can also affect the environment. Consequently, the method for pretreatment must
meet the coloring and finishing stage specifications.
Desizing It is a process to treat the fabric for hydrolyzing the excess starch, using
synthetic detergents and sodium hydroxide and/or acids or enzymes. “Size” is an
adhesive material used to make weaving easier. Size generally has a high demand for
biological oxygen and significantly contributes at waste effluent. Generally, there are
three methods that are adopted for desizing. They are acid desizing, oxidative
desizing, and enzyme desizing. Desizing techniques are tending to hydrolyze the
starch. However, synthetic starches are differing from natural starches that remain
intact during desizing process. It can be retrieved and recycled (Kavitha et al. 2020).
The characteristics of textile wastewater depend on the sizes used in the desizing
process. Normally, the total BOD and total solids load of textile wastewater seem to
be high. Far from the desizing stage, almost 50% of the total BOD in fabric treatment
is derived when starch is used as a size (Araújo et al. 2008).
Scouring Natural fibers have impurities, such as oils, fats, waxes, minerals, leafy
matter, and motes, that mess during dyeing and printing. During the scouring,
detergents, soaps, and other supporting agents, such as alkaline solutions, surfactants, defoamers, and emollients, are exploited (Rahman Bhuiyan et al. 2016).
Scouring effluents have been characterized as high concentrations of BOD and
COD, high temperatures (70
C–80
C), pH value as high as 10–12, enriched with
sodium cations, and small quantities of TDS. Dyeing effluents have elevated temperature, excessive concentrations of solids, high COD, alkaline pH, and a considerable proportion of augmented sodium ions (Unido 1992).
Bleaching It is a process to remove the natural coloring matter by using calcium
hypochlorite, sodium hypochlorite, and hydrogen peroxide. The bleaching unit
effluents have low level of BOD. However, the nonvolatile constituents present in
the wastewater were observed to be high (Tzanov et al. 2001).
Mercerizing In this process, fabrics are permeated with concentrated sodium
hydroxide solution aimed to attain enhanced luster, strength, and dye affinity to
fabrics. A cold sodium hydroxide solution is applied, which enables the fibers to
swell and follow a circular cross section. Most mercerization units have their own
caustic recovery platform to ensure the waste minimization. Wastewaters from
mercerized unit is characterized as typically low BOD and enriched with suspended
solids (Orhon et al. 2001).
2.2 Coloration Process
The dyeing unit in the textile industries has a great impact for polluting the water
bodies and surrounding environment. Dye(s) plays a vital role in adding value,
beauty, and satisfying the customer’s anticipation. In the dying unit, the use of
synthetic dye(s) is found to be increased rapidly due to its cost-effectiveness and
10 A Harmless Approach on Textile Effluent Detoxification: Bioremediation and. . .
199
meet the coloring and finishing stage specifications.
Desizing It is a process to treat the fabric for hydrolyzing the excess starch, using
synthetic detergents and sodium hydroxide and/or acids or enzymes. “Size” is an
adhesive material used to make weaving easier. Size generally has a high demand for
biological oxygen and significantly contributes at waste effluent. Generally, there are
three methods that are adopted for desizing. They are acid desizing, oxidative
desizing, and enzyme desizing. Desizing techniques are tending to hydrolyze the
starch. However, synthetic starches are differing from natural starches that remain
intact during desizing process. It can be retrieved and recycled (Kavitha et al. 2020).
The characteristics of textile wastewater depend on the sizes used in the desizing
process. Normally, the total BOD and total solids load of textile wastewater seem to
be high. Far from the desizing stage, almost 50% of the total BOD in fabric treatment
is derived when starch is used as a size (Araújo et al. 2008).
Scouring Natural fibers have impurities, such as oils, fats, waxes, minerals, leafy
matter, and motes, that mess during dyeing and printing. During the scouring,
detergents, soaps, and other supporting agents, such as alkaline solutions, surfactants, defoamers, and emollients, are exploited (Rahman Bhuiyan et al. 2016).
Scouring effluents have been characterized as high concentrations of BOD and
COD, high temperatures (70
C–80
C), pH value as high as 10–12, enriched with
sodium cations, and small quantities of TDS. Dyeing effluents have elevated temperature, excessive concentrations of solids, high COD, alkaline pH, and a considerable proportion of augmented sodium ions (Unido 1992).
Bleaching It is a process to remove the natural coloring matter by using calcium
hypochlorite, sodium hypochlorite, and hydrogen peroxide. The bleaching unit
effluents have low level of BOD. However, the nonvolatile constituents present in
the wastewater were observed to be high (Tzanov et al. 2001).
Mercerizing In this process, fabrics are permeated with concentrated sodium
hydroxide solution aimed to attain enhanced luster, strength, and dye affinity to
fabrics. A cold sodium hydroxide solution is applied, which enables the fibers to
swell and follow a circular cross section. Most mercerization units have their own
caustic recovery platform to ensure the waste minimization. Wastewaters from
mercerized unit is characterized as typically low BOD and enriched with suspended
solids (Orhon et al. 2001).
2.2 Coloration Process
The dyeing unit in the textile industries has a great impact for polluting the water
bodies and surrounding environment. Dye(s) plays a vital role in adding value,
beauty, and satisfying the customer’s anticipation. In the dying unit, the use of
synthetic dye(s) is found to be increased rapidly due to its cost-effectiveness and
10 A Harmless Approach on Textile Effluent Detoxification: Bioremediation and. . .
199