Biodegradation and detoxification of reactive textile dye by isolated Pseudomonas sp. SUK1

Biodecolorization and biodegradation of Reactive Green 12 textile industry dye and their post-degradation phytotoxicity-genotoxicity assessments

The employment of versatile bacterial strains for the efficient degradation of carcinogenic textile dyes is a sustainable technology of bioremediation for a neat, clean, and evergreen globe. The present study has explored the eco-friendly degradation of complex Reactive Green 12 azo dye to its non-toxic metabolites for safe disposal in an open environment. The bacterial degradation was performed with the variable concentrations (50, 100, 200, 400, and 500 mg/L) of Reactive Green 12 dye. The degradation and toxicity of the dye were validated by high-performance liquid chromatography, Fourier infrared spectroscopy analysis, and phytotoxicity and genotoxicity assay, respectively. The highest 97.8% decolorization was achieved within 12 h. Alternations in the peaks and retentions, thus, along with modifications in the functional groups and chemical bonds, confirmed the degradation of Reactive Green 12. The disappearance of a major peak at 1450 cm-1 corresponding to the -N=N- azo link validated the breaking of azo bonds and degradation of the parent dye. The 100% germination of Triticum aestivum seed and healthy growth of plants verified the lost toxicity of degraded dye. Moreover, the chromosomal aberration of Allium cepa root cell treatment also validated the removal of toxicity through bacterial degradation. Thereafter, for efficient degradation of textile dye, the bacterium is recommended for adaptation to the sustainable degradation of dye and wastewater for further application of degraded metabolites in crop irrigation for sustainable agriculture.

Visible light assisted photooxidative facile degradation of azo dyes in water using a green method

In this study, the methyl orange (MO) dye has been degraded after screening several azo dyes due to its effective results and being toxic and carcinogenic to aquatic life and humans. An environmentally friendly, economical, and green method for water purification was used in this study using the photooxidative method. Several organic acids were screened for oxidative applications against various azo dyes but due to better results, methyl orange was selected for the whole study. Ascorbic acid, also known as vitamin C, was found to be best for photodegradation due to its high oxidative activity among various organic acids utilized. A newly developed photoreactor box has been used to conduct the photooxidation process. To evaluate the degradation efficiency of AsA, photooxidative activity was monitored periodically. When the dose of AsA was used at a contact time of 180 minutes, degradation efficiency was 96%. The analysis of degraded products was performed using HPLC and GC-MS. The nucleophilicity of HOMO-LUMO and MEPs was confirmed using density functional theory. For the optimization of the process, central composite design (CCD) in Response Surface Methodology (RSM) was utilized.

Biodegradation of commercial textile reactive dye mixtures by industrial effluent adapted bacterial consortium VITPBC6: a potential technique for treating textile effluents

Textile industries release major fraction of dyestuffs in effluents leading to a major environmental concern. These effluents often contain more than one dyestuff, which complicates dye degradation. In this study ten reactive dyes (Reactive Yellow 145, Reactive Yellow 160, Reactive Orange 16, Reactive Orange 107, Reactive Red 195, Reactive Blue 21, Reactive Blue 198, Reactive Blue 221, Reactive Blue 250, and Reactive Black 5) that are used in textile industries were subjected to biodegradation by a bacterial consortium VITPBC6, formulated in our previous study. Consortium VITPBC6 caused single dye degradation of all the mentioned dyes except for Reactive Yellow 160. Further, VITPBC6 efficiently degraded a five-dye mixture (Reactive Red 195, Reactive Orange 16, Reactive Black 5, Reactive Blue 221, and Reactive Blue 250). Kinetic studies revealed that the five-dye mixture was decolorized by VITPBC6 following zero order reaction kinetic; Vmax and Km values of the enzyme catalyzed five-dye decolorization were 128.88 mg L-1 day-1 and 1003.226 mg L-1 respectively. VITPBC6 degraded the dye mixture into delta-3,4,5,6-Tetrachlorocyclohexene, sulfuric acid, 1,2-dichloroethane, and hydroxyphenoxyethylaminohydroxypropanol. Phytotoxicity, cytogenotoxicity, microtoxicity, and biotoxicity assays conducted with the biodegraded metabolites revealed that VITPBC6 lowered the toxicity of five-dye mixture significantly after biodegradation.

Chitosan and silica nanoparticles-modified xanthan gum-derived bio-nanocomposite hydrogel film for efficient uptake of methyl orange acidic dye

In this contribution, a bio-nanocomposite hydrogel film (CS/XG.SiO2) of chitosan/silica NPs-modified xanthan gum was prepared via a facile solution casting blending approach and utilized to capture the anionic methyl orange (MO) from aqueous solution. A Taguchi standard method was used to optimize the hydrogel nanocomposite synthesis reaction conditions after comprehensive characterization using various techniques. Under various operating parameters, the hydrogel biofilm was tested for its effectiveness in adsorbing MO dye in a batch process. In agreement with Langmuir isotherm, the CS/XG.SiO2 biofilm was capable of adsorbing MO at a maximum capacity of 294 mg/g at pH 5.30, contact time 45 min, temperature 25 °C, and concentration (C0) 50 mg/L. Pseudo-second-order model and adsorption kinetics data well matched. The thermodynamic data indicate that adsorption occurred spontaneously and exothermically. The main mechanisms driving the adsorption are electrostatic interactions and hydrogen bonding between the CS/XG.SiO2 nanocomposite and the dye. Furthermore, the biofilm is regenerative, allowing for up to five reuses while maintaining a 75 % dye removal efficiency. This study highlights that the CS/XG.SiO2 hydrogel nanocomposite is an inexpensive, reusable, and eco-friendly bio-adsorbent that is capable of anionic dye adsorption.

Tungsten-based Lindqvist and Keggin type polyoxometalates as efficient photocatalysts for degradation of toxic chemical dyes

Photocatalytic dye degradation employing polyoxometalates (POMs) has been a research focus for several years. We report the facile synthesis of tungsten-based Lindqvist and Keggin-type POMs that degrade toxic chemical dyes, methyl orange (MO) and methylene blue (MB), respectively. The Lindqvist POM, sodium hexatungstate, Na2W6O19, degrades MO under 100 W UV light irradiation within 15 min, whereas the Keggin POM, Ag4PW11VO40, degrades MB under 20 W visible light source within 180 min. The effect of various operating parameters, such as photocatalyst concentration, pH, time, and initial dye concentration, were assessed in the degradation of both dyes. The photoelectrochemical performance of the as-synthesized polyoxometalates shows that the Ag4PW11VO40 shows 2.4 times higher photocurrent density than Na2W6O19 at a potential of 0.9 V vs. Ag/AgCl. Electrochemical impedance analysis reveals that Ag4PW11VO40 exhibits much lower charge transfer resistance as compared to Na2W6O19, which indicates facile charge transfer at the electrode-electrolyte interface. Further Mott-Schottky measurements reveal that both the catalysts possess n-type semiconductivity and the charge carrier concentration of Ag4PW11VO40 (5.89 × 1019 cm-3) is 1.4 times higher as compared to Na2W6O19 (4.25 × 1019 cm-3). This work offers a new paradigm for designing polyoxometalates suitable for efficient photocatalytic degradation of organic dyes.

Bioactive interpenetrating hybrids of poly(hydroxyethyl methacrylate-co-glycidyl methacrylate): Effect of polysaccharide types on structural peculiarities and multifunctionality

Crosslinked poly(hydroxyethyl methacrylate-co-glycidyl methacrylate) hybrids prepared in the same experimental condition by adding various polysaccharides of different chemical types; inulin, Na-alginate, starch and κ-Carrageenan were qualitatively compared. The results are presented to extract relevant physicochemical properties for qualitative comparison of structures within the same synthesis batch. Elastic properties and swelling degree of hybrids can be tightly regulated using different types of polysaccharides and by controlling effective cross-linking density. Addition of κ-Carrageenan to copolymer network increased elastic modulus by 6.2-fold in as-prepared state, but greatest increase in effective cross-link density through swelling was observed in alginate-doped gels. An overshooting effect was observed for alginate-doped hybrids; swelling first to a maximum, followed by a gradual deswelling until equilibrium was reached. Compressive elasticity of hybrids is mainly controlled by type of polysaccharides and cross-linking density but also depends on polymerization temperature. The obtained hybrid gels displayed excellent adsorption performance for methyl orange (MO). The highest adsorption capacity was reached with inulin-doped hybrids. The rate of adsorption was very fast and reached equilibrium with 98.9 % efficiency at about 90 min. This approach to modify the properties of hybrid gels with various types of polysaccharides may find wide use in biomaterials and water purification applications.

Natural bamboo powder and coffee ground as low-cost green adsorbents for the removal of rhodamine B and their recycling performance

Bamboo and coffee, which are abundant and inexpensive, have been used as green adsorbents for the adsorption of industrial dye rhodamine B (RB). Bamboo and coffee are natural sources of cellulose, hemicellulose, and lignin, making them promising green materials for industrial dye removal. The effects of various adsorption conditions, such as contact time, temperature, dose of bamboo powder (BP), coffee ground (CG), initial concentration of RB, and pH values of RB solution, were measured. Consequently, the kinetics of RB adsorption onto bamboo and coffee was in accordance with the pseudo-second-order model, with an activation energy of 29.51 kJ mol-1 for bamboo and 27.46 kJ mol-1 for coffee. The Langmuir model is well fitted to the whole adsorption period at different temperatures, in which the increase in the tested temperature has improved the adsorption capacity (i.e., BP: 6.76 mg g-1/30 °C, 6.96 mg g-1/40 °C, 7.64 mg g-1/50 °C and CG: 6.53 mg g-1/30 °C, 6.80 mg g-1/40 °C, 7.51 mg g-1/50 °C). Moreover, the spontaneous nature of the adsorption was based on the negative Gibbs free energy values obtained (i.e., from - 11.09 to - 14.30 kJ mol-1 [BP] and from - 10.34 to - 13.07 kJ mol-1 [CG]). These revealed that RB adsorption occurred at physical and chemical adsorption states. In addition, the recycling capability of adsorbents was determined in five cycles. Therefore, these materials are promising candidates for low-cost adsorbents.

Adsorption Kinetics of Methyl Orange from Model Polluted Water onto N-Doped Activated Carbons Prepared from N-Containing Polymers

This study aimed to assess the role of polymeric sources (polypyrrole, polyaniline, and their copolymer) of nitrogen (N)-doped activated carbons (indexed as PAnAC, PPyAC, and PnyAC, respectively) on their adsorption efficiency to remove methyl orange (MO) as a model cationic dye. The adsorbents were characterized using FTIR, SEM, TGA, elemental analysis, and surface area. The kinetic experiments were performed in batches at different MO concentrations (C₀) and adsorbent dosages. The adsorption kinetic profiles of pseudo-first-order, pseudo-second-order (PSO), Elovich, intraparticle diffusion, and liquid film diffusion models were compared. The results showed a better fit to the PSO model, suggesting a chemisorption process. The adsorption capacity (q_e, mg/g) was found to have increased as MO C₀ increased, yet decreased as the adsorbent quantity increased. At the adsorption operating condition, including MO C₀ (200 ppm) and adsorbent dose (40 mg), the calculated q_e values were in the order of PAnAC (405 mg/g) > PPyAC (204 mg/g) > PnyAC (182 mg/g). This trend proved the carbon precursor's importance in the final properties of the intended carbons; elemental analysis confirmed that the more nitrogen atoms are in the activated carbon, the greater the number of active sites in the adsorbent for accommodating adsorbates. The diffusion mechanism also assumed a rate-limiting step controlled by the film and intraparticle diffusion. Therefore, such an efficient performance may support the target route's usefulness in converting nitrogenous-species waste into valuable materials.

Selective adsorption of anionic and cationic dyes on mesoporous UiO-66 synthesized using a template-free sonochemistry method: kinetic, isotherm and thermodynamic studies

In this study, template-free mesoporous UiO-66(U) has been successfully synthesized in shortened time by sonochemical methods and provided energy savings. The synthesized mesoporous UiO-66(U) demonstrated irregular morphology particle around 43.5 nm according to the SEM image. The N₂ adsorption-desorption isotherm indicated an irregular, 8.88 nm pore width mesoporous structure. Ultrasonic irradiation waves greatly altered mesoporous materials. A mechanism for mesoporous UiO-66(U) formation has been proposed based on the present findings. Sonochemical-solvent heat saves 97% more energy than solvothermal. Mesoporous UiO-66(U) outperformed solvothermal-synthesized UiO-66(S) in adsorption. These studies exhibited that mesopores in UiO-66 promote dye molecule mass transfer (MO, CR, and MB). According to kinetics and adsorption isotherms, the pseudo-second-order kinetic and Langmuir isotherm models matched experimental results. Thermodynamic studies demonstrated that dye adsorption is spontaneous and exothermically governed by entropy, not enthalpy. Mesoporous UiO-66(U) also showed good anionic dye selectivity in mixed dye adsorption. Mesoporous UiO-66(U) may be regenerated four times while maintaining strong adsorption capability.

Defective multi-element hydroxides nanosheets for rapid removal of anionic organic dyes from water and oxygen evolution reaction

Water pollution by dyes is one of the biggest environmental problems. Adsorption technology has been widely used in wastewater treatment. In this work, high-entropy concept is used to design surface defective hydroxides realizing the rapid removal of dyes from water. Multi-element hydroxides (MEHs) containing three (CoMnNi, MEH-Ternary), four (CoMnNiZn, MEH-Quaternary), and five (CoMnNiZnFe, MEH-Quinary) metal elements are successfully synthesized through a polyol process. These as-synthesized MEHs are composed of nanosheets with a brucite-like structure. Along with the increase in compositional complexity (i.e., configurational entropy), the thickness of the nanosheets in these MEHs decreases, while the degree of surface defects increase. These surface defects are probably the active sites for anionic dyes adsorption, suggesting rapid adsorption kinetics with shortened diffusion path length. For MEH-Quinary in 0.2 mM Congo red (CR) and MEH-Ternary in 0.4 mM methyl orange (MO) aqueous solutions, respectively, high removal efficiency > 99.0% is achieved in the first 30 s. Their pseudo-second-order rate constants are two orders of magnitude higher than that of activated carbon and hydrotalcite. MEH-Quinary has maximum CR and MO adsorption quantity of 546.4 and 404.9 mg g^-1, respectively, by Langmuir model. The MEH-Quinary is also a potential electrocatalyst for oxygen evolution reaction.

Nitrogen-Rich Polyaniline-Based Activated Carbon for Water Treatment: Adsorption Kinetics of Anionic Dye Methyl Orange

In the present work, a nitrogen-rich activated carbon (PAnAC) was prepared using polyaniline (PAn) as a precursor to represent one possible conversion of nitrogen-containing polymeric waste into a valuable adsorbent. PAnAC was fabricated under the chemical activation of KOH and a PAn precursor (in a 4:1 ratio) at 650 °C and was characterized using FTIR, SEM, BET, TGA, and CHN elemental composition. The structural characteristics support its applicability as an adsorbent material. The adsorption performance was assessed in terms of adsorption kinetics for contact time (0-180 min), methyl orange (MO) concentration (C₀ = 50, 100, and 200 ppm), and adsorbent dosages (20, 40, and 80 mg per 250 mL batch). The kinetic results revealed a better fit to a pseudo-second-order, specifically nonlinear equation compared to pseudo-first-order and Elovich equations, which suggests multilayer coverage and a chemical sorption process. The adsorption capacity (q_e) was optimal (405.6 mg/g) at MO C₀ with PAnAC dosages of 200 ppm and 40 mg and increased as MO C₀ increased but decreased as the adsorbent dosage increased. The adsorption mechanism assumes that chemisorption and the rate-controlling step are governed by mass transfer and intraparticle diffusion processes.

Towards passive bioremediation of dye-bearing effluents using hydrous ferric oxide wastes: Mechanisms, products and microbiology

A novel, circular economy-inspired approach for the "passive" (non-powered and reagent-free) treatment of dye-bearing effluent is presented. The treatment utilises the biogeochemical interaction of dye-bearing wastewater with hydrous ferric oxide (HFO) bearing sludges. The work presented demonstrates for the first time the reuse of HFO-rich waste sludges from potable water and mine water treatment. The waste was used directly without modification or reagent addition, as media/substrate in simple flow-through reactors for the decolourisation and biodegradation of methyl orange (MO) and mixed dyes textile effluent. Three phases of exploratory proof of concept work were undertaken. Columns containing HFO sludges were challenged with solution of MO, and MO amended with glycerol (Phase I), MO in a synthetic textile effluent recipe (Phase II), and real mixed textile effluent containing a mixture of dyes (Phase III). After an initial lag period extensive decolourisation of dye was observed in all cases at rates comparable with pure strains and engineered bioreactor processes, with evidence of biodegradation beyond simple cleavage of the mono azo chromophore and mineralisation. The microbiology of the initial sludge samples in both cases exhibited a diverse range of iron oxidising and reducing bacteria. However, post experiment the microbiology of sludge evolved from being dominated by Proteobacteria to being dominated by Firmicutes. Distinct changes in the microbial community structure were observed in post-treatment MWTS and WTWS where genera capable of iron and sulphate reduction and/or aromatic amine degradation were identified. Average nitrogen removal rates for the columns ranged from 27.8 to 194 g/m³/day which is higher than engineered sequential anaerobic-aerobic bioreactor. Postulated mechanisms for the fast anaerobic decolourisation, biodegradation, and mineralisation of the dyes (as well nitrogen transformations) include various direct and indirect enzymatic and metabolic reactions, as well as reductive attack by continuously regenerated reductants such as Fe(II), HFO bound Fe(II), FeS, and HS^-. The ability of iron reducers to degrade aromatic rings is also considered important in the further biodegradation and complete mineralisation of organic carbon. The study reveals that abundant and ubiquitous HFO-rich waste sludges, can be used without amendment, as a substrate in simple flow-through bioremediation system for the decolourisation and partial biodegradation of dyes in textile effluent.

Methyl Orange Biodegradation by Immobilized Consortium Microspheres: Experimental Design Approach, Toxicity Study and Bioaugmentation Potential

Methyl orange (MO) is categorized among the recalcitrant and refractory xenobiotics, representing a significant burden in the ecosystem. To clean-up the surrounding environment, advances in microbial degradation have been made. The main objective of this study was to investigate the extent to which an autochthonous consortium immobilized in alginate beads can promote an efficient biodegradation of MO. By employing response surface methodology (RSM), a parametric model explained the interaction of immobilized consortium (Raoultella planticola, Ochrobactrum thiophenivorans, Bacillus flexus and Staphylococcus xylosus) to assimilate 200 mg/L of MO in the presence of 40 g/L of NaCl within 120 h. Physicochemical analysis, including UV-Vis spectroscopy and FTIR, and monitoring of the degrading enzymes (azoreductase, DCIP reductase, NADH reductase, laccase, LiP, MnP, nitrate reductase and tyrosinase) were used to evaluate MO degradation. In addition, the toxicity of MO-degradation products was investigated by means of phytotoxicity and cytotoxicity. Chlorella vulgaris retained its photosynthetic performance (>78%), as shown by the contents of chlorophyll-a, chlorophyll-b and carotenoids. The viability of normal lung and kidney cell lines was recorded to be 90.63% and 99.23%, respectively, upon exposure to MO-metabolic outcomes. These results reflect the non-toxicity of treated samples, implying their utilization in ferti-irrigation applications and industrial cooling systems. Moreover, the immobilized consortium was employed in the bioremediation of MO from artificially contaminated agricultural and industrial effluents, in augmented and non-augmented systems. Bacterial consortium remediated MO by 155 and 128.5 mg/L in augmented systems of agricultural and industrial effluents, respectively, within 144 h, revealing its mutual synergistic interaction with both indigenous microbiotas despite differences in their chemical, physical and microbial contents. These promising results encourage the application of immobilized consortium in bioaugmentation studies using different resources.

Decolorization of Textile Dye by Spore Surface Displayed Small Laccase for the Enhanced Thermal Stability and Robust Repeated Reaction

In this study, we tried to decolorize synthetic dyes using small laccase (SLAC) from Streptomyces coelicolor, which is resistant to pH, temperature change, and traditional inhibitors for the actual industrial applications using spore surface display system. We inserted SLAC-His6 tag at the C-terminal of CotE anchoring motif. The proper surface expression of CotE-SLAC fusion protein on the surface of Bacillus subtilis spore was verified with flow cytometry using FITC labeled anti-His6 tag antibody. After 6 h of reaction, more than 90% of Indigo carmine was decomposed using recombinant SLAC displaying Bacillus spore, whereas less than 10% of Indigo carmine was decomposed with wild type spore. Over 70% of laccase activity was retained with recombinant SLAC displaying spore, which was heat-treated for 3 h at 90°C. For eight rounds of repeated decomposition of Indigo carmine, no significant decrease of enzymatic activity was observed. This showed the robust characteristics of spore display format for repeated and harsh condition reactions.

Current perspective of innovative strategies for bioremediation of organic pollutants from wastewater

Organic contaminants in water are a growing environmental threat to sustainable development, with detrimental effects on the biosphere. In recent years, researchers have increasingly focused their attention on the area of bioremediation as an important tool to eliminate harmful pollutants from the environment. This review examines the application of bioremediation technologies to the removal of organic pollutants, with an emphasis on hydrocarbons and textile dyes. It applies a descriptive bibliometric analysis to study statistical practicality-vs-applicability of bioremediation of emerging organic pollutants. The paper identifies efficient pathways for bioremediation of different types of organic pollutants and outlines the potential for an eco-friendly and economical approach for the biological remediation of micropollutants by microalgae. Facts and figures on various hazardous pollutants, constraints in their current removal from water at an industrial level, and promising future solutions are carefully presented here.

Statistical modeling of methylene blue degradation by yeast-bacteria consortium; optimization via agro-industrial waste, immobilization and application in real effluents

The progress in industrialization everyday life has led to the continuous entry of several anthropogenic compounds, including dyes, into surrounding ecosystem causing arduous concerns for human health and biosphere. Therefore, microbial degradation of dyes is considered an eco-efficient and cost-competitive alternative to physicochemical approaches. These degradative biosystems mainly depend on the utilization of nutritive co-substrates such as yeast extract peptone in conjunction with glucose. Herein, a synergestic interaction between strains of mixed-culture consortium consisting of Rhodotorula sp., Raoultella planticola; and Staphylococcus xylosus was recruited in methylene blue (MB) degradation using agro-industrial waste as an economic and nutritive co-substrate. Via statistical means such as Plackett-Burman design and central composite design, the impact of significant nutritional parameters on MB degradation was screened and optimized. Predictive modeling denoted that complete degradation of MB was achieved within 72 h at MB (200 mg/L), NaNO3 (0.525 gm/L), molasses (385 μL/L), pH (7.5) and inoculum size (18%). Assessment of degradative enzymes revealed that intracellular NADH-reductase and DCIP-reductase were key enzymes controlling degradation process by 104.52 ± 1.75 and 274.04 ± 3.37 IU/min/mg protein after 72 h of incubation. In addition, azoreductase, tyrosinase, laccase, nitrate reductase, MnP and LiP also contributed significantly to MB degradation process. Physicochemical monitoring analysis, namely UV-Visible spectrophotometry and FTIR of MB before treatment and degradation byproducts indicated deterioration of azo bond and demethylation. Moreover, the non-toxic nature of degradation byproducts was confirmed by phytotoxicity and cytotoxicity assays. Chlorella vulgaris retained its photosynthetic capability (˃ 85%) as estimated from Chlorophyll-a/b contents compared to ˃ 30% of MB-solution. However, the viability of Wi-38 and Vero cells was estimated to be 90.67% and 99.67%, respectively, upon exposure to MB-metabolites. Furthermore, an eminent employment of consortium either freely-suspended or immobilized in plain distilled water and optimized slurry in a bioaugmentation process was implemented to treat MB in artificially-contaminated municipal wastewater and industrial effluent. The results showed a corporative interaction between the consortium examined and co-existing microbiota; reflecting its compatibility and adaptability with different microbial niches in different effluents with various physicochemical contents.

Decolorization and degradation of reactive orange 16 by Bacillus stratosphericus SCA1007

Efficient bacterial strain was isolated from the dye contaminated area and identified as Bacillus stratosphericus SCA1007 based on 16S rRNA gene sequence (GenBank under accession number KY992944). This isolate was selected based on its potential to efficiently decolorize reactive orange 16 dye which is extensively used in textile industries. Various culture conditions like dye concentration, temperature, pH, salinity, and additional nitrogen source were optimized in the present study. The optimal conditions for decolorization of reactive orange 16 was found to be: dye concentration 150 mg/L, pH 7, temperature 35 °C, and yeast extract as nitrogen source. The isolate was also resistant to 4% saline culture condition. Decolorization and degradation of dye were confirmed through UV-visible spectroscopy, Fourier transform infrared (FTIR) and liquid chromatography-mass spectrometry analysis (LC-MS). Toxicity studies were performed on Escherichia coli and Vigna radiata to confirm the non-toxic nature of the degraded metabolites. This is the first study demonstrating complete decolorization of reactive orange 16 dye by Bacillus stratosphericus SCA1007 at high salinity within 10 h of incubation under optimized conditions.

Microbial degradation of dyes: An overview

Industrialization increases use of dyes due to its high demand in paper, cosmetic, textile, leather and food industries. This in turn would increase wastewater generation from dye industrial activities. Various dyes and its structural compounds present in dye industrial wastewater have harmful effects on plants, animals and humans. Synthetic dyes are more resistant than natural dyes to physical and chemical methods for remediation which makes them more difficult to get decolorize. Microbial degradation has been researched and reviewed largely for quicker dye degradation. Genetically engineered microorganisms (GEMs) play important role in achieving complete dye degradation. This paper provides scientific and technical information about dyes & dye intermediates and biodegradation of azo dye. It also compiles information about factors affecting dye(s) biodegradation, role of genetically modified organisms (GMOs) in process of dye(s) degradation and perspectives in this field of research.

A strategy towards the synthesis of superhydrophobic/superoleophilic non-fluorinated polypyrrole nanotubes for oil-water separation

Superhydrophobic/superoleophilic materials have shown great potential for applications in oil/water separation. However, practical applications of these materials are restricted due to their toxicity and complicated, expensive, and non-eco-friendly fabrication procedures. Here, we have successfully developed an easy, simple, cost-effective, and environmentally friendly strategy towards the synthesis of superhydrophobic and superoleophilic porous polypyrrole nanotubes. Such wettability has been introduced into polypyrrole by co-doping with sodium dodecylbenzenesulfonate, a surfactant for lowering surface energy and controlling the morphology of the nanotubes. These non toxic and environment friendly polymer nanotubes exhibit oil absorption capability from oil/water mixtures with a reasonable efficiency with good reusability.

A study on the utility of immobilized cells of indigenous bacteria for biodegradation of reactive azo dyes

Azo dyes are recalcitrant compounds used as a colorant in various industries. The pollution caused by their extensive usage has adversely affected the environment for years. The existing physicochemical methods for dye pollution remediation are rather inefficient and hence there is a dearth of low-cost, potential systems capable of dye degradation. The current research studies the biodegradation potential of immobilized bacterial cells against azo dyes Reactive Orange 16 (RO-16) and Reactive Blue 250 (RB-250). Two indigenous dye degrading bacteria Bacillus sp. VITAKB20 and Lysinibacillus sp. KPB6 was isolated from textile sludge sample. Free cells of Bacillus. sp. VITAKB20 degraded 92.38% of RO-16 and that of Lysinibacillus sp. KPB6 degraded 95.36% of RB-250 within 72 h under static conditions. Upon immobilization with calcium alginate, dye degradation occurred rapidly. Bacillus. sp. VITAKB20 degraded 97.5% of RO-16 and Lysinibacillus sp. KPB6 degraded 98.2% of RB-250 within 48 h under shaking conditions. Further, the nature of dye decolorization was biodegradation as evident by high-performance liquid chromatography (HPLC), and Fourier-transform infrared spectroscopy (FTIR) results. Phytotoxicity and biotoxicity assays revealed that the degraded dye products were less toxic in nature than the pure dyes. Thus, immobilization proved to be a highly likely alternative treatment for dye removal.

The ant Lasius niger is a new source of bacterial enzymes with biotechnological potential for bleaching dye

Industrial synthetic dyes cause health and environmental problems. This work describes the isolation of 84 bacterial strains from the midgut of the Lasius niger ant and the evaluation of their potential application in dye bioremediation. Strains were identified and classified as judged by rRNA 16S. The most abundant isolates were found to belong to Actinobacteria (49%) and Firmicutes (47.2%). We analyzed the content in laccase, azoreductase and peroxidase activities and their ability to degrade three known dyes (azo, thiazine and anthraquinone) with different chemical structures. Strain Ln26 (identified as Brevibacterium permense) strongly decolorized the three dyes tested at different conditions. Strain Ln78 (Streptomyces ambofaciens) exhibited a high level of activity in the presence of Toluidine Blue (TB). It was determined that 8.5 was the optimal pH for these two strains, the optimal temperature conditions ranged between 22 and 37 °C, and acidic pHs and temperatures around 50 °C caused enzyme inactivation. Finally, the genome of the most promising candidate (Ln26, approximately 4.2 Mb in size) was sequenced. Genes coding for two DyP-type peroxidases, one laccase and one azoreductase were identified and account for the ability of this strain to effectively oxidize a variety of dyes with different chemical structures.

Treatment of synthetic textile wastewater containing dye mixtures with microcosms

The aim was to assess the ability of microcosms (laboratory-scale shallow ponds) as a post polishing stage for the remediation of artificial textile wastewater comprising two commercial dyes (basic red 46 (BR46) and reactive blue 198 (RB198)) as a mixture. The objectives were to evaluate the impact of Lemna minor L. (common duckweed) on the water quality outflows; the elimination of dye mixtures, organic matter, and nutrients; and the impact of synthetic textile wastewater comprising dye mixtures on the L. minor plant growth. Three mixtures were prepared providing a total dye concentration of 10 mg/l. Findings showed that the planted simulated ponds possess a significant (p < 0.05) potential for improving the outflow characteristics and eliminate dyes, ammonium-nitrogen (NH₄-N), and nitrate-nitrogen (NO₃-N) in all mixtures compared with the corresponding unplanted ponds. The removal of mixed dyes in planted ponds was mainly due to phyto-transformation and adsorption of BR46 with complete aromatic amine mineralisation. For ponds containing 2 mg/l of RB198 and 8 mg/l of BR46, removals were around 53%, which was significantly higher than those for other mixtures: 5 mg/l of RB198 and 5 mg/l of BR46 and 8 mg/l of RB198 and 2 mg/l of BR46 achieved only 41 and 26% removals, respectively. Dye mixtures stopped the growth of L. minor, and the presence of artificial wastewater reduced their development.

Mineralization of a sulfonated textile dye Reactive Red 31 from simulated wastewater using pellets of Aspergillus bombycis

BACKGROUND

Reactive Red 31, applied extensively in the commercial textile industry, is a hazardous and persistent azo dye compound often present in dye manufacturing and textile industrial effluents. Aspergillus bombycis strain was isolated from dye contaminated zones of Gujarat Industrial Development Corporation, Vatva, Ahmedabad, India. The decolorization potential was monitored by the decrease in maximum absorption of the dye using UV-visible spectroscopy. Optimization of physicochemical conditions was carried out to achieve maximum decolorization of Reactive Red 31 by fungal pellets.

RESULTS

Pellets of A. bombycis strain were found to decolorize this dye (20 mg/L) under aerobic conditions within 12 h. The activity of azoreductase, laccase, phenol oxidase and Manganese peroxidase in fungal culture after decolorization was about 8, 7.5, 19 and 23.7 fold more than before decolorization suggesting that these enzymes might be induced by the addition of Reactive Red 31 dye, and thus results in a higher decolorization. The lab-scale reactor was developed and mineralization of Reactive Red 31 dye by fungal pellets was studied at 6, 12 and 24 h of HRT (hydraulic retention time). At 12 h of HRT, decolorization potential, chemical oxygen demand (COD) and total organic carbon reduction (TOC) was 99.02, 94.19, and 83.97%, respectively, for 20 mg/L of dye concentration.

CONCLUSIONS

Dye decolorization potential of A. bombycis culture was influenced by several factors such as initial dye concentration, biomass concentration, pH, temperature, and required aerated conditions. Induction of azoreductase, laccase, phenol oxidase, and Mn-peroxidase enzymes was observed during dye decolorization phase. A. bombycis pellets showed potential in mineralization of dye in the aerobic reactor system. Isolated fungal strain A. bombycis showed better dye decolorization performance in short duration of time (12 h) as compared to other reported fungal cultures.Graphical abstractDegradation of RR31 dye in developed aerobic fungal pelleted reactor.

Degradation and detoxification of methylene blue dye adsorbed on water hyacinth in semi continuous anaerobic–aerobic bioreactors by novel microbial consortium-SB

Combinatorial adsorption–biodegradation treatment of textile wastewater provides a cost effective and ecofriendly alternative to conventional physicochemical treatment methods.

Biotransformation studies of textile dye Remazol Orange 3R

In the present study, biotransformation of Remazol Orange 3R (RO3R) was studied using well-known bacterial isolate Pseudomonas aeruginosa strain BCH. The dye was decolorized up to 98 % within 15 min. The induction in the level of various oxidoreductive enzymes viz. laccase, tyrosinase, veratryl alcohol oxidase and DCIP reductase were observed in the cells obtained after decolorization of RO3R, which supports their role in decolorization. The metabolites of RO3R obtained after biodegradation were identified and characterized by various analytical techniques viz, HPLC, FTIR, and GC–MS. The RO3R was transformed to the N-(7 amino 8 hydroxy-napthalen-2yl) actamide (m/z, 198), Acetamide (m/z, 59) and Napthalen-1-ol (m/z, 144).

Preferential biodegradation of structurally dissimilar dyes from a mixture by Brevibacillus laterosporus

Biodegradation of a mixture containing seven commercial textile dyes with different structures and color properties has been investigated by an ecofriendly strain--Brevibacillus laterosporus MTCC 2298. It showed 87% decolorization in terms of ADMI removal (American Dye Manufacturing Institute) within 24h. The effective decolorization of dye mixture was attained in the presence of metal salt--CaCl(2) and nitrogen sources. The induction of oxido-reductive enzymes such as veratryl alcohol oxidase, tyrosinase, NADH-DCIP reductase and azo reductase was found to be responsible for biotransformation of dyes. High performance thin layer chromatography exposed the mechanism of preferential biodegradation of dyes at different time periods. Significant change in the high pressure liquid chromatography and Fourier transform infrared spectroscopy of sample before and after treatment confirmed the biodegradation of dye mixture. Phytotoxicity study revealed the much less toxic nature of the metabolites produced after the degradation of dyes mixture.

A study on significant microbial interaction leading to decolorization and degradation of textile dye Rubine 3GP

The present study evaluates an obligatory interaction between the yeast Saccharomyces cerevisiae NCIM 3312 and the bacterium Pseudomonas sp. strain BCH3 for the biodegradation of the dye Rubin 3GP (R3GP). No significant degradation of R3GP was observed either by Saccharomyces cerevisiae NCIM 3312 or by Pseudomonas sp. strain BCH3, when both the cultures were tested individually under their respective optimum medium conditions. However, when both of them were allowed to intermingle with each other, R3GP was found to be degraded within 72 h, with a steady increase in β -1,3-glucanase, chitinase and protease activity in the culture supernatant; indicating the possible role of Pseudomonas sp. strain BCH3 in cell wall lysis of S. cerevisiae NCIM 3312. The present study elucidates a rare microbial interaction where the bacterium Pseudomonas sp. strain BCH3 utilizes lysed yeast cells as the sole source of nutrients for its own growth and subsequently performs decolorization and degradation of R3GP. Enzymatic status showed involvement of various oxidoreductive enzymes like lignin peroxidase, laccase, DCIP reductase and azo reductase, indicating their role in decolorization and degradation of R3GP. Degradation was confirmed using HPLC, FTIR analysis and the biochemical pathway of degradation was elucidated by using GC-MS analysis.