Biodecolorization and Biodegradation of Dyes: A Review

Dyes are one of the most widely used chemical substances in day-to-day life, including in different industries. Dye manufacturers, as well as users, are experiencing great difficulty in complying with stringent regulations on wastewater containing dyes and derivatives. Most of the industries still use age-old technology and machinery and thus find it difficult to cope with the change in the scenario of current stringent environmental regulations on disposable limits, which are improvised by pollution control boards. The inherent difficulties because of technical inadequacies during dyeing result in a large amount of dyestuff getting directly lost to the industrial effluents. Synthetic dyes are quite stable recalcitrant compounds. Henceforth, the release of dyes poses an ecotoxic hazard and potential danger of bioaccumulation, eventually affecting flora and fauna. Huge quantities of water consumption generate large volumes of highly contaminated effluents. Conventional treatment processes have limitations in the color removal from wastewater. Although physico-chemical techniques are practiced, it still suffers from the ‘economy-to-scale of application’ paradigm and generation of polluting and toxic byproducts, posing disposal problems. In contrast, biological processes involving microbes, plants, or their products (such as enzymes) are touted as alternate cost-effective methods for decolorization and degradation of such synthetic dyes, albeit with limited full-scale successful applications. Biodegradation of such xenobiotics has been the topic of research for over two decades, with limited success because of the production of toxic secondary metabolites and byproducts. This review paper is an effort towards discussing the importance of biodecolorization and biodegradation of dyes, with emphasis on some recent updates such as immobilization techniques and in-silico modelling methods and future possibilities.