Department of Textile Engineering Management (43rd Batch), Bangladesh University of Textiles
ABSTRACT
Sustainable technologies have gained much greater attention in every production sector due to their special features and eco-friendly approach. Textile sectors are no exception to these features. That is why environment-friendly technology more specifically termed sustainable technology has become a promising candidate for textile production. Conventional technologies for textile production have been prevalent in the world since ancient times and they have the same principle in every part of textile production, such as dyeing. Minimizing power consumption, use of water, production costs and reducing the amount and the pollutant content of waste-water are complex problems that cannot be solved by the conventional dyeing methods. An attractive approach to tackle environmental problems associated with dyeing is ecofriendly and sustainable production methods. This project emphasizes about sustainable dyeing process and pollution free environment.
OBJECTIVES
The main objectives of this project are:
To evaluate current system of dyeing used in the textile sector.
To find out the more sustainable dyeing process (Best Available Techniques-BAT) by which we can attain sustainability in dyeing process.
INTRODUCTION
Textiles constitute an important part of human being’s everyday life. Environmentalists have been calling for the industries to incorporate sustainability principles into their production processes. In comparison with other processes, dyeing is considered to be major contributor towards environmental pollution and is subject to creating various ecological. It is the foremost process in terms of the waste discharged volume and the composition of the wastewater.
Textile dyeing processes require large volumes of fresh water, gas, electricity, other natural resources and discharge large volumes of effluent which are generally with intense color, toxic chemical, high concentration of organic compounds and are responsible for various forms of environmental pollution.
Sustainable dyeing process is important in order to efficient use of resources, reduction of waste, and related costs. There are several reference documents that are suggesting techniques to analyze and modify the dyeing process to decrease the consumption of water and energy resulting in the reduction of the pollution.
BACKGROUND
The main damages caused by the dyeing industry to the environment, however, are those resulting from the discharge of untreated effluents into the water bodies. In the composition of most of the residual waters of the dyeing industry there are relatively high levels of biochemical oxygen demand and chemical oxygen demand [1]. Due to this nuisance, our hands are forced to use technologies which will be of help in becoming efficient in using scarce resources like water & electricity. The greater emphasis should be attributed to the large amount of non-biodegradable organic compounds, especially textile dyes [2]. The dyes are soluble organic compounds, especially those classified as reactive, direct, and basic and acids. They exhibit high solubility in water making it difficult to remove them by conventional methods [3]. The color associated with textile dyes causes aesthetic damage to the water bodies.
Hence to get rid of the harmful consequences of dyeing and achieve sustainability, we must establish the usage of modern technologies which are proved to be commercially efficient and ecofriendly.
Figure 1. Total
water consumption during wet processing of textile industry
1. LITERATURE REVIEW
1.1 Supercritical CO2 dyeing
Supercritical fluids have special properties that could lead to substantial improvements when utilized as replacements for water in wet processing of textiles. These fluids have densities and solvating powers similar to liquid solvents combined with viscosity values and diffusion coefficients like those observed for gases. In particular, these properties make supercritical carbon dioxide (SC-CO2) one of the most beneficial and environmentally acceptable solvents used in manufacturing processes today. Therefore, it is anticipated that commercial textile processes using SC-CO2 will have many advantages when compared to conventional aqueous processes [4]
1.2 Sustainable textile dyeing processes
Textile effluents are characterized by high chemical oxygen demand, biological oxygen demand, total dissolved solids, pH and color. Fabric preparation steps, such as desizing, scouring, bleaching and mercerizing, use various chemicals and plenty of water. The occurrence of unfixed dyes and other electrolytes in effluents poses serious threats to the environment. Available end-of-pipe treatment procedures are either expensive or not efficient; hence, a large number of small-scale industries succumb to this problem. So, finding an alternative eco-friendly process of textile production is of paramount interest. Here, we review three potential eco-friendly systems applicable to textile dyeing processes to minimize salt and water consumption. [5]
1.3 Dyeing of textiles with use of Supercritical CO2
Supercritical CO2 dyeing methods are a promising technology. It has temperature controllers and a heated stainless steel container with a monometer and a strong cooler. This machine can hold capacity pressure of 350 bars and under 100 °C. Disperse dyes can be fed into the machine along with supercritical CO2 fluid prior to combination with the goods, whereas in conventional dyeing the opposite is the case. In this method, the dyes have a very good diffusion property, which results in high evenness on the surface as well as in the interior structure of the fabric or fiber material. The residual dye can be extracted prior to the dyeing process and collected for reuse. Generally, color strength is exponentially dependent on the dye concentration; this trend is similar in the case of supercritical CO2 dyeing methods. Temperature is another parameter that plays a vital role in dyeing with respect to dye diffusion, followed by color strength. It is evident that a higher temperature can improve dye adsorption because there is greater freedom of molecule movement at a higher temperature. [6]
1.4 Natural colorants for ecofriendly process
The Use of natural colorants, without any harmful effects on environment and aquatic ecosystem, and with more developed functionalities simultaneously. Advanced developments for the natural bio-resources and their sustainable use for multifunctional clothing are gaining pace now. [7]
2. METHODOLOGY
This research paid high attention on sustainable solution to dyeing process in textile sector. We collected factory machine data then analysis and compare with the conventional machine data. Suggested more sustainable advance dyeing technologies. We also surveyed about the adaptabilities of these new technologies with dyeing professionals and discussed about the limitations of the new technology adaptation.
2.1 Sample size
In our research sphere, we mainly collected data from two machines of dyeing.
Name:
Then a survey was created to gather data directly from dyeing professionals working in reputed textile industries and to help alleviate the lack of sustainable dyeing processes in the dyeing section of textile industry. About 30 respondents have been reached out for data collections from various textile industries.
2.2 Data collection
This section provided working definitions and assumption related in the study, followed by detailed descriptions of the data collection methods which were used. The information and data collected were scrutinized and properly arranged so that further study and analysis could be performed. By visiting factory and following up dyeing process of two different machines we managed to get data. Then we also collected data through questionnaire using google form. We contacted with dyeing professionals working in reputed textile industries though social media such as Facebook, WhatsApp and LinkedIn etc. and collect their responses on sustainable issues. The project tried to find out the comparison between conventional machines & the current machines being used for dyeing and the lacking of current dyeing technologies. Then we discussed the latest dyeing machines which can bring out the solutions to the shortcomings of the present situation. The purpose was to evaluate the current state of dyeing technologies and discuss about new updated sustainable technologies and their limitations.
2.3 Research Process
Firstly we collected information from Knit Concern Group dyeing section. Here we acquired data from two dyeing machines where fabric was being dyed.
First machine that we follow-up was low temperature environmental dyeing machine in which cotton fabric was being dyed with reactive dyes.
Second one is high temperature dyeing machine in which cotton-polyester blend fabric was being dyed with disperse and reactive dyes.
Table 1. Specifications of the low temperature environmental dyeing machine
Machine Type
Environmental
Capacity
1200 kg
Cycle Time
3 Min
No. of Cycle
12
Power
400 V / 50 Hz
Design Temperature
98 °C
Design Pressure
1 Bar
Nozzle
4N
In this environmental low temperature machine we follow-up dyeing process of cotton fabric. Where 450 kg knit fabric (cotton) was dyed at 60°C -80°C temperature.
Figure 2. FONG’S
Dyeing Machine
Table 2.Specifications of the high temperature dyeing machine
Machine Type
High Temperature
Capacity
1800 kg
Cycle Time
3 Min
No. of Cycle
12
Power
400 V / 50 Hz
Design Temperature
140°C
Design Pressure
3 Bar
Nozzle
6N
In this high temperature machine, we follow-up dyeing process of 500 kg PC fabric. Where polyester part was dyed at 130°C temperature and cotton part is dyeing at 60°C -80°C temperature. But it has been needed to drain the liquor of disperse dye after polyester part dyeing. Then in new liquor cotton part is dyeing by using reactive dye.
From observing these dyeing process of knit fabric of 450 kg and 500 kg in these two machines mentioned above, where the liquor ratio being used was M:L=1:8, we gathered information about the consumption of electricity, water, steam, chemical wastage etc.
We run our survey on dyeing floor engineer to get information about sustainability. We did try to the best of our capabilities to collect valuable responses from engineers working on dyeing executives working in reputed textile companies & gather their professional perspective on using sustainable dyeing technologies.
2.4 Research Approach
3. ANALYSIS
3.1 Process findings from Knit Concern’s machines
In knit concern Ltd. we observed the high temperature dyeing machines working on low temperature dyeing machine getting used on 450 kg 100% cotton knit fabric & 500 kg cotton-polyester blend knit fabric. The collected data is given below in the tables.
Water consumption
Table 3. Dyeing process water consumption
Name
Low temperature
(environmental) dyeing machine
High temperature
dyeing machine
Total water
consumption for dyeing
16035 L
28200 L
Water
consumption per kg
35.63 L
56.4 L
From the table given above , we get to see the water consumption of high temperature dyeing machine is 28200 L for whole dyeing process ( 56.4 L per kg of fabric ) whereas the water consumption of low temperature ( environmental ) dyeing machine is 16035 L for complete dyeing process ( 36.63 L per kg of fabric ). It can be concluded that the low temperature (environmental) dyeing machine is proved to be a water saving technology compared to the high temperature dyeing machine.
Electricity consumption
Table 4. Dyeing process electricity consumption
Name
Low temperature (environmental) dyeing machine
High temperature dyeing machine
Total electricity consumption for dyeing
185 KWh
420KWh
Electricity consumption per kg
0.41 KWh
0.84 KWh
From the table given above, we get to see the electricity consumption of high temperature dyeing machine is 420 KW-h for whole dyeing process 0.84 KW-h per kg of fabric) whereas the electricity consumption of low temperature (environmental) dyeing machine is 185 KW-h for complete dyeing process (0.41 KW-h per kg of fabric). We can jump to the conclusion that the low temperature (environmental) dyeing machine is proved to be an electricity saving technology compared to the high temperature dyeing machine.
Time consumption
Table 5. Dyeing process time consumption
Name
Low temperature (environmental) dyeing machine
High temperature dyeing machine
Total time consumption for dyeing
370 min
525 min
Time consumption per kg
0.82 min
0.95 min
From the table given above, we get to see the time consumption of high temperature dyeing machine is 525 min for whole dyeing process (0.95 min per kg of fabric) whereas the time consumption of low temperature (environmental) dyeing machine is 370 min for complete dyeing process (0.82 min per kg of fabric). We can reach to the conclusion that the low temperature (environmental) dyeing machine is proved to be a time saving technology compared to the high temperature dyeing machine.
3.2 Conventional machine data
Table 6. Conventional (Low Temp) machine dyeing process water, electricity & time consumption
Conventional dyeing machine (Low Temp)
For 450kg 100% cotton knit fabric
Water
28080 L
62.4 L/kg
Electricity
270 KWh
0.6 KWh/kg
Time
475 min
1.05 min/kg
From the table given above, we get to see the of conventional (Low Temp) dyeing machine for 450kg 100% cotton knit fabric. Where per kilogram water consumption is 62.4 L, electricity consumption is 0.6 KWh & time consumption is 1.05 min.
Table 7. Conventional (High Temp) machine dyeing process water, electricity & time consumption
Conventional dyeing machine (High Temp)
For 500 kg cotton-polyester blend knit fabric
Water
32053.5 L
71.23 L/kg
Electricity
490 KWh
0.98 KWh/kg
Time
597 min
1.19 min/kg
From the table given above, we get to see the water, electricity & time consumption of Conventional (High Temp) dyeing machine for 500 kg cotton-polyester blend knit fabric. Where per kilogram water consumption is 71.23 L, electricity consumption is 0.98 KWh & time consumption is 1.19 min.
3.3 Comparative analysis between conventional and Knit Concern’s dyeing machine
For 450kg 100% cotton knit fabric:
The table below is to show the comparative analysis of collected data between conventional dyeing machine & low temperature (environmental) dyeing machine for 450 kg (100% cotton knit fabric) in respect of water, electricity & time consumption.
Table 8. Conventional machine VS Knit Concern dyeing machine
Consumption
Conventional dyeing machine
Low temperature (environmental) dyeing machine
Water
62.4 L/kg
36.63 L/kg
Electricity
0.6 KWh/kg
0.41 KWh
Time
1.05 min/kg
0.82 min/kg
For 500 kg cotton-polyester blend knit fabric:
The table below is to show the comparative analysis of collected data between conventional dyeing machine & high temperature dyeing machine for 500 kg (cotton polyester blend knit fabric) in respect of water, electricity & time consumption.
Table 9. Conventional machine VS Knit Concern dyeing machine
Consumption
Conventional dyeing machine
High temperature dyeing machine
Water
71.23 L/kg
56.4 L/kg
Electricity
0.98 KWh/kg
0.84 KWh
Time
1.19 min/kg
0.95 min/kg
By Comparative analysis between conventional and Knit Concern dyeing machine we have found dyeing machines of knit concern Ltd to be less electricity and water consuming and time efficient compared to the conventional dyeing machines.
3.4 Survey results analysis
3.4.1 Personal Characteristics of the Participants
We collected our survey responses from engineers who currently work on dyeing section of different reputed textile industries.
3.4.2 Questionnaires and Response analysis
Q1. Do you think dyeing technologies used in Bangladesh are sustainable enough?
Response:
Overwhelming percentage of dyeing professionals are firm in their belief that the machines that are being used in dyeing industries at present are neither enough sustainable nor eco-friendly.
Q2. Do the machines that are used currently in dyeing section help reducing uses of water, power & chemicals satisfactorily than the conventional machines?
Response:
Majority of the professionals are convinced that the recent technologies dedicated in dyeing are not enough power efficient & they also doubt the capabilities of these machines being ecofriendly.
Q3. Why are we still far behind in adopting new technologies like waterless dyeing?
Response:
Majority of dyeing engineer thinks that we are still far behind in adopting new technologies like waterless dyeing because of companies focus more on profit without considering damage done on environment. Because of the high competitiveness of RMG Sector here is so less chance to test new technologies and further it is also hard to invest big money.
Q4. Can we see more improved sustainable dyeing machines like Supercritical CO2 or Air dyeing technologies in Bangladesh near future?
Response:
Nearly all of the learned engineers are in agreement with the harsh reality that no matter how dire the need of latest technologies (super critical co2 & air dyeing) is, it still is a pipe dream & far from becoming a reality simply because of the installation cost of those machines being too high & unaffordable. On the other hand, there are a few optimistic executives who believe, hope is there at the end of the tunnel & latest dyeing technologies being used in the industry will become a real scenario in near future.
Q5. Keeping in mind the benefits like saving water and energy usage in dyeing, do the upgraded sustainable technologies properly justified with the astronomical initial cost of installment?
Response:
Though a negligible percent of dyeing engineer thinks that the companies don’t want investment much higher amount in new technologies but majority of them think that company emphasize more on profit. The high competitiveness in Bangladesh RMG sector plays a vital role in this matter.
Q6. Do you think that harmful chemical based dyeing can be fully substituted by natural and harmless dyeing technologies?
Response:
Almost every engineers stationed in dyeing are optimistic about removing the usage of harmful chemicals & dyeing technologies completely & establish the sustainable technologies which are considered green & also shy in chemical discharge into natural water bodies.
Q7. Does the effluent treatment plant be our only defense against the harmful effects of dyeing process which responsible for destroying Mother Nature?
Response:
The effluent treatment plant being important as it is, still far for being the sole defense against the destructive consequences of harmful dye chemicals released in the natural water resources. Sustainable dyeing technologies is something which can be proven beneficial to solving the ecological disaster due to dyeing sector.
Q8. Is it possible to reuse the wastewater of dyeing after treatment?
Response:
The professionals believe that the reuse of wastewater in dyeing is a risky move but with proper & thorough treatment of wastewater it is very much a possibility & considered an admirable step towards being sustainable.
4. DISCUSSION
In the past, winch machines were used to dye knitted fabrics, with a material to liquor ratio of 1:20. Now, a new range of dyeing machines is available with lower M:L ratio 1:4-8. In soft flow dyeing machines, the fabrics are circulated using the liquor, which needs some amount of liquor. In Knit Concern air flow dyeing machines are used which resemble soft flow dyeing machines, with the difference being that the fabrics are circulated using an air stream instead of the water or dye liquor used in the case of soft flow dyeing, thereby reducing the water consumption. Multi nozzle air flow dyeing machines offer higher productivity and drastically reduce the material to liquor ratio.
These air flow dyeing machines perform more sustainably than conventional machines because of:
Flexible method to transport fabrics using air which able to process fabric weights ranging between 50 and 800 g per square meter.
Extremely low material to liquor ratio of 1:2 for MMF and 1:3–1:4 for natural fibers.
Energy saved when compared with conventional soft flow dyeing machines.
Reduced process time.
Though dyeing machines used in knit concern Ltd have got technical edge in some aspects compared to the conventional dyeing machines, still there is a long way to go to become fully sustainable maintaining efficiency.
4.1 Solutions to achieve sustainability with new technologies
Now-a-days there are many dyeing technologies which are proved to be more sustainable than these machines. Where the uses of water and energy is very low compared to the currently used machines. Among them air dyeing technology & super critical CO2 dyeing are of the most prominent ones.
Table 10. Important features of the Supercritical CO2 and Air-dyeing process
Main power source
Supercritical carbon dioxide
process
Air-dye process
Working Condition
High pressure and temperature are
required
dyeing liquor is first atomized,
then mixed with high-pressure airflow, finally sprayed on fabric to be dyed
Synthetic and natural dye
The technology developed and optimized for the dyeing of polyester, acetate and nylon while some experimental study on natural fibers available
The technique works on synthetic
materials. Dyeing in cotton fabrics with specialized treatment to the raw
cotton is reported.
Speed and efficiency
Due to the favorable diffusion
properties, the times needed for the dissolution of the solid dyestuff will be cut to a negligible minimum
Coloring and printing can be done
in a short time with full accuracy and efficiency. A reduction in the overall
process time of approximately 25 percent.
Colorfastness
Good Colorfastness
Good Colorfastness
Water and energy use
CO₂ dyeing is a dry process, eliminating the need to evaporate water. Technology is very energy efficient.
Use 90 to 95% less water and save
86% of the energy
Reuse
CO2 can be
vacuumed out after use, allowing for 95%recovery and reuse
Air-dye recycles paper used in
the process and the dyes are inert, which can go back to their original state
and be reused
Environmental sustainability
Ecologically harmless, non-toxic
and non-explosive. A green method for the sustainable and eco-friendly
textile industry.
Causes minimum harm to the
environment and reduces the industry’s share of global
warming by 84%
Installation cost
Expensive
Expensive
4.2 Limitations of Supercritical CO2 and Air-dyeing process in Bangladesh
The limitation of this revolutionary technology is that it can only be used at synthetic fibers. The textile industries of Bangladesh are heavily depended on cotton. Bangladesh is one of the leading countries in importing cotton. On the other hand production of synthetic based product is very rare compared to the cotton. So utilizing the air dye technique vastly in context of our country is impossible unless a developed method has been introduced for cotton based textile materials.
As the installation cost of waterless dyeing machines are astonishing compared to the ones those used in dyeing industry at present, it remains cost prohibitive for the likes of our country which is very much depending on the production of low price RMG products rather than value added items.
CONCLUSION
Sustainability in textile industry has become an extensively debated issue due to the nature of the industry. Textile is considered globally as one of the most hazardous both to environment and society if not operated in a controlled way. Unfortunately, in Bangladesh textile industries still has a huge scope of improvement. Without being sustainable the survival of the textile industries is becoming difficult. The first reason behind the current situation of the industries is the lack of knowledge on the concept of sustainability, budget limitation on investment in new technologies.
In total, the global textile industry does not operate environmentally friendly and sustainably right now. However, there are numerous starting points to improve the sustainability. Small & medium enterprises dominate our textile industry having strict budget constraint. That’s why investing a big chunk of money in upgrading the dyeing machines at once to attain sustainability is a bit too far-fetched dream for entrepreneurs or businesses to pursue.
Furthermore, wet procedures use up a lot of water, energy, and chemicals, all of which are expensive to separate out during treatment. In the project study we have suggested cleaner production approaches in place of the end-of-pipe approach. In this research, we conducted analysis of the dyeing method that has the potential to win the war against industrial pollution while still being economically and commercially sensible. The procedures and methods covered above are the only path to a secure and safe future is through the use of sustainable textile production methods.
REFERENCES
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[2] A. d. R. J. M. J. B. F. C. F. Orts, “Electrochemical treatment of real textile wastewater: Trichromy Procion HEXL®,” Journal of Electroanalytical Chemistry, vol. 808, pp. 387-394, 2018.
[3] B. &. F.-P. C. &. P. J. &. P. J. Lellis, “Effects of textile dyes on health and the environment and bioremediation potential of living organisms,” Biotechnology Research and Innovation, vol. 3, p. 2, 2019.
[4] W. HENDRIX, “Progress in Supercritical CO2 Dyeing,” Journal of Industrial Textiles , vol. 31, pp. 43-56, 2001.
[5] L. Lara, I. Cabral and J. Cunha, “Ecological Approaches to Textile Dyeing,” vol. 14, p. 8353, 2022.
[6] B. (. S. C.-d. A. D. o. T. A. E. B. W. D. P. Agrawal, “Supercritical Carbon-dioxide Assisted Dyeing of Textiles,” An Environmental Benign Waterless Dyeing Process, 2015.
[7] M. S. M. &. M. Yusuf, “Natural Colorants: Historical, Processing and Sustainable Prospects,” Nat. Prod. Bioprospect, vol. 7, pp. 123-145, 2017.
APPENDIX
Questionnaires used for data collection:
Designation and company name?
Do you think dyeing technologies used in Bangladesh are sustainable enough?
Do the machines that are used currently in dyeing section help reducing uses of water, power & chemicals satisfactorily than the conventional machines?
Can we see more improved sustainable dyeing machines like Supercritical CO2 or Air dyeing technologies in Bangladesh near future?
Why are we still far behind in adopting new technologies like waterless dyeing?
Keeping in mind the benefits like saving water and energy usage in dyeing, do the upgraded sustainable technologies properly justified with the astronomical initial cost of installment?
Do you think that harmful chemical based dyeing can be fully substituted by natural and harmless dyeing technologies?
Does the effluent treatment plant be our only defense against the harmful effects of dyeing process which responsible for destroying Mother Nature?
