Different industries used varying amounts of water in their product manufacturing. Among all the industries, the textile industry is one of the water–intense sectors and uses a colossal amount of water. According to Fibre2Fashion, knit mills use around 10 gallons of water per pound production.
In addition to extensive water use, various textile industries like cotton, woolen, etc., produce vast quantities of wastewater which contains many harmful contaminants. For example, according to a research, woolen industries produce 2,700 cubic meters of wastewater per day.
Textile industries carry out two major processes: dry processes and wet processes. In the dry process, solid wastes like yarn, fibers, waxes, vegetable matter, paper, rope, etc., are generated, whereas, in wet techniques, liquid waste, i.e., wastewater, is generated.
Wet processes in the textile industry that produces wastewater
- Sizing and desizing
- Bleaching process
- Mercerization process
- Dyeing and printing process
- Finishing process
Wet processes in the textile industry generate a high amount of wastewater, containing a large amount of color, biological oxygen demand, chemical oxygen demand, dyes & chemicals, total suspended solids, and total dissolved salts.
The most toxic contaminants present in textile effluent are DYES, and if released untreated into natural water bodies, such contaminated wastewater is harmful to humans and aquatic life. Thus, textile wastewater treatment is essential.
What are the different types of textile wastewater treatments?
- Coagulation and flocculation
During coagulation, alum and iron salts are used as a coagulant to stimulate the floc formation in wastewater, which are then removed through sedimentation.
This method is essential for removing dispersed dyes from wastewater. However, this wastewater treatment method does not deliver effective results when water contains reactive and vat dyes.
- Adsorption method
Adsorption has gained much attraction for textile wastewater treatment because adsorbent election parameters have high affinity and capability. However, its limitations are the high cost and difficulty of recycling or desorption.
Many industrialists use low-cost adsorbents to remove the dye to solve this problem, but their regeneration and desorption have always been a problem. Thus, the adsorption method is used when the water has a low concentration of contaminants.
- Ion exchange method
The ion exchange method uses cation and anion to remove charged pollutants from water, and it is widely used for softening hard water. However, it has limitations in textile wastewater treatment, as it is less efficient for water-insoluble dyes.
Chemical treatment method
- Advanced oxidation process
Here, oxidizing agents treat chromophore molecules and organic and inorganic compounds. One of the most effective and potent oxidizing agents is Hydroxyl radicals, which react with most dyes at a high reaction rate. Other agents include Cl, O3, ClO2, and H2O2.
- Chemical oxidation treatment
It uses oxidizing agents like O3 and H2O2, and one of the most common methods used is the ozonation process to remove synthetic dyes from wastewater. The significant advantage here is that ozone is used as a gas, and it does not alter wastewater volume, nor does it generate solid waste as a by-product.
The biodegradation process is widely used to remove organic molecules from water in wastewater treatment. The degradation of artificial dyes through microbes involves a complex mechanism because it requires deep knowledge about microorganisms but is easy to process. The efficient textile wastewater treatment through biodegradation depends on the selection of microorganisms and enzyme activity. Therefore, different types of dyes present in textile effluent are removed by microorganisms like,
- Fungal culture can adapt to environmental changes and can remove various types of dyes like azo dyes, disperse dyes, etc.
- Algae remove dyes through three processes: dye consumption for their growth, decolorizing dyes through enzymes, and chromophore sorption onto the algal surface.
- The use of bacteria for textile effluent treatment started two decades ago, and many anaerobic bacteria are efficient in removing azo dyes.
Hybrid treatment methods
Often biological treatment methods do not deliver efficient results because some water-soluble molecules and dye particles are difficult to treat through biodegradation alone. Similarly, chemical treatment methods cannot treat cent percent of pollutants in wastewater.
Hence, effective wastewater treatment requires a combination of both biological and chemical methods.
Membrane technology is one of the most sustainable wastewater treatments in the textile sector. It involves ultrafiltration, nanofiltration, microfiltration, and reverse osmosis, and the selection of filtration technique depends on the type of pollutants present in wastewater.
Membrane filtration reduces chemical oxygen demand, biological oxygen demand, and colors from effluent.
As the effluent from the textile industry contains a high amount of toxic substances, it is imperative to treat its wastewater and save the environment. It can be treated using various methods to reduce the health risks to humans and aquatic life.