Typical Dye House Water Quality

Dyeings Water Quality Component Permissible Concentration mg/L Hardness 0-25 CaCO3 Iron .02-.1 Manganese .02 Silica .5-3.0 Alkalinity to Ph 4 35-65 CaCO3 Dissolved Solids 65-150 The water may pass from the primary source into a settling pond, from which water can be drawn after any small particles have settled to the bottom, or it may be filtered by passage through a bed of fine sand. For particles smaller than about 0.02 mm, a coagulant aids sedimentation and clarification of the water. Addition of small quantities of sodium aluminate (NaAlO2) or aluminium sulphate, and adjustment to around pH 7, give a gelatinous precipitate of aluminium hydroxide that imprisons the small particles and accelerates sedimentation or filtration. Addition of a flocculant, such as a polyacrylic acid–polyacrylamide copolymer, gives better particle adhesion and a higher rate of sedimentation. This type of treatment also improves the colour of the water. Soluble impurities in the water, such as iron, pollutants, and organic matter, are a real problem. Good aeration of the water will usually convert iron into Fe3+, which precipitates as ferric hydroxide unless the water is quite acidic.