A Review on Elimination of Colour and Dye Products from Industrial Effluent

Abstract

Every industry now takes clean technology very seriously. Particularly in textile dying facilities, a lot of water, energy, dyeing colours, and chemicals are used. Significant issues with air and water pollution may result from this. The wastewater is quite colourful and smells poisonous. It also has high chemical oxygen demand (COD) and biochemical oxygen demand (BOD) levels. Reactive dyes found in wastewater include orange OGR, red DB-8, black DN, and turquoise DG. It has been demonstrated that the type of dye, the dosage of coagulant, and the pH of the sample all affect how effectively dye is removed. Also, the effectiveness of COD and colour elimination in single-stage and multi-stage ozonation-biological process methods were studied. The functional groups of azo dye are changed by ozonation to produce more readily removable biodegradable byproducts. Ozonation changes the functional groups in azo dye, resulting in more biologically degradable byproducts that are simply eliminated through biological treatment. Activated sludge treatment as well as the coagulation-flocculation technique with 80% waste water removal efficiency. Sequencing batch reactor is a fill-and- draw activated sludge-based system for wastewater treatment and has been proposed as an alternative technique for treating industrial effluents. We briefed a promising novel technology for textile effluent de-colorisation in this chapter.

1. Introduction

There is a growing freshwater issue worldwide as a result of the fast growth in the world’s populace, climate change, and industrial expansion. As a result, numerous freshwater users and polluters make a major contribution to its depletion [1, 2]. Among them, the majority of significant contributors of industrial pollutants come from different industries including fabric, leather, pharmacy, varnish, and pulp-based sectors. These dyes contain methylene blue (MB), methyl orange (MO), Disperse Violet 26, crystal violet and so on [3, 4]. A recent estimate places the yearly global production of dyes at over 7,000,000 tonnes [5]. Humans as well as the environment are put at risk by the discharge of this industrial waste dye into the water.

Nowadays, one of the main problems disturbing the whole world was water pollution brought on through textile manufacturers’ incapacity to suitably dispose its waste water. In many nations, particularly China and the estuaries of South Africa, the textile industry has an important negative effect on the environment and the world economy [6]. Because of its textile industry’s large-scale production of extremely coloured effluent. This effluent comprising a diversity of persistent pollutants, effluent like dyes were an important ecological polluter that also negatively influences public health [7]. Around 107 tonnes of synthetic dyes are developed per year; the fabric industry employs over 10,000 tonnes of these colours [8]. As per their origin, assembly, and intended usage, dyes are often divided to several groups [9, 10].

The textile industry frequently employs azo, mordant, acid-basic, dispersion, and sulphide dyes among these synthetic pigments (Figure 1). In addition, a lot of toxic chemicals were utilised in the fabric industry at diverse stages of manufacturing method like agents for sizing, softening, desizing, brightening, and finishing. Textile dyes, are released as effluent in addition to wastewater into aquatic ecosystems including lakes, streams, and ponds without being treated. This will create main ecotoxicological risks with detrimental impacts on living things. Textile colourants does not adhere closely to fabric; therefore, they are harmful to living things [11, 12].

Figure 1.

Different types of dyes and its probable industrial uses.

Heavy elements like mercury, cadmium, arsenic, etc. that are necessary in the synthesis of fabric dye colour pigments, and aromatic complexes have been detected in textile effluent. The creation of textile dye colour pigments requires an abundance of heavy metals like mercury, cadmium, arsenic, etc. [13]. Along with the wastewater, these hazardous substances are transported over great distances. They persist in the water as well as soil for an extended period, causing major health concerns to living things, depleting soil fertility, impairing aquatic plants’ ability to photosynthesize, and ultimately creating anoxic circumstances for aquatic fauna and flora [14]. The aesthetic value of water bodies is also diminished by textile dyes, which increase the biochemical and chemical oxygen demand (COD). It will hinder photosynthesis, prevents the development of plants, enters the food chain, causes resistance and biological accumulation, and might even enhance toxicity, muta-genicity, and carcino-genicity [15]. Due to the exceptionally long lifespan and solubility of artificial colours in water, the substantial quantities of water utilised in fabric production. This leads to wastewater that is similarly large and contains a significant quantity of dissolved solids, metals, and refractory dyes [16]. Since traditional alternatives to treatment are frequently ineffective, it is necessary to use advanced methods due to secondary pollution and incompetent elimination of natural load upon discoloration. Consequently, it was urgently necessitated to grow management process which are both economical and environmentally friendly for properly cleaning effluent that comprises dye before it is finally disposed of [17]. According to this premise, this assessment will give readers a thorough understanding of the damaging effects. Moreover, dye-comprising textile effluent has on living things and natural ecological systems, as well as various cutting-edge approaches for managing textile wastewater in a way that promotes ecological safety.

2. Toxicity and its effect of fabric dyes

Most of the organic contaminants found in the unprocessed effluents discharged by the textile sector are textile colours. Azo dyes were quite common dyes in fabric industry and comprise the highest class among the major classes of textile dyes. Azo dyes chemically include one or more azo groups. Nearly 15–50 percent of azo dyes which were not attached to fibres and fabrics are discharged to produced effluent as a result of ineffective textile dyeing procedures [18]. Though few textile industries cleanse their effluent to break down the free azo dyes discharged to the atmosphere, others dump industrial waste straight to water bodies, posing main ecotoxicological risks and toxic impacts on living things (Figure 2). The soil quality and crop germination rates suffered when farmers in underdeveloped nations used wastewater containing untreated industrial effluents to irrigate their agricultural holdings. Azo dyes released into water diminish light penetration, has an impact on aquatic plant and algae development [13]. Furthermore, the colours that fish as well as living creatures perceive may be converted in its bodies to dangerous intermediate chemicals that could be hazardous to the fish’s welfare and to the well-being of their predators [19].

Figure 2.

Effects of dye fabric sewage on its surroundings and live beings from an ecotoxicological perspective.

Azo dyes included in industrial effluent can be ingested through humans as well as other species. Several bodily tissues are adversely affected by the transformation of azo dyes into toxic amino acids by the microbes that live in the human gut [20]. Furthermore, human skin-derived microbes have the capacity of converting azo dyes into hazardous amines. Because of its growing number of textile firms as well as the massive quantities of effluent comprising dyes, proper and efficient treatment measures are needed to avert ecosystem infection and to advance sustainability [11]. Nevertheless, it is vital to consider the existence of other artificial and organic compounds, their harmful effects, and the relevant environmental outflow levels in order to choose the best option [21].

3. Physicochemical characteristics of textile wastewater

The wastewater from the textile factory was thought to be one of the main causes of non-biodegradable chemicals entering natural water sources. During the dyeing process, a considerable amount of chemicals and colours do not adhere to the fibre. Moreover, surplus was released to atmosphere as effluent. Eighty percent of dyes and chemicals can be absorbed by textile fabrics [22]. Figure 3 depicts the many steps in the manufacturing of textiles as well as the primary contaminants found in textile wastewater. Starch, which is produced from the tissue, is one of the substances that are employed to produce biological oxygen demand (BOD) during the desizing stage [23]. The process of scouring involves removing the fabric’s other non-cellulosic components (fats, oils, and herbicides) through alkaline washing having detergents, producing effluent with a pH level that is elevated. Caustic soda is used to wash the fabrics during the mercerizing step in order to enhance fabric strength and colour retention, which raises the pH of the wastewater [24]. The bleaching stage creates white cloth by using hypochlorite, peracetic acid, and enzymes to create light and bright colours. Since several heavy metals are employed as auxiliaries in the method of dyeing to enhance the adsorption of the dye on the fibres through complexation processes. They might be introduced to the wastewater during the dyeing stage [25]. Since a significant portion of the dye is not absorbed by the fabric during this stage (20–30%), colour, BOD, and COD are significantly elevated. This phase is thought to provide the highest degree of contaminants. Urea, additional colours, or metals are added during printing. Adsorbable organic halogens, enzymes, surfactants, detergents, sodium or disodium thiosulfate, and BOD are primarily added during the washing processes of prewash bleaching, stone or acid or enzyme wash, as well as softener. Utilising compounds made for crosslinking, softening, and water resistance, the final stage softens the materials [25].

Figure 3.

Green technology necessary properties for wastewater treatment.

4. Numerous techniques for wastewater treatment

Obtaining safe water to consume is the most important world concerns impacting people nowadays due to human activity and dangerous access. By 2030, the availability of clean water might be a problematic for nearly 47 percent of the world’s populace [26]. The circumstance for removing microbes and natural impurities like textile dyes are attaining support globally to attain the aim of having clean and secure water to drink. But the materials needed to purify water are costly, making them inaccessible for a great deal of middle- and low-income nations. China is becoming a significant manufacturer of textiles for roughly 55 percent of global textile consumption [27]. China have occurred as a big textile producer, nearly for more than 55 percent of world fabric usage. Nearly 10,000 distinct synthetic colours and dyes are employed in the fabric and paper industries that is harmful to both the natural world and human wellness [28]. Cellulosic fibres, protein fabrics like silk, and synthetic fibres like nylon, and polyester are formed in textile industries by wet and dry techniques [7].

The final stage of textile colouring is the washing cycle. It eliminates excess colour and dyes which are poured to water and create water pollution since they have dyes with different chromophoric families which are extensively hazardous and possibly cancer-causing. In addition, colours from textiles discharged into the atmosphere and groundwater resources persist there for a very long period [28]. The development of a procedure that can be kept up with is necessary for colour eradication technology to evolve. Regarding regulation, there was still no worldwide agreement on the discharge of wastewater comprising dyes and related textile wastes, particularly azo dyes. Usually, azo dye limits are included with restrictions on the physico-chemical characteristics of treated effluent. The treatment of wastewater can be physico-chemical, biological/amalgamation of this methods, depending on the characteristics of the effluent. The following are a few of the most popular strategies [29].

4.1 Physical methods for fabric dye effluent

According to the mass transfer system, different physical methods, including adsorption, and membrane filtration, were employed to treat dye-comprising effluent with extremely higher elimination efficiencies that range from 85 to 99 percent [17]. Physical approaches give several advantages, such as uncomplicated designs, ease of use, cost, fewer chemical needs. It has no repressive effects because of its lack of toxic substances. These technologies are, however, largely unpopular owing to its variety of problems like the production of toxic by-products and sludge, followed by their inadequate applicability. Higher temperatures, COD, BOD, colour, and heavy metals are often obstacles to their usage in the process of textile effluent [30].

4.1.1 Adsorption and its mechanism

In the surface-based method of adsorption, adsorbed ions or molecules are drawn to a solid adsorbent surface. Physisorption and chemisorption were the two main kinds of adsorption. Depends on how the dye compound was adsorbed to the adsorbent surface, this classification is made. Several forces, including van der wall, and electrostatic connections might be present during the adsorption of dye molecules. Adsorbents are recycled, the procedure is extremely efficient, and colour elimination from effluent only takes a shorter time [31]. Adsorbents that frequently have porous shapes that enhance the total exposed surface area. It is needed for the quick and effective adsorption of dye substances from effluent, are the foundation of the adsorption method. For the elimination of dye from wastewater, several adsorbents like zeolites, silica gel, and activated carbon, etc. are extensively employed. On the other side, activated carbon is a frequently utilised adsorbent in industry [32, 33].

Numerous adsorption techniques are utilised to achieve the adsorption of dye from polluted water on the surface of an adsorbent. It must be denoted that electrostatic attraction, pi-pi interactions, van der Waals forces, hydrogen bonds, acid-base reactions, and hydrophobic interaction plays a main part in the adsorption of water contaminants on adsorbents [1]. According to Shen and Gondal’s findings, the adsorption of Rhodamine dye on the surface of the adsorbent was controlled through electrostatic and intermolecular connections [34]. According to Zheng et al., ion exchange and electrostatic attraction are both involved in the adsorption of anionic dyes [35]. Figure 4 exemplifies the mechanism of dye adsorption in wastewater effluent.

Figure 4.

Dye adsorption method for dye wastewater effluent.

According to Ebrahimian study, the elimination of MB dye from wheat straw preserved with sodium hydroxide and permeated with Fe₃O₄ involves two main mechanisms: the development of an exterior complex and ion exchange among the dye substance and adsorption surfaces [36]. The adsorption method was characterised through ion binding to different surface functional groups exist on the surface of adsorbent and electrostatic interaction. Among the adsorbent-adsorbate surfaces, includes the mechanism of the development of a surface complex. According to Cojocaru et al., the adsorption process was elucidated through the creation of hydrogen bonds among the adsorbents and Acid Orange 7 dye [37]. Siddiqui et al. claim that, interaction among the -OH groups in MnO₂/BC as well as the acceptor in MB substances are what causes H-bonds to form between MB and MnO₂/BC [38]. Like electrostatic interactions, pi-effects involve pi systems, in which positively charged substances connect with negatively charged surfaces. Furthermore, many mechanisms may operate concurrently throughout the adsorption process [39].

4.1.2 Membrane filtration (MF)

Membrane filtration (MF) are the most cutting-edge physical techniques for treating of effluent comprising colours. This method employs membranes with tiny pores, and a dye-free solution is created as a result of solutes greater than these pores getting trapped between them. Although simple and effective, this procedure occasionally necessitates replacing the membranes [17]. Figure 5 represents the MF method for dye wastewater effluent.

Figure 5.

Membrane filtration method for dye wastewater effluent.

In order to distinguish between particles that are suspended and colours in wastewater, the microfiltration (MF) method employs a conventional membrane with pore sizes that vary from 0.1 to 10 m. The purification of wastewater comprising dyes has recently been carried out using nanofiltration (NF), a cutting-edge membrane technique with average membranes with a diameter ranging from 0.5 to 0.2 nm. Consequently, nanofiltration technologies can remove colour components from effluent solutions by utilising size and electrostatic repulsion concepts. Ultrafiltration (UF) membranes are additionally suitable to eliminate natural colourants from textile effluent, with membrane widths that vary from 0.1 to 0.001 m [30]. Despite being fewer costly and requiring lesser pressure than nanofiltration, ultrafiltration still has a lower separation rate due to the enormous membrane pore size. Reverse osmosis (RO), a membrane filter technique was commonly employed in industry to remove dye-containing effluent and create higher-quality water. The advantage of RO technology is that it makes concentration and separation possible without using heat or state-changing energy [40]. Table 1 summarises the benefits and effects various methods in dye removal.

S. No.	Techniques used	Pros	Cons
1	Physical method
	(i) Adsorption process	Complete elimination of an extensive range of colours	Expensive
	(ii) Membrane filtration	All the dyes were removed	Development of concentrated sludge
2	Chemical method
	(i) Advanced Oxidation	Easy to use	Needs activation agent
3	Biological method
	(i) Microbial process	Elimination in 24 to 30 hr.	Azo-based dyes are not simply metabolised below; aerobic circumstances
	(ii) Enzyme assisted method	A combination of two or more enzymes used to convert toxic intercedes to insoluble end-products	Higher cost of pure enzymes
	(iii) Yeast	Viable, cost-effective	Time consuming

Table 1.

An outline of the pros and cons of various dye removal techniques.

4.2 Chemical methods for fabric dye effluent

Dye-containing wastewater is processed chemically utilising methods like electrochemistry, and sophisticated processes for oxidation. With the notable exception of electrochemical technological advances, these techniques are frequently more costly than physical and biological methods [11]. The major difficulties for marketable usage of chemical methods for eliminating dyes from textile effluent include the higher electrical energy needs, massive volumes of utilised chemicals as well as the requirement for the appropriate equipment. Chemical approaches for colour elimination are more difficult since they produce potentially dangerous metabolites and residues [41, 42].

4.2.1 Advanced oxidation approaches

Diverse methods for cleaning up dye-containing effluent are being studied. Advanced oxidation constitutes a few of these techniques, and it is based on the idea that dye effluent can be treated by creating hydroxyl radicals (OH•), which are strong oxidising agents. Photocatalysis, ozonation, and electrochemical procedures are a few examples of advanced oxidation methods. With these methods, dye may be quickly and efficiently eliminated in challenging situations without creating sludge. They have their own disadvantages such higher cost, pH dependence, and dangerous by-products. The development of OH• as well as the deterioration of textile effluent have both been extensively investigated via the photocatalysis approach [43]. The process through which dangerous coloured molecules are destroyed through photocatalysis. Nanoparticles like zinc oxide and titanium peroxide are employed as photocatalytic materials to develop the free radicals required for the breakdown of dye through photocatalysis. Superoxide was created by electrons acting as reducing agents, and OH• and mineralisation byproducts were created by holes oxidising the organic dye components. The Fenton and photo-Fenton methods are two extensively employed progressive oxidation procedures for the disintegration of natural contaminants in effluent, like pigments. This procedure depends on an existence of H₂O₂ and soluble iron [44, 45].

4.3 Biological methods for fabric-based dye effluent

Biological methods for the cleansing of dye-comprising sewage more ensuring than both chemical and physical methods were readily necessary to develop fewer sludge. It will use smaller number of chemical reagents that are cheaper, has energy-saving characteristics are ecologically safer, as well as the by-products produced during bacterial metabolic processes are non-toxic [7]. Furthermore, applying biological techniques results in total dye mineralisation and is cost-effective for use in underdeveloped countries. The aim of biological therapy was to turn refractory organic dyes to non-toxic products. The major benefit of a biological approach is the usage of microbes by an excellent biodegradable capability, either alone or in consortia, to treat effluent dyes. Adsorption and deterioration are the two main techniques used to treat textile effluent for dye decolorization [46]. These activities can take place in either aerobic or anaerobic circumstances. Since the primary by-products of the aerobic process are biomass, carbon dioxide, and water, while the major by-product of anaerobic processing is methane. Appropriate biological alternatives for treating textile dye effluent and changing dye substances to non-toxic products including microbes, algae, fungi, and enzyme-based methods [47].

4.3.1 Microbial-assisted deprivation of dye-comprising effluent

It has been demonstrated that many bacterial species are more effective than other microbes at breaking down wastewater that contains dye. The adaptability and capacity of the bacteria to digest dye under the existing environmental conditions determines the efficiency of dye deprivation by microbes [48]. It has been demonstrated that a wide variety of bacterial species, like Klebsiella, Bacillus, Shigella, etc. are capable of degrading azo dyes. The major benefits of utilising microbe in dye deprivation include their ease of cultivation, higher specific growth rates, and varied catalytic abilities for mineralizing azo dyes contained in effluent [49]. Numerous microbial species have utilised azo reductase enzymes to biologically degradable azo dyes via azo reductase underneath aerobic or anaerobic circumstances as the initial phase of the microbial deterioration mechanism. Under anaerobic conditions, bacterial azo dye decolorization frequently takes place via azo bond reduction, resulting in the synthesis of colourless amino acids. However, because these derived chemicals are mutagenic and carcinogenic, they must undergo an additional aerobic step of microbial deprivation in order to lessen their toxicity and change to compounds that are harmless to the environment [50]. Reactive Orange M2R’s decolorization by Lysinibacillus sp. KMK-A was predominantly attributable to azo bond decrease and the creation of metabolites; as a result, the rate of dye decolorization can be gauged in terms of BOD and COD decrease. The evaluation of natural load and level of mineralisation depend on these two variables [51].

Microbial consortia usually outclass a single strain in terms of dye elimination efficiency, and microbes have shown nearly 100 percent efficacy in the biodegradation of dye-comprising textile effluent. Bacillus megaterium, B. cereus, and B. subtilis are only a few of the five strains of distinct Bacillus species that make up the bacterial consortium known as SKBII found to be more efficient at dye decolorization compared with discrete strains [52]. Additionally, degradation of Red HE3B by a consortium of bacteria made up of Pseudomonas aeuroginosa BCH and Providencia sp. SDS that were separated from dye-contaminated soil. It was shown that the consortium’s intense metabolic action caused the decolorization and degradation of 50 mg/L of Red HE3B dye to occur at a pace that was 100 percent faster than that of individual bacterial strains within 1 hour. By employing a microbial consortium BP made up of Bacillus flexus TS8, and Pseudomonas aeruginosa NCH separated from textile sewage and dye-contaminated soil, Mohanty and Kumar examined the decolorization of Indanthrene Blue RS. The BP consortium outperformed the individual strains in terms of dye decolorization. The performance of the BP consortium was also increased by an introduction of residual farming wastes. Enhanced intracellular enzyme concentrations and non-toxic produced metabolites were a result of oxido reductive enzymes’ involvement in the complete deprivation mechanism. Thus, it was inferred that a wide range of specific microbial strains as well as consortia can degrade a wide range of colours employed in fabric production. This green method holds promise for the processing of effluent that comprises dyes, and it might be a cutting-edge and ground-breaking method for large-scale dye decolorization [53].

4.3.2 Enzyme-based deprivation of dye-containing effluent

Pure enzymes were not usually the first option for processing of wastewater comprising dyes due to their expensive cost. On the other hand, industrial enzymes stand out due to their affordability, effectiveness, and availability in liquid form. As an illustration, laccases and azo reductases were efficient at breaking down wastewater containing azo dyes. These dyes convert such complex natural pollutants to simpler compounds, and eliminating them from effluent containing textiles through flocculation. Enzymes are therefore commonly utilised in the chemical and biotechnology fields. Biocatalyst deactivation as a result of denaturation, however, is one of the most challenging elements of enzymatic degradation [17]. The action of numerous enzymes during the breakdown of azo dyes has recently been the subject of several investigations, the oxidoreductase enzyme class being one of the extensively studied. The most common enzymes against a variety of industrial dyes are peroxidase enzymes, which also have a wider pH range and higher temperature tolerance [54]. With immobilisation technologies making substantial development and enhancing enzyme performance in a variety of applications, enzyme immobilisation emerges as a capable element in textile dye biological degradation. Almost every type of enzyme can be utilised with cross-linking, making it a widely used immobilisation technique. Several items, such as charcoal and calcium alginate gel capsules are employed to immobilise dye-degrading enzymes. To enhance azo dye (such as Acid Red) decolorization, Malani et al. employed immobilised horse radish peroxidase (HRP) and a sono-enzymatic combination processing technique, obtaining up to 61 percent. For the breakdown of azo dyes with 85 percent azoreductase action has also been created [55, 56].

Additionally, Bilal et al. examined the dye decolorization effectiveness of chitosan-encapsulating HRP in a packed-bed reactor and discovered that Remazol Brilliant Blue R, Crystal Violet, Congo Red, and Reactive Black-5 were decolored by 82.17, 87.43, 94.35, and 97.82 percent. This immobilisation technique further enhanced the heavy metal inhibition resistance of the enzyme [57]. Additionally, Bilal et al. looked into how HRP immobilised on an environmentally friendly agarose-chitosan hydrogel support material degraded the Reactive Blue 19 dye. At 50 and 70°C, the immobilised enzyme system had more catalytic action than the free enzyme under alkaline conditions. Finally, Indigo Carmine through laccase revealed 82 percent better dye deprivation when ionic solutions were utilised [58].

4.3.3 Yeast-based deterioration of dye-comprising effluent

When it comes to bacterial and filamentous fungus degradation of textile colours, yeasts have several advantages. Yeasts has the possible to be employed as an alternative for the treatment of wastewater comprising dyes because of its quick development rates and capacity to withstand challenging ecological circumstances like lower pH. Only a few accounts, nevertheless, specifically mention yeasts’ destruction and removal of colours. The ascomycetous yeast species Debaryomyces, Candida, Kluyveromyces, and Saccharomyces have all been observed to digest wastewater containing colour. On the other side, the most capable basidiomycetous yeast include Trichosporon and Rhodotorula. Numerous yeasts, like Scheffersomyces spartinae, and Sterigmatomyces halophilus, has revealed the capacity to destroy textile colours, like azo dyes, and also to endure difficult circumstances, including higher salt concentrations in textile effluent [59]. The two main mechanisms through which yeast strains can eliminate higher amounts of various colours from effluent are biosorption as well as reductive cleavage. Debaryomyces hansenii F39A, an Antarctic yeast, was examined by Ruscasso et al. for its potential to be used as a biological sorbent for the reactive textile dyes. The collected data demonstrated that no poisonous or dangerous compounds were released which results in adsorption during the first 15 minutes of the operation [17, 60].

5. Conclusion

Scientists made an effort to reconsider the accessibility of clean and safe water due to the environmental impact of coloured dye wastewater disposal. It was documented that an occurrence of poisonous and coloured substances in dye-containing effluent has consequences on living organisms such as cancer, mutagenesis, allergies, and dermatitis. Textile effluent comprises a variety of detrimental xenobiotics which were found in higher concentrations and are hazardous to atmosphere as well as common people well-being. Since textile industries around the world releasing millions of gallons of contaminated sewage, toxicity dye-comprising effluent was an important problem. Contrarily, treating effluent that comprises dye is a substantial difficulty because no effective treatment that is also economically feasible currently exists. There are many tried-and-true and cutting-edge techniques for handling dye-containing wastewater. Wastewater containing dye can be effectively removed or degraded by employing physico-chemical process. Nevertheless, these techniques come with higher operational costs and unfavourable effects. In comparison to physico-chemical process, the bacteria-based technique to dye-comprising effluent treatment is more practical, ecologically safe, and socially and acceptable. Nevertheless, a drawback of biological techniques is that they are ineffective and necessitate a long period of administration. More study is needed to provide an advanced, waste-free technique and to lower ecological and human health threats when scaling up from lab use to the pilot level.

Acknowledgments

This work was supported by the Nanodot Research Pvt. Ltd. Neyyattinkara, Trivandrum.

Conflict of interest

The authors declare that they have no conflict of interests for this chapter.