Studies on degradation and mineralization of synthetic dyes present in industrial effluents by heterogeneous Photocatalysis

Abstract

Industrial effluents detoxification is one of the most challenging global problems. Dyes, phenols, pesticides, fertilizers, detergents, herbicides, surfactants and other synthetic organic compounds are disposed of directly into the environment, without being treated, controlled or uncontrolled and without an effective treatment strategy. Their toxicity, stability to natural decomposition and persistence in the environment has been the cause of much concern to societies and regulation authorities around the world. Synthetic dyes employed more frequently on industrial scale are azo (monoazo, diazo, triazo), anthraquinone, phthalocyanine, triarylmethane and xanthenes derivatives. These dyes are released in the aqueous streams from the effluents of various industries viz. textiles, paper, leather and plastics etc. These dyes create severe environmental pollution problems by releasing toxic and potential carcinogenic substances into the aqueous phase. The dyeing and finishing industry is one of the major polluters in the industrial sector. Only 45-47% dyestuffs has been reported biodegradable and residual colour is usually due to insoluble dyes which have low biodegradability. Because of the toxicity and persistence of the dyes, their removal from the textile wastewater has become an issue of interest during the last few years. The complete degradation of the dyes is not possible by conventional methods such as precipitation, adsorption, flocculation and biological treatment that having its inherent limitations in applicability such as less efficiency, production of secondary sludge and further the disposal are a costly affair. Merely transferring toxic materials from one medium to another is not a long term solution to the problem of hazardous waste loading on the environment. The current developments in water decontamination processes are concerned with the oxidation of bio-recalcitrant organic compounds.