TABLES

Table 1: Key Organizations in the Textile Industry
Table 2: Waste Streams Produced and Contaminants of Concern for the Textiles Industry
Table 3: Common Solid Wastes Produced by Textile Manufacturing
 

1. EXECUTIVE SUMMARY

This report gives a brief overview of the U.S. textile industry, with an emphasis on efforts to incorporate pollution prevention and clean technologies into its manufacturing operations. This report is not intended to be a comprehensive industry guide or study. Rather, it can be used as guidance material for those seeking general information about the industry and its use of technologies and processes that reduce or prevent pollution.

The textile industry has a long history in the United States, dating back to the onset of the Industrial Revolution. Despite competition from textile producers in South America and Asia, which have lower costs and lower wages, textile remains one of the largest, most diverse, and most dynamic segments of the U.S. manufacturing sector. In 1992 the industry produced a record US$70 billion in shipments and employed an estimated 630,000 people. The industry maintains its strength by focusing on production of high-quality, high-value luxury items; launching campaigns to encourage consumers to buy products made in the United States; modernizing mills with state-of-the-art manufacturing technology, and adopting "just in time" manufacturing strategies that permit the industry to respond quickly to changing consumer demands.

For many years, the textile industry has realized the benefit of incorporating clean technologies into its manufacturing operations, and several industry leaders have formed alliances to further these goals. The term "clean technologies" is defined as "manufacturing processes or product technologies that reduce pollution or waste, energy use, or material use in comparison to the technologies that they replace."

Key resources used by the industry include the following:

Water. Textile manufacturing is one of the largest industrial users of process water in the United States. Approximately 20 gallons (160 pounds) of water are needed to produce one pound of textile product. Water is used extensively throughout textile-processing operations, and consumption varies widely among the unit processes.

Fiber Resources. Fibers used include both natural and man-made fibers. Cotton is the most important natural fiber used to make textiles in the United States, followed by wool. In recent years, man-made fibers such as nylon, polyester, and acetate have replaced cotton as the primary raw material used in textile production, accounting for 68 percent of total fiber consumption in 1989.

Both natural and man-made fibers contain impurities such as metals, lubricants, and other residues that contribute to pollution in mill effluent.

Key environmental issues for the U.S. industry include the following:

Water. Primary pollutants of concern are biochemical oxygen demand (BOD), chemical oxygen demand (COD), color, metals, and electrolytes (salt). About half of the mills in the United States discharge effluent that exhibits some degree of aquatic toxicity, which is a major concern for the industry. Reduction of water use is also an important goal.

Air. The textile industry is a relatively minor source of hazardous air pollutants (HAPs) compared with other manufacturing industries, but air emissions have been identified as the second greatest pollution problem (after aqueous effluent). Because many different commodity and specialty chemicals are used to manufacture textiles, characterization and management of air emissions for textile mills is a challenging responsibility. Emissions of concern include volatile organic compounds (VOCs) from coating, drying, and curing operations; particulates, nitrous oxides, and sulfur dioxide from boiler operation; and emissions from bulk storage tanks for commodity and specialty chemicals, spills, solvent-based cleaning, wastewater treatment plant operation, and warehouses used to store finished fabric.

Solid Waste. Solid waste is the largest waste stream produced (by volume) following aqueous effluent. Wastes generated include fiber wastes (reworkable and nonreworkable), packaging wastes, selvage, trimmings, and sludge from wastewater treatment.

Chemical Releases. Chemical releases from the textile industry are not well quantified, and data on releases, particularly air emissions, are not readily available. Most estimates are based on mass-balance calculations rather than direct measurement. The industry is coming together to develop ways to identify and quantify releases.

Currently, there is no specific regulatory mandate driving clean technology implementation. Existing regulations for effluent and air emissions, however, are becoming increasingly stringent and more rigorously enforced, which is prompting the industry to develop alternative methods for the management of process wastes.

Clean technologies discussed in this report that are generally being adopted by the industry include the following:

• Pad-batch dyeing. A "cold-dyeing" method that uses padders to press dyes into fabric, followed by storage of the fabric to allow dye to react.
• Low-bath-ratio dyeing. Use of a lower than standard weight of water per weight of goods for batch dyeing.
• Low salt/high fixation dyeing. Use of dyes that have a higher degree of fixation on the fabric and that require less salt for fixing
• Dyebath reuse. Replenishment and reuse of dyebath fluid to extend life of bath up to 25 times.
• Continuous dyeing for knits. Use of continuous dyeing, which uses less process water than batch dyeing.
• Automated color mix kitchen.Use of computer-controlled machinery to mix and batch colors.
• Automated chemical dosing. Use of computer-controlled machinery to meter chemicals into the dyeing process according to a specific dosing strategy.
• Transfer printing. Use of a paper substrate as a medium for transferral of print onto fabric.
• Laser engraving of printing screens. Use of digital scanning or on-screen design of prints in lieu of photographic screen creation.
• Surfactant substitution. Use of surfactants that have less overall negative impact on the environment, such as lower aquatic toxicity.
• Recovery of synthetic sizes. Use of membrane filtration or another process to capture, recover, and reuse synthetic size chemicals.
• Countercurrent washing. A multistage washing strategy that saves water consumption by introducing fresh water only at the final wash stage and by recirculating this water successively through each of the previous wash stages.
• Low add-on finishing. Use of special equipment to apply a low volume of finish chemicals to fabric.
• Mechanical finishing. Use of mechanical rather than chemical methods to perform finishing functions such as shaping, shrinkage reduction, and softening.
• Waste reclamation systems for spinning. Use of special equipment to capture and reuse spinning wastes, which otherwise would be discarded.

Emerging technologies that have been demonstrated on a pilot scale and may have full-scale implementation in the future include the following:

• Direct dyebath monitoring and control systems. Control strategy that adjusts the dyeing process in real time to account and correct for uncontrollable parameters.
• Real-time adaptive control systems. Control strategy to adjust dyeing or other processing steps in real time to account and correct for uncontrollable parameters.
• Ink-jet printing. Droplets of dye solution are directed onto fabric to form a pattern, eliminating photographic screen making and color mix kitchen activities.
• Supercritical fluid dyeing. Uses carbon dioxide (CO₂) as the fluid medium on disperse-dyed synthetics, eliminating aqueous effluent.
• Ultrasound dyeing. Uses ultrasound waves to impart dyes to fabric, eliminating aqueous effluent.
• Radio frequency drying. Uses radio waves rather than ovens to dry yarn or fabric.

Both industry and government recognize that the potential cost savings that can be realized through implementation of clean technology is significant. Current annual resource utilization by the industry includes:

• 133 billion gallons of water consumed, of which 53 billion gallons are treated at a cost of US$146 million
• 237 million pounds of knit fabric wasted, at a loss of US$474 million to the industry
• 30 percent of reactive dyes discharged in wastewater, with a lost value of US$66 million
• 742 million pounds of salt consumed.

Implementation of pollution prevention and clean technology will thus allow the industry to synthesize its goals of product quality, cost savings, increased profitability, and environmental stewardship.

ACRONYMS

2. INDUSTRY BACKGROUND

2.1 Description and History

The textile industry has a long history in the United States, dating back to the onset of the Industrial Revolution in the 1790s. Despite strong competition from lower-wage, nondomestic textile producers, the industry remains one of the largest, most diverse, and most dynamic segments of the U.S. manufacturing sector. The industry has maintained a competitive position by specializing in high-value luxury items, launching successful campaigns to encourage consumers to buy domestically made products, modernizing old mills with the newest technology, and adopting quick-response and "just in time" manufacturing strategies that permit the industry to respond rapidly to changing demands, particularly in the apparel and home furnishings markets.

2.2 Industry Demographics

There are more than 6,000 textile establishments in the United States. The industry consists of a diverse, fragmented group of facilities that range from small, family-owned and -operated facilities that typically use older, traditional manufacturing techniques to huge integrated mills that operate the most up-to-date machinery and production equipment.

Economies of scale in textile manufacturing are significant and limit entry of new mills into the market. The cost of building a new, state-of-the-art fiber plant is estimated at approximately US$100 million. Compared to the global industry, the United States has built few entirely new textile mills during the past two decades. Instead, state-of-the-art equipment is installed as part of planned capital expansions and retrofits.

In 1992 the textile industry produced a record US$70 billion in shipments, and employment was about 630,000. Annually, the industry spends 4%B6% of sales on capital expansion and modernization and reportedly spends about US$25 million per year on pollution and safety controls for its mills.

Textile establishments prepare and transform fibers into yarn, thread, or webbing, convert the yarn into fabric or related products, and dye and finish these materials at various stages of production. Many textile facilities also produce final products for consumption (e.g., thread, yarn, bolt fabric, towels, and sheets), whereas the rest produce transitional products for use by other textile establishments and by establishments classified in the apparel or other industries. The facilities fall into the following major categories, in order of most numerous to least numerous:

• Knitting mills
• Miscellaneous textile products
• Broadloom mills (for cotton, wool, and man-made fibers, including silk)
• Textile finishing (including dyeing)
• Yarn and thread mills
• Carpet and rug mills
• Narrow fabric mills

Because of the complexity and economics of converting raw fiber material into finished apparel and nonapparel textile products, most textile mills specialize. One notable exception are mills that combine spinning and weaving operations; there are about 300 such mills in the United States. Still, these mills do not normally conduct their own finishing operations. Nearly 700 textile finishing and dyeing mills perform these steps.

In the United States, it is uncommon for apparel customers to purchase a "package" of finished goods from a single supplier or source. Rather, the customer may buy fabric from one source, order trim from a second source, and contract with a third source to have garments cut and sewn. U.S. customers find it most cost-effective to do business in this manner, which is reflected in the historically fragmented nature of the textile industry.

The industry is geographically concentrated in the south and mid-Atlantic regions of the United States because these areas were originally the primary cotton-growing regions of the country. A considerable amount of fabric finishing and dyeing takes place in the northeastern United States.

Production of man-made fibers is highly concentrated among a small number of chemical companies. The U.S. man-made fiber industry consists of more than 100 companies operating about 150 plants, but only a handful are major producers. The top six companiesCDuPont, Hoescht Celanese, BASF, Allied-Signal, Monsanto, and AmocoCaccount for 80% of the production of man-made fibers in the United States. Approximately 60% of producers specialize in olefin fiber production, and the remaining market segments are controlled by a small number of firms. For instance, three firms account for all U.S. production of acrylic, modacrylic, and rayon, whereas two firms account for all U.S. production of acetate fiber and spandex.

Table 1 provides a brief listing of some of the major companies and organizations associated with the U.S. industry. This list is not intended to be exhaustive but rather provides a short overview of industry players, which include textile mills, man-made fiber manufacturers, equipment and chemical suppliers, dyestuff manufacturers, process design and consulting engineers, professional trade associations, and research institutions.

2.3 Use of Natural Resources

Water

Textile manufacturing is one of the largest industrial users of process water. In the United States, approximately 20 gallons (160 pounds) of water are used to make one pound of textile product. Water is used extensively throughout textile processing operations, and consumption varies widely among the unit processes. Water use can also vary widely among similar operations, depending on the type of equipment used. Dyeing and fabric preparation are among the most water-intensive processes in textile production. Reducing water consumption use is a foremost goal of the U.S. industry.

Fiber Resources

Fiber resources used by the industry include natural fibers (e.g., cotton, wool, and linen) and man-made fibers (e.g., nylon, acetate, and rayon). Cotton is the most important natural fiber used to make textiles in the United States, followed by wool. Cotton is relatively easy to produce domestically and is suitable for a wide variety of finished products, including apparel and home furnishings.

In recent years, man-made fibers have replaced cotton as the primary raw material used in textile production. In 1989 man-made fiber accounted for 68% (8.8 billion pounds) of the total mill fiber consumption of 12.9 billion pounds. Man-made fibers include purely synthetic materials derived from petrochemicals (e.g., nylon and polyester) and regenerative cellulosic materials manufactured from wood fibers (e.g., rayon and acetate).

Both natural and man-made fibers contain impurities that contribute to pollution in mill effluent. Impurities found in natural fibers include agricultural residues, natural waxes and oils, pesticides, and metals. Some of these impurities are inherent in the raw material, whereas others are a result of harvesting and processing. Many of the impurities present in man-made fibers, such as metals and hydrocarbons, are applied intentionally as part of spin finishes to improve the physical properties and workability of the fibers. These finishes are typically removed before final processing and thus contribute to pollution in the effluent.
 

2.4 Waste Streams of Concern

Textile manufacturing produces aqueous, air, and solid waste streams that must be managed, recovered, treated, and/or disposed of. Table 2 presents a list of the aqueous and air waste streams produced and their associated contaminants of concern for several textile processes. Table 3 provides a listing of solid wastes generated during textile processing.

Aqueous effluent from textile mills has been identified as the primary pollution problem for the industry. Effluent includes aqueous discharges from fiber preparation, fabric preparation, dyeing, finishing, and other operations. Because of the large volume of water used in manufacturingCabout 20 gallons (160 pounds) used per pound of product madeCmost mills operate their own wastewater treatment or pretreatment plants to remove biochemical oxygen demand (BOD), chemical oxygen demand (COD), and other contaminants from effluent prior to discharge to receiving waters or a publicly owned treatment works (POTW). Of particular concern are dyes, which are often sources of metals, salt, and color in effluent; sizes, which have high BOD and COD levels; and surfactants, which are strongly linked to aquatic toxicity.

Although the textile industry is a relatively minor source of HAPs compared with other manufacturing industries, air emissions have been identified as the second greatest pollution problem (after aqueous effluent) for the industry. Because many different types of commodity and specialty chemicals are used to manufacture textiles, characterization and management of air emissions for textile mills is a challenging responsibility.

Emissions comprise both point sources and fugitive emissions. Point sources include high-temperature coating, drying, and curing ovens, which emit volatile organic compounds (VOCs); boilers, which are a source of particulates, nitrous oxides, and sulfur dioxide; and bulk storage tanks for commodity and specialty chemicals. Fugitive air emissions result from spills, solvent-based cleaning, wastewater treatment plant operation, and warehouses used to store finished fabric.

Solid waste is the largest waste stream produced (by volume) following aqueous effluent. The quantity of solid waste generated depends on the size and type of textile operation, the nature of the waste, and the efficiency of the machinery used. Not surprisingly, solid waste generation varies widely among mills. According to a 1994 survey conducted by the American Textile Manufacturers Institute (ATMI), total monthly solid waste generation for the 290 facilities surveyed was more than 51,000 tons per month. Table 3 shows a list of common solid wastes produced during textile manufacturing.

The industry shows a trend toward increased recycling of solid waste. The 1994 survey showed that 65% of solid waste produced by textile mills was recycled rather than landfilled, compared with 23% in 1989. Although the industry is making concerted efforts to recycle and reduce fiber and packaging wastes in particular, solid wastes are of relatively less concern in the United States compared to aqueous effluent and air emissions.

Chemical Releases

Many different types of commodity and specialty chemicals are used during textile production, which makes sampling, analysis, treatment, and prevention of chemical releasesCparticularly air emissionsC complex. Although there is much speculation about the types and quantities of chemicals released to the environment during textile manufacturing, there are few data about actual releases and these data are not readily available. Most published data for air emissions are based on mass-balance calculations rather than direct measurements. Efforts are under way to establish reliable emission factors for textile mills, but no reliable set of factors is currently available.

3. ENVIRONMENTAL ISSUES AND REGULATIONS

The textile industry is subject to U.S. environmental regulations for effluent, air emissions, and solid wastes.`Effluent guidelines have been in place for the textile industry since 1974. These guidelines fall under the purview of the Clean Water Act (CWA), which is intended to restore and maintain the chemical, physical, and biological integrity of the nation's surface waters. Under the CWA, the National Pollutant Discharge Elimination System (NPDES) program controls direct discharges of effluent into navigable waters. Permits are issued either by the U.S. Environmental Protection Agency (EPA) or a state environmental agency and require regular and periodic characterization, measurement, and monitoring of effluent and its contents. Many mills in the United States hold NPDES permits because they discharge large volumes of effluent to streams and rivers. Parameters often regulated by NPDES permits in the textile industry include BOD, COD, total suspended solids (TSS), temperature, and aquatic toxicity.

The industry is also subject to specific provisions of the Clean Air Act (CAA), which is designed to protect and enhance the nation's air resources to protect public health and welfare. The CAA establishes limits for air pollutants such as carbon monoxide, nitrous oxides, sulfur oxides, and particulate matter.

A few mills may also generate waste streams that are subject to regulations of the Resource Conservation and Recovery Act (RCRA), which outlines requirements for the identification, treatment, storage, and disposal of hazardous wastes. Most textile operations produce little or no hazardous waste as part of their routine operations, but about 10%B20% of mills are classified as hazardous waste generators because of the volume of solvents they produce by dry-cleaning fabrics and by maintaining and cleaning manufacturing equipment.

Chemicals of Concern

The textile industry is chemical intensive; wastewater from textile processing contains bath residues from preparation, dyeing, finishing, application of sizing
(a process sometimes called slashing) and other operations. Reduction of chemical usage, and substitution of less harmful chemicals for traditional ones, is a primary goal of the industry. The following describes some of the more commonly used chemicals and the environmental impacts of each of them.

Sizing

Sizes are applied to fibers in a process sometimes to improve the strength and bending behavior of fibers during fabric weaving. Size serves no long-term purpose for the fabric, which is treated (or "desized") after weaving to remove sizing chemicals. The three main classes of sizes are natural sizes or starch, derived from corn or potatoes, which accounts for two-thirds of size chemicals by weight used in the United States, synthetic sizes such as polyvinyl alcohol (PVA), which accounts for most of the remaining use of sizes, and semisynthetic sizes, which blend starch with synthetic products.

The U.S. industry consumes an estimated 200 million pounds per year of size chemicals, more than 90% of which is disposed of in aqueous effluent. This makes size chemical disposal one of the largest industrial waste streams in the United States. Starch sizes contribute large amounts of BOD and COD to effluent streams. BOD from starch sizes is sometimes as high as 600,000 parts per million (ppm). Synthetic sizes, which are not as biodegradable as starches, can pass through conventional wastewater treatment systems and are often linked to aquatic toxicity in receiving waters.

Dyeing

Most dyes used in the United States are synthetic and are manufactured from coal-tar and petroleum-based intermediaries. Dyeing operations are of primary environmental concern for the U.S. industry because:

• Dyeing is a water-intensive process.
• Large amounts of salt are often needed to improve dye fixation on the textile material.
• Many dyes contain heavy metals (e.g., chromium and copper) as either a dye component or as a contaminant.
• Unfixed dye releases high doses of color to mill effluent, as well as salt and metals.

Color in effluent from textile dyeing and printing is being increasingly regulated and is widely recognized as a compliance problem within the industry. Effluent from most dyeing operations has a dark reddish-brown hue that is readily apparent to the naked eye when discharged to receiving waters. Extremely high doses of color, which are rare, can interrupt photosynthesis and lower the dissolved oxygen content of receiving waters, which may lead to algae blooms and fish kills. Color, however, is primarily an aesthetic pollutant that is easily targeted as a nuisance problem for textile effluent, whereas salt and metals in dye house effluent are sometimes linked to aquatic toxicity.

Surfactants

Surfactants and related compounds, such as detergents, emulsifiers, and dispersants, are used in the formulation of chemicals used for almost every textile process. Of all the chemical specialties used in the industry, surfactants are the primary contributors to aquatic toxicity in effluent. To a lesser extent, they also contribute to the effluent BOD load. The degree of treatability by conventional wastewater treatment varies among surfactants. Those that are relatively more treatable tend to have high BOD levels, whereas less-treatable surfactants are the ones that pass through and are linked to aquatic toxicity. Foaming can also result when surfactants that pass through the treatment system are released to receiving waters.

Coatings and Finishes

Several types of chemical specialties are applied to textiles as coatings and finishes during spinning, weaving, finishing, and/or knitting. These chemicals contribute various types of organic and inorganic pollutants to water and air during normal application and subsequent washing or removal steps. Many coatings and finishes used to make "performance fabrics"Cthose that are waterproof, water resistant, soil repellant, flame retardant, wrinkle resistant, and the likeCare of particular concern because their ingredients are typically guarded as trade secrets, which makes characterization of emissions and pollutants from these processes difficult.

4. CLEAN TECHNOLOGY DEVELOPMENTS

This section provides a brief description of clean technologies and pollution prevention techniques used by the U.S. textile industry. These technologies vary in their acceptance and adoption by industry, which will also be discussed. "Clean technologies" are defined as "manufacturing processes or product technologies that reduce pollution or waste, energy use, or material use in comparison to the technologies that they replace."

The technologies described in this section are:

• Pad-batch dyeing
• Low bath ratio dyeing
• Low salt/high fixation dyeing
• Dyebath reuse
• Continuous dyeing for knits
• Automated color mix kitchen
• Automated chemical dosing
• Transfer printing
• Laser engraving of printing screens
• Surfactant substitution
• Recovery of synthetic sizes
• Countercurrent washing
• Low add-on finishing
• Mechanical finishing
• Waste reclamation systems for spinning

Technology Adoption and Implementation

It is important to note that relatively few large, new textile mills have been built in the United States in the past two decades. Instead, mills have been updated via expansions and retrofits. As for other U.S. industries, textile mills must constantly balance their own quality requirements and customer demands with consideration of the environmental impacts of their operations. Technologies and processes that can prevent pollution while reducing costs and maintaining or even improving product quality are the ones most likely to be adopted by the industry. These issues and tradeoffs are discussed in the context of each technology, where applicable.

4.1 Pad-Batch Dyeing

Description. This "cold dyeing" method is most appropriate for cellulosic fabrics (e.g., cotton and cotton/polyester blends). Fabric is saturated with dye paste and passed through a padder that forces the dyestuff inside the fabric, while simultaneously absorbing excess dye solution. The fabric is then stored or "batched" on rolls or in boxes for several hours, during which the dyestuff reacts with the fibers and penetrates the fabric, resulting in even, consistent color. This method requires fiber-reactive dyes that are highly reactive at normal ambient temperatures and works best when ambient temperatures are relatively steady or can be controlled.

Benefits. Pad-batch dyeing offers several benefits over traditional batch dyeing:

• No salt or chemical specialty agents are needed in the dye.
• More efficient use of dye leaves less color in dye house effluent.
• Water and energy consumption is low or nonexistent.
• Energy consumption is reduced by up to 70 percent.
• Use of dyestuffs are reduced.
• Dye quality is more consistent, although sensitive to ambient temperature fluctuations.
• Process is applicable to both woven and knit fabrics.
• Equipment is simple, flexible, and inexpensive.

Status of Use in the United States. Dye houses employ this technique when it is suitable for the fabrics they are dyeing. The low cost of adopting this technology makes it attractive to both small and large dye houses.

4.2 Low Bath Ratio Dyeing

Description. This batch dyeing process uses a lower than standard weight of water per unit weight of fabric or fiber dyed. Several new types of jet and package dyeing machines offer low bath ratio dyeing (in the range of 3:1 to 5:1 for weight of dye liquid per weight of material dyed, compared with a typical value of 12:1). Ultra low liquor ratio (ULLR) machines offer the lowest bath ratios.

Benefits. Low bath ratio dyeing conserves water, energy, dyestuffs, and auxiliary dye components such as salt. Dyes used in these machines must have a high degree of solubility, good leveling, good washing off, and very good "right the first time" dye performance.

Status of Use in the United States. Reduced bath ratio dyeing has become increasingly popular among mills that actively practice pollution prevention and energy conservation. Low bath ratio concepts, particularly ULLR, however, cannot be retrofitted to existing equipment, nor is reduction of water volume in dye baths sufficient to ensure high-quality dyeing. Given the long life of dyeing equipment, the high capital cost of installing new low bath ratio machines generally discourages replacement of existing equipment.

4.3 Low Salt/High Fixation Dyeing

Description. Almost all of the large dye manufacturers offer at least a small range of products that require less salt addition and have a higher degree of fixation compared to their traditional dye lines.

Benefits. Use of these dyes reduces the quantity of salt and the amount of color contained in dye house effluent and reduces color problems as well. These dyes are best used with continuous rather than batch dyeing processes.

Status of Use in the United States. Mills select the dyes they use based on quality, customer requirements, and cost-competitiveness. If low salt/high fixation dyes prove cost-competitive and if apparel and home furnishings dyed with these products prove popular, mills will move toward increased use of these dyes. It is expected that these dyes will increase in popularity as the industry attempts to minimize the impact of textile dyeing.

4.4 Dyebath Reuse

Description. In this process, exhausted hot dye baths are analyzed for residual color content, replenished as necessary, and reused to dye additional batches of fabric. Dye baths can be reused from 5 to 25 times if the process is properly controlled and if the dyes used are appropriate for the fabric to be dyed. Generally speaking, acid, basic, direct, and disperse dyes are most amenable to reuse, whereas vat, sulfur, and fiber-reactive dye baths are least amenable.

Benefits. Dyebath reuse offers several advantages:

• Reduced consumption (and subsequent discharge) of dyestuffs and auxiliary chemicals
• Reduced water and energy consumption
• Reduced effluent volume.

Status of Use in the United States. If quality standards for finished products are high, dyebath reuse is not favored because there is a higher risk of shade variation due to fabric impurities and bath impurities (e.g., surfactants and salt) that build up over time. Reuse also requires advance scheduling, which limits its use for small lots and "just in time" manufacturing. Dye houses, however, use this technique when it is suitable for the quality requirements of the fabrics they are dyeing and when it is cost-effective.

4.5 Continuous Dyeing for Knits

Description. Conventional continuous dyeing ranges have typically been limited to nonknit fabrics because of their inherently high tension. Several equipment manufacturers have recently begun offering lower-than-standard tension or tensionless continuous dyeing machines that do not pull or stretch fabric out of shape. Individual equipment vary in design and capacity.

Benefits. Continuous processes have several advantages over batch dyeing:

• They use less process water.
• Dyes having high fixation are typically used, which require less salt and leave less color in the spent dyebath for discharge.

Status of Use in the United States. Continuous dyeing is gaining popularity in the United States with both knit and nonknit fabrics.

4.6 Automated Color Mix Kitchen

Description. Colors are mixed and batched by computer-controlled machinery rather than by mill workers. Machinery is also available for dye dispensing of powder or liquid dyes in batch or continuous houses. Similar systems are available to improve speed and accuracy in color matching while mixing. In some cases, these systems connect directly to intermediate bulk containers (IBCs) for chemicals.

Benefits. Automated mix kitchens offer several advantages:

• Reduction of human error, spills, leaks, and overuse of dyes
• Shorter runs for continuous dyeing are more economical.

Capital investments for automated equipment may be substantial, but savings realized by reduced waste generation should be figured into the payback period for investment.

Status of Use in the United States. The United States is beginning to invest in automated mix kitchens for use in sophisticated dyeing and printing operations.

4.7 Automated Chemical Dosing

Description. Automated dosing systems meter chemicals into the dye process according to a specific dosing strategy that has been predetermined by the mill, based on product and dye specifications. The dosing strategy is computer controlled and can be adjusted continually to account for changes in product standards, fabric quality, and the like.

Benefits. Automated dosing reduces human error, spills, leaks, and overuse of chemicals. Capital investments for automated equipment may be substantial, but savings realized from reduced chemical use, fewer spills, and a higher percentage of "right the first time" dyeing should be figured into the payback period for investment.

Status of Use in the United States. Automated dosing systems are gaining popularity in the United States, particularly during retrofits of existing facilities.

4.8 Transfer Printing

Description. Dye is printed onto a paper substrate, which is laid onto the fabric to be printed. Temperature and pressure are applied to the paper substrate, which transfers the dye to the fabric by sublimation. Most transfer printing is done on polyester or high polyesterBcontent blends with disperse dyes and, less frequently, solvent dyes.

Benefits. Transfer printing offers several benefits:

• Dyestuff consumption is lower.
• Energy requirements for printing are reduced.
• Little to no printing effluent is generated.
• No washing or after-treatment is required.
• Color changeovers are instantaneous.
• Equipment is inexpensive.
• Short runs are easy to manufacture.
• Printing of paper is more efficient.

Status of Use in the United States. Transfer printing is the newest, fastest-growing printing method in the United States. This method, however, has limitations:

• Limited to volatile dyes
• Does not work on natural fibers
• Does not work on knits because dye penetration into the fabric is limited.

4.9 Laser Engraving of Printing Screens

Description. Laser engraving allows for direct digital scanning or on-screen design of prints. This technique avoids the use of photographic processes in screen making for printing.

Benefits. Laser engraving offers several benefits:

No toxic photographic residues, which typically contain silver, are generated.

• Screen quality is improved.
• Screen changes are simpler.
• Small lots are easier to manufacture.

Status of Use in the United States. Several laser printing systems have been installed in the past several years in the United States.

4.10 Surfactant Substitution

Description. Surfactants, which are used in formulating virtually all chemical specialties used by the textile industry, are one of the primary causes of aquatic toxicity, foaming, and, to a lesser extent, BOD in mill effluent. Because of the many different types of surfactants available, selecting the correct one for a particular function requires good understanding of performance and pollution issues. The wide variety of surfactants available facilitates selection of less-polluting alternatives. For instance, cationic surfactants are rarely used in the United States because they exhibit extremely high aquatic toxicity, and alkylphenol (AP) has been replaced by linear alcohol ethoxylate (LAE), which is more biodegradable and exhibits lower toxicity.

Benefits. Despite the higher BOD values of biodegradable surfactants, they are generally preferred over those that pass through treatment because they exhibit a lower degree of aquatic toxicity and are less likely to foam on discharge to receiving waters.

Status of Use in the United States. The industry is actively researching and substituting less harmful surfactants, as well as other chemicals such as sizes, in all areas of textile processing. Unfortunately, information about surfactant performance and pollution issues is often unavailable to the person selecting these products, which makes selection of "least-impact" surfactants difficult.

4.11 Recovery of Synthetic Sizes

Description. Synthetic sizes, such as PVA, can be used in place of starch for many textile products. Unlike starch, which degrades during desizing, recovery and reuse of synthetic sizes is technically feasible. Recovery of PVA is usually accomplished by membrane filtration.

Benefits. Recovery of synthetic size saves on purchase costs and use and reduces BOD and COD in mill effluent.

Status of Use in the United States. Some U.S. mills have used and recovered synthetic sizes in their preparation and finishing operations for more than 25 years. Size recovery, however, is not widely practiced in the industry. PVA and other synthetic sizes are generally not biodegradable by typical wastewater treatment practices; unrecovered size chemicals may pass through conventional treatment systems and can cause foaming and aquatic toxicity in receiving waters. The cost for equipment needed for size recovery is prohibitively high, as are shipping costs for concentrate solutions. Also, most U.S. mills prefer to use starch size because it is less costly than synthetic size and gives a softer "hand" to the fabrics treated. Although high-BOD starches are not recoverable, they are treatable by conventional wastewater treatment. Industry must weigh both the costs and benefits of using nonrecoverable, high-BOD starch sizes and using recoverable synthetic sizes.

4.12 Countercurrent Washing

Description. This technique is used in multistage washing operations, on the principle that fresh, clean water need not be used for all washing steps, particularly during the early wash stages when the fabric is "dirtiest." In countercurrent washing, clean water is used only during the final wash stage. This wash water is circulated for successive reuse in each of the previous stages until reaching the first stage, after which it is discharged for treatment. In this manner, the cleanest water is used to wash fabric during the last stage when it is "cleanest" and the most contaminated water is used for gross washing operations during the first stage.

An important variant of the countercurrent principle is the "horizonal" or "inclined" washer. Fabric enters the bottom of the machine and exits through the top. Wash water is introduced from the top down, causing a water flow within the machinery that is inherently countercurrent in nature. Countercurrent washing is useful after continuous dyeing, printing, desizing, scouring, and bleaching.

Benefits. Countercurrent washing can reduce water usage by 50%B80%, depending on the throughput and number of washing stages.

Status of Use in the United States. Countercurrent washing is widely practiced in the textile industry. Equipment and machinery are readily available, and existing equipment can be retrofitted.

4.13 Low Add-On Finishing

Description. Several types of machines can apply a low volume of finish solution to the fabric. Some popular methods and machinery used for low add-on finishing include hydroextraction, vacuum extraction, sprays, foams, and kiss rolls.

Benefits. Low add-on finishing has several benefits:

• Reduced energy requirements
• Reduced chemical usage
• Prevention of leaching or transport of chemicals from fiber interiors to fabric surface, thus improving fastness and softness of finished goods.

Status of Use in the United States. Low add-on methods are used by U.S. mills when the final product can meet performance specifications, and when capital costs for new equipment can be recovered within a reasonable time frame. Although capital costs can be substantial, this equipment is usually purchased by mills during upgrades and expansions.

4.14 Mechanical Finishing

Description. Mechanical methods can be used to perform many of the same finishing functions as chemical methods, including stabilization, shrinkage reduction, optical finishing, and softening.

Benefits. The primary benefit of mechanical finishing is elimination of the use of finishing chemicals, thereby saving costs on chemical purchase, chemical disposal, and wastewater treatment.

Status of Use in the United States. Energy requirements for mechanical finishing are generally higher, which must be considered when choosing between chemical and mechanical methods. The costs and benefits of using mechanical compared with chemical finishing need to be quantified to aid in decision making. Often, performance specifications for the finished product dictate the type of finishing required.

4.15 Waste Reclamation Systems for Spinning

Description. Special equipment is used to remove, separate, and collect impurities, trash, and tangled fiber masses from cotton stock. In the past, this nonreworkable waste was discarded during the spinning operation.

Benefits. Reclamation systems allow for efficient capture and collection of spinning wastes, which can be sold for use in padded mailing envelopes, compressed into dense fuel pellets for boilers, or reused in other applications.

Status of Use in the United States. The industry is adopting these reclamation systems as part of a concerted effort to reuse process wastes.

5. FUTURE TRENDS

There are several apparent trends and research and development activities ongoing within the textile industry in the areas of pollution prevention and clean technology implementation.

Regulatory Incentives

Although there are no industry-specific mandates driving clean technology implementation for textiles, increased stringency and more rigorous enforcement of existing regulations for effluent and air emissions will prompt mills and finishers to adopt new processes and develop alternative methods for managing process wastes.

Emerging Technologies

Several clean technologies and processes have proved effective on a pilot scale but are not yet ready for full-scale implementation. These include:

• Direct dyebath monitoring and control systems. A control strategy that adjusts the dyeing process in real time to account and correct for uncontrollable parameters.
• Real-time adaptive control systems. Control strategy to adjust dyeing or other processing steps in real time to account and correct for uncontrollable parameters.
• Ink-jet printing. Droplets of dye solution are directed onto fabric to form a pattern, eliminating photographic screen making and color mix kitchen activities.
• Supercritical fluid dyeing. Uses carbon dioxide (CO₂) as the fluid medium on disperse-dyed synthetics, eliminating aqueous effluent.
• Ultrasound dyeing. Uses ultrasound waves to impart dyes to fabric, eliminating aqueous effluent.
• Radio frequency drying. Uses radio waves rather than ovens to dry yarn or fabric.

Full-scale implementation of these technologies is at least 5B10 years away.

Chemical Specialties and Dye Composition

In future years, information about the composition and environmental effects of chemical specialties and dyes will not be shared as readily by manufacturers, who are feeling increasingly compelled to protect proprietary information to remain competitive. This trend is becoming apparent despite the widespread knowledge that mills need this information to make informed decisions about the products they use. In particular, dyes are expected to become much more proprietary, with an associated lack of needed information available to the user. The color index (CI), a dual classification system that groups dyes according to chemical structure and application class, has historically been a standard means of identification for textile dyes. Based on the CI, a dye house could make inferences about the possible environmental effects of dye use. Use of the CI system is waning, however, due to loss of support from dye manufacturers

The trend toward nondisclosure will make evaluation of clean technology and pollution prevention techniques for producing textiles even more challenging. Industry, however, is working together to identify ways to overcome this barrier.

Solid Waste Reduction

Mills will continue to look at ways to reduce solid waste generation, to use less packaging or packaging that is reusable (such as IBCs for chemical storage), to reuse reworkable fiber, to find new markets for nonreworkable and hard fiber waste, and to train and educate workers to reduce selvage, cuttings, and trim waste. Reduction of solid waste generation coupled with strategies to reuse or sell wastes has widespread economic appeal due to cost savings and cost recovery realized by these efforts. This is particularly true of the carpet and rug industry, in which significant cost savings can be realized by even incremental reductions in solid waste generation.

Mechanical versus Chemical Finishing

Mills will increasingly consider using mechanical methods for fabric finishing. Mechanical finishing can be used to perform many of the same functions as chemical finishing, including stabilization, shrinkage reduction, optical finishing, and softening. The costs and benefits of using mechanical compared with chemical finishing will be further quantified to aid in decision making.

Chemical Substitutions

Mills will continue to research the use of more-benign chemicals in all areas of textile processing, including sizing, dyeing, and finishing. Ancillary operations such as solvent-based dry cleaning and maintenance and operation of machinery will also be targeted as a focus area for chemical substitution.

The large size and fragmented nature of the U.S. textile industry creates special challenges for implementation of clean technology. Yet, the industry, buoyed by strong performance and cooperative alliances intended to prevent pollution, recognizes that the potential cost savings that can be realized by implementing clean technology is significant. Current annual resource utilization by the industry includes:

• 133 billion gallons of water consumed, of which 53 billion gallons are treated at a cost of US$146 million
• 237 million pounds of knit fabric wasted, at a loss of US$474 million to the industry
• 30% of reactive dyes discharged in wastewater, with a lost value of US$66 million
• 742 million pounds of salt consumed.

Implementation of pollution prevention and clean technology will thus allow the industry to synthesize its goals of product quality, cost savings, increased profitability, and environmental stewardship.

REFERENCES

EPA, Best Management Practices for Pollution Prevention in the Textiles Industry, EPA/625/R-96/004 (Washington: EPA Office of Research and Development, September 1996).

EPA, Development Document for Effluent Limitations Guidelines and Standards for the Textile Mills: Point Source Category, (Washington: EPA Office of Water, October 1979).

Tuggle, L. "Solid Waste Management in the Textile Plant" in Proceedings of the Conference for Executives and Managers of Environmental Issues Affecting the Textiles Industry (Raleigh: North Carolina Department of Environment, Health, and Natural Resources, 1993).

Selected articles from:

• America's Textiles International
• Textile Technology Digest

Selected publications of:

• American Association of Textile Chemists and Colorists (AATCC)
• American Textiles Manufacturers Institute (ATMI)
• The AMTEX Partnership Program Office
• The Carpet and Rug Institute
• U.S. Department of Energy, Office of Industrial Technology