Safest and most effective textile dyeing wastewater treatment 2022

Treatment of textile dyeing wastewater is extremely necessary and urgent. The garment is a strategic spearhead of the economic industry, attracting a lot of physical resources and human resources to serve. Significantly improve our country's unemployment (accounting for 10.3% of the existing labor force).

However, this is also an industry that generates a huge amount of wastewater and sludge. Wastewater is extremely difficult to treat with a variety of chemicals, in most stages such as dyeing, printing, washing, and packaging. Without effective safe treatment methods and systems, the environment will be severely affected.

hệ thống xử lý nước thải dệt nhuộm
A textile wastewater treatment system

In this article, let's analyze and analyze the remaining problems of textile dyeing wastewater treatment.

What is wastewater, textile dyeing sludge? Ingredients and properties

When manufactured, textile chemicals are mainly composed of auxiliaries, macromolecular compounds, polymers, and heavy metals. The direct discharge will destroy ecosystems, environmental landscapes, and health. According to experts, wastewater, and textile dyeing sludge is one of the most polluting substances throughout the history of human industrial development.

Wastewater, textile dyeing sludge often contains impurities such as grease, nitrogen-containing dissolved substances, and dirt. Each fabric production process (sizing, bleaching, bleaching, polishing, dyeing, printing, and finishing) releases a large number of chemicals, dye solutions, bleach, etc. source of this industrial waste.

Wastewater, textile dyeing sludge with extremely high BOD, and COD will affect aquatic life, and even change the genetic structure of organisms in the water, thereby causing direct harm to humans when consuming these products. Seafood products.

In addition, starch, Sulfuric Acid ((H2SO4), Acetic Acid (CH3COOH)), Sodium Hydroxide (NaOH), Sodium Hypochlorite (NaOCl), Hydrogen Peroxide (H2O2),... are present in dyes, inserts, and stimulants. Colorants, bleaches, and intensifiers are extremely toxic with only a small residue.

Pollutants from textile manufacturing processes

Production stage Pollutants in wastewater, textile dyeing sludge Characteristics of wastewater
Sizing, gluing Glucozo, starch, carboxymethyl cellulose, polyvinyl alcohol, resin, fat, wax, alcohol, etc. High BOD (34 – 50 total BOD)
Cooking, bleaching NaOH, waxes, grease, ash, soda, sodium silicate shredded yarn High alkalinity, high BOD, dark color
Bleaching Hypochlorite, compounds containing chlorine, NaOH, AOX, acids, etc. High alkalinity, low BOD (accounting for 5% of total BOD)
Polishing NaOH, impurities High alkalinity, low BOD (Below 1% of total BOD)
Dyeing The main dyes include reconstituted, reactive, dispersed, direct dyes, acids, cations, metal salts, etc. High coloration, high BOD (6% of total BOD), high SS
Printing Colorants, starches, oils, clays, metal salts, acids, etc. High color, high BOD, grease
Finishing Starch streaks, animal fats mild alkaline salts, low BOD, small waist
Industrial washing General washing, denim High color, low BOD

Table of indicators of initial wastewater properties

Targets Unit Result
Domestic wastewater Sulfide wastewater Detergent wastewater
pH 10 – 11 > 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 – 30.000
N Total mg/l 5 – 15 100 – 1.000 200 – 1.000
P total mg/l 0.7 – 3 7 – 30 10 – 30
SS (Suspended Substance) 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

In addition, chemicals released from different processes and fabrics will be different. For example, raw wool and cotton materials will have high color, alkalinity, suspension, and BOD. With synthetic fiber materials, chemicals in the bleaching and dyeing stages are the cause of pollution. Therefore, it is necessary to have advanced textile dyeing wastewater treatment technologies to minimize these pollution indicators.

Textile dyeing wastewater treatment technology

Textile dyeing wastewater treatment technology helps to remove toxic components in wastewater such as temperature, pH, suspended solids, COD, BOD5, heavy metals, etc. in ponds, lakes, rivers, and streams, minimizing the impact on the environment.

sơ đồ xử lý nước thải dệt nhuộm
Current popular textile dyeing wastewater treatment scheme

Current textile dyeing wastewater treatment technology

  • Physical and chemical combination (flocculation, flocculation), filtration (Pre-treatment or primary treatment).
  • Combination of physicochemical and aerobic biology (Basic treatment or secondary treatment).
  • Combination of physicochemical and aerobic physicochemical biology (Basic treatment or secondary treatment).
  • Combination of Physico-chemical, biological, and filtration (sand filter or activated carbon) (Additional treatment or tertiary treatment).
xử lý hóa lý kết hợp xử lý sinh học
physicochemical treatment combined with biological treatment (Source: Vietnam Environment Administration)

Finally, the sludge will be passed through the sludge dewatering to remove excess water, for easier and more economical transportation and treatment.

  • For the raw materials used in the production process, which are Polyester and blended fibers (combining Cotton and Polyester), the flocculation/flocculation process is usually applied before the biological process. Biological can be anaerobic UASB or EGSB, aerobic can be activated sludge suspended or attached.
  • The tertiary treatment includes: flocculation/flocculation and sterilization; filtration (sand filter and activated carbon) and sterilization; enhanced oxidation (ozone or Fenton) and pH correction to neutral. The tertiary treatment process is applied to thoroughly treat the remaining pollutants in the wastewater or reuse it.
  • For the raw material source is Cotton, the reverse treatment technology for the raw materials is Polyester and blended fibers is a biological process before the physicochemical process. The third stage of treatment is applied: filtration (sand filter and activated carbon). calculation) and sterilization; enhanced oxidation (ozone or Fenton) and pH correction to neutral.

Advantages of textile dyeing wastewater treatment technology

  1. The process of wastewater treatment technology is easy and easy to operate.
  2. Biogas generated from the system can be recovered.
  3. Generates highly active sludge.
  4. Waste water after being treated meets the standards to be put into the receiving source.
  5. With advanced sludge, the sludge is pressed dry, tight, and low in moisture.

Disadvantages of textile dyeing wastewater treatment technology

  1. In-depth training of workers is required to operate.
  2. It takes a lot of space to create sludge and is difficult to control the sludge process.
  3. Space-consuming to treat textile dyeing wastewater.
  4. Textile dyeing wastewater treatment system

Technological process of textile dyeing wastewater treatment system

The technological process of the textile dyeing wastewater treatment system includes the following stages:

1. Collection tank

Wastewater sources, when passing through the drainage system, will be blocked by the garbage screen of the collection tank and retain solid waste and metal fragments. In addition, this physical process also helps to reduce the suspended matter by 5% and the COD index by 5%. Wastewater that has just entered the collection tank often has a high temperature, so before moving on to the next stage, people will use a cooling tower so that the water temperature is only about 40 degrees Celsius.

Song chắn rác xử lý nước thải dệt nhuộm
Garbage barrier

The collection tank is also known as Stage I treatment. This stage is usually divided into pre-treatment of wastewater and preliminary treatment of wastewater. Mostly to remove coarse and hard impurities, floating and heavy objects (sand, stones, gravel, etc.), grease, etc. to protect pumps, pipelines, etc.

The equipment of this treatment stage is usually: Song, garbage screen, possibly with crusher and shredder, sand settler, conditioning tank, neutralization tank, flotation and sedimentation 1, adsorption filter with activated carbon count.

2. Air conditioning tank

The tank has the function of regulating the flow of water and the concentration of pollution in the wastewater. Here, nutrients such as N and P are added to the tank in the ratio of BOD:N:P = 100:5:1 to buffer the biodegradation process at a later stage.

Bể điều hòa xử lý dệt nhuộm
A conditioning tank in the wastewater treatment system (source: internet)

The bottom of the tank is equipped with an aeration system to mix the additives with the wastewater faster and more evenly. After that, the wastewater will be pumped into the reaction tank and carry out the flocculation - flocculation process.

3. Coagulation tank – flocculation

bể keo tụ tạo bông bùn
flotation tank (flocculation) – source: Internet

Coagulation chemicals such as PAC aluminum alum, and polymer will be added to the wastewater to form larger-sized flocs and adhere, under the action of gravity, the flocs will settle into the tank, thereby creating sludge.

This is considered the heart of the wastewater treatment system. Mainly physicochemical, chemical, mechanical, or combined processes are applied. At this stage, most of the pollutants in the wastewater will be treated.

Chemical and physical treatment is one of the most common methods in industrial wastewater treatment. The Physico-chemical treatment stage can be a stand-alone treatment stage or a combined treatment with mechanical, biological, and chemical treatment in a full wastewater treatment technology line.

Chemical and physical methods are commonly used 

The physicochemical methods commonly used to treat textile dyeing wastewater include coagulation, flotation, adsorption, extraction, and ion exchange.

  • Coagulation is the process of gluing colloidal particles contained in wastewater due to thermal movement, due to disturbance and the result is from very small colloidal particles to form a larger size and are easy to settle. to the bottom. The coagulants commonly used in wastewater treatment are PAC aluminum alum (Al2(SO4)3.18H2O) and iron alum (FeSO4.7H2O).
  • Flotation is the process of molecular adhesion of dirt particles to the dividing surface of two phases: gas - water and forming a mixture of "solid particles - air bubbles" that rise to the surface of the water and then is removed. Go.
  • Adsorption is the process of attracting or concentrating impurities in wastewater to the surface of the adsorbent. Common adsorbents in wastewater treatment technology include activated carbon, bone coal, activated soil (bentonite), silica gel, and synthetic resin capable of ion exchange. Used for adsorption: Detergents, dyes, chlorinated compounds, phenol or hydroxyl derivatives, odor and taste compounds, trace pollutants, and heavy metals.
  • Ion exchange is often used to treat heavy metals in wastewater by passing heavy metal-containing wastewater through a cation exchange resin column, where the metal cations are replaced by hydrogen ions (or Na+) exchange.

Biological method of textile dyeing wastewater treatment

Wastewater often has different pH values, to be well treated by biological methods, it is necessary to adjust the pH to 6.6 - 7.6.

Wastewater with high acidity or high alkalinity should not be discharged into drainage systems and water sources. In textile dyeing factories, the pH of wastewater ranges from 4 to 12, so it is necessary to neutralize it to create an optimal pH for the flocculation process. Chemicals used to neutralize acidic wastewaters are caustic soda or lime. In textile and dyeing factories to neutralize acidic and alkaline wastewater, people often mix these types of wastewater.

4. Anaerobic methods

Based on the metabolism of organic matter in the absence of oxygen thanks to many anaerobic microorganisms existing in wastewater. The products of the process are CH4, CO2, N2 , H2S, NH3, of which CH4 occupies the most.

Anaerobic digestion can be divided into 6 processes

  • Polymer hydrolysis.
  • Fermentation of sugars and amino acids.
  • Anaerobic degradation of long-chain fatty acids and alcohols.
  • Anaerobic decomposition of volatile fatty acids (except acetic acid).
  • Formation of methane and acetic acid.
  • Formation of methane and acetic acid.2.

These processes can be combined into four phases occurring simultaneously

  • Hydrolysis: Under the action of enzymes, bacteria secrete complexes and insoluble substances into simpler complexes or soluble substances (such as amino acids, and fatty acids). This process is slow. The rate of hydrolysis depends on pH, particle size, and the degradability of the substrate.
  • Acidification: Fermentative bacteria convert soluble substances into simple substances such as volatile fatty acids, alcohols, lactic acid, methanol, CO2, H2, NH3, H2S and new biomass.
  • Anticipation: Acetic bacteria convert the products of the acidification phase into acetate, H2, CO2 and new biomass.
  • Methanolization: This is the final stage of the anaerobic decomposition of acetic acid, H2, CO2, formic acid, and methanol into methane, CO2, and new biomass.

Anaerobic treatment technology needs to pay attention to important factors

  • Maintain microbial biomass as much as possible.
  • Provide sufficient contact between the microbial biomass and the wastewater.
  • When the above two factors meet the anaerobic treatment works, very high loads can be applied.

5. Anaerobic treatment tank

Anaerobic treatment tank without sludge circulation, suitable for wastewater treatment with a high concentration of easily degradable organic matter or organic sludge treatment. The anaerobic contact process consists of two stages: complete disturbance anaerobic digestion, sedimentation, or separation of the biological residue. The sludge after separation is recirculated back to the anaerobic digester.

The anaerobic contact system can operate at organic loads of 0.5 to 10 kg COD/m3/day with a retention time of 12 hours to 5 days.

The anaerobic filter is a column filled with inert solid material that is a fixed substrate for anaerobic microorganisms living on the surface. That substrate can be stone, gravel, coal, synthetic resin ring, plastic sheet, porcelain ring, etc.

The wastewater stream is evenly distributed, going from the bottom up, in contact with the microbial film adhering to the surface of the substrate. Due to the good adhesion of the biofilm, it leads to an increase in the amount of biomass in the tank and a longer sludge retention time.

6. Textile dyeing wastewater treatment settling tank

Wastewater, after passing through the settling tank to remove suspended matter and floc, will be transferred to an anoxic treatment tank. In the anoxic tank at this time, the process of reducing NO3 to N2 will occur. When Nito will escape. The process is contributed by the bacteria Nitrosomonas and Nitrobacter. Next, the wastewater will be transferred to an aerobic biological tank – MBBR and a biological settling tank.

7. Aerobic biological tank – MBBR

Thanks to the activity of microorganisms, using organic matter and some minerals as food for growth and development. They will reduce the organic matter containing carbon in the wastewater. It is usually expressed as BOD (biochemical oxygen demand, total organic carbon TOC or COD (chemical oxygen demand), reduction of nitrate, phosphorus, etc.

Decomposes easily degradable organic matter into inorganic substances and converts stable organic matter into floc that can be easily removed from the water.

The blower operates continuously to provide oxygen for aerobic bacteria to work. They breathe aerobically and break down organic compounds containing N and P into CO2 and H2O. They proliferate on substrates.

On the substrate, when microorganisms multiply to thicken the biomass layer, the innermost layers will no longer receive oxygen, causing anaerobic bacteria to work. Anaerobic bacteria shed the biomass layer from the substrate, forming a new sludge layer. This process is repeated with a new layer of aerobic microbial biomass until BOD and organic matter are completely decomposed.

Thanks to that, the MBBR biological process is highly efficient. Specifically, BOD reduced 85-95%, Nitrogen decreased 80-85%, and phosphorus decreased 70-75%. After the process is completed, the water will be transferred to the settling tank.

8. Aerobic bio-flocculation tank – Aerotank

The process of transforming matter in the Aerotank when polluted water or wastewater is added is completely due to the living activities of many different microbial species. The microorganisms in the Aerotank tank exist in suspension. The microorganisms in the Aerotank tank tend to settle to the bottom, so the mixing and gas supply in the aero tank is very necessary.

Impact of the air supply system

  • Supply oxygen to microbial cells.
  • Disturb the solution, increasing the contact between microbial cells and matter.
  • Accelerate the reproduction of bacteria.
  • Accelerate the escape of the solution of gases formed during fermentation.
  • Heat release.

Supply oxygen to the aerotank

Gas distribution pipe works
Gas distribution pipe works

To provide oxygen for aerotank people use the following ways: blowing air; compressed air; mechanical ventilation; blowing, compressing air with a mechanical system. When supplying gas to the aerotank, the following points should be noted:

  • Air must be supplied sufficiently and evenly throughout the Aerotek to increase treatment efficiency.
  • Exhaust gas distribution holes are evenly distributed in the air outlet ducts.

Effect of stirring

  • Increases the solubility of oxygen.
  • Increases contact between microorganisms and organic matter in Aerotank.
  • Increases the ability of bacteria to separate two cells during reproduction by the mechanical action of the flow.

Factors affecting

  • The amount of oxygen consumed: must make the dissolved oxygen content not less than 2mg/l.
  • Organic matter concentration.
  • Nutrients: It is necessary to ensure the nutritional elements BOD:N:P = 100:5:1
  • Toxins: phenols, heavy metals, inorganic salts, and NH3.

9. Intermediate tank – Decolorization technology

This tank will aerate continuously so that the wastewater and color compound mix. In particular, people use HANO chemicals to decolorize.

10. Sterilization stage

The pathogenic bacteria will be treated by a strong oxidation method with Chlorine. Chlorine destroys metabolism and kills organism cells. This is also known as the tertiary treatment process with commonly used disinfection methods: water chlorination, ozone, and ultraviolet light. Disinfection with chlorine gas, liquid, and hypochlorites are most commonly used.

In addition, this step may require further improvement of the treated water quality. Reuse or discharge into a high-demand receiving source. The commonly used methods are:

  • Microfiltration or sand filter, membrane filter, etc. to filter in water.
  • Chemical precipitation and coagulation.
  • Adsorption through activated carbon to remove all heavy metals, organics, colors, odors, etc.
  • If the water is still high in nitrogen and phosphorus, it needs to be treated separately.

11. Sludge storage tank and treatment of textile dyeing sludge

bể chứa bùn nhà máy nhuộm
Dye factory sludge storage tank

Textile dyeing waste sludge after recovery will be stored in the sludge tank and dewatered. Sludge is compressed to reduce volume using sludge separators.

Textile dyeing waste sludge can be used as fertilizer for soil and used for leveling. When used as fertilizer, heavy metals need to be treated to allowable levels. In addition, sludge stabilization is required to reduce pathogenic effects, reduce odors, reduce or eliminate the possibility of rotting, and facilitate sludge drying. People often use chlorine and quicklime for this purpose.

Finally, the yard to dry the sludge. The method of drying mud is too outdated, consuming space and time. Nowadays, it is best to use a slurry press.

Sludge dewatering for textile dyeing factory

vận hành máy ép bùn nước thải dệt nhuộm
Operating a decanting centrifuge to treat textile dyeing wastewater

Depending on the advanced level of sludge dewatering used, the moisture content of the discharged sludge will vary. ARK Vietnam is currently manufacturing and distributing modern, high-tech mud presses according to Korean import lines, committed to pressing low-moisture, stable sludge. Sludge dewatering ARK Vietnam is suitable for all types of sludge from many different industries, textile dyeing sludge is no exception.

 

Waste sludge after being mixed with polymer
Waste sludge after being mixed with polymer
nước sau khi tách bùn
The water after separating from the sludge does not have any suspended particles
Sludge is pressed from textile dyeing wastewater
Sludge is pressed from textile dyeing wastewater

The water after being squeezed out is transferred back to the conditioning tank for re-treatment. The dry sludge will be collected by specialized vehicles. The more water is forced out, the smaller the volume of the sludge, the easier and more economical it is to transport.

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