**4. Waste water treatment**

These days, environmental pollution can undoubtedly be regarded as one of the main prob‐ lems in developed and developing countries. This is due, not just to one, but to a number of factors, such as the misuse of natural resources, inefficient legislation and a lack of environ‐ mental awareness. Fortunately, in recent years there has been a trend for change and a series of scientific studies are being used as an important tool in the development of new treat‐ ment technologies and even in the implementation of processes and environmentally friend‐ ly actions [64,81-84].

Every industrial process is characterized by the use of inputs (raw materials, water, energy, etc.) that undergo transformation giving rise to products, byproducts and waste. The wastes produced at all stages of the various types of human activity, both in terms of composition and volume, vary according to the consumption practices and production methods. The main concerns are focused on the impact these can have on human health and the environ‐ ment. Hazardous waste, produced mainly by industry, is particularly worrying, because when incorrectly managed, it becomes a serious threat to the environment and therefore to human health. Thus the study of new alternatives for the treatment of different types of in‐ dustrial effluent continues to be a challenge to combat anthropogenic contamination.

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‐

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‐

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‐

These days, environmental pollution can undoubtedly be regarded as one of the main prob‐ lems in developed and developing countries. This is due, not just to one, but to a number of factors, such as the misuse of natural resources, inefficient legislation and a lack of environ‐ mental awareness. Fortunately, in recent years there has been a trend for change and a series of scientific studies are being used as an important tool in the development of new treat‐ ment technologies and even in the implementation of processes and environmentally friend‐

Every industrial process is characterized by the use of inputs (raw materials, water, energy, etc.) that undergo transformation giving rise to products, byproducts and waste. The wastes produced at all stages of the various types of human activity, both in terms of composition and volume, vary according to the consumption practices and production methods. The main concerns are focused on the impact these can have on human health and the environ‐ ment. Hazardous waste, produced mainly by industry, is particularly worrying, because when incorrectly managed, it becomes a serious threat to the environment and therefore to

ing that they also remain in the environment for a long time [32].

pared according to defined procedures [80].

ing dyes from effluents.

162 Eco-Friendly Textile Dyeing and Finishing

ly actions [64,81-84].

**4. Waste water treatment**

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 and economical than those currently available are required.

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

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‐ organisms, and degradation using advanced oxidation processes (AOP) such as Fenton, photo-Fenton and heterogeneous photocatalysis, which are highlighted below.

proved to be independent of the pH of the solution and of the type of substituent on the aro‐

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Canle et al. (2005) studied the behavior of the adsorption of aniline and dimethyl aniline on‐ to three species of TiO2 (P25, anatase and rutile) and established that the greatest adsorption occurred onto TiO2 P25. The effect of pH on the degradation provided by these compounds was also evaluated, and lower mineralization percentages were observed in acidic media. This type of behavior can be attributed to the positive charges on both the aniline and the semiconductor, providing electrostatic repulsion between the two species. Thus, an alkaline medium has been recommended as the most appropriate one to promote the mineralization

Chu et al. (2007) observed the effects of pH variation and the addition of hydrogen peroxide on the degradation of 2-chloroaniline using TiO2 as a semiconductor, with and without the application of UV radiation. The results showed that the addition of low concentrations of H2O2 to the UV/TiO2system provided a significant increase in degradation of the aromatic amine. The addition of an excess of H2O2 promoted no increase in degradation, as expected; to the contrary, a reduction in the reaction rate was observed. The variation in pH was eval‐ uated in both systems, and the condition leading to the highest percentages of mineraliza‐

Low et al. (1991) monitored the inorganic products resulting from the degradation of several organic nitrogenated, sulfured and halogenated compounds. Degradation was carried out using TiO2 as the semiconductor and artificially illuminated UV radiation. Ammonium ions were found to be present in higher concentrations than nitrate ions, which can be explained by the fact that compounds having a nitrogen element in their structure pass through a com‐ plex degradation step where the generation of ammonium ions is more favorable than the generation of nitrate ions. In turn, compounds with nitro groups in their structures, showed higher concentrations of nitrate ions. Under ideal conditions, all the elements were convert‐ ed into their respective inorganic forms. Organic carbon was converted to CO2, the halogens to their corresponding halide, sulfur compounds to sulfate, the phosphate to phosphorus and nitrogen to ammonium and nitrate [100]. However, all these studies used a photocata‐

lytic titanium suspension, requiring a subsequent step to remove the semiconductor.

shown potential success in organic residue mineralization processes [92,96, 101-103].

With a view to these problems, a new technique that has been studied recently, with signifi‐ cant success, is the oxidation of organic matter via the generation of hydroxyl radicals (OH•). This kind of effluent treatment has been highlighted for its destructive character with respect to the organic matter. The advanced oxidation processes (AOP) are processes based on the generation of highly oxidizing species, the hydroxyl radical (OH•), which can oxidize the organic contaminants present in water, air or soil. These radicals have a high oxi‐ dation potential (E \* = +2.72 V vs. the normal hydrogen electrode, NHE), which results in high reactivity with organic pollutants. This may initiate different types of reaction with dif‐ ferent functional groups in organic compounds, forming unstable organic radicals which are then easily oxidized to CO2, H2O and inorganic acids, derived from this heteroatom. Many techniques have being developed using this principle as the method of treatment, and have

of aromatic amines using a TiO2 P25 type semiconductor [98].

tion was obtained in an alkaline medium using H2O2/UV/TiO2 [99].

matic ring of the amine [97].

The use of microorganisms cultivated specifically for the degradation of polluents to in‐ crease the yield of degradation, has been reported by some authors. For example, Flores et al. (1997) examined the behavior of 25 N-substituted aromatic compounds such as organic compounds,azo dyes and nitro, using the methanogenic bacteria acetoclastic, and found that under anaerobic conditions it was easy to mineralize various of the compounds evaluated with a good yield, especially the nitroaromatic and azo dyes [91].

Bornick et al. (2001) evaluated the use of aerobic microorganisms to degrade aromatic amines present in sediments of the river Elbe in Germany. The results obtained showed that it was possible to predict the qualitative degradation of the aromatic amines using degrada‐ tion constants [92].

Using a structural design, Wang et al.(2007) isolated a bacterium capable of promoting the degradation of the compounds pentyl amine and aniline present in water oil extraction in China. Under conditions of neutral pH and complete aeration of 6 mg O2 / l at a temperature of 30 ° C, they obtained degradation yields of 82% and 78%, respectively, for pentyl amine and aniline [93].

However, in general, although the use of microorganisms in the treatment of industrial and laboratory wastes containing aromatic amines deserves attention, mainly due to the low in‐ vestment and maintenance costs, the results are far from ideal, due to the low biodegrada‐ tion yields, long treatment times, and the generation of sludge deposited at the bottom of the treatment ponds [94].

Of the studies carried out using a source of hydroxyl radicals with oxidizing agents, the photo Fenton system developed by Fukushima et al., 2000 to promote the degradation of aniline stands out. This method has shown promise for the mineralization of aromatic amines, obtaining a reduction of approximately 85%. However, high performance liquid chromatography (HPLC) identified a number of intermediate species formed during the degradation of the aniline, such as p-aminophenol, p-hydroquinone, maleic and fumaric acids and NH4 + [95].

Studies involving heterogeneous photocatalysis also deserve attention: for example Pra‐ mauro et al., (1995) promoted the degradation of various aniline derivatives using TiO2 par‐ ticles suspended in a solution. Under optimal conditions, the method developed showed rapid mineralization of the aromatic amines examined in less than 1 hour of analysis. Byproducts generated during the degradation of these compounds were identified at the start of the reaction, but none were identified at the end of the reaction. The use of solar radiation was also evaluated, but was shown to be less efficient than artificial radiation [96].

Augugliaro et al.(2000), confirmed that heterogeneous photocatalysis using TiO2 as a semi‐ conductor may be a suitable method for the complete photodegradation of aniline, 4-ethyla‐ niline and 4-chloroaniline in an aqueous medium. The kinetic parameters for the Langmuir-Hinshelwood model were used to describe the importance of the adsorption results, which proved to be independent of the pH of the solution and of the type of substituent on the aro‐ matic ring of the amine [97].

organisms, and degradation using advanced oxidation processes (AOP) such as Fenton,

The use of microorganisms cultivated specifically for the degradation of polluents to in‐ crease the yield of degradation, has been reported by some authors. For example, Flores et al. (1997) examined the behavior of 25 N-substituted aromatic compounds such as organic compounds,azo dyes and nitro, using the methanogenic bacteria acetoclastic, and found that under anaerobic conditions it was easy to mineralize various of the compounds evaluated

Bornick et al. (2001) evaluated the use of aerobic microorganisms to degrade aromatic amines present in sediments of the river Elbe in Germany. The results obtained showed that it was possible to predict the qualitative degradation of the aromatic amines using degrada‐

Using a structural design, Wang et al.(2007) isolated a bacterium capable of promoting the degradation of the compounds pentyl amine and aniline present in water oil extraction in China. Under conditions of neutral pH and complete aeration of 6 mg O2 / l at a temperature of 30 ° C, they obtained degradation yields of 82% and 78%, respectively, for pentyl amine

However, in general, although the use of microorganisms in the treatment of industrial and laboratory wastes containing aromatic amines deserves attention, mainly due to the low in‐ vestment and maintenance costs, the results are far from ideal, due to the low biodegrada‐ tion yields, long treatment times, and the generation of sludge deposited at the bottom of

Of the studies carried out using a source of hydroxyl radicals with oxidizing agents, the photo Fenton system developed by Fukushima et al., 2000 to promote the degradation of aniline stands out. This method has shown promise for the mineralization of aromatic amines, obtaining a reduction of approximately 85%. However, high performance liquid chromatography (HPLC) identified a number of intermediate species formed during the degradation of the aniline, such as p-aminophenol, p-hydroquinone, maleic and fumaric

Studies involving heterogeneous photocatalysis also deserve attention: for example Pra‐ mauro et al., (1995) promoted the degradation of various aniline derivatives using TiO2 par‐ ticles suspended in a solution. Under optimal conditions, the method developed showed rapid mineralization of the aromatic amines examined in less than 1 hour of analysis. Byproducts generated during the degradation of these compounds were identified at the start of the reaction, but none were identified at the end of the reaction. The use of solar radiation

Augugliaro et al.(2000), confirmed that heterogeneous photocatalysis using TiO2 as a semi‐ conductor may be a suitable method for the complete photodegradation of aniline, 4-ethyla‐ niline and 4-chloroaniline in an aqueous medium. The kinetic parameters for the Langmuir-Hinshelwood model were used to describe the importance of the adsorption results, which

was also evaluated, but was shown to be less efficient than artificial radiation [96].

photo-Fenton and heterogeneous photocatalysis, which are highlighted below.

with a good yield, especially the nitroaromatic and azo dyes [91].

tion constants [92].

164 Eco-Friendly Textile Dyeing and Finishing

and aniline [93].

acids and NH4

the treatment ponds [94].

+ [95]. Canle et al. (2005) studied the behavior of the adsorption of aniline and dimethyl aniline on‐ to three species of TiO2 (P25, anatase and rutile) and established that the greatest adsorption occurred onto TiO2 P25. The effect of pH on the degradation provided by these compounds was also evaluated, and lower mineralization percentages were observed in acidic media. This type of behavior can be attributed to the positive charges on both the aniline and the semiconductor, providing electrostatic repulsion between the two species. Thus, an alkaline medium has been recommended as the most appropriate one to promote the mineralization of aromatic amines using a TiO2 P25 type semiconductor [98].

Chu et al. (2007) observed the effects of pH variation and the addition of hydrogen peroxide on the degradation of 2-chloroaniline using TiO2 as a semiconductor, with and without the application of UV radiation. The results showed that the addition of low concentrations of H2O2 to the UV/TiO2system provided a significant increase in degradation of the aromatic amine. The addition of an excess of H2O2 promoted no increase in degradation, as expected; to the contrary, a reduction in the reaction rate was observed. The variation in pH was eval‐ uated in both systems, and the condition leading to the highest percentages of mineraliza‐ tion was obtained in an alkaline medium using H2O2/UV/TiO2 [99].

Low et al. (1991) monitored the inorganic products resulting from the degradation of several organic nitrogenated, sulfured and halogenated compounds. Degradation was carried out using TiO2 as the semiconductor and artificially illuminated UV radiation. Ammonium ions were found to be present in higher concentrations than nitrate ions, which can be explained by the fact that compounds having a nitrogen element in their structure pass through a com‐ plex degradation step where the generation of ammonium ions is more favorable than the generation of nitrate ions. In turn, compounds with nitro groups in their structures, showed higher concentrations of nitrate ions. Under ideal conditions, all the elements were convert‐ ed into their respective inorganic forms. Organic carbon was converted to CO2, the halogens to their corresponding halide, sulfur compounds to sulfate, the phosphate to phosphorus and nitrogen to ammonium and nitrate [100]. However, all these studies used a photocata‐ lytic titanium suspension, requiring a subsequent step to remove the semiconductor.

With a view to these problems, a new technique that has been studied recently, with signifi‐ cant success, is the oxidation of organic matter via the generation of hydroxyl radicals (OH•). This kind of effluent treatment has been highlighted for its destructive character with respect to the organic matter. The advanced oxidation processes (AOP) are processes based on the generation of highly oxidizing species, the hydroxyl radical (OH•), which can oxidize the organic contaminants present in water, air or soil. These radicals have a high oxi‐ dation potential (E \* = +2.72 V vs. the normal hydrogen electrode, NHE), which results in high reactivity with organic pollutants. This may initiate different types of reaction with dif‐ ferent functional groups in organic compounds, forming unstable organic radicals which are then easily oxidized to CO2, H2O and inorganic acids, derived from this heteroatom. Many techniques have being developed using this principle as the method of treatment, and have shown potential success in organic residue mineralization processes [92,96, 101-103].

The association of the electrochemical properties with the photocatalytic properties of a semiconductor, have allowed for the development of a promising system, representing a very efficient technique as an AOP method that has received much attention in recent years, assigned as a photoelectrochemical process. The process gained notoriety for the possibility of forming hydroxyl radicals via the oxidation of water. The technique is based on the action of ultraviolet light (hυ) on a semiconductor capable of generating charges and e- / H+ , whose separation is facilitated by applying a positive potential (EAPP), greater than the potential of a flat band photocatalytic material. The generation of a potential gradient in the photoactivat‐ ed semiconductor directs the electrons to an auxiliary electrode (cathode), delaying recombi‐ nation between the holes (h+ ) generated in the valence band (VB), and making them available for oxidation processes and the generation of hydroxyl radicals of interest [104].

moval of these compounds present in the medium can trigger further damage human health and the environment is fundamental importance. The understanding of the composition of waste generated is extremely significant to develop these methods of treatment due to the high complexity by virtue of huge number of compounds which are added at different

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Environmental problems with used dye baths are related to the wide variety of different components added to the dye bath, often in relatively high concentrations. In the future, many of textile factories will face the requirement of reusing a significant part of all incom‐ ing freshwater because traditionally used methods are insufficient for obtaining the required

However, due to dwindling supply and increasing demand of water in the textile industries, a better alternative is to attempt to further elevate the water quality of wastewater effluent from a secondary wastewater treatment plant to a higher standard for reuse. Thus far very

Therefore, the investment in the search for methodologies to more effective treatment of these effluents can be much smaller than that spent in tertiary treatment to remove these products in low level of concentrations and in the presence of much other interference. This requires action that the cost / benefit are reviewed and the development of new techniques for wastewater treatment capable of effective removal of these dyes is intensified and made

An alternative to minimize the problems related to the treatment of textile effluents would be the development of more effective dye that can be fixed fiber with higher efficiency de‐ creasing losses on tailings waters and reducing the amount of dye required in the dyeing

It was concluded that the synthetic textile dyes represent a large group of organic com‐ pounds that could have undesirable effects on the environment, and in addition, some of them can pose risks to humans. The increasing complexity and difficulty in treating textile wastes has led to a constant search for new methods that are effective and economically via‐ ble. However, up to the present moment, no efficient method capable of removing both the color and the toxic properties of the dyes released into the environment has been found.

This work was supported by the Faculty of Pharmaceutical Sciences at Ribeirão Preto - Uni‐

process, reducing certainly improve the cost and quality of the effluent.

versity of São Paulo, Brazil, and by FAPESP, CAPES and CNPq.

stages of the dyeing fabrics.

economically viable [105,106].

**6. Conclusion**

**Acknowledgments**

little attention has been paid to this aspect [105].

water quality.

The results of this process were very promising because of the relatively short treatment time but with great efficiency, both in the removal of color and in the reduction of the organ‐ ic load. However, the limitations of this technique are related mainly to the choice of the ide‐ al catalyst for promoting the generation of these oxidizing species. Catalysts that promote the generation of radicals absorbing radiation in the visible spectral region are the most de‐ sirable for this type of reaction, due to the large percentage emitted in the solar spectrum (approximately 45%) [104].

Thus, the development of an ideal process that promotes color removal and a reduction in the organic load of wastewater from the textile industry with great efficiency is a major challenge in all fields of science, since the synthesis of the best catalyst to take advantage of solar radia‐ tion, thus reducing the operating costs, and at the same time solve the problems involved in the hydrodynamics of the reactors, is of importance in the development of the treatment.

The expectations for developing an effective method for the treatment of these wastes are quite promising, but require continuous optimization and knowledge of new aspects. These include better fixation of the dyes to the fibers, process with less water consumption, less hazardous dyes with respect to human health and methods capable of identifying these compounds with more efficacy and rapidity and assays to identify any potential carcinogen‐ ic and / or mutagenic properties in the dyes and their derivatives; genetic improvements to produce more efficient culture mediums and resistant biological treatments, leading to a re‐ duction in the generation of sludge; the synthesis of materials that catalyze reactions in the visible spectral regions, leading to a more economic photoeletrochemical method, and also new engineering advances for the construction of more effective reactors, which can take ad‐ vantage of all these developments in an integrated system, extending the performance of a process more appropriate for the treatment of such a complex effluent.
