Effects of pH, Initiator, Scavenger, and Surfactant on the Ozonation Mechanism of an Azo Dye (Acid Red-151) in a Batch Reactor

In this study, an initiator (Fe2+) and a scavenger (CO32(-)) were used at different concentrations in a batch reactor to investigate the reaction mechanism of ozonation of a model azo dye, namely Acid Red-151 (AR-151). Also, the effect of a nonionic surfactant known as a major pollutant in many industrial wastewaters, namely polyethylene glycol (PEG), was observed on the degradation rate of AR-151. The experimental parameters and their ranges were: pH (2.5-10), initiator (0.8-50mg/L of Fe2+), surfactant (10-200mg/L of PEG), and scavenger (10-500mg/L of CO32-); the initial concentration of the azo dye was kept constant at 20mg/L in all the experiments. Results showed that decomposition of ozone was enhanced with increasing pH and increasing initiator (Fe2+) concentration at a scavenger concentration of 100 mg/L, when there is no dye in the medium. A scavenger concentration of 100 mg/L CO32- was not sufficient to terminate the chain reactions of ozone decomposition. It was concluded that the dominant mechanism in the degradation of AR-151 was its direct oxidation with ozone molecules in water. The data obtained for the dye and chemical oxygen demand (COD) removals and total oxidation rate constants at different operating conditions were assessed in order to estimate the possible contribution of dye-oxidation by free radicals.