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Potential Wastes from Textile Wet Processing Industries and their Management

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Sk Mohammad Raafi, Research Assistant

Introduction

Increasing global population and elevated living standards have resulted in more demand and consumption of textiles to fulfill one of the basic human needs. Also, the fast fashion trends have led to overconsumption. Because of these, the chemical-intensive textile and clothing industry which is already among the most polluting industries, has been gaining critical concerns regarding the disposal of textile wastes around the globe. Dumping the solid wastes is extremely risky and its thoughtless disposal can cause serious land and air pollution which can be detrimental to human health and environment.

Background

The textile industry is one of the largest industries in the world. The global textile and apparel market is expected to grow at a compound average annual growth rate of 3.7% and to exceed 100 million tons by 2025. This enlargement is leaving pollution footprints and potential environmental problems and hazards in each step of textile life cycle. According to physical characteristics, textile waste can be classified into two main groups, which are wastewater and solid waste.

Characterization of Wet Processing Wastewater

Textile wet processing industries are completely relying on fresh, soft water for pretreatment, coloration and finishing of textiles. Water is used to rinse or remove unwanted chemicals out of the fabric and as a chemical carrier to the fiber. The textile industry is responsible for about 17–20% of industrial water pollution.

Figure 1: Characteristics of Wastewater from Different Wet Processes

Figure 1: Characteristics of Wastewater from Different Wet Processes

To bestow fabrics with multiple benefits like enhanced luster, improved moisture absorption (by 7.5–8.5 %), wet resistance, lint reduction, and dyeing methods capable of creating brighter and deeper colors cellulosic fibers (e.g., cotton, hemp, and linen) can be mercerized after weaving. Despite these benefits, the textile mercerization creates negative environmental impacts because of the use of high concentration of sodium hydroxide (NaOH). About 2,000–3,000 ppm of salt concentrations are found in most cotton fabric production wastewater that significantly exceeds the federal limit of 230 ppm.

Dyeing processes necessitate the use of multiple toxic chemicals (e.g., heavy metals, pigments, ammonia, and alkali salts). Over 40 % of dyeing colorants include a carcinogenic material-bound chlorine, and mordants (color fixer), such as chromium. Additionally, dyeing consumes the largest amount of water in garment manufacturing processes. Presently, the textile mills conduct approximately 3,600 types of textile dyeing procedures using over 8,000 chemicals. The average-sized mills use approx. 0.26 million liters of water to dye 8,000 kg of fabric every day; this means each kilogram of fabric consumes about 30–50 L of water.

Apart from dyeing, traditional textile printing methods contain many non-eco-friendly aspects. For instance, after each printing, approximately 1.5 gallons of printing paste remains in the printing screen, and equipment that must be cleaned with solvents (such as toluene, xylene, and methanol) which uses a great amount of water and electricity. These toxic chemicals pollute water sources when they are drained, often untreated. Moreover, according to US Environmental Protection Agency (EPA), every textile printing line of the textile mills emits annually an average VOC (volatile organic compound) of approximately 14.3 tons for roller and 32 tons for flat and rotary screens. These toxic solvent vapors are released throughout the printing manufacturing areas and cause skin and eye irritations to factory operators.

Major Hazards in the Textile Industry

The hazards happening in the textile industries are classified as mechanical, physical, chemical, ergonomic hazards, and physiological hazards. Textile wet processing industries are mostly associated with chemical hazard. Operators, working in the section of dyeing, printing, and finishing in the textile industry are likewise exposed to chemicals- benzidine, optical brighteners, solvents and fixatives, formaldehyde from wrinkle resistance finish, organophosphorus and organobromine from fire retardants.

 Chemicals in the Textile Wet Processing Industry and their Alternatives

Table 1: Toxic Chemicals in the Textile Wet Processing Industry and their Alternatives

Depending on the level of exposure, dyes can be hazardous. Reactive dye is the most common hazard for respiratory issues because of the inhalation of dye particles. The respiratory indications incorporate watery eyes, sniffling, and manifestations of asthma, for example cough and wheezing.

Pretreatment, dyeing, printing, finishing are also linked with Ergonomic Hazards. This type of hazard deals with the accumulation of workers, improper condition of the machine, despicable ventilation and absence of proficient well-being measures if there should be an occurrence of crises. Carpal passage disorder, epicondylitis, lower arm tendinitis, lower back agony, neck torment, bicapital tendinitis, shoulder torment, and osteoarthritis of the knees are some of the musculoskeletal disarranges that have been seen among the operators because of poor ergonomic conditions.

Managing Water Consumption

Reducing water consumption in textile processing is important for furthering pollution prevention efforts, in part because excess water use dilutes pollutants and adds to the effluent load. A reduction in water use of 10 to 30 percent can be accomplished by taking fairly simple measures like-

  • Repairing leaks, faulty valves etc.
  • Turning off running taps and hoses and water valves when water is not required
  • Turn off water when machines are not running (during breaks and at the end of the process)
  • Reducing the number of process steps
  • Optimizing process water usage (like using batch or stepwise rinsing rather than overflow rinsing, counter-current washing in continuous ranges, and installing automatic shut-off valves).
  • Re-use process water (final rinse water from one process can be used for the first rinse of another process
  • Using water efficient processes and equipment (modern machines operate at lower liquor ratios)

Chemical Management

To successfully manage the chemicals, regulatory awareness and compliance knowledge is necessary. Hazards of each chemicals used in every stage of production have to be assessed. Preferred substances and safer alternatives should be chosen over restricted substances and substances of high concern. It is the best practice to adopt sustainable chemistry for continuous improvement. Some prescribed ways for managing chemical consumption are:

Pathways for Chemical Management

Figure 2: Pathways for Chemical Management

Waste Management

In managing the wastes, some considerations should be made. Firstly, systematic identification and quantification of all chemical wastes is necessary to realize their costs. Then, the hazardous wastes should be classified correctly. For example, according to the European Waste Regulations, sludges from on-site effluent treatment containing dangerous substances are marked as H4, H7, H10, H6 denoting irritant, carcinogenic, repro-toxic and toxic respectively. Setting up a waste action plan is very effective in establishing waste inventories, evaluating the possibility of upcycling and recycling the waste and disposing the hazadous wastes. Working procedures and instructions on the safe handling and emergency response should be readily accessible. Appropriate personal protective equipment must be provided and used in line with MSDS requirements.

Environmental Management of a Facility

Figure 3: Environmental Management of a Facility

A proper waste management plan should be implemented to resist waste generation at source. If waste generation is unavoidable then the potential for recycling or reuse should be explored. Up to a maximum of 30% textile ETP sludge may be reused to manufacture non-structural building materials.

Wastewater Treatment

Wastewater treatment process is an overall water treatment system, comprised of pre-treatment, primary treatment, secondary treatment and tertiary treatment employed to treat the waste/effluent water from industry. In the pretreatment phase, insoluble particles are removed so that they are restricted from reaching treatment zone, which may hinder treatment operation.

Overview of Pre-treatment Possibilities of Waste water

Table 2: Overview of Pre-treatment Possibilities of Waste water

Based on the effluent nature, the primary treatment suspends the total settleable organic and inorganic solids of the liquid waste into coagulant by chemical methods, resulting in floating material (scum) and heavy solids (sludge).

Overview of Primary Treatment Possibilities of Waste water

Table 3: Overview of Primary Treatment Possibilities of Waste water

Secondary treatment mainly employs biological method to cause reduction of chemicals either by aerobic, (with oxygen) or anaerobic, (without oxygen) reactions, which also results in sludge. The main principle of this is, micro-organisms consume organic matter from the wastewater, using oxygen for respiration.In most cases, secondary treatment follows primary treatment and removes biodegradable dissolved and colloidal organic matter using aerobic biological treatment processes.

Overview of Secondary Treatment Possibilities of Waste water

Table 4: Overview of Secondary Treatment Possibilities of Waste water

Tertiary or advanced wastewater treatment may use biological or physical-chemical treatment processes to remove water contaminants that are not removed by primary and secondary treatment, such as colour, nutrients, toxic materials or additional suspended solids and BOD. Thus, it improves the quality of treated water to comply with discharge standards. The treatment may involve a process called disinfection (using chlorine, ozone, UV light in common) for removing any unwanted microbes.

Overview of Tertiary Treatment Possibilities of Waste water

Table 5: Overview of Tertiary Treatment Possibilities of Waste water

As the name suggests, ‘Zero Liquid Discharge (ZLD)’ is an advanced wastewater treatment process in which all wastewater is purified and recycled; and so, leaving zero discharge at the end of the treatment cycle. ZLD method implies ultrafiltration, reverse osmosis, evaporation/crystallization, fractional electrode-ionization etc. for its ultimate success.

 Zero Liquid Discharge (ZLD) System

Figure 4: Zero Liquid Discharge (ZLD) System

Sludge Management

Sludge is a residual semi-solid complex material with heterogeneous toxic substances that is formed as a by-product from effluent treatment plants independent of applied treatment (physio-chemical/ biological/ chemical). The hazardous sludge harms human health and the environment including soil, air and aquatic systems. It could potentially contain high levels of chemicals, and requires proper handling and disposal. Sludge from textile industry mainly belongs to category B and category C. Sludge that is categorized as ‘C’ is extremely hazardous (highly flammable, explosive, oxidizing, poisonous, infectious etc.).

Options for Textile Sludge Management

Figure 5: Options for Textile Sludge Management

Eco-friendly Alternatives to Conventional Manufacturing

To resolve environmental issues created by traditional manufacturing processes, innovative and eco-friendly technologies are being used by many textile companies. These sustainable alternatives include Air Dyeing Technology (ADT), enzymatic one-bath pretreatment, laser bleaching and washing, digital printing etc. Natural dyeing methods are useful to minimize the environmental impacts of dyeing processes, though they require equal to double the amount of dyeing materials (such as wild plants and lichens) and mordant to the fiber weight.

Entrepreneurs, industry owners and concerned all need to be aware of the necessity of adopting environmentally sustainable textile wet processing methods as well as being capable of generating production efficiencies.

References

  1. ‘Sustainable Chemical & Environment Management’ workshop by GIZ- BUTEX
  2. Muthu, S. S. (2017). Sustainability in the Textile Industry.
  3. Pensupa, N., Leu, S. Y., Hu, Y., Du, C., Liu, H., Jing, H., … & Lin, C. S. K. (2017). Recent trends in sustainable textile waste recycling methods: Current situation and future prospects. In Chemistry and Chemical Technologies in Waste Valorization (pp. 189-228). Springer, Cham.
  4. Yalcin-Enis, I., Kucukali-Ozturk, M., & Sezgin, H. (2019). Risks and Management of Textile Waste. In Nanoscience and Biotechnology for Environmental Applications (pp. 29-53). Springer, Cham.
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