**1.1 Pollution caused by dyes and their harmful effects on aquatic environment**

Food dyes are promising colorants globally used to color a broad spectrum of food products. Food dyes not only impart color to food but also boost up appetite and promote attractiveness and esthetic appeal of food for consumer. According

to recent financial reports, 7 x 105 tons of 10,000 different dyes and pigments are produced worldwide, and its market is skyrocketing each year and has exceeded over US \$11 billion by 2008 [1]. Approximately 1-2% of dyes stuffs are lost during production and about 10-15% of dyes are discharge as effluent during dye applications [2]. From an environmental perspective, the discharge of dye effluents from dye manufacturing or consuming units into the water bodies poses potential threats to the quality of water and induces serious health problems to human, plants and animal life in particular and aquatic biota in general. The presence of dyes in wastewater even in trace amounts (less than 1 mg/dm3 for few dyes) is remarkably objectionable and undesirable [3]. Most of the organic dyes used to color food products, for example, azo dyes, have aromatic centres in their molecular structures, and their metabolic and degradation products like aromatic amines (anilines), benzidines and benzene sulphonic acids are well-established carcinogens, mutagens and DNA adducts and hence induces subsequent deadly effects on cells [4]. Moreover dyes can make water colored, thereby reducing the transparency (sunlight penetration) and aeration of water body, which badly affects the efficacy of crucially important photosynthesis, consequently reducing significantly the dissolved oxygen (DO) levels in water. The discharge of dye effluents in water bodies poses direct and indirect consequences to aquatic ecosystem. The direct effects includes depletion of dissolved oxygen levels, decreased reoxygenation potential, leaching of dyestuff from soil into groundwater, reduced light penetration into water which hinders photosynthesis (which gives red signal to aquatic flora and fauna) and esthetic issue of water downstream [5, 6]. The bird's eye view of indirect effects caused by dye effluents includes death of aquatic organisms, genotoxicity and microtoxicity imposed by colored allergens, depression of human immune system, allergic reactions, hyperactivity in kids (ADHD), bladder cancer in humans and deadly process of water eutrophication [7].

## **1.2 Application of dyes**

Both natural and synthetic dyes have indeed revolutionized the modern world both at domestic and industrial sectors. More recent and independent reviews have reported that over 100,000 different dyes and pigments are in practice, and their annual production has exceeded over 7 × 107 tons. Nowadays the use of dyes is indispensable because dyes are widely used in electronics; textile; rubber; food; leather; cosmetics; paper and pulp; photography; solar cells/solar penal, i.e. dye-sensitized solar cells; pharmaceuticals; pigment; agriculture research; paints; printing inks; cosmetics; coloring of plastics products; and many other fields of domestic and industrial interest [8, 9]. Similarly dyes are also used to assess the efficacy of sewage and wastewater treatment plants as well as agriculture research. Textile industries consume more than 70% of total dyes produced worldwide [10]. Dyes in textile, food or in any other industries are used in minute quantities; for instance, it has been reported that one ton of textile dye is more than enough to color 42,000 clothes/suits [11].

## **2. Techniques incorporated for dye removal from wastewater**

Purification of water from dyes tuff is of tremendous importance from both perspectives, i.e. water purification and its reusability. Pollution caused by dyes has attracted the attention of environmental chemists worldwide more specifically in developed countries like the USA, United Kingdom, Germany, China, Japan, Scandinavian countries, etc., which have incorporated rapid

**115**

*Contamination of Water Resources by Food Dyes and Its Removal Technologies*

industrializations and are more vulnerable to dye pollution. Nevertheless dyes cause severe water pollution; hence these dyes need to be eventually removed to minimize or eliminate their dreadful impacts. Consequently the worldwide environmental standards so far have turned more stringent, seeking more precise technological tools to cope with this global environmental issue, and that is why it has attracted the attention of environmental scientists worldwide from past two decades. Various techniques like physicochemical methods, enzymatic degradation, microbiological treatment, chemical methods and advanced oxidation techniques have been developed so far [12–14]. But unfortunately most of the organic dyes are non-biodegradable, thermally stable and refractory with respect to biochemical oxidation due to their large/complex sizes and inert nature. These characteristics have rendered organic dyes reluctant with respect to decolourization by using conventional methods of wastewater treatment like filtration, coagulation, biochemical and physicochemical techniques. Thus from the last two decades, research for more efficient and sophisticated techniques for removal of these dyes from wastewater to minimize or eliminate the water pollution has been turned the core interest to environmental scientists worldwide [15]. The dye abatement techniques in water are broadly classified into two

Segregation techniques involve separation of dyes pollutants via multiple physical techniques like adsorption, filtration/nanofiltration or coagulation processes. These traditional water purification methods like filtration, ion exchange, coagulation by lime or by using salts of iron/aluminium, adsorption over activated carbon and other low-cost adsorbents have been proven to be very effective decolourization methods. Among techniques decontamination of dyes by adsorption offer the most promising, simple and efficient technique. Similarly the use of low-cost adsorbents such as vegetable matter, saw dust, fruits peels, hen feathers, other carbonaceous materials, etc. make the dye removal process more economical and feasible [16, 17], but their utility is limited by production of associated hazardous sludge which poses an another issue of their disposal at suitable safe site. Similarly the use of adsorption and coagulations techniques for decolourization of wastewater is limited by regular regeneration of adsorbent and coagulant materials after dye adsorption and coagulation, respectively, which is much needed (to make the process economical and efficient), so this in turn gives

Over the past two decades, chemical techniques are also withdrawing the attention of environmental chemists; these techniques include chemical oxidation

high efficiency and reproducibility. But this technique has a major disadvantage with respect to relatively high prices and production of secondary pollutants like chlorinated hydrocarbons which are known carcinogens; similarly the difficulty in storage and transportation of reactants causes a substantial inconvenience for safe operation [20]; thus environmental scientists are looking for more, convenient, advanced, safe, efficient and sophisticated techniques which must be incorporated

), chlorine dioxide or ozone which has always shown

*DOI: http://dx.doi.org/10.5772/intechopen.90331*

principal types.

**2.1 Segregation techniques**

rise to other issues [18, 19].

**2.2 Degradation techniques**

by using hypochlorite (OCl<sup>−</sup><sup>1</sup>

for removal of dyes from wastewater [12] .

*2.2.1 Chemical techniques*

*Contamination of Water Resources by Food Dyes and Its Removal Technologies DOI: http://dx.doi.org/10.5772/intechopen.90331*

industrializations and are more vulnerable to dye pollution. Nevertheless dyes cause severe water pollution; hence these dyes need to be eventually removed to minimize or eliminate their dreadful impacts. Consequently the worldwide environmental standards so far have turned more stringent, seeking more precise technological tools to cope with this global environmental issue, and that is why it has attracted the attention of environmental scientists worldwide from past two decades. Various techniques like physicochemical methods, enzymatic degradation, microbiological treatment, chemical methods and advanced oxidation techniques have been developed so far [12–14]. But unfortunately most of the organic dyes are non-biodegradable, thermally stable and refractory with respect to biochemical oxidation due to their large/complex sizes and inert nature. These characteristics have rendered organic dyes reluctant with respect to decolourization by using conventional methods of wastewater treatment like filtration, coagulation, biochemical and physicochemical techniques. Thus from the last two decades, research for more efficient and sophisticated techniques for removal of these dyes from wastewater to minimize or eliminate the water pollution has been turned the core interest to environmental scientists worldwide [15]. The dye abatement techniques in water are broadly classified into two principal types.

### **2.1 Segregation techniques**

*Water Chemistry*

to recent financial reports, 7 x 105

of water eutrophication [7].

color 42,000 clothes/suits [11].

**1.2 Application of dyes**

water even in trace amounts (less than 1 mg/dm3

and their annual production has exceeded over 7 × 107

tons of 10,000 different dyes and pigments are

for few dyes) is remarkably objec-

tons. Nowadays the use of

produced worldwide, and its market is skyrocketing each year and has exceeded over US \$11 billion by 2008 [1]. Approximately 1-2% of dyes stuffs are lost during production and about 10-15% of dyes are discharge as effluent during dye applications [2]. From an environmental perspective, the discharge of dye effluents from dye manufacturing or consuming units into the water bodies poses potential threats to the quality of water and induces serious health problems to human, plants and animal life in particular and aquatic biota in general. The presence of dyes in waste-

tionable and undesirable [3]. Most of the organic dyes used to color food products, for example, azo dyes, have aromatic centres in their molecular structures, and their metabolic and degradation products like aromatic amines (anilines), benzidines and benzene sulphonic acids are well-established carcinogens, mutagens and DNA adducts and hence induces subsequent deadly effects on cells [4]. Moreover dyes can make water colored, thereby reducing the transparency (sunlight penetration) and aeration of water body, which badly affects the efficacy of crucially important photosynthesis, consequently reducing significantly the dissolved oxygen (DO) levels in water. The discharge of dye effluents in water bodies poses direct and indirect consequences to aquatic ecosystem. The direct effects includes depletion of dissolved oxygen levels, decreased reoxygenation potential, leaching of dyestuff from soil into groundwater, reduced light penetration into water which hinders photosynthesis (which gives red signal to aquatic flora and fauna) and esthetic issue of water downstream [5, 6]. The bird's eye view of indirect effects caused by dye effluents includes death of aquatic organisms, genotoxicity and microtoxicity imposed by colored allergens, depression of human immune system, allergic reactions, hyperactivity in kids (ADHD), bladder cancer in humans and deadly process

Both natural and synthetic dyes have indeed revolutionized the modern world both at domestic and industrial sectors. More recent and independent reviews have reported that over 100,000 different dyes and pigments are in practice,

dyes is indispensable because dyes are widely used in electronics; textile; rubber; food; leather; cosmetics; paper and pulp; photography; solar cells/solar penal, i.e. dye-sensitized solar cells; pharmaceuticals; pigment; agriculture research; paints; printing inks; cosmetics; coloring of plastics products; and many other fields of domestic and industrial interest [8, 9]. Similarly dyes are also used to assess the efficacy of sewage and wastewater treatment plants as well as agriculture research. Textile industries consume more than 70% of total dyes produced worldwide [10]. Dyes in textile, food or in any other industries are used in minute quantities; for instance, it has been reported that one ton of textile dye is more than enough to

**2. Techniques incorporated for dye removal from wastewater**

Purification of water from dyes tuff is of tremendous importance from both perspectives, i.e. water purification and its reusability. Pollution caused by dyes has attracted the attention of environmental chemists worldwide more specifically in developed countries like the USA, United Kingdom, Germany, China, Japan, Scandinavian countries, etc., which have incorporated rapid

**114**

Segregation techniques involve separation of dyes pollutants via multiple physical techniques like adsorption, filtration/nanofiltration or coagulation processes. These traditional water purification methods like filtration, ion exchange, coagulation by lime or by using salts of iron/aluminium, adsorption over activated carbon and other low-cost adsorbents have been proven to be very effective decolourization methods. Among techniques decontamination of dyes by adsorption offer the most promising, simple and efficient technique. Similarly the use of low-cost adsorbents such as vegetable matter, saw dust, fruits peels, hen feathers, other carbonaceous materials, etc. make the dye removal process more economical and feasible [16, 17], but their utility is limited by production of associated hazardous sludge which poses an another issue of their disposal at suitable safe site. Similarly the use of adsorption and coagulations techniques for decolourization of wastewater is limited by regular regeneration of adsorbent and coagulant materials after dye adsorption and coagulation, respectively, which is much needed (to make the process economical and efficient), so this in turn gives rise to other issues [18, 19].

### **2.2 Degradation techniques**
