**3. Sources of dyes in wastewaters and wastewater characterization**

There is a special register called *Colour Index* for dyes first published in 1924. The dual classification system *Colour Index* includes: *Colour Index Generic Name (CIGN)*, e.g. Disperse Yellow 1, which is the name describing the kind of dye as regards its technical application and colour as well as chronological notation in the register and for the known and published chemical structure, so-called *Colour Index Constitution Number (CICN)* in this case C.I. 10345 [3]. Their largest use was recorded in 2008 in Asia, particularly in China and India (Figure 1) [4]. The yearly world production of dyes is 700, 000–1000, 000 tones, which corresponds to over

Natural dyes such as indigo, woad, or madder lost their position due to dynamic development of textile industry in the XVIIIth century. In the second half of the XIXth century, there started a synthesis of intermediate products and new dyes not having equivalents in nature of various

The first synthetic dyes were fuchsine (prepared in 1855 by J. Natanson) and mowein (prepared in 1856 by W. Perkin) [1]. Development of dyes synthesis is promoted by their huge application in many fields of industry. The large tonnage consumer of dyes is textile industry. Moreover, they are applied in electronic industry for the production of liquid crystal and electrochromium visual indicators as well as in technology of optical recording, photographic (for creating coloured pictures), reprography (ink, non-carbon paper), food dyeing as well as for dyeing biological material, paper, leather, wood and cosmetics and also as indicators (e.g. redox, pH).

100, 000 commercial products whereby azo dyes constitute 70% [5-11].

40 Ion Exchange - Studies and Applications

**Figure 1.** World dyes demand by the regions in 2008

colours, shades, and high quality (resistance to chemical factors, light, friction).

The basic sources of dyes in industrial wastewaters are complex technological processes in organic dye production plants, textile and paper plants as well as furrier and tanning ones. Waste products containing dyes from plastic production, food processing, petroleum, polygraphic, cosmetic, photographic and electronic industries are in somewhat lower amounts. Wastewaters from intermediate products and organic dyes production usually contain various chemical compounds which occur not only in the form of aqueous solutions but also in liquids, emulsions suspensions and pitch sparsely soluble in water. Besides residues of raw and intermediate materials such as benzene, aniline, phenol, amine, nitro compounds, alcohols, esters, salts, inorganic acids (mainly HNO3, H2SO4), they contain those of ready-made products or dyes. The weight amounts of unreacted substrates, by-products or auxiliary compounds largely exceed the amounts of the main product. They are characterized by intense colouring despite insignificant dye concentration as well as smell and taste due to the presence of nitro compounds. Some aniline dyes are distinctly visible even at the concentration about 40 mg/L [12]. Table 2 presents the characteristics of wastewaters from organic dyes production [12].


**Table 2.** Characteristics of wastewaters from organic dyes production plant

Amount and composition of wastewaters originated from textile plants depend on many factors, among others, on the kind of fibre or fabric, way of dyeing (kind of used dyes) as well as apparatus. Their largest amounts have arisen during chemical treatment of textile products. Textile plants in the three-shift (24 h/day and night) system equipped with 40 dyeing machines generate enormous amounts of effluents 2400–5200 m3 /day and night assuming the average capacity of dyeing machine 200–6500 L and taking into account 7–10 fillings (baths) of the machine during one dyeing process [13].

Processes of chemical treatment of textile products are a separate branch of producing of above wares likewise mechanical treatment [14]. Their main aim is to give textile products suitable properties facilitating their further treatment and desirable usable features like shape stability, resistance to outer factors' action (washing, friction, dirt, sweat) as well as surface appearance (smooth, creased, shiny, dull, colorful). The above mentioned properties of textile products are obtained during their treatment using various chemical substances: alkalis, acids, salts, surface active substances, oxidizers, reducers, dyes, thickeners, water, solvents and many others. The amounts of substances added to dyeing baths depending on colouring intensity are given in Table 3 [13, 15].


**Table 3.** Load of impurities carried in dyeing bath

These compounds are a main load in textile wastewaters; and besides dyes, they remain in wastewaters in the concentration close to the initial one (part is deposited on the textile product) as suitable dying conditions are created. The average water consumption in all processes of chemical treatment is from about 150 to over 300 liters per one kilogram of fibre causing formation of the same amount of strongly contaminated wastewaters [14]. Beside dyes and auxiliaries, textile industry wastewaters contain specific contaminations such as fat, wax, dextrin, starch, dressing or casein. Organization for Economic Cooperation Development estimated that 7–20% of acid dyes, 5–20% of direct dyes and 20–50% of reactive dyes were lost in the effluents in Europe [16-19]. A large percentage of pollution generated by the textile industry can be attributed to salts, sizing agents, preparation agents, detergents and organic acids [16], see Figure 2.

**Figure 2.** Percentage of non-fixed dyes and auxiliaries that may be discharged in the textile effluent (based on the data presented in the paper [16])

For example, reactive dyeing of 1 kg of cotton requires about 150 L of water, 0.6–0.8 kg of NaCl and about 40 g of reactive dye. One can easily imagine the total amount of generated pollution. According to Epolito et al. [19] under typical dyeing conditions, up to 50% of the initial dye concentration remains in the spent dye bath in its hydrolyzed form. Thus after dyeing wastewaters are characterized not only by intensive and difficult colour removal but also by high pH, suspended and dissolved solids, chemical and biochemical oxygen demands. Typical characteristics of raw textile wastewaters are presented in Table 4 [12–14, 20, 21].


\* Colour threshold – given according to the platinum scale (e.g. in mg Pt/L) or in a descriptive way giving dilution extent at which specific colour disappears

#### **Table 4.** Composition of textile wastewaters

resistance to outer factors' action (washing, friction, dirt, sweat) as well as surface appearance (smooth, creased, shiny, dull, colorful). The above mentioned properties of textile products are obtained during their treatment using various chemical substances: alkalis, acids, salts, surface active substances, oxidizers, reducers, dyes, thickeners, water, solvents and many others. The amounts of substances added to dyeing baths depending on colouring intensity

**auxiliaries**

These compounds are a main load in textile wastewaters; and besides dyes, they remain in wastewaters in the concentration close to the initial one (part is deposited on the textile product) as suitable dying conditions are created. The average water consumption in all processes of chemical treatment is from about 150 to over 300 liters per one kilogram of fibre causing formation of the same amount of strongly contaminated wastewaters [14]. Beside dyes and auxiliaries, textile industry wastewaters contain specific contaminations such as fat, wax, dextrin, starch, dressing or casein. Organization for Economic Cooperation Development estimated that 7–20% of acid dyes, 5–20% of direct dyes and 20–50% of reactive dyes were lost in the effluents in Europe [16-19]. A large percentage of pollution generated by the textile industry can be attributed to salts, sizing agents, preparation agents, detergents and organic

**Figure 2.** Percentage of non-fixed dyes and auxiliaries that may be discharged in the textile effluent (based on the data

For example, reactive dyeing of 1 kg of cotton requires about 150 L of water, 0.6–0.8 kg of NaCl and about 40 g of reactive dye. One can easily imagine the total amount of generated pollution.

**Inorganic auxiliaries** **Electrolytes NaCl, Na2SO4**

**Depth of shade Dyeing bath composition (g/kg textiles) Dyes Organic**

Light shade 0.5–4 0–30 50–250 90–400 Medium shade 5–30 30–150 600–700 Deep shade 30–80 0–35 800–1500

are given in Table 3 [13, 15].

42 Ion Exchange - Studies and Applications

**Table 3.** Load of impurities carried in dyeing bath

acids [16], see Figure 2.

presented in the paper [16])

Wastewaters coming from tannery, besides impurities removed from leather (hair, blood, epidermis, fat tissue) contain significant amounts of chemicals: sulfuric acid and hydrogen chloride, lime, soda, sodium sulfide, chromium (III) compounds, detergents and organic solvents [14]. Water consumption in tanneries and furriery plants is from 30 to 81 m3 and from 8.5 to 400 m3 , respectively, for 1000 leathers depending on their kind. Concentration of organic impurities from furriery plants is somewhat smaller than from tannery. Dyes contained in these wastewaters come from tanning, dyeing and rising of raw material and their concentra‐ tion is 1 kg/m3 [21]. They constitute 17–32.5% of the total amount of wastewater generated by these plants [12]. The composition of wastewaters from the tannery and furriery plants is presented in Table 5 [21].

Wastewaters from paper factories containing dyes particularly aniline and sulfur ones are generated from the paper treatment process consisting in the addition of fillers and dyes to the bleached cellulose material. As a result of multi-stage purification of wastewaters from the cellulose plants, there is obtained a low value of BOD (biochemical oxygen demand) – 4 mg/L but COD (chemical oxygen demand) is maintained on the level 75 mg/L. These waste‐ waters contain a small amount of suspended matter – 5 mg/L, but they are characterized by intensive colour – 40 mg Pt/L [21].


**Table 5.** Concentration of impurities in wastewaters from the tannery and furriery plants
