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
Indicator	Unit	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: Textile 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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