Biosorption of Dye Molecules

Synthetic Dyes And Related Issues

Synthetic dyes contribute largely to the group of hazardous compounds that are not easily biodegradable. Their presence in water bodies is undesirable as they are difficult to eliminate due to their persistent and recalcitrant nature. Dyes display a significant diversity in their molecular structure and can be classified in several ways, sometimes based on their chemical structure while sometimes on the basis of their application to the fiber type and so on. A broad classification of the dyes based on the ionic charge on the dye molecules can be presented as follows:

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  Non-Ionic: Disperse dyes

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  Cationic: Basic dyes

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  Anionic: Direct, acid, and reactive dyes

The properties of the dyes vary greatly with their molecular structure. The synthetic origin and complex molecular structure of the dyes makes them more stable and difficult to be biodegraded. Therefore they can pose tremendous threat on the environment and the natural ecosystems. Most of the dyes especially cationic dyes are highly toxic while their degradation products can be carcinogenic as well (El-Sayed, 2007). Generally either an anthroquione or an azo group is present in non-ionic and anionic dyes Anthraquinone containing dyes are greatly resistant to degradation because of their complex aromatic structures and therefore stay behind unaffected in the wastewater. Reactive dyes typically contain an azo group associated with different types of reactive groups such as chlorotriazine or vinyl sulphone. Most of the metal complex dyes contain chromium which is a potential carcinogenic. Disperse dyes remain undissociated in aqueous medium while there some disperse dyes that have a propensity to bioaccumulate.

The toxic components of the dyes can adversely affect the ecosystem in different ways, such as: