Water usage at textile mills can generate millions of gallons of dye wastewater daily. The unnecessary usage of water adds substantially to the cost of finished textile products through increased charges for fresh water and for sewer discharge. Additionally, wastewaters from textile dyeing processes impose substantial pollutant loads on downstream publicly owned treatment works due to high levels of color, chemical oxygen demand (COD), biological oxygen demand (BOD) and suspended solids.
Various processes have been utilized to reduce pollutant loadings in textile mill wastewater discharge. These "end-of-pipe" treatment systems treat the mill discharge just prior to discharge to the local sewer system. End-of-pipe treatment systems include flocculation, membrane filtration, chemical oxidation and activated carbon adsorption. For example:
- the use of cationic polymers to flocculate organic compounds in wastewater discharge from textile yarn and fabric manufacturing operations.
- the use of a macroamine polymer as the sole flocculating agent for clarifying and decolorizing wastewater.
- purifying wastewater effluent generated during the manufacture of dyestuffs. The process employs lime to remove heavy metals from the wastewater, followed by carbon adsorption and secondary biological treatment.
- purifying/decolorizing dyeing wastewaters using a membrane separation process.
- decolorizing dye wastewater which first acidifies the wastewater, then adds a cationic flocculating agent followed by a reducing agent.
Many of the afore-mentioned processes can effectively treat and recycle a portion of the wastewater effluent discharged from textile mills. However, the capital and operating costs of these systems are high. The use of large quantities of chemicals or the use of membranes, which foul easily, leads to operating costs that in many cases exceed the savings in reduced water and sewer discharge costs.
In spite of environmental regulations the implementation of wastewater treatment systems at many textile mills is solely an economic decision. In many areas, the local textile mill can threaten to relocate to a region with looser regulations resulting in a loss of jobs to the region.