The textile industry is very water intensive. Water is used for cleaning the raw material and for many flushing steps during the whole production. Produced waste water has to be cleaned from, fat, oil, color and other chemicals, which are used during the several production steps. The cleaning process is depending on the kind of waste water (not every plant uses the same way of production) and also on the amount of used water.
Also not all plants uses the same chemicals, especially companies with a special standard (environmental) try to keep water cleaned in all steps of production. So the concepts, to treat the water can differ from each other.
Water treatment with different kind of pollutants, is large-scale, because of the many cleaning and removing steps involved.