Advanced treatment of dyeing wastewater for reuse

As one of the main pollution sources in Hong Kong, the textile dyeing and finishing industry creates a significant proportion of water pollution in nearby harbour zones. Generally speaking, conventional biological treatment processes have difficulties in degrading many dye chemicals causing high COD and colour in dyeing wastwaters. Studies using physical and chemical processes to further reduce COD and colour from dyeing wastewater have been intensively reported. The use of a photocatalytic process in the presence of TiO2 to degrade many different types of dye chemicals has been confirmed. However, how to efficiently separate and reuse TiO2 from treated wastewater became a notable problem in the application of a TiO2 photo-oxidation process. This study aims to develop an advanced treatment process for dyeing wastewater treatment. In which dyeing wastewater was initially treated by an Intermittently Decanted Extended Aeration (IDEA) reactor to initially remove those biodegradable matters and further treated by a TiO2 photocatalytic reactor as advanced treatment for complete decolorization and high COD removal. Suspended TiO2 powder used in photooxidation was separated from slurry by a membrane filter and recycled to the photoreactor continuously. The results demonstrated that photocatalytic-oxidation process could degrade those non-biodegradable organic substances in the effluent treated by the biological treatment process and also remove the colour from the effluent completely. TiO2, as catalyst, was successfully recovered by a membrane filter and continuously reused in the photoreactor. The quality of dyeing wastewater treated by the advanced treatment process can be good enough for reuse in the textile dyeing processes. (C) 1999 Published by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved.