Removal and recovery of dyestuffs from dyeing wastewaters

The toxic nature of some dyestuffs (DSs) has long been recognized. Accordingly, dyeing wastewaters represent a source of water contamination, and should be treated in some way so as to reduce the concentration of the polluting DSs to permissible limits, prior to dumping its wastewater. In addition, some DSs can be recovered for reuse, a point which should represent saving in the overall cost of the dyeing process. Extensive publications on the removal of DSs from dye house wastewaters have been cited in the literature in which many techniques have been applied, biological treatment being the method most widely used as a primary treatment. However, only few publications have been concerned with recovery of DSs from their wastewaters. In the present paper, numerous techniques, if not all, that are presently used for either removal or recovery of DSs have been reviewed, evaluated and compared.