Enzymatic decolorization of dye house effluents

The textile industry consumes large quantities of water during process. The predominant part of the waste water is produced in pretreatment and dying processes. The amount of effluents may vary in textile dying from 70 to 350 m³ waste water per ton of textiles. The effluents are extremely variable in composition and they contain complex, synthetic and often recalcitrant compounds. The effluents vary considerably in different dye houses and even in one dye house the variations may be large due to seasonal changes in the process. The traditional treatments for textile dye house effluents are often ineffective, costly, complicated and have sludge disposal problems. The conventional physical and chemical effluent treatments cannot remove or degrade all dyes used in the textile industry, and some dyes are even converted to more toxic compounds. Combined anaerobic and aerobic microbial effluent treatments have been suggested for textile dye house effluents. However, under anaerobic conditions azo-dyes are converted to the corresponding amines, many of which are harmful and carcinogenic. Promising results have been obtained in decolorization of dye house effluents by isolated enzymes, especially oxidoreductases. Laccases and different peroxidases are shown to effectively decolorize various textile dyes. These enzymes are surprisingly unspecific for their substrates and they can oxidize various aromatic compounds. The enzyme-treated effluents can be reused in the process thus reducing the water consumption in the dye house. The paper discusses the potential and recent development of laccases and peroxidases for decolorization of dye house effluents.