Industrial effluent treatment plays a key role in the development of a sustainable environment. Classical approaches have several limitations to produce reusable water. Moreover, the preparation of reusable waste- water is a necessity to reduce water utility. Last few decades industries have adopted several methods for the effluent treatment process, but their efficiency is too low. Recently, biotechnologist has developed several reactor based strategies to remove toxic substances from the industrial effluents which have several advantages than the classical methods. High COD containing effluents are easily treated by anaerobic reactors, which help to produce energy generation and low sludge production. However, in realistic applications, anaerobic treatment experiences the low growth rate of the microorganisms, a little settling rate, unstable end products, and the need for post-treatment of the toxic anaerobic effluent, which often contains hydrogen sulfide (HS-) and ammonium ion (NH4+). The systems such as a stined tank reactor, air-lift, and bubble column reactor, fixed- bed bioreactor, rotating disk reactor, and silicone-membrane reactor have been widely used. Following are the several reactor systems employed for bioremediation of textile effluent using microorganisms (Figure 8.10) such as, (i) up-flow anaerobic sludge blank reactor (UASB), (ii) Rotating drum bioreactor (RDBR), (iii) up-flow column reactor (UFCR), (iv) Fluidized bed reactor (FBR), (v) Anaerobic baffled reactor (ABR), (vi) Continuous packed bed bioreactor, (vii) Pulsed packed bed bioreactor, (viii) Airlift reactor, and (ix) Tubular photobioreactor for cyanobacteria. The choice of reactor depends on the organism that is used for the treatment and process of interest (Padmanaban et al., 2013). Decolorization of textile industrial effluents is a continuous process, which required continuous flow bioreactors. For example, continuous with fixed film bioreactors remove disperse dye (Red-553) up to 80% within 20 days (Yang et al., 2003).

Darwesh et al. (2015) designed prototype bioreactor with dual oxygenation (anoxic and aerobic) level for the decolorization of azo dye Reactive Blue by Pseudomonas aeruginosa strain OS4. This bioreactor consists of two compartments, up-flow fixed film column (UFC), and continuously stined aerobic (CSA) container. The bioreactor could be operated at a flow rate of 50ml per hour with a hydraulic retention time (HRT) of 20 hours using the immobilized bacterial cell. This system showed 99% decolorization of Reactive blue in sequential anoxic and aerobic treatment and found that decolorization of dye is due to the formation of lignin peroxidase in both conditions. They prepared and modified surface properties of lignin peroxidase magnetic nanoparticle and tested it for bioremediation of reactive blue.

(a) Conical up-flows system, (b) Stined reactor, and (c) Bubble column reactor

FIGURE 8.10 (a) Conical up-flows system, (b) Stined reactor, and (c) Bubble column reactor.

Andleeb et al. (2012) studied the anthraquinone dye biodegradation by immobilized flavus in fluidized bed bioreactor. The reactor

functions continuous flow mode, at room temperature (25-30°C). The reactor was filled with sand-inunobilized fungal mass, and simulated textile effluent (STE) medium with 50 mg I-1 of dye concentration was fed into the reactor. The reactor effectively removes overall biological oxygen demand (BOD), COD, and color up to 85.57%, 84.70%, and

71.3%, respectively. Buitron et al. (2004), studied the application of sequencing batch reactor (SBR) pilot system biofilter filled with porous volcanic rock for the aerobic degradation of the azo dye acid red 151, which removes the color up to 99% using an initial concentration of 50 mg AR151.

Atrickling filter system was made with small river rock of2.5 to 7.5 cm for the treatment of textile effluent. It reduces the BOD level in wastewater from 600 to 100 mg/L (Shanooba et al., 2011). Efficient decolorization of Reactive Red 198 (>90%) was possible in anaerobic/aerobic SBR system. The color removal above 90% was attained under anaerobic phase, and concentration of Reactive Red 198 at 20 and 50 mg I-1 did not create an adverse effect on the activity of the microorganisms (Kocyigit and Ugurlu, 2015). Sandhya et al. (2005) reported about 94% azo dye color removal in microaerophilic-aerobic condition. Hosseini Koupaie et al. (2013) conducted biodegradation of Acid Red 18 in integrated anaerobic-aerobic fixed bed sequencing batch biofilm reactor and observed approximately 90% removal of color, COD, and intermediate compounds. They found polyethylene as a medium for immobilization of microorganisms for better azo dye removal.

Upflow Column Bioreactor was used for mineralization and detoxification of the carcinogenic azo dye Congo red. In this system, the textile effluent is treated by a Polyurethane Foam Immobilized Microbial Consortium. A bacterial consortium consisting of Providencia rettgeri strain HSL1 and Pseudomonas sp. SUK1 reduce azo dye Congo red under microaerophilic incubation conditions and yield toxic aromatic amines, biphenyl-4,4’-diamine and sodium-3,4-diaminonaphthalene- 1-sulfonate. Biphenyl-4,4’-diamine and sodium-3,4-diaminonaphtha- lene-1-sulfonate converted into biphenyl and naphthalene respectively in a consequent aerobic process due to the activities of oxidative enzyme, laccase (Figure 8.11).

Textile effluents composition is obviously variable, comprising organics, nutrients, sulfur compounds, salts, and toxic chemical substances because of usage of wide varieties of synthetic dye that have the different chemical structure (Chen et al., 2003; Pearce et al., 2003; Ghodake et al., 2009b). Therefore, bacterial decolorization is directly influenced by several factors includes oxygen concentration, the level of agitation, pH, temperature, the structure of dye, dye concentration, carbon, and nitrogen source availability, electron donor, and redox mediator (Saratale et al.,


Biodegradation of Congo red

FIGURE 8.11 Biodegradation of Congo red.


Azo compounds constitute the most diverse group of human-made synthetic dyes and are widely used in several industries such as textiles, food, cosmetics, and paper printing. Azo dyes are resistant to biodegradation due to their recalcitrant nature. However, microbes are highly adaptable in extreme environments and synthesis of different enzymes for the decolorization and mineralization of dyes under suitable environmental conditions. Several genera of bacteria have been reported for azo dyes degradation. Anaerobic or aerobic azo dye degradation by several puie and mixed bacterial cultures has been reported. Different mechanisms, including enzymatic as well as RMs, have been used for this non-specific reductive cleavage. However, few aerobic bacteria that can utilize azo dye as their growth substrates. Through biotechnological advancements, various reactor systems are devised and are employed for decolorization and degradation of textile dyes using microorganisms. The systems such as UASB, ABR, FBR, and RDBR are suitable for bacterial operation. The selection of an appropriate type of reactor system facilitated with a suitable condition can efficiently remove the dyes from the textile industrial effluents.


  • • aerobic degradation
  • • anaerobic degradation
  • • azo dyes
  • • azo-reductases
  • • bacterial decolorization
  • • bioreactor based decolorization
  • • bioremediation
  • • laccases
  • • oxidoreductases
  • • physical methods
  • • polyphenol oxidases
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