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Effluent Treatment Process in Garment Manufacturing

Importance, merits, de-merits, techniques, technologies used in Textile Effluent Treatment Plants (ETP)

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The textile industry is one of the leading sectors in the economy as it contributes to total industrial production. The untreated textile wastewater can cause rapid depletion of dissolved oxygen if it is directly discharged into the surface water sources due to its high BOD value. The effluents with high levels of BOD and COD values are highly toxic to biological life.

The high alkalinity and traces of chromium which is employed in dyes adversely affect the aquatic life and also interfere with the biological treatment processes. The quality of such effluent can be analyzed by their physicochemical and biological analysis. Monitoring of the environmental parameters of the effluent would allow having, at any time, a precise idea on performance evaluation of ETP and if necessary, appropriate measures may be undertaken to prevent adverse impact on the environment. The obtained results will be very much useful in the identification and rectification of operational and maintenance problems and they can be also utilized to establish methods for improvement.

ETP FOR TEXTILE INDUSTRY

Categorization of Waste Generated in Textile Industry:

Textile waste is broadly classified into four categories, each having characteristics that demand different pollution prevention and treatment approaches.

  1. Hard to Treat Wastes

    This category of waste includes those that are persistent, resist treatment, or interfere with the operation of waste treatment facilities. Non-biodegradable organic or inorganic materials are the chief sources of wastes, which contain color, metals, phenols, certain surfactants, toxic organic compounds, pesticides, and phosphates. The chief sources are:

    • Colour & metal à dyeing operation
    • Phosphates à preparatory processes and dyeing
    • Non-biodegradable organic materials à surfactants
    • Since these types of textile wastes are difficult to treat, the identification and elimination of their sources are the best possible ways to tackle the problem. Some of the methods of prevention are chemical or process substitution, process control, optimization recycle/reuse, and better work practices.
  2. Hazardous or Toxic Wastes

    These wastes are a subgroup of hard-to-treat wastes. But, owing to their substantial impact on the environment, they are treated as a separate class. In textiles, hazardous or toxic wastes include metals, chlorinated solvents, non-biodegradable or volatile organic materials. Some of these materials often are used for non-process applications such as machine cleaning.

  3. High Volume Wastes

    The large volume of wastes is sometimes a problem for the textile processing units. The most common large-volume wastes include:

    • The high volume of wastewater
    • Wash water from preparation and continuous dyeing processes and alkaline wastes from preparatory processes
    • Batch dye waste containing large amounts of salt, acid, or alkali
    • These wastes sometimes can be reduced by recycling or reuse as well as by process and equipment modification.
  4. Dispersible Wastes

    The following operations in the textile industry generate highly dispersible waste:

    • The waste stream from continuous operation (e.g. preparatory, dyeing, printing, and finishing)
    • Print paste (printing screen, squeeze and drum cleaning) Lint (preparatory, dyeing and washing operations)
    • Foam from coating operations Solvents from machine cleaning
    • Still bottoms from solvent recovery (dry cleaning operation)
    • Batch dumps of unused processing (finishing mixes)

POLLUTION PROBLEMS IN THE TEXTILE INDUSTRY

Colour

  • The presence of color in the wastewater is one of the main problems in textile
  • Colors are easily visible to human eyes even at very low concentrations. Hence, color from textile wastes carries significant aesthetic
  • Most of the dyes are stable and has no effect of light or oxidizing
  • They are also not easily degradable by the conventional treatment
  • Removal of dyes from the effluent is a major problem in most textile

Dissolved Solids:

  • Dissolved solids contained in the industry effluents are also a critical paremeters
  • The use of common salt and Glauber salt in processes directly increase the total dissolved solids (TDS) level in the effluent.
  • TDS are difficult to be treated with conventional treatment systems
  • Disposal of high TDS bearing effluents can lead to an increase in TDS of groundwater and surface water

Toxic Metals

Wastewater of textiles is not free from metal contents. There are mainly two sources of metals.

  1. The metals may come as impurities with the chemicals used during processing such as caustic soda, sodium carbonate, and salts.
  2. The source of metal could be dyestuffs like metalized mordant dyes. The metal complex dyes are mostly based on chromium

Others

Textile effluents are often contaminated with non-biodegradable organics termed refractory materials.
Detergents are a typical example of such materials. The presence of these chemicals results in high chemical oxygen demand (COD) value of the effluent.

Organic pollutants, which originate from organic compounds of dyestuffs, acids, sizing materials, enzymes, tallow, etc are also found in textile effluent, such impurities are reflected in the analysis of biochemical oxygen demand (BOD) and COD.

PRECONDITIONS AND MEANS FOR RESOLVING THE PROBLEM

For a long time, the toxicity of released wastewater was mainly determined by the detection of biological effects from pollution, high bulks of foam, or intensively colored rivers near textile plants. Today, the identification and classification of wastewater are in accordance with existing municipal regulations. General regulations define the most important substances that are critically controlled by consumers and propose a set of activities that should be applied in order to minimize the amount of released hazardous substances.

The characteristics of textile effluents vary and depend on the type of textile manufactured and the chemicals used. The textile wastewater effluent contains high amounts of agents causing damage to the environment and human health including suspended and dissolved solids, biological oxygen demand (BOD), chemical oxygen demand (COD), chemicals, contain trace metals like Cr, As, Cu, and Zn and Color.

The activities to treat hazardous wastes can range from legal prohibition to cost-saving recycling of chemicals. Depending on the type of product and treatment, these steps can show extreme variability. Effluents treatment plants are the most widely accepted approaches towards achieving environmental safety. But, unfortunately, no single treatment methodology is suitable or universally adaptable for any kind of effluent treatment. Therefore, the treatment of waste stream is done by various methods, which include physical, chemical, and biological treatment depending on pollution load. Our aim is to adopt technologies giving minimum or zero environmental pollution.

During the last 50-75 years, there have been ever-increasing efforts to somehow arrange manufacturing processes in such a way that they cause minimal damage to the environment. At the same time, these efforts are aimed at developing appropriate technologies for wastewater treatment and establishing an adequate relationship between regulators and industry. To decrease the quantity of generated wastewaters it is necessary applying of a systematic approach to reducing the generation of waste at the source. In other words, this approach prevents the creation of wastewaters in the first place, rather than treating it once it has been produced by end-of-pipe treatment methods.

Action plan to minimize the present problems associated with the wastewater released from textile plant
Action plan to minimize the present problems associated with the wastewater released from a textile plant

 

This is a technique that should be applied to all inputs and outputs of a production process. Once waste minimization has been carried out in the factory, effluent will still be produced that will require some form of treatment prior to disposal to sewage, river, or sea. Reducing the quantities of generated wastewater is important because it contributes to reducing operating costs, the risk of liability, and the need to treat the effluents with end-of-pipe methods. It also helps to increase the efficiency of production processes, environmental protection and health, increasing awareness, and raising the morale of employees.

Treatment of Textile Effluents

Typically, textile effluent would involve the following steps

  • Reactive dye concentrates can be treated in a conventional anaerobic digester
  • Exposure to the biomass to achieve de‐colorization and tolerance of the microorganisms to concentrations of the dye
  • Additional carbon source( eg. glucose) is necessary to maintain the microbial metabolic state
  • The presence of Nitrate in the system inhibits de‐colorization
  • Adsorption of the dye to the biomass also causes de‐colorization
  • The degradation products of the dye after anaerobic digestion may be isolated and identified
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