Methods for Wastewater Treatment in Textile Dyeing Industry

Textile Dyeing Wastewater Treatment Methods

Md. Didarul Islam1 & Md. Rafiul Monim2
Dept. of Textile Engineering,
BGMEA University of Fashion and Technology (BUFT)
Email: didarul.buft@gmail.com1 & rafiulbuft@gmail.com2

 

Introduction:
The textile dyeing industry consumes large quantities of water and produces large volumes of wastewater from different steps in the dyeing and finishing processes. Wastewater from printing and dyeing units is often rich in color, containing residues of reactive dyes and chemicals such as complex components, many aerosols, high chroma, high COD (Chemical Oxygen Demand) and BOD (Biochemical Oxygen Demand) concentration as well as much more hard-degradation materials.

The toxic effects of dyestuffs and other organic compounds, as well as acidic and alkaline contaminants, from industrial establishments on the general public are widely accepted. At present, the dyes are mainly aromatic and heterocyclic compounds, with color-display groups and polar groups. In this review, we will discuss different methods of textile dyeing wastewater treatment.

Dyeing Process in Textile Industry:
In the textile dyeing industry, bleaching is an important process. It has three technologies; sodium hypochlorite bleaching; hydrogen peroxide bleaching and sodium chlorite bleaching. Sodium hypochlorite bleaching and sodium chlorite bleaching are the most commonly used processes. Normal concentration of chlorine dioxide in bleaching effluent is 10-200 mg/L. And it is a strong oxidant, which is very corrosive and toxic as well.

Let’s know about dye chemical on variety fiber:

Fiber The commonly used dyes
Cellulose fiber Direct dyes, Reactive dyes, Vat dyes, Sulfide dyes, Azo dyes
Wool Acid dyes
Silk Direct dyes, Acid dyes
Polyester Azo dyes, Disperse dyes

Methods for Wastewater Treatment in Textile Dyeing Industry:
A large number of complex components are present in the textile dyeing wastewater with high organic, color-related and changing characteristics. The wastewater created by dyeing cotton with reactive dyes has been badly contaminated due to their high BOD/COD, coloration and salt load. Few technologies are usually highly efficient for the textile dyeing wastewater treatment. Here we will describe three methods of textile dyeing wastewater treatment.

textile dyeing wastewater treatment plant
Fig: Textile dyeing wastewater treatment plant

1. Physicochemical wastewater treatment

a. Floatation: The floatation produces a large number of micro-bubbles in order to form the three-phase substances of water, gas, and solid. Dissolved air under pressure may be added to cause the formation of tiny bubbles which will attach to particles. Under the effect of interfacial tension, buoyancy of bubble rising, hydrostatic pressure and variety of other forces, the microbubble adheres to the tiny fibers. Due to its low density, the mixtures float to the surface so that the oil particles are separated from the water. As a result, this method can effectively remove the fibers in wastewater.

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b. Coagulation flocculation sedimentation: Coagulation flocculation sedimentation is one of the most used methods, especially in the conventional treatment process. Active on suspended matter, colloidal type of very small size, their electrical charge gives repulsion and prevent their aggregation. Adding in water electrolytic products such as aluminum sulphate, ferric sulphate, ferric chloride, giving hydrolysable metallic ions or organic hydrolysable polymers (polyelectrolyte) can eliminate the surface electrical charges of the colloids. This effect is named coagulation. Normally the colloids bring negative charge, so the coagulants are usually inorganic or organic cationic coagulants (with positive charge in water).

c. Adsorption: It is the most used method in physicochemical wastewater treatment, which can mix the wastewater and the porous material powder or granules, such as activated carbon and clay, or let the wastewater through its filter bed composed of granular materials. Through this method, pollutants in the wastewater are adsorbed and removed on the surface of the porous material or filter.

2. Chemical oxidation water treatment:

a. Fenton reaction: It is mainly used as a pre-treatment for wastewater resistant to biological treatment or/and toxic to biomass. The reaction is exothermic and should take place at temperature higher than ambient. In large scale plants, however, the reaction is commonly carried out at ambient temperature using a large excess of iron as well as hydrogen peroxide. In such conditions ions do not act as catalyst and the great amount of total COD removed has to be mainly ascribed to the Fe(OH)3 co-precipitation.

b. Ozone oxidation: It is a very effective and fast decolorizing treatment, which can easily break the double bonds present in most of the dyes. it can improve the biodegradability of those effluents which contain a high fraction of nonbiodegradable and toxic components.

Full scale applications are growing in number, mainly as final polishing treatment, generally requiring up-stream treatments such as at least filtration to reduce the suspended solids contents and improve the efficiency of decolorizations. Sodium hypochlorite has been widely used in the past as oxidizing agent. In textile effluent it initiates and accelerates azo bond cleavage. The negative effect is the release of carcinogenic aromatic amines and otherwise toxic molecules and, therefore, it should not be used

3. Biological wastewater treatment method:

a. Oxidation ditch process: It is a variant of activated sludge, which is a special form of extended aeration. The oxidation ditch is generally consisted of the ditch body, aeration equipment, equipment of the water in or out, diversion and mixing equipment. The shape of the ditch body is usually ring; it also can be rectangular, L-shaped, round or other shape. The side shape of the oxidation ditch generally is rectangular or trapezoidal. Since oxidation ditch has long hydraulic retention time (HRT), low organic loading and long sludge age, compared to conventional activated sludge process, the equalization tank, primary sedimentation tank, sludge digestion tank can be omitted.

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b. Anaerobic biological treatment process: It is a method that make use of the anaerobic bacteria decompose organic matter in anaerobic conditions. This method was first used for sludge digestion. The anaerobic-aerobic treatment process is usually adopted in actual project that is using anaerobic treatment to treat high concentration wastewater, and using aerobic treatment to treat low concentration wastewater.

Currently, the hydrolysis acidification process is the main anaerobic treatment process, which can increase the biodegradability of the sewage to facilitate the following biological treatment process.

Conclusion:
At present, wastewater from textile dyeing is one of the most significant sources of pollution. The form of this waste water has higher color value, BOD and COD characteristics, complex structure, broad emissions, widely dispersed and difficult degradation characteristics. If discharged immediately without being treated, the natural ecosystem would be severely impaired.

Prevention and treatment of wastewater contamination by dyeing is complementary. We may use both preventive measures and a range of approaches for waste management and the use of filtered water. This not only reduces the use of water, but also significantly reduces the emissions of waste water from printing and dyeing and achieves a sustainable development of society.

References:

  1. Characterization and Treatment of Textile Wastewater By Himanshu Patel and R.T. Vashi
  2. P. Hauser, in Advances in treating textile effluent , 2011.
  3. Handbook of Textile Effluent Remediation By Mohd Yusuf
  4. A. S. Ponnusamy Senthil Kumar, “Sustainable wastewater treatments in textile sector,” Sciencedirect, 2017.
  5. S. K. M. M. Praveen Kr. Navin, Textile Wastewater Treatment: A Critical Review, IJERT, 2018.

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