Sulphide mainly comes from the sulphur used in

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bodies and therefore must be kept under check. Sulphide mainly comes from the sulphur used in sulphur dyes which are preferred due to their low price. However, sulphur is highly toxic and its use is forbidden in a number of developed nations. A list of the pollutants present in textile wastewater is given in Table 3 . 3.1 Colour/Dyes The presence of colour in the ef fl uent from dyeing and printing processes is one of the main problems in textile industry. The colour of the dye comes from the chromophore in the dye. Colour in water is easily visible to the naked eye even at very low concentration. Hence, colour from textile wastes carries signi fi cant aes- thetic importance. Most of the dyes are stable and is not degradable even under the effect of light or ozone. Another reason for concern is that the conventional treat- ment methods do not degrade the dyes completely. Due to this reason, removal of dyes from the wastewater ef fl uent remains a major problem in most of textile industries. Aniline is one of the organic compounds which are mainly released from the dyes used. Dyes such as Congo red, amino or azo groups contain benzene rings Table 3 Pollutants from various processes in textile industry (Wang et al. 2011 ) Process Compounds Desizing Sizes, enzymes, starch, waxes, ammonia Scouring Disinfectants and insecticides residues, NaOH, soaps, surfactants, fats, waxes, pectin s, oils, spent solvents, enzymes Bleaching H2O2, sodium silicate or organic stabilizer, high pH Mercerizing High pH, NaOH Dyeing Colour, metals, salts, surfactants, organic dyes, sulphide, acidity, alkalinity, formaldehyde Printing Urea, solvents, colour, metals Finishing Resins, waxes, chlorinated compounds, acetate, stearate, spent solvents, softeners Nanochemicals and Ef fl uent Treatment in Textile Industries 65
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which lead to increased carbon rings and nitrogen groups in the wastewater streams, which are extremely dif fi cult to degrade. 3.2 Dissolved and Suspended Solids Another critical parameter which has to be kept under constant check in ef fl uent from textile industries is the amount of dissolved solids present. Common salt and Glauber salt, which are used for the recovery of dyes in textile industries, lead to a rapid increase in the total dissolved solids (TDS) of the ef fl uent. However, just like dyes, it is dif fi cult to treat TDS with conventional treatment systems. The presence of high TDS in the ef fl uent can lead to an increase in TDS of surface water and groundwater sources which can be catastrophic as groundwater and surface water are subject to human consumption. The presence of dissolved solids in ef fl uent may also be harmful to crops and in turn restrict the use of water for agricultural purposes. The sources of suspended solids during the production process include undis- solved raw materials, such as cellulose and pulp and fi bre scrap. They can be removed by suitable mechanical separation methods. The secondary sedimentation tank out fl ow therefore contains large amount of suspended solids.
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  • Fall '19
  • N. Gokarneshan

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