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1. Sustainability of vat and Sulphur dyeing
1. Improved Sustainability of Cotton Sulfur Dyeing by Pad-Ox Processes
Abstract:
Sulfur dyeing of cotton textiles is widely practiced in textile industry for producing inexpensive black,
navy, brown, olive, and green shades in medium to heavy depths. As a part of sulfur dyeing process,
intensive rinsing is carried out to remove unfixed dyes after dyeing. The unfixed dyes produce high
sulfide content and hence undesirable levels of oxygen demands to the effluent. Clariant Ltd.
introduced eco-sustainable processes for sulfur dyeing, generally known as padox, using Diresul RDT
sulfur dyes. This chapter presents a study on comparing effluent quality, ultimate color yield and
colorfastness, and cost of pad-ox dyeing methods with the conventional pad-steam dyeing. The
study showed that the pad-ox processes produce reduced oxygen demands of effluent with higher
color yield and acceptable colorfastness. Interestingly, a review on water and energy consumption
showed that pad-ox dyeings are cheaper than the conventional dyeing.
Introduction:
Sulphur dyes are the most economical dyes ever introduce. They are widely used in the textile
industry for dyeing cotton to produce inexpensive black, navy, brown, olive, and green shades in
medium to heavy depth. There are many methods to apply the Sulphur dyes to cotton but the Pad-
ox method is more sustainable and less expensive method because 100% dyes are applicable and
less cost of energy is used. This method also give better results than the other methods.
Methods
Clariant-recommended methods were adopted. All fabrics were dyed to a heavy color depth of 120
g/l. Concentrations of dyeing auxiliaries are given in Table 1.
Pad-Steam Dyeing
Fabric samples were padded in dyeing solution (70% liquor pick-up, ambient tem- perature, Rapid P-
B1 horizontal padder), steamed (wet-temperature of 101–102○
C, 100% moisture, 60 s, Rapid H-TS-3
laboratory steamer), rinsed as per Table 2, oxidized (70○
C, 60 s), rinsed (60○
C, 180 s), soaped (90○
C,
180 s), rinsed (60○
C, 180 s), hydro-extracted (Haier HWS60-40 spin dryer), and finally dried (ambient
air). Rinsings, oxidation, and soaping were carried out on a Rapid HT dyeing machine.

2. Table 1 Concentrations of dyeing auxiliaries
Concentration (g/l)
Auxiliaries Pad-steamPad-ox Pad-dry-ox Pad-steam-
ox
Padding solution
Reducer RDT 25 15 15 15
Sodium hydroxide 50% 20 15 15 15
Penetrant EH 2 3 3 6
Landiquest1097N – 3 3 3
Sirrix AK liquid 2 – – –
Sodium hydrosulfite 2 – – –
Oxidation solution
Diresul oxidant BRI 6 25 25 25
Acetic acid 80% 4 25 25 25
Indosol E-50 – 23 23 23
Leveler F – 5 5 5
Sodium sulfate – 30 30 30
Soaping solution
Sirrix AK liquid 2 – – –
Sodium carbonate 2 – – –
Table 2 Initial rinsing
conditions after
steaming
Pad-Ox Dyeing
Fabric samples were padded (60○
C), subjected to ambient airing (60 s), oxidized (75○
C, pH of 4–4.5,
60 s), rinsed (75○
C, 180 s), hydro-extracted, and finally dried (ambient air).
Black Brown and navy
Rinsing
steps
Temperature
(○
C)
Time
(s)
Temperature
(○
C)
Time
(s)
1 50 60 40 60
2 60 60 50 60
3 70 60 60 60

3. Pad-Dry-Ox Dyeing
Fabric samples were padded (60○
C), dried (100○
C, 60 s, Thermostatic GZX-GF- 101 drying box),
oxidized (75○
C, pH of 4–4.5, 60 s), rinsed (75○
C, 180 s), hydro- extracted, and finally dried (ambient
air).
Pad-Steam-Ox Dyeing
Fabric samples were padded (60○
C), steamed (wet-temperature of 101–102○
C, 100% moisture, 60 s),
oxidized (75○
C, pH of 4–4.5, 60 s), rinsed (75○
C, 180 s), hydro-extracted, and finally dried (ambient
air).
Testing of different samples by different method and comparison
Colorfastness
As given in Table 3, pad-ox and pad-dry-ox produced less rubbing fastness than pad-steam. This may
be because fabric is subjected to dry air after padding, which results in poorer rubbing fastness. Pad-
steam-ox produced similar rubbing.
Table 4 Effluent
testing
results
Process COD (ppm) BOD (ppm)
Pad-steam 134 63
Pad-ox 114 53
Pad-dry-ox 108 48
Pad-steam-ox 119 51

4. fastness to pad-steam. Colorfastness to washing and to light produced by the new processes is
generally similar to that produced by pad-steam process. In fact, pad- dry-ox and pad-steam-ox
produced slightly better washing and light fastness.
Effluent Quality
Effluent testing results for black are given in Table 4. Note the new processes provide a 10–18%
reduction in COD and 15–23% in BOD. The pad-dry-ox gave better reduction in oxygen demands
among the three new processes. These are encouraging results for ecological benefit and may be for
economic benefit in terms of costs of effluent purification or load-based penalties on more polluted
effluent.
The new processes still produce certain levels of COD and BOD. This is because of the use of
conventional reduction and oxidation chemicals. A considerable reduction in the level of oxygen
demands may be expected by utilizing ecology alternatives for reduction and oxidation treatments in
pad-ox processes.
Thecoloryield,colorfastness,andeffluentqualityconclusionscouldbeusefulfor the selection of a
new process having known the need of a customer or the end use.
Water and Energy Consumption
Water consumption has a considerable influence on the economy of any process. Two rinsings and
soaping steps are eliminated in the new processes if compared with pad-steam process. Therefore,
the new processes save around 90% of the amount of water consumed in conventional dyeing.
Further, the energy consumption in terms of power and steam is minimized. The cost on soaping
chemicals is also saved. The pad-ox is cheaper than pad-dry-ox and pad-steam-ox because drying
and steaming consume a significant amount of energy.
Conclusion
The new pad-ox processes for dyeing cotton with sulfur dyes are effective for reducing effluent load
and the cost. The processes produced higher color yields and acceptable colorfastness. Pad-ox
processes generally resulted around 15–23% reduction in oxygen demands of the effluent. The
reduced effluent load, around 90% reduction in the amount of water use, considerable reduction in
the amount of energy consumption, and not using soaping chemicals offer a great cost and
sustainability advantage to dye-houses. Further, it is expected that more reduction in the effluent
load can be obtained if pad-ox processes are carried out using eco- sustainable chemicals for
reduction and oxidation treatments.
2. Sustainable dyeing of denim using indigo dye recovered with PVDF ultrafiltration
membranes
Introduction
Indigo is one of the most consumed dyes in the textile sector, as it is widely used for the
dyeing of denim clothes. About 15% of indigo used in the dyeing process is discharged to
the wastewater treatment plants or sometimes into rivers, in countries where regulations
are not strictly applied.In this work, real effluents that contained indigo dye were treated
by means of 4 different ultrafil- tration membranes. The feasibility to recover the

5. concentrated dye with lab and semi-industrial pilots was also investigated. The studied
membranes achieved up to 99% colour removal and 80% chemical oxygen demand (COD)
decrease. Finally, the concentrates containing 20 g L—1
of indigo dye were reused in new
dyeing processes. Colour differences (DECMC) and rubbing and washing fastnesses were
evaluated. Fabrics dyed with the recovered indigo concentrates exhibited similar
characteristics than the ones obtained with the commercial dye.
Treatment steps
Pretreatment of effluent
Three industrial effluents supplied by the denim yarn factory “Tejidos Royo”
(Alcudia de Crespins, Valencia, Spain) were selected to be treated. They were collected from the
first washing tank, after the dyeing process, and correspond to different type of fibres and
production periods.The effluents used for the lab tests were preserved in a ther- mostated
room at 20 ○C. Before the membrane treatment, samples were pre-filtered (pore diameter 500
mm) in order to remove the higher size particles and fibres. The concentration of indigo was
immediately determined before and after the ultrafiltration.
Ultrafiltration module
In this work, four hollow fibre membranes were selected to carry out the
indigo dye recovery tests:ZeeWeed-1 (GE Power & Water, Canada), UOF-1b (Motimo
Membrane Technology, China), UOF-4 (Motimo Membrane Technology, China) and FP-
T0008 (Motimo Membrane Technology, China), referred herein after as ZW-1, U-1b, U-4 and
FP-T,respectively. InTable 1 are described the main characteristics of these membranes.
Three pilot plants were built to position the different membrane modules, according to their
geometry and specific requirements.
Pilot 1 (Fig. 1) was equipped with U-1b membrane. It was fed by a 100 L tank. Peristaltic
pumps were used for feed, permeate, and concentrate effluents. Pilot 2 operated in cycles
of 15 min of filtration and 30 s of backwashing with permeate.
Pilot 2 (Fig. 2) was designed to be equipped with ZW-1 module. The membrane reactor was a 20
L cylindrical vessel. It was fed from a 20 L tank by a centrifugal pump. A peristaltic pump was
used for the permeate effluent. The membrane module had an air inlet with the purpose to
decrease the fouling. This pilot also operated in cycles of 15 min of filtration and 30 s of
backwashing with permeate.
Pilot 3 (Fig. 3) was a semi-industrial system designed to place two membrane modules. The first
one was the U-4 membrane able to concentrating up to 3 g L—1
. The volume of feeding tank was
1000 L. The concentrate obtained was then applied as a feed to FP-T module which volume was
100 L. In this way, the indigo was concentrated until 20 g L—1
. U-4 membrane operated in cycles
of 30 min of filtration and 30 s of backwashing with permeate and FP- T membrane worked in
cycles of 15 min of filtration and 30 s of backwashing.
Finally, after each filtration process, membranes were cleaned with a sodium dithionite
alkaline solution (pH 11), followed by rinsing with a sodium hypochlorite solution (5 mg L—
1
).

6. Table 1
Membranes characteristics.
Membra
ne
Configurati
on
Pore size
(mm)
Membrane area
(m2
)
U-1b External 0.04 0.5
ZW-1 Submerged 0.04 0.05
U-4 External 0.03 40
FP-T Submerged 0.1 1
Results of pretreated water and percentage of dye:

7. The efficiency of the membrane process in the recovery of indigo dye from textile effluents was
determined by means of permeate characterization. Permeate samples were taken and
analysed daily. It can be seen in Fig. 4 that 96% dye removal was achieved. This result confirmed
the almost full retention of the dye in the concentrate, which indicated the high efficiency of
the ultrafiltra- tion membranes in the recovery of indigo dye. In addition, the COD removal was
about 40%, increasing at the end of the experiment. A layer of dye was formed on the
membrane surface, which acted as a barrier and increased the process efficiency. The increase
of colour and COD removal along the treatment has also been reported by different authors
(Alventosa-deLara et al., 2014; Aouni et al., 2011; He et al., 2008; Kim et al., 2005).
Fig. 4. Dye and COD removal with U-1b me 1
There are two commonly used membrane:
Pilot 2 with ZW-1 membrane
Semi-industrial system
Permeate use
Although the aim of this work was the indigo dye reuse, it is important to highlight the quality
of the permeate obtained after the membrane treatment (Table 5).
Both membranes provided permeates with similar characteris- tics: very low dye concentration
(<2 mg L—1
) and low organic matter content (<250 mg L—1
). According to the mill experience
(Tejidos Royo), these values enable to reuse the effluent in a new indigo dyeing process directly
or partially diluted.
Permeate reuse is an important challenge. It is estimated that the annual consumption of fresh
water in the textile industry at the Eu- ropean level is 600 million m3
(Vajnhandl and Valh, 2014).
Regarding the denim industry, Chico et al. (2013) reported that about 3000 m3
of water is needed
per trouser from fibre production stage to fabric production. Despite the clear benefits of water
reuse, its imple- mentation is still not a common practice in the textile sector.
Conclusions
Indigo dye from wastewater can be successfully removed by means of PVDF ultrafiltration
membranes.
Among the studied membranes, the external hollow fibre module (U-1b membrane) was able to
treat wastewater containing indigo dye and it enabled to concentrate the dye up to 3 g L—1
.

8. Higher concentration was discarded due to the fouling on the membrane surface. This
concentration is acceptable when the effluent is directly reused. The U-1b membrane allowed
obtain a permeate free of dye (96% dye removal) and a 40% COD reduction. According to the
results, the submersible hollow fibre module (ZW-1 membrane) enabled to obtain a
concentrate with 20 g L—1
indigo dye, which is the required concentration for automated dyeing
processes. In addition, the permeate characterization showed 99% dye retention and 80% COD
reduction.
The study in semi-industrial system showed that the combination of external and submerged
PVDF membranes was able to treat wastewater that contained indigo dye. The COD and dye
removal obtained was 67 and 98% respectively.
Finally, the study of indigo dye reuse carried out with the concentrate obtained in both
submersible hollow fibre module and semi-industrial system, showed the feasibility of the
membrane technology to recover indigo dye. The dyeing made with recovered dye exhibited similar
characteristics than dyeing with commercial dye.
Similar we also recover the vat dyes and Sulphur dyes.
3. Direct reduction of vat dyes without use of chemical with electrochemical method
Introduction:
Until now, in most industrial vat dyeing processes, vat dyes are reduced mainly
using sodium dithionite. This process produces large amounts of sodium sulphate
and sulphite as by-products which increase the costs for waste water treatment.
Hence, many attempts are being made to replace the environmentally unfavourable
sodium dithionite by ecologically more attractive alternatives, such as organic
reducing agents or catalytic hydrogenation. In recent investi- gations to improve the
biocompatibility of the vatting process even further, various electrochemical
reducing methods have been described, such as indirect electrochemical reduction
employing a redox mediator, direct electrochemical reduction of indigo via the
indigo radical, electrocatalytic hydrogenation and direct electrochemical reduction
of indigo itself on graphite. These methods offer tremendous environmental
benefits, since they minimize the consumption of chemicals as well as effluent load.
However, most of these electrochemical processes are still in the development
stage. This gives an overview of the processes most commonly used and the state
of development of recent electro- chemical innovations. There are different
techniques:
Vat process with an ultrasonic reactor
Catalytic hydrogenation—pre-reduced dye
Electrochemical techniques
Mediator-enhanced electrochemical reduction
Direct electrochemical reduction of indigo via the indigo radical
Direct electrochemical reduction of indigo on graphite electrodes
Stabilization or regeneration of dithionite by electrolysis

9. electrolytic hydrogenation of indigo 1
Mechanism of the direct electrochemical 1
4. Employing a biochemical protecting group for a sustainable indigo dyeing strategy
Indigo is an ancient dye uniquely capable of producing the signature tonesin in blue denim; however,
the dyeing process requires chemical steps that are environmentally damaging. We describe a
sustainable dyeing strategy that not only circus vent the use of toxic reagents for indigo chemical
synthesis but also removes the need for a reducing agent for dye solubilization. The strategy utilizes
a glucose moiety as a biochemical protecting group to stabilize the reactive indigo precursor indoxyl
to indicane, preventing spontaneous oxidation to crystalline indigo during microbial fermentation.
Application of a b-glucosidase removes the protecting group from indicane resulting in indigo crystal
formation in cotton fibers. We identified the gene coding for the glucosyltransferase PtUGT1 from
indigo plant Polygonum tinctorium and solved the structure of PtUGT1. Heterologous expression of
PtUGT1 in Escherichia coli supported high indicane conversion and biosynthesized indican was used
to dye the cotton.

10. 5. Electrochemical Degradation of C.I. Vat Orange 2 Dye on Carbon Electrode
The electrochemical degradation of industrial wastewater has become an attractive method in
recent years. In this work simulated dye wastewater containing vat dye C.I. Vat Orange 2 is degraded
from electrochemical method using graphite carbon electrodes. The experimental results indicated
that initial pH, current density and supporting electrolytes were played an important role in the
degradation of dye. Electrochemical behavior of dye has been studied with cyclic voltammetry in
basic medium using glassy carbon as working electrode. The potentials selected for the dye was in
the range-0.4 to-1.2 V. The UV-Vis and chemical oxygen demand (COD) studies were selected to
evaluate the degradation efficiency. The maximum colour removal efficiency of 99.24% and chemical
oxygen demand (COD) removal of 72.26% could be achieved for dye, at 25 g L-1 of NaCl
concentration. The LC-MS and FTIR studies revealed the degradation of dye and confirmed that
aromatic rings were destroyed. The results revealed the suitability of the present process for the
effective degradation of dye C.I. Vat Orange 2.
There are other many articles I have studied on the sustainability of vat dyeing some are related. The
above all data I have studied from journals, articles and books. I explain some articles more because
it crucial for explanation.