Degradation and Decolourization of Reactive Black 5 Dye using Sono Photo Fenton

Abstract

Wastewaters from textile and dye industries are highly coloured with significant amount of auxiliary chemicals. The discharge of these wastewater introduced intensive colour and toxicity to aquatic environment causing serious environmental problem. Reactive dyes are widely used in the textile industries because of its simple dyeing procedure and good stability during washing process. Reactive black 5 (RB5) gives bright, high intensity color to water which is one of the most important sources of environmental pollution and because of their visibility and bearing toxic chemicals, it is very important to be treated before released into the environment. Due to the complex aromatic structure and stability of these dyes, conventional biological treatment methods are ineffective for degradation. Hence, the concentration remains constant in the environment or these techniques transfer the toxic dyes from one medium to the other without converting it to harmless non-toxic substances. A number of physical and chemical techniques had been reported for the treatment of dye effluents. In this direction, Advanced Oxidation Processes (AOPs), based on the generation of highly reactive hydroxyl radicals (HO*) as primary oxidant, appear as the emerging alternatives for the organic pollutants abatement. These, the advanced oxidation processes are more efficient as they are capable of mineralizing a wide range of organic pollutants ranging from chlorophenols, chlorobenzene, nitrophenols and dye pollutants. Among various AOP’s, Fenton’s and photo- Fenton’s type reactions are very promising since they achieve high reaction yields with a low treatment cost. These AOPs have been successfully applied to treat reactive dyes as well as textile effluents. In the present work, we investigated that oxidative degradation and decolourization of the RB5 occurs by dark fenton, photo fenton, sono fenton and sono photo fenton. Batch runs were carried out to investigate the process’s optimal operational conditions: pH, H2O2 dosage, Fe+2 dosage and RB5 concentration, to obtain the best results at low cost, render AOP competitive with other processes and to ensure the rapid and complete transformation of the toxic organic compounds to benign chemicals. Degradation observed was 55% under Dark Fenton, 61% under Sono Fenton and 92% under Photo Fenton with optimized conditions i.e. 4 pH, catalyst (FeSO4.7H2O) concentration of 0.15 mM and oxidant dose (H2O2) of 4.4 mM after 20 mins. Sono Photo Fenton treatment enhances the degradation up to 98% with optimized parameters. The results of Sono Photo Fenton degradation of dye showed that it could be used as efficient and environmental friendly technique for the complete degradation of recalcitrant organic pollutants which will increase the chances for the reuse of wastewater.