**3. Finishing and waste water**

The contamination of natural waters has become one of the biggest problems in modern so‐ ciety, and the economical use of this natural resource in production processes has gained special attention, since in predictions for the coming years, the amount of water required per capita is of concern. This environmental problem is related not only to its waste through misuse, but also to the release of industrial and domestic effluents [64].

ness of the fiber-liquid boundary layer), and swelling (enhancement of dye diffusion rate in‐

According to Vankar & Shanker (2008), ultrasound allows for process acceleration, obtaining the same or better results than existing techniques, but under less extreme conditions, i.e., lower temperatures and lower concentrations of the chemicals used. Wet textile processes assisted by ultrasound are of great interest to the textile industry for this reason [61], and Khatri et al. (2011) showed that the dyeing of polyester fiber using ultrasonic energy result‐

Due to the revolution in environmental protection, the use of ultrasonic energy as a renewa‐ ble source of energy in textile dyeing has been increased, due to the variety of advantages associated with it. On the other hand, there is a growing demand for natural, eco-friendly dyeing for the health sensitive application to textile garments as an alternative to harmful

Ultrasonic energy can clean or homogenize materials, accelerating both physical and chemi‐ cal reactions, and these qualities can be used to improve textile processing methods. Envi‐ ronmental concern has been focused on textile processing methods for quite some time, and the use of ultrasonic energy has been widely studied in terms of improving washing fast‐ ness. The textile dyeing industry has long been struggling to cope with high energy costs, rapid technological changes and the need for a faster delivery time, and the effective man‐ agement of ultrasonic energy could reduce energy costs and improve productivity [35]. Ul‐ trasonic waves are vibrations with frequencies above 17 kHz, out of the audible range for humans, requiring a medium with elastic properties for propagation. The formation and col‐ lapse of the bubbles formed by ultrasonic waves (known as cavitation) is generally consid‐ ered to be responsible for most of the physical and chemical effects of ultrasound in solid/ liquid or liquid/liquid systems [63]. Cavitation is the formation of gas-filled microbubbles or cavities in a liquid, their growth, and under proper conditions, their implosive collapse [59]. It has been reported that ultrasonic energy can be applied successfully to wet textile process‐ es, for example laundering, desizing, scouring, bleaching, mercerization of cotton fabrics, enzymatic treatment, dyeing and leather processing, together with the decoloration/mineral‐

In addition, ultrasonic irradiation shows promise, and has the potential, for use in environ‐ mental remediation, due to the formation of highly concentrated oxidizing species such as hydroxyl radicals (HO•), hydrogen radicals (H•), hydroperoxyl radicals (HO2• ) and H2O2, and localized high temperatures and pressures [59]. Therefore, the use of ultrasonic energy

The contamination of natural waters has become one of the biggest problems in modern so‐ ciety, and the economical use of this natural resource in production processes has gained

could indeed reduce the environmental impact caused by the textile industry.

synthetic dyes, which poses a need for suitable effective dyeing methodologies [62].

ed in an increased dye uptake and enhanced dyeing rate [35].

ization of textile dyes in waste water [60].

**3. Finishing and waste water**

side the fiber) [59,60].

160 Eco-Friendly Textile Dyeing and Finishing

Of the industries with high-polluting power, the textile dyeing industry, responsible for dyeing various types of fiber, stands out. Independent of the characteristics of the dyes chos‐ en, the final operation of all dyeing process involves washing in baths to remove excesses of the original or hydrolyzed dyes not fixed to the fiber in the previous steps [36]. In these baths, as previously mentioned, it is estimated that approximately 10-50% of the dyes used in the dyeing process are lost, and end up in the effluent [17,21,22], contaminating the envi‐ ronment with about one million tons of these compounds [65]. The dyes end up in the water bodies due mainly to the use of the activated sludge treatment in the effluent treatment plants, which has been shown to be ineffective in removing the toxicity and coloring of some types of dye [33,60,66,67]. Moreover, the reduction of azo dyes by sodium hydrosulfite and the successive chlorination steps with hypochlorous acid, can form 2-benzotriazoles fenil‐ benzotriazol (PBTA) derivatives and highly mutagenic aromatic amines, often more muta‐ genic than the original dye [68]. In an aquatic environment, this dye reduction can occur in two phases: 1) The application of reducing agents to the newly-dyed fibers to remove the excess unbound dye, which could lead to "bleeding" of the fabrics during washing, and 2) The use of reducing agents in the bleaching process, in order to make the effluent colorless and conform with the legislation. This reduced colorless effluent containing dyes is sent to the municipal sewage treatment plant, where they chlorinate the effluents before releasing them into water bodies where they may generate PBTAs. Several different PBTAs are al‐ ready described in the literature, and their chemical structures vary depending on the dyes that originated them [63,69].

So the release of improperly treated textile effluents into the environment can become an important source of problems for human and environmental health. The major source of dye loss corresponds to the incomplete fixation of the dyes during the textile fiber dyeing step [36].

In addition to the problem caused by the loss of dye during the dyeing process, within the context of environmental pollution, the textile industry is also focused due to the large volumes of water used by its industrial park, consequently generating large vol‐ umes of effluent [64]. It has been calculated that approximately 200 liters of water are needed for each kilogram of cotton produced [70]. These effluents are complex mixtures of many pollutants, ranging from original colors lost during the dyeing process, to asso‐ ciated pesticides and heavy metals [71], and when not properly treated, can cause seri‐ ous contamination of the water sources [64]. So the materials that end up in the water bodies are effluents containing a high organic load and biochemical oxygen demand, low dissolved oxygen concentrations, strong color and low biodegradability. In addition to visual pollution, the pollution of water bodies with these compounds causes changes in the biological cycles of the aquatic biota, particularly affecting the photosynthesis and oxygenation processes of the water body, for example by hindering the passage of sun‐ light through the water [72].

Moreover, studies have shown that some classes of dye, especially azo dyes and their byproducts, may be carcinogenic and / or mutagenic [27,33,67,73-77], endangering human health, since the wastewater treatment systems and water treatment plants (WTP) are inef‐ fective in removing the color and the mutagenic properties of some dyes [78,79]. The diffi‐ culty in removing them from the environment can be attributed to the high stability of these compounds, since they are designed to resist biodegradation to meet the demands of the consumer market with respect to durability of the colors in the fibers, consequently imply‐ ing that they also remain in the environment for a long time [32].

human health. Thus the study of new alternatives for the treatment of different types of in‐

Textile Dyes: Dyeing Process and Environmental Impact

http://dx.doi.org/10.5772/53659

163

Amongst that of several other industries, the textile sector waste has received considerable attention in recent years, since it can generate large volumes of effluents that, if not correctly treated before being disposed into water resources, can be a problem, as previously men‐ tioned. Effluents from the textile industry are extremely complex, since they contain a large variety of dyes, additives and derivatives that change seasonally, increasing the challenge to find effective, feasible treatments. Currently, the processes developed and available for these industries are based on methods that were designed for other waste, and have limitations when applied to textile effluents. As a consequence, these industries produce colored waste‐ water with a high organic load, which can contribute enormously to the environmental pol‐ lution of surface water and treatment plants if not properly treated before disposal into the water resources [85]. The ingestion of water contaminated with textile dyes can cause seri‐ ous damage to the health of humans and of other living organisms, due to the toxicity, high‐ lighting mutagenicity of its components [86,87]. Therefore treatments that are more efficient

There are several techniques for the treatment of effluents, such as incineration, biological treatment, absorption onto solid matrices, etc. However, these techniques have their draw‐ backs, such as the formation of dioxins and furans, caused by incomplete combustion dur‐ ing incineration; long periods for biological treatment to have an effect, as also the adsorptive process, that is based on the phase transfer of contaminants without actually de‐ stroying them [88,89]. The problem is further aggravated in the textile industry effluents, due to the complexity of their make-up. Thus it can be seen that processes are being used that are not entirely appropriate for the treatment of textile effluents, thereby creating a ma‐ jor challenge for the industry and laundries that need to adapt to current regulations for the

The use of filtration membranes and/or separation [90] and biological methods [91], in addi‐ tion to incineration processes involving adsorption onto solid matrices, has also being adopted by the textile industry and is receiving considerable attention. However, all these processes only involve phase transfer, generating large amounts of sludge deposited at the end of the tanks and low efficiency in color removal and reduction of the organic load. Ac‐ cording to this scenario, many studies have been carried out with the aim of developing new technologies capable of minimizing the volume and toxicity of industrial effluents. Unfortu‐ nately, the applicability of these types of system is subject to the development of modified procedures and the establishment of effluent recycling systems, activities that imply evolu‐ tionary technologies and which are not yet universally available. Thus the study of new al‐ ternatives for the treatment of many industrial effluents currently produced is still one of

the main weapons to combat the phenomenon of anthropogenic contamination.

Due to their considerable danger, several authors have attempted to find new forms of treat‐ ment to reduce the serious environmental and toxicological risks caused by various organic compounds. Amongst the many reported cases are those based on the use of specific micro‐

dustrial effluent continues to be a challenge to combat anthropogenic contamination.

and economical than those currently available are required.

control of the color of effluents with a high organic load.

With respect to the legislation, there is no consensus amongst the different countries con‐ cerning effluent discharge, and there is no official document listing the different effluent limit values applied in different countries. Many federal countries, such as the United States of America, Canada and Australia have national environmental legislation, which, as in Eu‐ rope, establishes the limits that must be complied with. Some countries, such as Thailand, have copied the American system, whereas others, such as Turkey or Morocco, have copied the European model. In some countries, for example India, Pakistan and Malaysia, the emis‐ sion limits are recommended, but are not mandatory [80]. With respect to the color, in some countries such as France, Austria and Italy, there are limits for the color of the effluent, but since they use different units, a comparison is impossible. The oldest unit is the Hazen, in use since the beginning of the 20th century, but in France, the current unit is (mg L-1Pt–Co). The coloration values are determined by a comparative analysis with model solutions pre‐ pared according to defined procedures [80].

Based on all the problems cited above regarding the discharge of effluents into the environ‐ ment, it is obvious there is a need to find alternative treatments that are effective in remov‐ ing dyes from effluents.
