Investigation of the photocatalytic degradation of the reactive azo dye (C.I. Reactive Red 45) in aqueous solution

Abstract

Wastewaters from dye production and application processes usually contain dyes as well as various by-products and auxiliary chemicals which are, besides being poorly biodegradable, often found to be toxic and carcinogenic. Therefore, there is a clear need to treat such wastewaters before they are discharged into the recipient. Technologies based on conventional physical and biological methods do not often prove to be sufficiently effective. Advanced Oxidation Processes (AOPs) in which highly reactive hydroxyl radicals are generated under the influence of chemical, electrical or radiation energy distinguish themselves as the ones with the ability of rapid and efficient degradation of organic pollutants in water and carbon dioxide with the minimum production of secondary waste. In this work the research of the application of UV, UV/TiO2, UV/H2O2, UV/H2O2/TiO2 and UV/H2O2/TiO2/Fe2+ processes for degrading reactive azo dye C.I. Reactive Red 45 (RR45) as a model pollutant in wastewater has been done. The influence of the change in pH, mass of photocatalyst, concentration of hydrogen peroxide and the ratio of Fenton‘s reagents on the efficiency of UV/H2O2/TiO2 and UV/H2O2/TiO2/Fe2+ processes has been investigated. Values of the process parameters yielding with the highest decolourization and mineralization degree of the model wastewater have been established. It has been demonstrated that the efficiency of degradability increases in the sequence UV < UV/TiO2 < UV/H2O2 < UV/H2O2/TiO2 < UV/H2O2/TiO2/Fe2+. By the application of UV/H2O2/TiO2/Fe2+ process the model wastewater becomes completely decolourized and the organic matter content is decreased by 89.0 %. Considering the obtained values of the water quality parameters; colour, TOC, AOX, COD and BOD5, the treated wastewater meets the criteria required for discharging water into natural recipients as well as into the public sewage system.