liquid boundary layer increases more and more with increasing dye concentration as a result of a chemical oxidation. Therefore, the enhancement factor depends on the type and concentration of the azo dyes. For RB 5, a diazo dye, an enhancement factor of E = 5.5 was observed for cd = 2,000 mgL(-1), RO 96, a mono azo dye, with a remarkably higher chemical oxidation rate shows an E = 16 for cd = 2,050 mgL(-1).

Ozonation of aqueous azo dye in a semi-batch reactor

The ozonation of wastewater containing azo dye in a semi-batch reactor has been studied. Results revealed that the rate of ozone transfer increased with increases in the initial dye concentration, the applied ozone dose and temperature. A model was developed to predict the enhancement factor of ozone mass transfer. This model enables the prediction of mass transfer coefficient of ozone from the following parameters: initial dye concentration, applied ozone dose, temperature and concentration of dissolved ozone in the organic-free water. This model was also valid for reactors of larger sizes. Result of kinetic studies showed that ozonation of the azo dye was a pseudo-first-order reaction with respect to dye. The apparent rate constant increased with the applied ozone dose and temperature. However, the apparent rate constant declined logarithmically with increasing initial dye concentration. In addition, ozonation reduced chemical oxygen demand and enhanced the biodegradability of the wastewater.