Page 113 - Materials Chemistry, Second Edition

94 Life Cycle Assessment of Wastewater Treatment

6.1 INTRODUCTION
6.1.1 THe environMenTal, HealTH, anD econoMic iMpacTs of TexTile
effluenTs
The textile and apparel industry is a solid and relevant industry in many developed
or developing countries, mainly in Asia. In this region, the production and marketing
of textiles are one of the primary sources of employment for millions of people and a
major contributor to export earnings and gross domestic product (Chen et al., 2017a).
Nowadays, world consumption of clothing fibers has reached the level of 11 kg per
capita, which represents a remarkable demand for raw materials and chemicals (Shui
and Plastina, 2013).
The chemical substances used in the manufacture of textiles can be categorized
into:

• Functional chemical substances: substances added to the textile fibers to
provide the desired properties of the final product (colorants and crease
resistant agents)
• Auxiliary chemical substances: those required in the textile manufacture
process (organic solvents, surfactants, softeners, salts, acids, bases, biocides)
• Chemical substances present as impurities and not intentionally added, such
as formaldehyde released from certain resins, polyaromatic hydrocarbons,
metals, and so on

These chemicals can be released and result in human and environmental exposure
during normal wear and tear, washing, or when disposed of as waste. Among the
substances mentioned in the preceding list, colorants arise as target contaminants
in textile wastewaters, because their presence is highly visible at very low concen-
trations (<1 mg L ), which negatively affects water transparency (Chequer et al.,
−1
2013). Decreasing light penetration into water decreases photosynthetic activity,
causing oxygen deficiency and de-regulating the biological cycles of aquatic biota
(Apostol et al., 2012). The term colorant encompasses both dyes and pigments, which
can be differentiated by their solubility. While dyes are soluble compounds, mainly
applied to textile materials in aqueous solution, pigments are insoluble, and they can
be added in the formulation of paints, printing inks, or plastics (Christie, 2001).
Until the mid-nineteenth century, only natural dyes with poor dyeing perfor-
mance were used. Therefore, as a result of the need for more resistant dyes with
easier application and improved thermal behavior, synthetic dyes were developed.
That is why, 50 years after the origin of the dye industry in 1856, 90% of the dyes
used were manufactured (Welham, 1963). The massive consumption of dyes in the
textile industry accounts for approximately 70% of the dyes used worldwide.
Colorants can be classified according to either their chemical structure or the
application method. The most important reference on the classification of dyes
and pigments is the Color Index, a report published by the Society of Dyers and
Colourists in 1924 (O’Neill et al., 1999). This book series provides a complete list-
ing of commercial dyes and known pigments, and it is periodically updated. Each