For microbial dye decolourisation not connected to the activated sludge process, bioreactors can be designed containing defined bacterial or fungal cultures, isolated enzymes or enzyme mixtures immobilised on a solid 212 Textile processing with enzymes carrier material. Such immobilised biocatalysts are much more susceptible to damage by harsh chemical environments than are the mixed cultures
Biotechnological methods
present in activated sludge systems. Thus, they are preferentially used to treat partial process streams within the plant where the composition and physical properties are rather more readily controlled than the overall plant effluent. For instance, exhausted dyeing bath solutions have been decolourised enzymatically using a laccase formulation and subsequently reused for the preparation of new dyeing baths (Abadulla et al., 2000). Similarly, hydrogen peroxide has been removed enzymatically from bleaching solutions using a catalase in an industrial pilot experiment . Owing to the use of high-specificity enzymes, only the target molecules are attacked while valuable additives or fibres are kept intact and can be reused.
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