Optimization of triazo Acid Black 210 dye degradation by Providencia sp. SRS82 and elucidation of degradation pathway

Potential of halophiles and alkaliphiles in bioremediation of azo dyes-laden textile wastewater: a review

Azo dye-laden textile wastewater must be treated before release due to various health and environmental concerns. Bioremediation of textile wastewater, however, is a challenge owing to its alkaline and saline nature as mesophilic microbes, in general, are either not able to thrive or show less efficiency under such hostile environment. Thus, pre-treatment for neutralization or salinity removal becomes a prerequisite before applying microbes for treatment, causing extra economical and technical burden. Extremophilic bacteria can be the promising bioremediating tool because of their inherent ability to survive and show toxicants removal capability under such extreme conditions without need of pre-treatment. Among extremophiles, halophilic and alkaliphilic bacteria which are naturally adapted to high salt and pH are of special interest for the decolorization of saline-alkaline-rich textile wastewater. The current review article is an attempt to provide an overview of the bioremediation of azo dyes and azo dye-laden textile wastewater using these two classes of extremophilic bacteria. The harmful effects of azo dyes on human health and environment have been discussed herein. Halo-alkaliphilic bacteria circumvent the extreme conditions by various adaptations, e.g., production of certain enzymes, adjustment at the protein level, pH homeostasis, and other structural adaptations that have been highlighted in this review. The unique properties of alkaliphiles and halophiles, to not only sustain but also harboring high dye removal competence at high pH and salt concentration, make them a good candidate for designing future bioremediation strategies for the management of alkaline, salt, and azo dye-laden industrial wastewaters.

Biological and molecular approaches of the degradation or decolorization potential of the hypersaline Lake Tuz Bacillus megaterium H2 isolate

The presence of synthetic dyes in water bodies and soil is one of the major issues affecting the global ecology, possibly impacting societal well-being adversely due to the colorants' recalcitrance and toxicity. Herein, the study spectrophotometrically monitored the ability of the Bacillus megaterium H2 azoreductase (AzrBmH2) to degrade four synthetic dyes, reactive blue 4, remazol brilliant red, thymol blue, and methyl red, followed by in-silico assessment using GROMACS. We found that the bacterium degraded as much as 60% of all four synthetic dyes at various tested concentrations. The genome analysis revealed five different azoreductase genes, which were then modeled into the AzrBmH21, AzrBmH22/3, and AzrBmH24/5 templates. The AzrBmH2-substrate complexes showed binding energies with all the dyes of between -10.6 to -6.9 kcal/mol and formed 4-6 hydrogen bonds with the predicted catalytic binding residues (His10, Glu 14, Ser 58, Met 99, Val 107, His 183, Asn184 and Gln 191). In contrast, the lowest binding energies were observed for the AzrBmH21-substrates (-10.6 to -7.9). Molecular dynamic simulations revealed that the AzrBmH21-substrate complexes were more stable (RMSD 0.2-0.25 nm, RMSF 0.05 - 0.3 nm) and implied strong bonding with the dyes. The Molecular Mechanics Poisson-Boltzmann Surface Area results also mirrored this outcome, showing the lowest azoreductase-dye binding energy in the order of AzrBmH21-RB4 (-78.18 ± 8.92 kcal/mol), AzrBmH21-RBR (-67.51 ± 7.74 kcal/mol), AzrBmH21-TB (-46.62 ± 5.23 kcal/mol) and AzrBmH21-MR (-40.78 ± 7.87 kcal/mol). In short, the study demonstrated the ability of the B. megaterium H2 to efficiently decolorize the above-said synthetic dyes, conveying the bacterium's promising use for large-scale dye remediation.Communicated by Ramaswamy H. Sarma.

Genome-Scale Investigation of the Regulation of azoR Expression in Escherichia coli Using Computational Analysis and Transposon Mutagenesis

Bacterial azoreductases are enzymes that catalyze the reduction of ingested or industrial azo dyes. Although azoreductase genes have been well identified and characterized, the regulation of their expression has not been systematically investigated. To determine how different factors affect the expression of azoR, we extracted and analyzed transcriptional data from the Gene Expression Omnibus (GEO) resource, then confirmed computational predictions by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Results showed that azoR expression was lower with higher glucose concentration, agitation speed, and incubation temperature, but higher at higher culture densities. Co-expression and clustering analysis indicated ten genes with similar expression patterns to azoR: melA, tpx, yhbW, yciK, fdnG, fpr, nfsA, nfsB, rutF, and chrR (yieF). In parallel, constructing a random transposon library in E. coli K-12 and screening 4320 of its colonies for altered methyl red (MR)-decolorizing activity identified another set of seven genes potentially involved in azoR regulation. Among these genes, arsC, relA, plsY, and trmM were confirmed as potential azoR regulators based on the phenotypic decolorization activity of their transposon mutants, and the expression of arsC and relA was confirmed, by qRT-PCR, to significantly increase in E. coli K-12 in response to different MR concentrations. Finally, the significant decrease in azoR transcription upon transposon insertion in arsC and relA (as compared to its expression in wild-type E. coli) suggests their probable involvement in azoR regulation. In conclusion, combining in silico analysis and random transposon mutagenesis suggested a set of potential regulators of azoR in E. coli.

Biotreatment of azo dye containing textile industry effluent by a developed bacterial consortium immobilised on brick pieces in an indigenously designed packed bed biofilm reactor

This study highlights the development of a lab-scale, indigenously designed; Packed-Bed Biofilm Reactor (PBBR) packed with brick pieces. The developed biofilm in the reactor was used for the decolourisation and biodegradation of the textile industry effluent. The PBBR was continuously operated for 264 days, during which 301 cycles of batch and continuous treatment were operated. In batch mode under optimised conditions, more than 99% dye decolourisation and ≥ 92% COD reduction were achieved in 6 h of contact time upon supplementation of effluent with 0.25 g L^-1 glucose, 0.25 g L^-1 urea, and 0.1 g L^-1 phosphates. A decolourisation rate of 133.94 ADMI units h^-1 was achieved in the process. PBBR, when operated in continuous mode, showed ≥ 95% and ≥ 92% reduction in ADMI and COD values. Subsequent aeration and passage through the charcoal reactor assisted in achieving a ≥ 96% reduction in COD and ADMI values. An overall increase of 81% in dye-laden effluent decolourisation rate, from 62 to 262 mg L^-1 h^-1, was observed upon increasing the flow rate from 18 to 210 mL h^-1. Dye biodegradation was determined by UV-Vis and FTIR spectroscopy and toxicity study. SEM analysis showed the morphology of the attached-growth biofilm.

Bacillus subtilis: As an Efficient Bacterial Strain for the Reclamation of Water Loaded with Textile Azo Dye, Orange II

The azo dye orange II is used extensively in the textile sector for coloring fabrics. High concentrations of it are released into aqueous environments through textile effluents. Therefore, its removal from textile wastewater and effluents is necessary. Herein, initially, we tested 11 bacterial strains for their capabilities in the degradation of orange II dye. It was revealed in the preliminary data that B. subtilis can more potently degrade the selected dye, which was thus used in the subsequent experiments. To achieve maximum decolorization, the experimental conditions were optimized whereby maximum degradation was achieved at: a 25 ppm dye concentration, pH 7, a temperature of 35 °C, a 1000 mg/L concentration of glucose, a 1000 mg/L urea concentration, a 666.66 mg/L NaCl concentration, an incubation period of 3 days, and with hydroquinone as a redox mediator at a concentration of 66.66 mg/L. The effects of the interaction of the operational factors were further confirmed using response surface methodology, which revealed that at optimum conditions of pH 6.45, a dye concentration of 17.07 mg/L, and an incubation time of 9.96 h at 45.38 °C, the maximum degradation of orange II can be obtained at a desirability coefficient of 1, estimated using the central composite design (CCD). To understand the underlying principles of degradation of the metabolites in the aliquot mixture at the optimized condition, the study steps were extracted and analyzed using GC-MS(Gas Chromatography Mass Spectrometry), FTIR(Fourier Transform Infrared Spectroscopy), ¹H and carbon 13 NMR(Nuclear Magnetic Resonance Spectroscopy). The GC-MS pattern revealed that the original dye was degraded into o-xylene and naphthalene. Naphthalene was even obtained in a pure state through silica gel column isolation and confirmed using ¹H and ¹³C NMR spectroscopic analysis. Phytotoxicity tests on Vigna radiata were also conducted and the results confirmed that the dye metabolites were less toxic than the parent dye. These results emphasize that B. subtilis should be used as a potential strain for the bioremediation of textile effluents containing orange II and other toxic azo dyes.

Synthesis, column packing and liquid chromatography of molecularly imprinted polymers for the acid black 1, acid black 210, and acid Brown 703 dyes

Molecularly imprinted polymers have been synthesized for the acid black 1, acid black 210, and acid brown 703 dyes using methacrylic acid, ethylene glycol, and azobisisobutyronitrile as the monomer, cross-linker, and initiator, respectively, in the ratio of 1 : 10 : 44 (template:monomer:cross-linker). The MIPs were used for the selective removal of their corresponding dyes. The selective nature of the MIPs towards their respective dyes was confirmed by a homemade liquid chromatography system. The resultant polymer materials were packed in a stainless steel column and checked for the separation of mixtures of dyes in liquid chromatography. The dyes complementary in structure to the imprinted cavities in the MIPs had long retention times, showing the highly selective nature of the MIPs. The pH, quantity of the MIPs, time, and concentration of the dyes were optimized for the highly efficient removal of the newly synthesized MIP adsorbents in batch adsorption studies. First-order, second-order, and intra-particle diffusion models were applied to all the three MIP-based adsorbents for their kinetic investigations towards the dyes. All the three MIPs selectively absorbed their target template molecule in the presence of four other template dyes having closely related structures with % RSD < 4% for the three batch experiments. The synthesized MIPs were characterized by FTIR, SEM imaging and liquid chromatography. FTIR results strongly confirmed the presence of hydrogen bonding interactions (600–900) between the template and the individual monomers present in the unwashed MIPs. Liquid chromatography revealed the highly selective nature of the MIPs towards their template molecules. The synthesized polymeric substances possess excellent thermal, chemical, and mechanical stability and can be reused several hundred times. The MIPs were applied in the removal of dyes from spiked water samples (river water, tap water and distilled water) where the % removal of the dyes by their corresponding MIPs was greater than 90%.

MIP synthesis for the recently emerging dyes, a new method for their characterization in liquid chromatography by packing packing the MIP particles in a stainless steel column, and their application in environmental remediation.

Biodegradation and Detoxification of Azo Dyes by Halophilic/Halotolerant Microflora Isolated From the Salt Fields of Tibet Autonomous Region China

This study aimed to decolorize azo dyes in high-salt industrial wastewater under high-salt and low oxygen conditions using extreme halophilic/halotolerant bacteria screened from the salt fields of Tibet, which consisted of Enterococcus, unclassified Enterobacteriaceae, Staphylococcus, Bacillus, and Kosakonia. Under the optimal conditions, 600 mg/l Congo red, Direct Black G (DBG), Amaranth, methyl red, and methyl orange could be completely decolorized in 24, 8, 8, 12, and 12 h, respectively. When the DBG concentration was 600 mg/l, NADH–DCIP, laccase, and azo reductase were confirmed to be the primary reductase and oxidase during the degradation process, and the degradation pathways were verified. The microflora could not only tolerate changes in salt concentrations of 0–80 g/l, but also displayed strong degradative ability. Under high-salt concentrations (≥ 60 g/l NaCl), NADH–DCIP reductase was primarily used to decolorize the azo dye. However, under low salt concentrations (≤ 40 g/l NaCl), azo reductase began to function, and manganese peroxidase and lignin peroxidase could cooperate to participate in DBG degradation. Additionally, the halophilic/halophilic microflora was shown to convert the toxic DBG dye to metabolites of low toxicity based on phytotoxicity analysis, and a new mechanism for the microflora to degrade DBG was proposed based on intermediates identified by liquid chromatography-mass spectrometry (LC–MS). This study revealed that the halophilic/halophilic microflora has effective ecological and industrial value for treating wastewater from the textile industry.

Biodegradation, Decolorization, and Detoxification of Di-Azo Dye Direct Red 81 by Halotolerant, Alkali-Thermo-Tolerant Bacterial Mixed Cultures

Azo dyes impact the environment and deserve attention due to their widespread use in textile and tanning industries and challenging degradation. The high temperature, pH, and salinity used in these industries render industrial effluent decolorization and detoxification a challenging process. An enrichment technique was employed to screen for cost-effective biodegraders of Direct Red 81 (DR81) as a model for diazo dye recalcitrant to degradation. Our results showed that three mixed bacterial cultures achieved ≥80% decolorization within 8 h of 40 mg/L dye in a minimal salt medium with 0.1% yeast extract (MSM-Y) and real wastewater. Moreover, these mixed cultures showed ≥70% decolorization within 24 h when challenged with dye up to 600 mg/L in real wastewater and tolerated temperatures up to 60 °C, pH 10, and 5% salinity in MSM-Y. Azoreductase was the main contributor to DR81 decolorization based on crude oxidative and reductive enzymatic activity of cell-free supernatants and was stable at a wide range of pH and temperatures. Molecular identification of azoreductase genes suggested multiple AzoR genes per mixed culture with a possible novel azoreductase gene. Metabolite analysis using hyphenated techniques suggested two reductive pathways for DR81 biodegradation involving symmetric and asymmetric azo-bond cleavage. The DR81 metabolites were non-toxic to Artemia salina nauplii and Lepidium sativum seeds. This study provided evidence for DR81 degradation using robust stress-tolerant mixed cultures with potential use in azo dye wastewater treatment.

Enzymatic biodegradation, kinetic study, and detoxification of Reactive Red-195 by Halomonas meridiana isolated from Marine Sediments of Andaman Sea, India

Azo dyes are a significant class of hazardous chemicals that are extensively utilised in diverse industries. Industries that manufacture and consume reactive azo dyes generate hyper-saline wastewater. The ability of halotolerant bacteria to thrive under extreme environmental conditions thus makes them a potential candidate for reactive azo dye degradation. An efficient halotolerant bacterium (isolate SAIBP-6) with the capability to degrade 87.15% of azo dye Reactive Red 195 (RR-195) was isolated from sea sediment and identified as Halomonas meridiana SAIBP-6. Strain SAIBP-6 maintained potential decolourisation under a wide range of environmental conditions viz. 35-45°C temperature, 50-450 mg/L RR-195, pH 7-9, and 50-150 g/L NaCl. However, maximum decolourisation occurred at 40°C, 200 mg/L RR-195 dye, pH 9, and 50 g/L NaCl, under static conditions. Tyrosinase and azoreductase were responsible for dye degradation. The reaction catalysed by these enzymes followed zero-order kinetics. The maximum velocity (Vmax) of the enzymatic reaction was 4.221 mg/(L.h) and the Michaelis constant (Km) was 517.982 mg/L. Strain SAIBP-6 also efficiently decolourised Reactive Black-5 and Reactive Yellow-160 dye. The biodegradation process was further studied with the help of UV-Vis spectral scan, ultra-high performance liquid chromatography (UPLC), fourier-transform infra-red spectroscopy (FT-IR), and proton nuclear magnetic resonance (¹H NMR) analysis. Finally, cytogenotoxicity assay conducted with the meristematic root tip cells of Allium cepa and phytotoxicity assay conducted with the seeds of Vigna mungo led to the inference that strain SAIBP-6 significantly reduced the toxicity of RR-195 after biodegradation.

Microbe mediated remediation of dyes, explosive waste and polyaromatic hydrocarbons, pesticides and pharmaceuticals

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Environmental pollutants dyes, pesticides, pharmaceuticals, explosive waste and polyaromatic hydrocarbons.

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Environmental pollutants toxicity.

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Possible microbial biodegradation pathways of environmental pollutants.

Industrialization and human activities have led to serious effects on environment. With the progress taking place in the biodegradation field, it is important to summarize the latest advancement. In this review, we intend to provide insights on the recent progress on the biodegradation of environmental contaminants such as dyes, pesticides, pharmaceuticals, explosive waste and polyaromatic hydrocarbons by microorganisms. Along with the biodegradation of environmental contaminants, toxicity effects have also been discussed.

Biological decolorization of Amaranth dye with Trametes polyzona in an airlift reactor under three airflow regimes

In the present work, a strain of the basidiomycete fungus Trametes polyzona was used to decolorize the Amaranth dye. The decolorization was carried out in an Airlift reactor with three flow regimes: 1, 2, and 3 vvm. The results showed that the decolorization was a function of the flow regime. The decolorization times for the regimes of 1, 2, and 3 vvm were 30, 25, and 19 days, respectively. The COD (Chemical Oxygen Demand) decreased from 1600 to 72 mg COD/L. The enzymatic activity kinetics of laccase (Lcc), lignin peroxidase (LiP), and manganese peroxidase (MnP) were determined. In all the treatments, the enzyme LiP was expressed during the first 6 days, at which point 80% decolorization was observed, whereas Lcc and MnP enzymes were produced from day 6 until the end of the decolorization process. The effluent generated showed no inhibitory effects on the growth of the algae Nannochloropsis salina. T. polyzona showed great versatility in the decolorization of synthetic effluents containing the Amaranth dye, and the fungus was able to use this dye as its only carbon source starting at the beginning of the process. LiP was the enzyme that contributed the most to the decolorization process, and on average, 95% decreases in color and the COD were observed.

Effects of the Addition of Fe, Co on the Azo Dye Degradation Ability of Mn-Al Mechanically Alloyed Powders

Azo compounds are used in the textile and leather industry. A significant step during the azo dyes treatment of water is the degradation by breaking the N=N bonds. This break produces the decolorization of water. In this research work, 10% atomic of Fe or Co was added to produce ternary Mn-Al-rich, nanostructured, mechanically alloyed powders in order to improve the decolorization of Reactive Black 5 solutions and to check Fe and Co addition’s influence. The microstructure was followed by X-ray diffraction, the morphology and composition by electronic microscopy and energy-dispersive X-ray spectroscopy (EDS) microanalysis. The dye degradation was monitored with ultraviolet/visible absorption spectrophotometry. After degradation, the remaining organic compound was checked by high-performance liquid chromatography (HPLC) and the functional groups of the powdered alloys by infrared spectroscopy. Fe addition to Mn-Al displayed faster kinetics and a higher efficiency than the Co addition. The Mn-Al-Fe solution (0.25 g/100 mL) was fully decolorized in 5 min. On the other side, Mn-Al-Co powders were able to successfully decolorize the dyed solution in 10 min under the same conditions. Thus, nanocrystalline Fe-doped Mn-Al alloys are good candidates for use in the decolorization process, in comparison with Co-doped and other intermetallic particles.

Degradation and Toxicity Analysis of a Reactive Textile Diazo Dye-Direct Red 81 by Newly Isolated Bacillus sp. DMS2

An efficient diazo dye degrading bacterial strain, Bacillus sp. DMS2 was isolated from a long-term textile dye polluted environment. The strain was assessed for its innate ability to completely degrade and detoxify Direct Red 81 (DR81) textile dye under microaerophilic conditions. The degradation ability of strain showed significant results on optimizing the nutritional and environmental parameters. Based on statistical models, maximum efficiency of decolorization achieved within 24 h for 100 mg/l of dye supplemented with glucose (0.02%), MgSO₄ (0.002%) and urea (0.5%) at 30°C and pH (7.0). Moreover, a significant catabolic induction of a laccase and azoreductase suggested its vital role in degrading DR81 into three distinct metabolites (intermediates) as by-products. Further, toxicity analysis of intermediates were performed using seeds of common edible plants, aquatic plant (phytotoxicity) and the nematode model (animal toxicity), which confirmed the non-toxic nature of intermediates. Thus, the inclusive study of DMS2 showed promising efficiency in bioremediation approach for treating industrial effluents.

Optimization for enhanced ecofriendly decolorization and detoxification of Reactive Blue160 textile dye by Bacillus subtilis

The bacterial strain capable of decolorization and detoxification of the Reactive Blue 160 dye was isolated from a dye waste disposal site of Tirupur textile industries. The bacterial strain was screened and selected based on its decolorization capability of RB 160dye, which was identified as Bacillus subtilis by 16S rRNA sequencing. The strain was tested for the decolorization potential under different physio-chemical experimental conditions (pH, temperature, agitation, non-agitation) and observed a complete decolorization at pH 7 and 35 °C under shaking condition within 48 h of time. The enzymes such as, Lignin peroxidase, azoreductase and NADH-DCI were significantly induced in the strain during the decolorization of RB160 dye. Phytotoxicity and microbial toxicity studies revealed that the decolorized product of RB160 dye is less toxic to the plants and microbes. Thus, our results recommend the prospective use of B subtilis in bioremediation of RB160 dye.

Performance of a Newly Isolated Salt-Tolerant Yeast Strain Sterigmatomyces halophilus SSA-1575 for Azo Dye Decolorization and Detoxification

The effective degradation of hazardous contaminants remains an intractable challenge in wastewater processing, especially for the high concentration of salty azo dye wastewater. However, some unique yeast symbionts identified from the termite gut system present an impressive function to deconstruct some aromatic compounds, which imply that they may be valued to work on the dye degradation for various textile effluents. In this investigation, a newly isolated and unique yeast strain, Sterigmatomyces halophilus SSA-1575, was identified from the gut system of a wood-feeding termite (WFT), Reticulitermes chinensis. Under the optimized ambient conditions, the yeast strain SSA-1575 showed a complete decolorization efficiency on Reactive Black 5 (RB5) within 24 h, where this azo dye solution had a concentration of a 50 mg/L RB5. NADH-dichlorophenol indophenol (NADH-DCIP) reductase and lignin peroxidase (LiP) were determined as the key reductase and oxidase of S. halophilus SSA-1575. Enhanced decolorization was recorded when the medium was supplemented with carbon and energy sources, including glucose, ammonium sulfate, and yeast extract. To understand a possible degradation pathway well, UV-Vis spectroscopy, FTIR and Mass Spectrometry analyses were employed to analyze the possible decolorization pathway by SSA-1575. Determination of relatively high NADH-DCIP reductase suggested that the asymmetric cleavage of RB5 azo bond was mainly catalyzed by NADH-DCIP reductase, and finally resulting in the formation of colorless aromatic amines devoid of any chromophores. The ecotoxicology assessment of RB5 after a decolorization processing by SSA-1575, was finally conducted to evaluate the safety of its metabolic intermediates from RB5. The results of Microtox assay indicate a capability of S. halophilus SSA-1575, in the detoxification of the toxic RB5 pollutant. This study revealed the effectiveness of halotolerant yeasts in the eco-friendly remediation of hazardous pollutants and dye wastewater processing for the textile industry.

Constructed wetland-microbial fuel cell for azo dyes degradation and energy recovery: Influence of molecular structure, kinetics, mechanisms and degradation pathways

Complete degradation of azo dye has always been a challenge due to the refractory nature of azo dye. An innovative hybrid system, constructed wetland-microbial fuel cell (CW-MFC) was developed for simultaneous azo dye remediation and energy recovery. This study investigated the effect of circuit connection and the influence of azo dye molecular structures on the degradation rate of azo dye and bioelectricity generation. The closed circuit system exhibited higher chemical oxygen demand (COD) removal and decolourisation efficiencies compared to the open circuit system. The wastewater treatment performances of different operating systems were ranked in the decreasing order of CW-MFC (R1 planted-closed circuit) > MFC (R2 plant-free-closed circuit) > CW (R1 planted-open circuit) > bioreactor (R2 plant-free-open circuit). The highest decolourisation rate was achieved by Acid Red 18 (AR18), 96%, followed by Acid Orange 7 (AO7), 67% and Congo Red (CR), 60%. The voltage outputs of the three azo dyes were ranked in the decreasing order of AR18 > AO7 > CR. The results disclosed that the decolourisation performance was significantly influenced by the azo dye structure and the moieties at the proximity of azo bond; the naphthol type azo dye with a lower number of azo bond and more electron-withdrawing groups could cause azo bond to be more electrophilic and more reductive for decolourisation. Moreover, the degradation pathway of AR18, AO7 and CR were elucidated based on the respective dye intermediate products identified through UV-Vis spectrophotometry, high-performance liquid chromatography (HPLC), and gas chromatograph-mass spectrometer (GC-MS) analyses. The CW-MFC system demonstrated high capability of decolouring azo dyes at the anaerobic anodic region and further mineralising dye intermediates at the aerobic cathodic region to less harmful or non-toxic products.

Anionic azo dyes removal from water using amine-functionalized cobalt–iron oxide nanoparticles: a comparative time-dependent study and structural optimization towards the removal mechanism

Efficient and selective removal of azo dyes from water by amine-functionalized-CoFe₂O₄ nanoparticles reliant on structural features such as size, charge, hydrophobicity/hydrophilicity, and S/C atoms.

Study of simultaneous bioremediation of mixed reactive dyes and Cr(VI) containing wastewater through designed experiments

Xenobiotic azo dyes and chromate (Cr(VI)) containing industrial wastewaters cause severe ecological problems. The present bioremediation study aims to treat wastewater containing Cr(VI) ions and mixed azo dyes (reactive red 21 (RR21) and reactive orange 16 (RO16)) by Pseudomonas aeruginosa 23N1. The process optimization of bioremediation is investigated using statistical designed experimental tool of response surface methodology. The ANOVA analysis is performed to evaluate optimal biodecolourization condition. This study shows that the amount of yeast extract has major influence on biodecolourization performance. The decolourization of individual RO16 and RR21 dye in presence of 60 mg/L of Cr(VI) ions is obtained as 88.5 ± 0.8 and 92.3 ± 0.7% for 100 and 150 mg/L initial dye concentrations, respectively. In this study, bacteria exhibit high Cr(VI) removal potential of ~ 99.1% against initial Cr(VI) concentration of 150 mg/L. The negative influence of Cr(VI) ions on biodecolourization is only noticed when initial Cr(VI) concentration in wastewater is found above 150 mg/L. The results reveal that bacteria studied here could be used to biodecolourize dyes even in high saline condition (> 6000 mg/L). The reduction of ~ 80% in American Dye Manufacturers Institute colour index value is achieved for mixed dyes solution containing 50 mg/L of both RR21 and RO16 dyes along with 50 mg/L Cr(VI) ions. Significant changes in the UV-visible and ATR-FTIR spectra are observed in treated water that confirms the biodegradation of dyes. Toxicity study with Vigna radiata reveals the non-toxicity of degraded metabolites and strain 23N1 is recommended as an effective bioremediation agent.

Removal of dimethachlon from soils using immobilized cells and enzymes of a novel potential degrader Providencia stuartii JD

The first potential degrader capable of detoxifying dimethachlon (NDPS) was isolated and identified as Providencia stuartii JD, whose free cells and freely crude enzymes degraded more than 80% and 90% of 50 mg L^-1 NDPS in liquid culture within 7 d and 2 h, respectively. Strain JD metabolized NDPS through the typical pathway, in which NDPS was firstly transformed into succinic acid and 3, 5-dichloroanilin, and the latter was then converted to phenol, which was subsequently degraded to muconic acid further subjected to the mineralization. The immobilization obviously improved the stability and adaptability of cells and enzymes. In laboratory non-sterile soils treated by free or immobilized cells and enzymes, 50 mg kg^-1 NDPS decreased to 15.66 and 13.32 mg kg^-1, or 8.32 and 2.18 mg kg^-1 within 7 d, respectively. In field, immobilized cells and enzymes exhibited significantly higher efficiencies in removing 20.250 kg a.i. ha^-1 NDPS wettable powder from soils after 9 d (96.02% and 98.56%) than free cells and enzymes (79.35% and 66.45%). This study highlights that strain JD promises the great potential to remove hazardous NDPS residues and its immobilized cells and enzymes possess the more promising advantages in the bioremediation of NDPS-contaminated soils in situ.

Optimization of complete RB-5 azo dye decolorization using novel cold-adapted and mesophilic bacterial consortia

Azo dyes are an important group of recalcitrant xenobiotics, which are difficult to degrade and deteriorate in cold environments. In this study, two microbial consortia consisting of cold-adapted and mesophilic bacteria were developed for effective decolorization of Reactive Black-5 azo dye. These bacteria were isolated from textile wastewater and soil of a cold region. Identification of bacterial isolates using 16s rRNA gene analysis revealed that they belong to genus Pseudoarthrobacter, Gordonia, Stenotrophomonas, and Sphingomonas. Decolorization assay was performed for every strain at dye concentrations of 25, 50 and 100 mg/L and the consortia PsGo consisting of mesophilic bacteria and StSp consisting of cold-adapted bacteria were constructed accordingly. Results showed that the consortia PsGo and StSp were able to decolorize 54 and 34 percent of RB-5 (50 mg/L) during 7 days. To improve the dye removal efficiency of the consortia, several parameters including temperature, pH, carbon and nitrogen sources were optimized. Over longer periods, StSp consortium managed to completely decolorize RB-5 (50 mg/L) at optimized conditions of 25-30 °C, pH 9, and using glucose and NH₄H₂PO₄ as carbon and nitrogen source respectively, whereas PsGo consortium decolorized RB-5 (50 mg/mL) completely at 37 °C, pH 11, and with lactose and NH₄H₂PO₄ used as carbon and nitrogen sources. Kinetic of reactions for StSp and PsGo consortia were found to be 0.05 and 0.13 day^-1 respectively, but became 0.71 and 0.9 day^-1 after optimization. In general, cold ecosystems are good sources for the isolation of novel bacterial strains with a potential application, especially when used as consortia, in environmental biotechnology such as decolorization of RB-5.

Convenient pH-responsive removal of Acid Black 1 by green l-histidine/iron oxide magnetic nanoadsorbent from water: performance and mechanistic studies

This study was aimed at developing green histidine-modified Fe3O4 nanoparticles (His-MNPs) for the adsorptive removal of Acid Black 1 (AB1) from aqueous solution. The His-MNPs were characterized by atomic force microscopy, scanning electron microscopy-energy dispersive X-ray spectrometry, infra-red spectra and thermogravimetry. These MNPs were spherical (average diameter 11-28 nm) with polydispersity index of 1.40 and about 13% mass coating of histidine. To optimize AB1 adsorption on His-MNPs and understand its mechanism, the influences of different operational variables (pH, adsorbent amount, temperature, initial AB1 concentration, contact time, ionic strength, etc.) on adsorption were examined with adsorption isotherms, kinetics and thermodynamic studies. The AB1 adsorption from water was fast with equilibrium time ≤ 45 min. The adsorption equilibrium was best fitted to the Langmuir isotherm model (q max = 166.7 mg g-1 at the adsorbent dose of 0.2 g L-1, temperature 30 °C and pH 4). The linearity order for other isotherms was as follows: Dubinin-Radushkevich (D-R) < Temkin < Freundlich. The kinetics of the AB1 adsorption demonstrated the best compliance with the pseudo-second-order model, predominantly controlled by film diffusion as compared to intraparticle diffusion. Thermodynamic parameters (ΔH° and ΔG°) reflected the exothermic and spontaneous adsorption process. The values of ΔG°, ΔH°, activation energy and D-R free adsorption energy were all consistent with the physisorptive removal of AB1. The spectral (electronic and IR) and pH studies further corroborated the mechanism of AB1 removal by His-MNPs. The His-MNPs showed efficient adsorption, easy regeneration and excellent reusability, assisted by their pH-responsive properties. The prepared adsorbent can provide a safe, effective and economical alternative strategy for removing azo dyes from wastewater.

Process optimization for effective bio-decolourization of reactive orange 16 using chemometric methods

Azo group containing reactive dyes are most commonly used in textile and tannery industries due to its bright appearance and stable color. This study aims to investigate the decolourization of reactive orange 16 (RO16) dye by Pseudomonas aeruginosa 23N1 along with removal of chromate (Cr(VI)) and evaluation of optimal process condition. The regular two-level factorial design is used to screen out operational parameters and selects their levels for further optimization process through central composite design (CCD) based response surface methodology (RSM). The result revealed that glucose and peptone have a negative effect on the performance of dye decolourization. Bacteria exhibit high decolourization potential in yeast extract supplemented culture medium with no addition of external carbon sources. The percentages of decolourization obtained in model validated experiments are obtained as 95.0 ± 0.4% and 95.1 ± 0.5% for initial dye 50 mg/L and 150 mg/L, respectively, which exhibit satisfactory correlation with model predicted response. The simultaneous dye and Cr(VI) removal has been explored in this study. The decolourization of dye is only affected due to presence of high Cr(VI) concentration (>120 mg/L). Bacteria have shown satisfactorily decolourization for RO16 contaminated industrial wastewater. The strain 23N1 could be a good biological agent for decolourization of RO16 dye.

Halomonas sp. strain A55, a novel dye decolorizing bacterium from dye-uncontaminated Rift Valley Soda lake

Considering the saline-alkaline nature of textile wastewater and treatment requirements, microbial samples were collected from Ethiopian Rift Valley Soda Lakes. A large number of bacteria (121) were isolated from dye-uncontaminated Lakes Chitu (81.0%), Abijata (15.7%) and Arenguadie (3.3%), of which 95 isolates (78.5%) were found dye decolorizer. Many dye decolorizer from Lake Chitu positively correlated with higher pH (10.3 ± 0.1), salinity (64.6 ± 2.0%), conductivity (6.1 ± 0.3 mS cm^-1) and Na+ (18.4 ± 0.6 g L^-1) values observed than Abijata and Arenguadie Lakes. Through subsequent screening mechanism, strain A55 was selected to investigate the effect of nutrient (carbon and nitrogen), dissolved oxygen and dye concentration using Reactive Red 184 (RR 184). Based on morphological, biochemical and 16S rRNA gene sequence analysis, the strain was identified as Halomonas sp. Decolorization efficiencies were significantly enhanced with carbon (≥98%) and organic nitrogen (∼100%) than non-carbon/nitrogen (both<55%) supplements. Complete decolorization efficiencies were also observed under anoxic and anaerobic growth conditions. However, growing the isolate with nitrate (<30%) and aerobic (<10%) condition significantly decreased (p < 0.05) color removal efficiency. Kinetic analysis showed that pseudo-first-order best describes RR 184 decolorization process. Overall, the ability of Halomonas sp. strain A55 decolorized different dyes indicate that alkaline soda lake isolates are the potential candidate for treating color containing effluent.

The efficacy of bacterial species to decolourise reactive azo, anthroquinone and triphenylmethane dyes from wastewater: a review

The industrial dye-contaminated wastewater has been considered as the most complex and hazardous in terms of nature and composition of toxicants that can cause severe biotic risk. Reactive azo, anthroquinone and triphenylmethane dyes are mostly used in dyeing industries; thus, the unfixed hydrolysed molecules of these dyes are commonly found in wastewater. In this regard, bacterial species have been proved to be highly effective to treat wastewater containing reactive dyes and heavy metals. The bio-decolourisation of dye occurs either by adsorption or through degradation in bacterial metabolic pathways under optimised environmental conditions. The bacterial dye decolourisation rates vary with the type of bacteria, reactivity of dye and operational parameters such as temperature, pH, co-substrate, electron donor and dissolved oxygen concentration. The present paper reviews the efficiency of bacterial species (individual and consortia) to decolourise wastewater containing reactive azo, anthroquinone and triphenylmethane dyes either individually or mixed or with metal ions. It has been observed that bacteria Pseudomonas spp. are comparatively more effective to treat reactive dyes and metal-contaminated wastewater. In recent studies, either immobilised cell or isolated enzymes are being used to decolourise dye at a large scale of operations. However, it is required to investigate more potent bacterial species or consortia that could be used to treat wastewater containing mixed reactive dyes and heavy metals like chromium ions.

A Doping Lattice of Aluminum and Copper with Accelerated Electron Transfer Process and Enhanced Reductive Degradation Performance

Treatment of azo dye effluents has received increasing concerns over the years due to their potential harms to natural environment and human health. The present study described the degrading ability of the as-synthesized crystalline Al-Cu alloys for removal of high-concentration Acid Scarlet 3R in alkaline aqueous solutions and its degradation mechanism. Al-Cu alloy particles with Al/Cu ratios 19:1 were successfully synthesized by high-energy mechanical milling. Characterization results showed that 10 h mechanical alloying process could lead to the formation of crystalline Al(Cu) solid solution. Batch experiment results confirmed the excellent ability of Al-Cu alloy particles for the degradation of 3R in aqueous solution. Under a certain condition ([Al-Cu]₀ = 2 g/L, [3R]₀ = 200 mg/L, [NaCl]₀ = 25 g/L, initial pH = 10.9), the 3R could be completely degraded within only 3 min. It was also found that the degradation reaction followed zero-order kinetics model with respect to the initial dye concentration. The intermediate compounds were identified by UV-vis, FT-IR and HPLC-MS, and a pathway was proposed. Additionally, post-treatment Al-Cu alloy particles were characterized by SEM and TEM, and the results showed that the degradation might be attributed to the corrosion effect of Al-Cu alloys.

Detoxification of azo dyes in the context of environmental processes

Azo dyes account for >70% of the global industrial demand (∼9 million tons). Owing to their genotoxic/carcinogenic potential, the annual disposal of ∼4,500,000 tons of dyes and/or degraded products is an environmental and socio-economic concern. In comparison to physico-chemical methods, microbe-mediated dye degradation is considered to be low-input, cost-effective and environmentally-safe. However, under different environmental conditions, interactions of chemically diverse dyes with metabolically diverse microbes produce metabolites of varying toxicity. In addition, majority of studies on microbial dye-degradation focus on decolorization with least attention towards detoxification. Therefore, the environmental significance of microbial dye detoxification research of past >3 decades is critically evaluated with reference to dye structure and the possible influence of microbial interactions in different environments. In the absence of ecosystem-based studies, the results of laboratory-based studies on dye degradation, metabolite production and their genotoxic impact on model organisms are used to predict the possible fate and consequences of azo dyes/metabolites in the environment. In such studies, the predominance of fewer numbers of toxicological assays that too at lower levels of biological organization (molecular/cellular/organismic) suggests its limited ecological significance. Based on critical evaluation of these studies the recommendations on inclusion of multilevel approach (assessment at multiple levels of biological organization), multispecies microcosm approach and native species approach in conjunction with identification of dye metabolites have been made for future studies. Such studies will bridge the gap between the fundamental knowledge on dye-microbe-environment interactions and its application to combat dye-induced environmental toxicity. Thus an environmental perspective on dye toxicity in the background of dye structure and effects of environmental processes has been developed. Based on past 3 decades of research on microbial dye detoxification, the current state of knowledge has been analyzed, environmental relevance of these studies was ascertained, research gaps in microbe-mediated azo dye detoxification have been identified and a research framework emphasizing a better understanding of complex interactions between dye-microbe and environmental processes has been proposed. It provides directions for undertaking environmentally sound microbial dye detoxification research.

Ecotoxicological risk assessment of the "Acid Black 210" dye

The "Acid Black 210" dye is one of the most used black dyes by the leather industry. This compound contains three azo groups in its chemical structure, and has been quoted as a non-regulated dye with toxicological concern, since it could generate carcinogenic aromatic amines. The objective of this study was to perform the ecotoxicological risk assessment of this dye through testing its toxicity in vitro and in vivo with the Ames test, the Comet assay, the Daphnia similis test, and the zebrafish embryo acute toxicity test. Moreover, we evaluated the presence of this dye in environmental samples related with a tannery industry. All the tests performed were negative, with the exception of the Ames test with the Salmonella typhimurium TA98 strain, which resulted in a low mutagenic potency. Due to the low concentrations of the "Acid Black 210" dye found in tannery effluents, and the high concentrations where any toxic activity is occasionally described, we concluded that this dye is safe from the ecotoxicological point of view in the areas evaluated and in the light of the current knowledge.

A low-cost wheat bran medium for biodegradation of the benzidine-based carcinogenic dye Trypan Blue using a microbial consortium

Environmental release of benzidine-based dyes is a matter of health concern. Here, a microbial consortium was enriched from textile dye contaminated soils and investigated for biodegradation of the carcinogenic benzidine-based dye Trypan Blue using wheat bran (WB) as growth medium. The PCR-DGGE analysis of enriched microbial consortium revealed the presence of 15 different bacteria. Decolorization studies suggested that the microbial consortium has high metabolic activity towards Trypan Blue as complete removal of 50 mg∙L⁻¹ dye was observed within 24 h at 30 ± 0.2 °C and pH 7. Significant reduction in TOC (64%) and COD (88%) of dye decolorized broths confirmed mineralization. Induction in azoreductase (500%), NADH-DCIP reductase (264%) and laccase (275%) proved enzymatic decolorization of dye. HPLC analysis of dye decolorized products showed the formation of six metabolites while the FTIR spectrum indicated removal of diazo bonds at 1612.30 and 1581.34 cm⁻¹. The proposed dye degradation pathway based on GC-MS and enzyme analysis suggested the formation of two low molecular weight intermediates. Phytotoxicity and acute toxicity studies revealed the less toxic nature of the dye degradation products. These results provide experimental evidence for the utilization of agricultural waste as a novel low-cost growth medium for biodegradation of benzidine-based dyes, and suggested the potential of the microbial consortium in detoxification.

Low-Cost Biodegradation and Detoxification of Textile Azo Dye C.I. Reactive Blue 172 byProvidencia rettgeriStrain HSL1

Present study focuses on exploitation of agricultural waste wheat bran (WB) as growth medium for degradation of textile azo dye C.I. Reactive Blue 172 (RB 172) using a single bacteriumP. rettgeristrain HSL1 (GenBank accession numberJX853768.1). The bacterium was found to completely decolorize 50 mg L−1of dye RB 172 within 20 h at 30 ± 0.2°C under microaerophilic incubation conditions. Additionally, significant reduction in COD (85%) and TOC (52%) contents of dye decolorized medium was observed which suggested its mineralization. Induction in the activities of azoreductase (159%) and NADH-DCIP reductase (88%) provided an evidence for reductive cleavage of dye RB 172. The HPLC, FTIR, and GC-MS analysis of decolorized products confirmed the degradation of dye into various metabolites. The proposed metabolic pathway for biodegradation of RB 172 has been elucidated which showed the formation of 2 intermediate metabolites, namely, 4-(ethenylsulfonyl) aniline and 1-amino-1-(4-aminophenyl) propan-2-one. The acute and phytotoxicity evaluation of degraded metabolites suggests that bacterial strain favors the detoxification of dye RB 172. Thus, WB could be utilized as a low-cost growth medium for the enrichment of bacteria and their further use for biodegradation of azo dyes and its derivatives containing wastes into nontoxic form.