Membrane Technology for the Treatment of Dyehouse Effluents

In general dyehouse effluents are coloured, high in temperature, chemical oxygen demand (COD), total dissolved solids and at times highly alkaline. Because of the variety of processing systems used, the wastewaters are variable both in strength and flow. Toxic compounds from process chemicals may also be present in the wastes. Discharges of coloured effluent into the environment normally result in strong public protest. In addition the colour may interfere with the transmission of sunlight into the water and therefore decrease photosynthesis. Most dyes are specially developed to be non-biologically degradable, and thus are not effectively removed through municipal biological wastewater treatment processes. The removal of colour from textile wastewaters is one of the major environmental problems facing the textile industry. Dye wastes and other effluents from textile processing can cause problems in the operation of sewage treatment plants. These include foaming, colour persistence, excesses in pH, temperature and heavy metals and variations in hydraulic flow rates. In this paper, dye chemistry is summarised and ten of the most commonly used dye types are identified. For colour removal purposes the dyes are grouped into three classes. Four membrane processes are described which have been used in South Africa for the treatment of dyehouse effluents.