Woven and knit fabrics cannot be processed into apparel and other finished goods until the fabrics have passed through several water-intensive wet processing stages. Wet processing enhances the appearance, durability and serviceability of fabrics by converting undyed and unfinished goods, known as gray or greige (pronounced gr~[zh]) goods, into finished consumers’ goods. Also collectively known as finishing, wet processing has been broken down into four stages in this section for simplification: fabric preparation, dyeing, printing and finishing. These stages, shown in Figure 10, involve treating gray goods with chemical baths and often require additional washing, rinsing and drying steps. Note that some of these steps may be optional depending on the style of fabric being manufactured.
In terms of waste generation and environmental impacts, wet processing is the most significant textile operation. Methods used vary greatly depending on end-products and applications, site-specific manufacturing practices, and fiber type. Natural fibers typically require more processing steps than man-made fibers. For most wool products and some man-made and cotton products, the yarn is dyed before weaving; thus, the pattern is woven into the fabric. Processing methods may also differ based on the final properties desired, such as tensile strength, flexibility, uniformity and luster (Snowden-Swan, 1995).
Most manufactured textiles are shipped from textile mills to commission dyeing and finishing shops for wet processing, although some firms have integrated wet processing into their operations. A wide range of equipment is used for textile dyeing and finishing (EPA, 1996). Much of the waste generated from the industry is produced during the wet processing stages. Relatively large volumes of wastewater are generated, containing a wide range of contaminants that must be treated prior to disposal. Significant quantities of energy are spent heating and cooling chemical baths and drying fabrics and yarns (Snowden-Swan, 1995).