Reuse of enzymatically treated reactive dyeing baths: Evaluation of the number of reuse cycles

Processing of textiles, especially dyeing, demands large quantities of water, generating huge amounts of effluents. A sustainable strategy to reduce the volume of textile effluents is treatment and reuse of the residual liquid waste. The aim of this study was to evaluate the number of reuse cycles of residual dyeing baths from reactive cotton dyeing treated with horseradish peroxidase. The enzymatic treatment achieved a 99% color removal permitting further reuse. Despite of the high decolorization efficiency residual impurities in the decolorized dyeing baths interfered negatively in cotton dyeing results with reactive dyes, and further dilution was found to be necessary. The best results were obtained with dilution rates of 70, 80 and 90% with distilled water, attaining acceptable color differences (Delta E) of 0.94, 0.73 and 0.52, respectively. These values could be maintained throughout ten reuse cycles, providing a water economy up to 30% per dyeing. Furthermore, the colored washing liquors originating from the post-dyeing washing steps received the same enzymatic treatment and could be reused in the same reactive dyeing procedures at a dilution of 90% with distilled water, providing Delta E values of 0.3-0.7. Furthermore, the reuse of enzymatically treated post-dyeing washing liquors was evaluated in the same reactive dyeing procedures. Similar decolorization was observed and reuse at 90% dilution was feasible. Without considering the reuse of the residual liquor of the washing step, 10-30% of water could be saved, which means per batch of 200 kg of cotton fabric, water savings of about 200-600 L.