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A BREAKTHROUGH IN COLOR TREATMENT OF TEXTILE DYEING WASTEWATER & INDUSTRIAL WASHING

Vietnam's garment industry is one of the key economic industries that attracts many laborers and brings a lot of foreign currency to the country. However, in the value chain of the industry, there are many production stages such as dyeing, printing, completing, industrial washing, discharging large amounts of wastewater, which has great impact to the environment.

SESSIONS OF THE GARMENT AND TEXTILE INDUSTRY

It is estimated that the amount of wastewater discharged from the textile dyeing processes is very large; from 120 to 300m3/ton of fabric, the weaving and dyeing stage requires from 12 to 65 liters of water for 1 meter of fabric and discharges from 10 to 40 liters of water. Textile wastewater is very diverse and complex. According to calculations from the types of chemicals used such as: dyes, surfactants, electrolytes, lozenges, media, starch, enamel, oxidants ...There have been hundreds of typical chemicals such as solutes and heavy metals.

1. Composition and characteristics of textile dyeing wastewater

Wastewater from textile industry includes main pollutants: High temperature, impurities separated from textiles such as grease, nitrogen-containing compounds, pectin, dirt sticking to fibers; chemicals used in technological processes such as starch starch, H2SO4, CH3COOH, NaOH, NaOCl, H2O2, Na2CO3, ... dyes, auxiliaries, soak, colorant, detergent. The amount of chemicals used depends on the type of fabric, color and mainly goes to the wastewater of the manufacturing stage.

1.1 Pollutants and wastewater characteristics of textile and dye industry

 

Stage

Pollutants in wastewater

Characteristics of wastewater

Sizing and desizing

Starch, glucozo, carboxymethyl cellulose, polyvinyl alcohol, plastic, fat and wax

High BOD

Boiling, discoloration

NaOH, wax and grease, ash, soda, sodium silicate and shredded fibers

High alkalinity, dark color, high BOD

White bleaching

Hipoclorite, chlorine compounds, NaOH, AOX, acids, etc

High alkalinity, accounting for 5% of BOD

Polishing

NaOH, impurities

High alkalinity, low BOD

Dyeing

The main dyes include reconstituted dyes, dispersants, active substances, direct agents, acids, cations, acids and metal salts.

High color, high BOD (6% of total BOD), high TSS

Printing

Pigments, starch, oil, clay, metal salts, acids, etc.

High color, high BOD and grease

Completing

Starch, animal fat, salt

Mild alkali, low BOD, small amount

Industrial washing

Regular washing or Denim washing

High color, low BOD

   (Source: Wastewater treatment technology using biological methods - Assoc. Prof. PhD. Luong Duc Pham)

1.2 Wastewater characteristics of some dyeing factories in Vietnam

 

Parameter

Unit

Woven cotton products

Knitwear products

Woolen textiles

Fiber

Wastewater

m3/t. of textile

394

264

114

236

Ph

-

8 – 11

9 – 10

9

9 – 11

TSS

mg/l

400 – 1000

950 – 1380

420

800 – 1300

BOD5

mg/l

70 – 135

90 – 220

120 – 130

90 – 130

COD

mg/l

150 – 380

230 – 500

400 – 450

210 -230

Color

Pt - Co

250 – 600

250 - 500

260 - 300

-

                                                  (Source: Faculty of Environment - Hanoi University of Science, 2004)

1.3 The composition of dyeing wastewater is presented in the following table:

 

Indicator

Unit

Result

Activated substance wastewater

Sulfur wastewater

Bleaching wastewater

pH

-

11-Oct

>11

>12

COD

mg/l

450 – 1.500

10.000 – 40.000

9.000 – 30.000

BOD5

mg/l

200 – 800

2.000 – 10.000

4.000 – 17.000

Total N

mg/l

5 – 15

100 – 1.000

200 – 1.000

Total P

mg/l

0.7 – 3

7 – 30

10 – 30

SS

mg/l

-

-

-

Color

Pt-Co

7.000 – 50.000

10.000 – 50.000

500 – 2.000

Turbidity

FAU

140 – 1.500

8.000 – 200.000

1.000 – 5.000

                                   (Source: Faculty of Environment - Ho Chi Minh City University of Technology)

Basically, textile-dyeing wastewater often has high temperature, high level of color, pH> 9, high BOD and COD. On the other hand, wastewater from textile industry contains some chemicals with heavy metals, toxic components that not only destroys aquatic organisms but also has negative and direct impact on human life.

Current technology of textile wastewater treatment

2. Wastewater treatment technology of textile and dyeing industry is currently applying common technologies:

• Combination of chemical-physical method (coagulation / flocculation) and filtration;

• Combination of chemical-physical method and aerobic biological treatment or vice versa;

• Combination of chemical-physical method, aerobic biological and chemical-physical treatment;

• Combination of chemical-physical method, biological treatment and filtration (sand filter or activated carbon)

Diagram of the current technological process of textile dyeing wastewater treatment:

In general, the traditional technologies currently applied to the textile wastewater treatment still have many difficulties for businesses, for example:

• Using chemicals mainly can eliminates dispersed colors only, more complex color components such as reactivation and reconstitution are often impossible to be removed.

• When using many chemicals, operating costs will be very high, it is especially difficult to quantify chemicals for flocculation steps, or Fenton due to production by order, color composition and pollution concentration of wastewater often fluctuates according to orders.

• Microbiological systems are often large, requiring a lot of space

NGO with breakthrough solution to color treatment

• Eliminates above 95% of all colors, including activated color, no use of flocculating or decolorizing chemicals, less produced sludge.

• Color treatment efficiency is independent of the microbiology and weather fluctuations

• Results are visible on the first day of operation, without waiting

* Color treatment process is extremely simple: Wastewater is firstly collected to the flow equalization basin with aeration, and then pumped onto the Decoloring Device by electrolytic oxidation; at this step, metal ions and electrons are generated, creating redox reactions to break down the emulsion, destroy colloids and suspended solids. Fe ++ or Al ++ ions are released from the electrode, creating stable flocculants to remove most of the color in wastewater by flotation or gravity deposition or mechanical filtration, leaving the clear water be discharged or pumped into the next treatment facility. In particular, the contaminated components including heavy metals, grease and most of the COD are also removed at the same time of color treatment.

3. Practical case studies in Vietnam

Mores: Wastewater treatment of textile and dyeing industry video:  https://www.youtube.com/watch

If your business is interested in solution to inlet water treatment, or has a demand for ion exchange materials, please contact NGO via phone number (024) 3566 8225 or email office@8ngo.com for direct consultation.

Source: NGO

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