- 1 1. Consumption and discharge of water in the Textile Industry
- 1.1 1.2. Typical composition of wastewater from the Textile Industry
- 2 2. Treatment and reuse of wastewater from the Textile Industry
- 2.1 2.1 Pre-treatment, physical-chemical: colour, solids and fats removal
- 2.2 2.2. Biological treatment: organic matter removal
- 2.3 2.3. Tertiary treatment: intensive color and recalcitrant organic compounds removal for water reuse.
- 3 3. SIGMA Case Studies in the Textile Industry
- 3.1 3.1. Wastewater treatment and reuse from the Textile Industry: DAF Technology. Case of ACAPERSA.
- 4 3.2. Wastewater treatment and reuse from the Textile Industry: BIOLOGICAL TREATMENT, DAF Technology and TERTIARY TREATMENT. Case of COLORTEX.
- 5 4. References
1. Consumption and discharge of water in the Textile Industry
The Textile Industry is one of the industries that consumes more water, between 80 and 150 litres per kilogram of processed fabric, which varies according to the nature of the material. The amount of water used in the manufacture of clothes varies according to the type of fibres (cotton, wool, nylon, polyester, etc.) and the machinery used in each of the processes.
It is also one of the industries that emits the most contaminating liquid waste given the large amount of reagents that it applies in the stages of its process, being mostly non-biodegradable and persistent in the environment, especially the aqueous environment.
The pigments used are highly polluting agents since they are manufactured to offer great resistance to biological degradation and great durability. In the manufacturing process, up to 200,000 tons of pigments and colorants can be lost per year if the water is not efficiently treated.
In recent decades, it is not only the treatment of wastewater that is interested in complying with the increasingly severe discharge restrictions, but also new technologies are designed and installed for the reuse of water and recovery of dyes to guarantee the sustainability of the industry. This is possible thanks to an efficient and intelligent design of the treatment process and the selection of the most robust technologies for water in this industry.
The objective of the treatment for reuse is to re-incorporate water in the textile manufacturing processes (washing, dyeing, heat treatment), in addition to allocating it to cleaning, plant toilets, irrigation of green areas, etc. which means the reduction of operating costs.
Wastewater from the Textile Industry is characterized and composed mainly of:
- Great variability of flow and pollutant load of each of the process lines.
- Colour.
- Biodegradable and non-biodegradable or “refractory” organic compounds
- Non-biodegradable inorganic compounds (reagents and additives added during the process): heavy metals, dyes, phenols, pesticides, surfactants, etc.
- Oils and fats.
- Total suspended solids (TSS).
- • Chemical oxygen demand (COD).
- • Biological oxygen demand (BOD5).
- • High levels of total dissolved solids (TDS).
- • Generally deficient in nutrients (nitrogen and phosphorus).
- • Virtually free of pathogens.
- • High content of chlorine and salinity
Dyes are considered the most polluting elements since they have a great impact on the environment: they reduce oxygen in water bodies by blocking light causing septic conditions, they are also mutagenic and carcinogenic agents for animals and humans and toxic for plants as they inhibit photosynthesis. High levels of TDS cause an increase in salinity, altering the natural pH of the water.
1.2. Typical composition of wastewater from the Textile Industry
Textile production has various stages in its production process, each one of them discharges wastewater with specific characteristics, however, in order to treat all the wastewater emissions of an industry, the wastewater from all process lines are homogenized.
The characteristics of the wastewater will depend on the type of fibres worked, the process stages applied and the machinery.
The most common stages and the contamination characteristics of the residual water of each one are collected in the following table:
Table 1. Characteristics of the water discharged in each of the stages. Generally, a homogenization is carried out to treat all the effluents together
Stage | Characteristics | pH | Dissolved solids (mg/L) | Suspended solids (mg/L) | Colour | BOD5 (mg/L) | COD (mg/L) | Chlorides (mg/L) | Sulphates (mg/L) |
|---|---|---|---|---|---|---|---|---|---|
Washing | High BOD5, biocides, disinfectants, insecticides, soda, soaps, solvents. | 9-14 | 12000-30000 | 1000-2000 | - | 2500-3500 | 10000-20000 | - | - |
Bleaching | Hydrogen peroxide, stabilizers, high basicity | 8-11 | 2500-11000 | 200-400 | - | 100-500 | 1200-1600 | - | - |
Mercerization | high basicity, soda | 8-10 | 2000-2600 | 600-1900 | strong colouring | 50-120 | 250-400 | 350-2000 | 100 - 350 |
Dyeing and finishing | heavy metals, high salinity, surfactants, dyes, high organic load, solvents, acids and base, suspended solids, waxes, resins. | 1-10 | 1500-4000 | 50-350 | strong colouring | 100-400 | 400-1400 | - | - |
Generally, the water coming from each stage of the industrial process is unified into a single effluent by means of a mixing and homogenizing tank or pit. This way, a unique effluent with the characteristics shown in Table 2 is generated for which the treatment plant is designed.
Table 2. Approximate characteristics of the unified wastewater from the Textile Industry.
Parameter | Value | Units |
|---|---|---|
pH | 10 | - |
Conductivity | 1380 | µS/cm |
Temperature | 20 - 40 | ºC |
TOC | 620 | mg/L |
TSS | 160 | mg/L |
COD | 1650 | mg/L |
BOD5 | 460 | mg/L |
Colour | 2900 | Hazen Units |
Total Phosphorus | 1,5 | mg/L |
Total Nitrogen | 25 | mg/L |
Chlorides | 1300 | mg/L |
2. Treatment and reuse of wastewater from the Textile Industry
The two main objectives of the treatment of wastewater from the Textile Industry for its discharge or reuse are:
- Organic matter removal
- Colour removal (representative of dyes and other pollutants)
The installation of an on-site treatment plant or decentralized treatment is an investment that ensures the operation and sustainability of the plant in the medium and long term. The main advantage of decentralized treatment is that it allows the treatment to be taken to the point of manufacture, saving costs for transporting the wastewater network and associated taxes and allowing the reuse of the treated water in the production plant itself. In addition, overexploitation of water resources is significantly reduced and savings in surface water catchment infrastructures are allowed.
The most important stages of wastewater treatment in the Textile Industry are as follows, although each specific case requires a study for the proper selection of the technologies that will be included in its treatment:
- Screening: removal of large solids (fibres, fluff, solid pieces, etc.)
- Removal of oils and fats: especially in the effluents of the wool processing industry.
- Homogenization: essential to solve fluctuations in the flow rate and concentration of any of the wastewater lines. It also allows the cooling of residual water when it comes at high temperatures.
- Neutralization: pH adjustment for the correct operation of the subsequent stages.
- Physical-chemical treatment: elimination of colour, solids and fats. Coagulation-flocculation, oxidation and filtration technologies are applied.
- Biological treatment: elimination of organic matter. Activated sludge technologies are applied.
- Tertiary treatment: intensive removal of colour and recalcitrant organic compounds. Enables the reuse of water. Membrane and filtration technologies are applied.
2.1 Pre-treatment, physical-chemical: colour, solids and fats removal
Main objectives of the pre-treatment are:
- Homogenization of the flows and temperature adjust.
- Reduction of the suspended solids concentration.
- Oils and fats removal.
- Adjustment of the pH.
Technologies of two different groups are generally applied: chemical oxidation and advanced oxidation and/or physical-chemical processes, as explained below.
Chemical oxidation and advances oxidation processes (AOPs): the trend in the reuse of water is increasingly towards the development of the efficiency of the oxidation processes for the elimination of organic matter and colour. They are easy to apply and allow the degradation of toxic agents and the by-products of their degradation. Chemical oxidation processes use oxidizing agents such as ozone O3 or hydrogen peroxide H2O2; in advanced oxidation processes, the hydroxyl radical · OH is generated, which is a powerful oxidizing agent. Table 3 shows the most effective chemical and advanced oxidation methods in the treatment of wastewater from the Textile Industry.
Table 3. Chemical oxidation and advanced oxidation processes used in the treatment of wastewater from the Textile Industry.
Oxidation process | Performance |
|---|---|
TiO2/UV/H2O2 |
|
Ozonisation O3 |
|
H2O2 at high temperature (150 - 200ºC) |
|
Fenton Process (Fe(II) + H2O2) |
|
Electro-Fenton |
|
Electrochemical oxidation (electrolytic cell) |
|
Hypochlorite ClO- |
|
Coagulation-flocculation: allows the elimination of suspended and colloidal matter (up to 95%) and the COD and BOD5 associated with them (between 60 - 80%). It allows the elimination of turbidity (above 70%) and colour (above 90%).
The most effective coagulants applied in the effluents of the Textile Industry are the salts of aluminium (including poly aluminium chloride) and iron (generally ferric chloride).
After a coagulation and flocculation stage, a DAF (Dissolved Air Flotation) equipment is installed to separate the flocs formed.
Activated Carbon filters are also used as pre-treatment: they allow the retention of colorants and toxic compounds so that they do not affect the biological treatment.
SIGMA is an expert in the design and construction of DAF flotation equipment. Our wide range can treat from 5 m3/h to 1,000 m3/h, including compact equipment.
Our DAF equipment can treat water with a pollutant load of up to 40 kg of solids per m2.
The range offered by SIGMA is the following, we design each equipment according to the requirements and characteristics of the water to be treated:
- SIGMA DAF FPAC: flow rates from 5 to 160 m3/h with very high solids load. High-Performance Cross Flow Equipment.
- SIGMA DAF FPBC: flow rates from 10 to 250 m3/h with solid loads between low - medium. High performance counter flow equipment.
- SIGMA DAF FPHF: flow rates from 200 to 1000 m3/h with very high solids load. The equipment combines countercurrent flow and cross flow, optimal performance.
- COMPACT DAF: compact equipment including coagulation-flocculation system and flotation equipment. They are installed in skid: space saving and energy saving.
Ventajas de los sistemas SIGMA DAF:
- Calidad alta y constante del clarificado.
- Rápida puesta en marcha.
- Mínima producción de lodos (concentraciones de lodos de hasta el 5%, mucho más altas que las alcanzadas por sedimentadores convencionales).
- Fácil de operar con sistemas de control sencillos, adaptables y eficaces.
- Tecnología conocida, flexible a cada caso y robusta.
2.2. Biological treatment: organic matter removal
The biological treatment allows the elimination of organic matter and nutrients through the action of microorganisms in various oxygenation conditions.
There are multiple designs of biological reactors, the MBR reactor or Membrane Bio Reactor being especially effective in the treatment of wastewater from the textile industry.
MBR Membrane Bio Reactors achieve an intensive biological treatment, allowing the cellular retention time to be extended and therefore working at very high biomass concentrations and allowing the elimination of slowly biodegradable products.
MBR reactors combine the biological treatment process with Ultrafiltration membranes as a separation technology for water and sludge. The biological process can be aerobic, anoxic or anaerobic, for the treatment of wastewater from the textile industry an aerobic treatment is commonly applied. The application of Ultrafiltration membranes as clarification technology allows reaching very high concentrations of biomass within the reactor, between 6000 and 12000 mg / L MLSS (mixed liquor suspended solids), much higher than that with a conventional activated sludge system followed by a decanter, which entails a high performance of the biological process since it allows working at high volumetric loads while presenting a minimum excess sludge production, therefore, the volumes of this type of reactors are much lower than those used in conventional biological processes.
With an MBR system, the elimination of COD and BOD5 from effluents of the Textile Industry can exceed 90%, although it always depends on the refractory nature of the dyes, which can be eliminated as explained in this article either in a pre-treatment or special tertiary treatment. The unique advantage of an MBR is that it combines biological treatment with membrane technology that allows the removal of refractory and biodegradable COD. In addition, the membranes, acting as a tertiary treatment, allow the immediate reuse of water (permeate) and the recovery of products (retained). For a much more intensive purification, MBR can be complemented with Reverse Osmosis membrane technology as a tertiary treatment, as explained in the next section
Detailed information about this technology can be found in the article “Application of CAF, DAF, MBR y Reverse Osmosis processes in the treatment and reutilization of wastewater in the cosmetic industry”.
Features of the plants SIGMA MBR:
- Continuous discharge of the clarified effluent.
- Complete sludge separation.
- Effluent fully free of suspended solids and particles.
- Organic matter removal over 90%.
- Reachable concentrations of biomass are very high: 6000 – 12000 mg/L MLSS.
- Reduced reactor volumes: space and energy savings.
- High resistance to oxidizing agents.
- Very high quality of the effluent, suitable for reuse.
- Sludge production is minimal.
SIGMA designs and builds modular MBR plants (possibility of adding extra membrane modules) and SMBR compact plants (the reaction zone and the filtration zone are included in the same equipment)
The advantages of the SIGMA SMBR compact devices are the following:
- PLUG&PLAY solution.
- Equipments are of great reliability and durability.
- An effluent of optimum and constant quality is obtained, suitable for reuse.
- Compact plant that allows the modular addition of Ultrafiltration membranes.
- Simple operation and control systems.
- With high resistance to oxidizing agents.
SIGMA SMBR plants can treat flowrates between 20 – 100 m3/day.
2.3. Tertiary treatment: intensive color and recalcitrant organic compounds removal for water reuse.
Tertiary treatments can be adsorption/absorption or advanced membrane filtration. Well designed, these processes allow the complete removal of colour, turbidity and recalcitrant contaminants making the effluent suitable for reuse.
Adsorption/absorption: sand filters and Activated Carbon filters
Advanced membrane filtration: membrane processes are combined with biological processes, for example after MBR, and with coagulation-flocculation processes when the biological stage is not used. The most efficient sequence has been the application of Ultrafiltration (membranes that generally constitute the MBR) followed by Reverse Osmosis. The application of Reverse Osmosis membranes allows the generation of a permeate free of dyes and suitable for reuse, while the concentrate retains the dyes that can be recirculated to the industrial process and therefore cease to be a waste to become a consumable reagent.
3. SIGMA Case Studies in the Textile Industry
SIGMA's experience in treating wastewater from the Textile Industry is extensive. Two examples of Case Studies are presented below.
To obtain more information about the processes offered by SIGMA, for the textile industry and any other type of industry in general, do not hesitate to contact us using the form on the right, or at the email info@sigmadafclarifiers.com, or by calling us at +34 972 223 481.
3.1. Wastewater treatment and reuse from the Textile Industry: DAF Technology. Case of ACAPERSA.
Year: 2011 Project location: Textile Factory ACAPERSA, Valencia. Objetives: Design and installation of a wastewater treatment plant to obtain very high quality water for reuse in the process, in addition to compliance with the discharge directives. Installed technology:
Capacity: 5 m3/h. |
Table 4. Characteristics of the wastewater and performance of the ACAPERSA Case Study.
Wastewater characteristics: OPAQUE WHITE COLOR | ||
|---|---|---|
COD (mg/L) | TSS (mg/L) | Turbidity (NTU) |
11630 | 470 | 2890 |
Removal efficiency of the physical-chemical and DAF treatment | ||
COD | TSS | Turbidity |
90% | 95% | 96% |
Wastewater from the textile industry is characterized by a high content of suspended solids, COD, colour and turbidity. There is a growing need for water reuse, which involves the removal of these contaminants through the use of high performance technology. SIGMA designs and installs intensive and effective treatment processes that include advanced technologies to allow them to meet reuse quality requirements. In the case of ACAPERSA, SIGMA designs and builds the pre-treatment of the residual effluent from the process. This pre-treatment is made up of a physical-chemical process, consisting of a coagulation and flocculation system, followed by a DAF FPBC model CPF equipment. The pre-treatment designed and installed by SIGMA achieves COD removal performance of 90%, removal of suspended solids of 95% and removal of turbidity and colour by 96%. These high yields are achieved thanks to the correct dosage of reagents and the special design of the FPBC-CPF equipment. The reagent dosage is established by Jar-Test with samples of the waste water. In the case of ACAPERSA, Aluminium Polychloride and a cationic polyelectrolyte are applied with optimal affinity for suspended solids and particles present in water. Separation of suspended solids, COD, colour and turbidity in SIGMA DAF equipment: - High and constant quality of clarification. - Quick start-up. - Minimal sludge production (sludge concentrations of up to 5%, much higher than those achieved by conventional settlers) - Easy to operate with simple, adaptable and effective control systems. - Known technology, flexible to each specific case and robust. |
3.2. Wastewater treatment and reuse from the Textile Industry: BIOLOGICAL TREATMENT, DAF Technology and TERTIARY TREATMENT. Case of COLORTEX.
Year: 2008 Project location: Textile Factory COLORTEX, Valencia. Objectives: Design and installation of a wastewater treatment plant to obtain very high-quality water for reuse in the process, in addition to compliance with the discharge directives. Installed technology:
Capacity: 150 m3/h. |
Table 5. Characteristics of the wastewater and performance of the COLORTEX Case Study.
Wastewater characteristics: OPAQUE BLACK COLOUR | ||
|---|---|---|
COD (mg/L) | TSS (mg/L) | Turbidity (NTU) |
4073 | 5000 | >500 |
Removal performance | ||
COD | TSS | Turbidity |
95% | 95% | 90% |
Wastewater from the textile industry is characterized by a high content of suspended solids, COD, colour and turbidity. There is a growing need for water reuse, which involves the removal of these contaminants through the use of high performance technology. SIGMA designs intensive and effective treatment processes that include advanced technologies to meet the quality requirements for reuse. In the case of COLORTEX, SIGMA designs the complete treatment of wastewater that enables its reuse and discharge, complying with administrative requirements. The treatment consists of: Upflow sludge blanket filter biological reactor: the unique inverted cone-shaped design allows the formation of a sludge filter, and allows for much more effective sludge and water separation than with a common settler. Filtration by sludge blanket allows the execution of all transformation processes in the same reactor, such as activation, nitrification, denitrification and dephosphorization. Reduces the space required and leads to low operating and maintenance costs. In-line flocculation equipment PFL-140: this physicochemical system is applied to the effluent from the biological reactor. In the PFL system, the processes of coagulation, flocculation, de-emulsification, precipitation and pH control are carried out under defined and extremely controlled conditions. Its advantages are: no maintenance cost, no moving parts, high quality materials and durability, no need for additional energy input, uniform floc formation, compact, total control of the process conditions. The reagent dosage is established by Jar-Test with samples of the water at the exit of the biological reactor. In the case of COLORTEX, a cationic polyelectrolyte is applied. Clarifier SIGMA DAF FPAC-160: this system is a low height cross flow separator. The injection of air microbubbles allows the separation of the flocs formed in the PFL and obtaining a clarified effluent free of suspended solids, turbidity and colour. The FPAC system allows the treatment of water with a high load of solids, it is a compact system, it includes a unique sludge dewatering and separation system allowing a sludge concentration of up to 5%, it requires low maintenance and is easy to operate. These systems can be designed exclusively for each type of effluent. Sand filter: it is applied as a tertiary treatment for the reuse of water in the production process. These filters make it possible to achieve optimal qualities of the treated water for its reincorporation as a raw material in the textile process. It is a robust, high-resistance and quality equipment, it includes a control panel that allows easy handling. With a tertiary treatment, a zero discharge is achieved and the conversion of a waste into a resource. The sludge treatment by thermal drying is also designed with a high efficiency cyclonic spiral system. This technology allows drying, condensing, dehydration and sterilization for absolute final dryness. The treatment designed and installed by SIGMA achieves COD removal performance of 95%, removal of suspended solids of 95% and removal of turbidity and colour of 90%. |
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