Microbial decolouration of azo dyes: A review

Oerskovia paurometabola can efficiently decolorize azo dye Acid Red 14 and remove its recalcitrant metabolite

The biodegradation of dyes remains one of the biggest challenges of textile wastewater. Azo dyes are one of the most commonly employed dye classes, and biological treatment processes tend to generate recalcitrant aromatic amines, which are more toxic than the parent dye molecule. This study aimed to isolate bacterial strains with the capacity to degrade both the azo dye and the resulting aromatic amines towards the development of a simple and reliable treatment approach for dye-laden wastewaters. A mixed bacterial enrichment was first developed in an anaerobic-aerobic lab-scale sequencing batch reactor (SBR) fed with a synthetic textile wastewater containing the model textile azo dye Acid Red 14 (AR14). Eighteen bacterial strains were isolated from the SBR, including members of the Acinetobacter, Pseudomonas and Oerskovia genera, Oerskovia paurometabola presenting the highest decolorization capacity (91% after 24 h in static anaerobic culture). Growth assays supported that this is a facultative bacterium, and decolorization batch tests with 20-100 mg AR14 L^-1 in a synthetic textile wastewater supplemented with yeast extract indicated that O. paurometabola has a high color removal capacity for a significant range of AR14 concentrations. In addition, a model typically used to describe biodegradation of xenobiotic compounds was adjusted to the results, to predict AR14 biodegradation time profiles at different initial concentrations. HPLC analysis confirmed that decolorization occurred through azo bond reduction under anaerobic conditions, the azo dye being completely reduced after 24 h of anaerobic incubation for the range of concentrations tested. Interestingly, partial (up to 63%) removal of one of the resulting aromatic amines (4-amino-naphthalene-1-sulfonic acid) was observed when subsequently subjected to aerobic conditions. Overall, this work showed the azo dye biodegradation potential of specific bacterial strains isolated from mixed culture bioreactors, reporting for the first time the decolorization capacity of an Oerskovia sp. with further biodegradation of a recalcitrant sulfonated aromatic amine metabolite.

Bacopa monnieri (L.) Pennell, a potential plant species for degradation of textile azo dyes

The current study highlighted the phytoremediation potential of Bacopa monnieri (L.) Pennell for most commonly used azo dyes which are resistant to degradation. Fourteen azo dyes (reactive: 09; direct: 05) upon treatments up to 40 mg/L were decolorized in the range of 90 to 100% after incubation of 2 weeks in in vitro and hydroponic cultures. No significant alteration in growth of B. monnieri was observed in the presence of dyes R. Magenta MB, R. Navy Blue M2R, Dt. Orange RS, Dt. T Blue GLL, Dt. Sky Blue FF alone, and together in the medium. However, at increasing concentrations (60-100 mg/L), the percent dye decolorization was declined and showed a toxic effect on plant growth. The chlorophyll content declined while membrane damage and osmolyte accumulation were increased in dye treated samples. The biological conversion of produced metabolites was analyzed using FTIR and GC-MS. Our results suggest that the intermediates of Dt. Blue GLL degradation consist L-Proline, N-valeryldecyl ester, 3,5 Di-tert-butyl-4-trimethylsiloxytoulene, and 1,2-benzenedicarboxylic acid, diisooctyl ester. The antioxidative and oxidative enzyme activities in roots and leaves were significantly higher in the presence of dyes over control indicate that these enzymes are involved in degradation of dyes. Percentage seed germination, shoot and root length of seedlings of legume, cereal, and oilseed crop was not affected, suggesting the compatible nature of the produced metabolites. Our results revealed the remarkable ability of Bacopa monnieri for long-term operations that lead to the practical application of phytoremediation in textile industries.

Brilliant red X-3B uptake by a novel polycyclodextrin-modified magnetic cationic hydrogel: Performance, kinetics and mechanism

A novel polycyclodextrin-modified magnetic cationic hydrogel (PCD-MCH) was developed and its performance, kinetics and mechanism for the removal of reactive brilliant red X-3B (X-3B) were studied. The results showed that the zeta-potential of PCD-MCH was 32.8 to 16.7mV at pH3.0-10.5. The maximum X-3B adsorption capacity of PCD-MCH was 2792.3mg/g. The adsorption kinetics could be well-described by the Weber-Morris model and the homogeneous surface diffusion model (HSDM). Diffusion stages corresponding to surface or film diffusion, intra-particle or wide mesopore diffusion, and narrow mesopore/micropore diffusion occurred at 0-120, 120-480 and 480-1200min, respectively. The latter two diffusion stages were rate-controlling for X-3B adsorption kinetics. At the initial X-3B concentration of 600mg/L, the diffusion coefficient (D_s) and external mass transfer coefficient in the liquid phase (k_F) were 3×10^-11cm²/min and 4.68×10^-6cm/min, respectively. X-3B approaching the center of PCD-MCH particles could be observed at 360min. At the end of the third diffusion stage, the C_p at q/q_e=0 was 45.20mg/L, which was close to the homogeneous C_p value of 46mg/L along the radius of PCD-MCH particles. At pH3.0-10.0, PCD-MCH showed stable X-3B adsorption capacities. After five regeneration-reuse cycles, the residual adsorption capacity of regenerated PCD-MCH was higher than 892.7mg/g. The corresponding adsorption mechanism was identified as involving electrostatic interactions, cyclodextrin cavities and hydrogen bonds, of which cyclodextrin cavities showed prominent capture performance towards dye molecules through the formation of inclusion complexes.

Simultaneous cleanup of Reactive Black 5 and cadmium by a desert soil bacterium

Multi-contaminated industrial wastewaters pose serious environmental risks due to high toxicity and non-biodegradability. The work reported here evaluated the ability of Pseudomonas aeruginosa strain Gb30 isolated from desert soil to simultaneously remove cadmium (Cd) and Reactive Black 5 (RB5), both common contaminants in various industrial effluents. The strain was able to grow normally and decolorize 50 mg L^-1 RB5 within 24 h of incubation in the presence of 0.629 m mol L^-1 of Cd²⁺. In order to evaluate strain performance in RB5 detoxification, a cytotoxicity test using Human Embryonic Kidney cells (HEK293) was used. Cadmium removal from culture media was determined using atomic adsorption. Even in presence of (0.115 + 0.157 + 0.401 + 0.381) m mol L^-1, respectively, of Cr⁶⁺, Cd²⁺, Cu²⁺ and Zn²⁺ in the growth medium, strain Gb30 successfully removed 35% of RB5 and 44%, 36%, 59% and 97%, respectively, of introduced Zn²⁺, Cu²⁺, Cr⁶⁺ and Cd²⁺, simultaneously. In order to understand the mechanism of Cd removal used by P. aeruginosa strain Gb30, biosorption and bioaccumulation abilities were examined. The strain was preferentially biosorbing Cd on the cell surface, as opposed to intracellular bioaccumulation. Microscopic investigations using AFM, SEM and FTIR analysis of the bacterial biomass confirmed the presence of various structural features, which enabled the strain to interact with metal ions. The study suggests that Pseudomonas aeruginosa Gb30 is a potential candidate for bioremediation of textile effluents in the presence of complex dye-metal contamination.

Preparation, Performances, and Mechanisms of Microbial Flocculants for Wastewater Treatment

In recent years, close attention has been paid to microbial flocculants because of their advantages, including safety to humans, environmental friendliness, and acceptable removal performances. In this review, the preparation methods of microbial flocculants were first reviewed. Then, the performances of bioflocculants in the removal of suspended solids, heavy metals, and other organic pollutants from various types of wastewater were described and commented, and the removal mechanisms, including adsorption bridging, charge neutralization, chemical reactions, and charge neutrality, were also discussed. The future research needs on microbial flocculants were also proposed. This review would lead to a better understanding of current status, challenges, and corresponding strategies on microbial flocculants and bioflocculation in wastewater treatment.

Vermiculite as heterogeneous catalyst in electrochemical Fenton-based processes: Application to the oxidation of Ponceau SS dye

Modified sodium vermiculite, an iron-rich clay mineral, has been used in novel heterogeneous electrochemical Fenton-based treatments, so-called electro-Fenton (EF)-vermiculite, UVA photoelectro-Fenton (PEF)-vermiculite and solar photoelectro-Fenton (SPEF)-vermiculite. Tests were made with 130 mL of 0.150 mM Ponceau SS diazo dye in 0.050 M Na₂SO₄ at pH 3.0, in the presence of 1.0 g L^-1 catalyst microparticles. The electrolyses were performed in an undivided cell with a boron-doped diamond anode (BDD) and air-diffusion cathode for H₂O₂ production, at 33.3 mA cm^-2. Decolorization and mineralization were upgraded in the sequence: EF-vermiculite < PEF-vermiculite < SPEF-vermiculite. The removal of organics occurred by the combined action of OH oxidant formed at the BDD surface and homogeneous and heterogeneous Fenton's reactions, along with the photolysis caused by UVA light or sunlight. The homogeneous Fenton's reaction resulted from iron ions leaching, but the heterogeneous mechanism was prevalent. Comparative treatments by anodic oxidation in the presence of H₂O₂ and homogeneous EF were less effective than EF-vermiculite. The diazo dye absorbance decays agreed with a pseudo-first-order kinetics. SPEF-vermiculite was the most powerful process, yielding total decolorization and 84.1% mineralization after 300 and 360 min, respectively. The influence of catalyst concentration, current density and diazo dye content on PEF-vermiculite performance was examined. Oxalic, oxamic, malic, tartronic and acetic acids were detected as final short-linear carboxylic acids.

Insights into the production of extracellular polymeric substances of Cupriavidus pauculus 1490 under the stimulation of heavy metal ions

Three different methods (a sulfuric acid method, sodium chloride method and vibration method) were used to extract extracellular polymeric substances (EPS) from Cupriavidus pauculus 1490 (C. pauculus 1490) in the present study. The sodium chloride method was able to extract the maximum amount of EPS (86.15 ± 1.50 mg g⁻¹-DW), and could ensure minimum cell lysis by detecting glucose-6-phosphate dehydrogenase activity and using scanning electron microscopy. This method was therefore selected as the optimal extraction method and used in subsequent experiments. On this basis, the tolerance of C. pauculus 1490 and variations in EPS secretion after the addition of different metal ions was investigated. The tolerance levels of C. pauculus 1490 to Cd(ii), Ni(ii), Cu(ii) and Co(ii) were 300 mg L⁻¹, 400 mg L⁻¹, 400 mg L⁻¹ and 400 mg L⁻¹, respectively. Low concentrations of these heavy metal ions could promote bacterial growth, while increased concentrations were found to inhibit it. The results show that metal ions, especially Cd(ii), stimulate the secretion of EPS, with an EPS yield reaching 956.12 ± 10.59 mg g⁻¹-DW at 100 mg L⁻¹. Real-time polymerase chain reaction (PCR) analysis showed that the key EPS synthetic genes, epsB, epsP and Wzz, were up-regulated. Fourier transform infrared spectroscopy analysis suggested that abundant functional groups in EPS play an important role in heavy metal ion complexation. These results will contribute to our understanding of the tolerance mechanism of microorganisms in the presence of different types and concentrations of metal ions.

Metal ions are shown to stimulate the secretion of EPS components of Cupriavidus pauculus 1490, especially Cd(II).

Bacterial degradation of anthraquinone dyes

Anthraquinone dyes, which contain anthraquinone chromophore groups, are the second largest class of dyes after azo dyes and are used extensively in textile industries. The majority of these dyes are resistant to degradation because of their complex and stable structures; consequently, a large number of anthraquinone dyes find their way into the environment causing serious pollution. At present, the microbiological approach to treating printing and dyeing wastewater is considered to be an economical and feasible method, and reports regarding the bacterial degradation of anthraquinone dyes are increasing. This paper reviews the classification and structures of anthraquinone dyes, summarizes the types of degradative bacteria, and explores the possible mechanisms and influencing factors of bacterial anthraquinone dye degradation. Present research progress and existing problems are further discussed. Finally, future research directions and key points are presented.

Application of Beauveria bassiana spore waste as adsorbent to uptake acid red 97 dye from aqueous medium

The adsorption of acid red 97 dye (RED 97) by the waste of the filamentous fungus Beauveria bassiana was analyzed. The adsorbent was obtained as a waste of a fermentative process, and characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffractometry (XRD), and specific surface area (BET). After the characterization, adsorption tests were carried out to determine the ideal conditions of pH, adsorbent mass, and contact time for the process. Adsorption isotherms, thermodynamic studies, and the treatment of textile effluent were also investigated. The adsorbent characterization allowed the visualization of its amorphous structure, with irregular and heterogeneous particles. The pore diameter was 51.9 nm and the surface area was 0.247 m² g^-1. 1.2 g L^-1 of the adsorbent and pH of 2.0 were the ideal conditions for RED 97 adsorption. The pseudo-second-order kinetic model was the most appropriate to represent the experimental data, being the equilibrium reached in about 110 min. The Langmuir model was the most suitable to represent the equilibrium data, with maximum adsorption capacity of 194.1 mg g^-1 at 45 °C. The adsorption processes was thermodynamically spontaneous, favorable, and exothermic. In the treatment of a real textile effluent, 5 g L^-1 of the spores was capable to decolorize 70% of the solution. Therefore, spore wastes of Beauveria bassiana were promising for RED 97 adsorption.

Microaerophilic biodegradation of raw textile effluent by synergistic activity of bacterial community DR4

Treatment of raw textile effluent (RTE) is very difficult, due to its inherent heterogeneous, low-biodegradable and toxic compositions. Pure and mixed microbial cultures have limited metabolic capabilities in effective mineralization of complex RTE. Therefore, in this study a novel bacterial community DR4 was enriched directly into a complex RTE consisting of 27 different dyes using textile dye polluted soil as an inoculum. The rigorous enrichment process resulted in acclimatization of a taxonomically distinct bacterial population, with an abundance of the genus Comamonas in the bacterial community DR4 as compared to the abundance of Pseudomonas in the RTE respectively, as revealed by high-throughput 16S rRNA gene (V3-V4 region) sequencing. Microaerophilic treatment of RTE by enriched bacterial community DR4, in the presence of optimized electron donor (sucrose) and nitrogen source (yeast extract) resulted in 88% of American Dye Manufacturer's Institute (ADMI) removal and 98% of Chemical oxygen demand (COD) reduction within 32 h at 37 °C. In silico prediction of the functional genes within bacterial community DR4 was made by Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analysis. The PICRUSt analysis revealed high abundance of xenobiotic degradation and metabolism genes. The predicted functional genes and textile dye degradation pathways were further validated using Ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared (FTIR) spectroscopy and High Resolution Liquid Chromatography coupled with Mass Spectrometry (HR-LCMS) based characterization of textile dye degradation metabolites. The activity of azoreductases in the cell-free extracts (CFE) of the enriched bacterial community DR4 was induced by 1.83-7.81 folds in the presence of representative textile dyes as compared to uninduced samples, which confirmed their role in textile effluent decolourization. The degradation of four representative azo dyes present in RTE such as Disperse orange 30, Reactive red 152, Direct blue 2 and Acid brown 15 depicted symmetric degradation of azo bonds by bacterial community DR4.

Facile synthesis of Fe2O3 nanoparticles from Egyptian insecticide cans for efficient photocatalytic degradation of methylene blue and crystal violet dyes

In this study, Fe₂O₃ (hematite) nanoparticles with different crystallite sizes (40-59 nm) were synthesized from Egyptian insecticide cans using the combustion method. The organic fuels were urea, glycine, L-alanine, and L-valine. Fe₂O₃ nanoparticles were characterized utilizing different devices such as BET, PL, FT-IR, XRD, HR-TEM, FE-SEM, UV-Vis, and DTG. Crystal violet (CV) and methylene blue (MB) dyes were efficiently removed from aqueous solution by photocatalytic degradation under UV irradiation in the presence of Fe₂O₃ and H₂O₂. The % degradation of 50 mL crystal violet or methylene blue dye (20 mg/L) using 0.1 g Fe₂O₃ in the presence of H₂O₂ was 100% after 30 or 40 min, respectively. Also, the degradation processes are fitted well with the first order model. Besides, the photocatalytic activity of Fe₂O₃ unaltered even after it was reused three times. Hence, the synthesized Fe₂O₃ nanoparticles can be considered a promising and efficient photocatalyst for the degradation of crystal violet and methylene blue dyes.

Enhancement in catalytic activity of CotA-laccase from Bacillus pumilus W3 via site-directed mutagenesis

CotA-laccases are potential enzymes that are widely used in decolorization of dyes and degradation of toxic substances. In this study, a novel CotA-laccase gene from Bacillus pumilus W3 was applied for rational design. After a series of site-directed genetic mutations, the mutant S208G/F227A showed a 5.1-fold higher catalytic efficiency (k_cat/K_m) than the wild-type CotA-laccase did. The optimal pH of S208G/F227A was 3.5 with ABTS as substrate. The residual activity of mutant S208G/F227A was more than 80% after incubated for 10 h at pH 7-11. Mutant S208G/F227A showed optimal temperature at 80°C with ABTS as substrate. The thermal stability of mutant laccase S208G/F227A was lower than that of wild-type CotA-laccase. This study showed that Gly208 and Ala227 play key roles in catalytic efficiency and it is possible to improve catalytic efficiency of CotA-laccase through site-directed mutagenesis.

Biological decolourization of textile industry wastewater by a developed bacterial consortium

Most currently employed textile effluent decolourization methods use physical and chemical processes where dyes do not get degraded instead concentrated or transferred into a solid phase. Therefore, further treatment processes are required to destroy dyes from the environment. In contrast, biological decolourization may result in degradation of the dye structure due to microbial activities and hence biological processes can be considered environmentally friendly. In the present study, bacterial strains with dye decolourization potential were isolated from the natural environment and their ability to decolourize four different reactive textile dyes was studied individually and in a bacterial consortium. The developed bacterial consortium composed with Proteus mirabilis, Morganella morganii and Enterobacter cloacae indicated more than 90% color removals for all four dyes and optimum decolourization of the dye mixture was observed at 40 °C and pH 7. The developed bacterial consortium decolourized 60% of dyes in textile industry effluent at 35 °C and pH 7 showing their ability to endure in highly complex and toxic environments and application in textile industry wastewaters.

Sequential electrochemical oxidation and bio-treatment of the azo dye congo red and textile effluent

Textile effluent is often difficult to manage as it contains a high concentration of toxic and recalcitrant synthetic dyes. In this study, congo Red and textile effluent were treated by electrochemical oxidation using RuO₂-IrO₂ coated titanium electrode as an anode followed by biodecolorization using Pseudomonas stutzeri MN1 and Acinetobacter baumannii MN3. Effluent pre-treatment is often necessary to minimize the inhibitory effects of textile dyes on dye degrading bacterial during bio-treatment. The pre-treatment of Congo Red by electrochemical oxidation for 10 min resulted in a decolorization rate of 98% at a pH, NaCl concentration, and current density of 7, 2 g L^-1, and 20 mA cm^-2. Subsequent bio-treatment of the pretreated Congo Red enhanced the biodegradation to 93%. The COD removal efficiency in real textile effluent following electrochemical pretreatment and biological treatment using bacterial consortium were 3.8% and 93%, respectively. Therefore, integrating electrochemical oxidation and microbial consortia offers an effective and environmentally friendly approach for treating complex industrial effluents.

Advanced oxidation processes applied for color removal of textile effluent using a home-made peroxidase from rice bran

Enzymes are becoming tools in industrial processes because of several advantages, including activity in mild environmental conditions, and high specificity. Peroxidase, for one, stably oxidizes several substrates. The present study aimed to develop advanced oxidation processes (AOP), using non-commercial rice bran peroxidase to remove color and toxicity of synthetic textile wastewater. Using a microwave and shaker system, we obtained 38.9% and 100% of effluent color removal after peroxidase treatment, respectively. In addition, the shaker system decants residual dye particles through filtration, providing the textile industry with an economical and environmentally viable alternative to effluent treatment. In toxicity tests results, both treatment systems damaged the used genetic material. This damage occurs because of industrial discharge of wastewater into water bodies; effluent dilution reduced this damage. The data suggest that peroxidase as a textile effluent treatment has potential uses in industrial processes, because rice bran peroxidase has demonstrated affinity with dyes.

The Adsorption of Methylene Blue by an Amphiphilic Block Co-Poly(Arylene Ether Nitrile) Microsphere-Based Adsorbent: Kinetic, Isotherm, Thermodynamic and Mechanistic Studies

Dye pollution is a serious problem in modern society. We desired to develop an efficient adsorbent for the decontamination of discharged dyes. In this work, the polymeric microspheres derived from a kind of amphiphilic block of co-poly(arylene ether nitrile) (B-b-S-P) were prepared on the basis of “oil-in-water” (O/W) microemulsion method. The B-b-S-P microspheres were found competent to remove the cationic dye, methylene blue (MB); and various influential factors, such as contact time, initial concentration, solution pH and temperature were investigated. Results indicated that the maximum adsorption capacity of B-b-S-P microspheres for MB was 119.84 mg/g at 25 °C in neutral conditions. Adsorption kinetics and isotherm dates were well fitted to a pseudo-second-order kinetic model and the Langmuir isotherm model, and thermodynamic parameters implied that the adsorption process was endothermic. The B-b-S-P microspheres also exhibited a highly selective adsorption for cationic dye MB, even in the presence of anionic dye methyl orange (MO). In addition, the possible adsorption mechanism was studied, suggesting that the electrostatic interaction and π–π interaction could be the main force in the adsorption process.

Decolorization and detoxification of Direct Blue 2B by indigenous bacterial consortium

Azo dyes are widely used in the textile industry despite being poorly biodegradable and highly toxic. Hence, azo dyes need to be removed from effluent prior to environmental discharge. Microbial communities are efficient for the degradation and mineralization of azo dyes. However, little is known about the functional microbial communities responsible for the degradation process. In this study, a novel indigenous bacteria consortium was developed for characterizing the functional microbial communities involved in the degradation of a sulfonated azo dye, Direct Blue 2B (DB2) in a simple batch reactor. The optimal temperature, pH, and salinity for the decolorization process were 38.70 °C, pH 7.57, and 20.10 g L^-1 NaCl, respectively. The effect of the operating conditions on microbial community structure were determined using high-throughput Illumina HiSeq sequencing. Gammaproteobacteria, Betaproteobacteria, and Bacilli were dominant under most of the operating conditions. At pH above 8 and NaCl concentration above 30 g L^-1, Firmicutes relative abundance did not significantly change suggesting tolerance towards alkaline and hypersaline environments. Tritium aestivum and Glycine max seed germination following exposure to YHK treated DB2 solution was above 80% compared to 50% in untreated DB2 solution. The YHK consortium decolorized dyes structurally different from DB2 such as trimethyl phenyl and direct dyes. The results of this study offer valuable data on improving optimization of dye biodegradation processes and the capability of YHK in in situ bioremediation.

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.

Functional and Transcriptomic Characterization of a Dye-decolorizing Fungus from Taxus Rhizosphere

We isolated three laccase-producing fungus strains from Taxus rhizosphere. Myrotheium verrucaria strain DJTU-sh7 had the highest laccase activity of 216.2 U/ml, which was increased to above 300 U/ml after optimization. DJTU-sh7 had the best decolorizing effect for three classes of reactive dyes. The DJTU-sh7-containing fungal consortium displayed the robust decolorizing ability. Both color removal efficiency and chemical oxygen demand were increased in the consortium mediated biotransformation. Transcriptome changes of M. verrucaria elicited by azo dye and phenolic were quantified by the high throughput transcriptome sequencing, and the activities of the selected oxidases and reductases were determined. The possible involvement of oxidases and reductases, especially laccase, aryl alcohol oxidase, and ferric reductase in the biotransformation of dye and phenolic compounds was revealed at both transcriptomic and phenotypic levels. Revealing the transcriptomic mechanisms of fungi in dealing with organic pollutants facilitates the fine-tuned manipulation of strains in developing novel bioremediation and biodegradation strategies.

We isolated three laccase-producing fungus strains from Taxus rhizosphere. Myrotheium verrucaria strain DJTU-sh7 had the highest laccase activity of 216.2 U/ml, which was increased to above 300 U/ml after optimization. DJTU-sh7 had the best decolorizing effect for three classes of reactive dyes. The DJTU-sh7-containing fungal consortium displayed the robust decolorizing ability. Both color removal efficiency and chemical oxygen demand were increased in the consortium mediated biotransformation. Transcriptome changes of M. verrucaria elicited by azo dye and phenolic were quantified by the high throughput transcriptome sequencing, and the activities of the selected oxidases and reductases were determined. The possible involvement of oxidases and reductases, especially laccase, aryl alcohol oxidase, and ferric reductase in the biotransformation of dye and phenolic compounds was revealed at both transcriptomic and phenotypic levels. Revealing the transcriptomic mechanisms of fungi in dealing with organic pollutants facilitates the fine-tuned manipulation of strains in developing novel bioremediation and biodegradation strategies.

Catalytic Oxidation Process for the Degradation of Synthetic Dyes: An Overview

Dyes are used in various industries as coloring agents. The discharge of dyes, specifically synthetic dyes, in wastewater represents a serious environmental problem and causes public health concerns. The implementation of regulations for wastewater discharge has forced research towards either the development of new processes or the improvement of available techniques to attain efficient degradation of dyes. Catalytic oxidation is one of the advanced oxidation processes (AOPs), based on the active radicals produced during the reaction in the presence of a catalyst. This paper reviews the problems of dyes and hydroxyl radical-based oxidation processes, including Fenton's process, non-iron metal catalysts, and the application of thin metal catalyst-coated tubular reactors in detail. In addition, the sulfate radical-based catalytic oxidation technique has also been described. This study also includes the effects of various operating parameters such as pH, temperature, the concentration of the oxidant, the initial concentration of dyes, and reaction time on the catalytic decomposition of dyes. Moreover, this paper analyzes the recent studies on catalytic oxidation processes. From the present study, it can be concluded that catalytic oxidation processes are very active and environmentally friendly methods for dye removal.

Performance of a newly enriched bacterial consortium for degrading and detoxifying azo dyes

To obtain a bacterial consortium that can degrade azo dyes effectively, a bacterial consortium was enriched that can degrade Metanil yellow effectively. After 6 h, 96.25% Metanil yellow was degraded under static conditions by the bacterial consortium, which was mainly composed of Pseudomonas, Lysinibacillus, Lactococcus, and Dysgonomonas. In particular, Pseudomonas played a main role in the decolorization process. Co-substrate increased the decolorization rate, and yeast powder, peptone, and urea demonstrated excellent effects. The optimal pH value and salinity for the decolorization of azo dyes is 4-7 and 1% salinity respectively. The bacterial consortium can directly degrade many azo dyes, such as direct fast black G and acid brilliant scarlet GR. Azo reductase activity, laccase activity, and lignin peroxidase activity were estimated as the key reductase for decolorization, and Metanil yellow can be degraded into less toxic degradation products through synergistic effects. The degradation pathway of Metanil yellow was analyzed by Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry, which demonstrated that Metanil yellow was cleaved at the azo bond, producing p-aminodiphenylamine and diphenylamine. These findings improved our knowledge of azo-dye-decolorizing microbial resources and provided efficient candidates for the treatment of dye-polluted wastewaters.

Degradation of azo dyes by Alcaligenes aquatilis 3c and its potential use in the wastewater treatment

In the present study, Alcaligenes aquatilis was found to decolorize 82% Synazol red 6HBN after incubation of 4 days at 37 °C and pH 7. Maximum decolorization was found under static conditions by using saw dust and yeast extract as carbon and nitrogen source. It also showed promising potential to decolorize mixture of multiple dyes at a rate of more than 86% in 5 days. Decolorization of dye had positive influence on the growth of bacterium as growth rate was increased along with decolorization. The cleavage of azo bond was confirmed through TLC, HPLC and GC–MS analysis. The dye metabolites produced during bacterial treatment are linked to various pathways including ATP synthesis process. The absence of peaks of wavelength 1612/cm and 1532/cm in bacterially treated FTIR sample demonstrated the cleavage of azo bond. Microbial growth in decolorized dye wastewater shows that bacterially decolorized wastewater is unharmful for the growth of micro-flora. The high decolorization ability of A. aquatilis 3c to convert toxic azo dyes into useful end products may find potential applications in the environmental biotechnology.

Demethylation and desulfonation of textile industry dye, Thiazole Yellow G by Aspergillus niger LAG

Filamentous fungi perform tremendously in adsorption of dyes from polluted environment. In this study, Aspergillus niger LAG decolorized thiazole yellow G dye within 5 days. Scale up studies done revealed that maximum decolorization (98%) was achieved at a concentration (10 mg L^-1), temperature (35 °C) and pH 6. The fungus exhibited significant inductions in laccase (71%) and lignin peroxidase (48%) respectively. Spectrometric analysis (UV-vis, HPLC and gas chromatography-mass spectrometry) was used in analyzing the degraded products of the dye. The GCMS analysis revealed the production of two metabolites; sodium 6-methyl-2-phenyl-1,3-benzothiazole-7-sulfonate and 2-phenyl-4,5-dihydro-1,3-thiazole after degradation of thiazole yellow G dye. A metabolic pathway of thiazole yellow G dye degradation by Aspergillus niger was proposed. Significant growth in plumule and radicle couple with an attendant increase in germination further confirmed the detoxified status of the dye after degradation.

Impact of Crystal Types of AgFeO2 Nanoparticles on the Peroxymonosulfate Activation in the Water

A simple co-precipitation method was developed to synthesize AgFeO₂ nanoparticles (NPs) with hexagonal 2H and 3R polytypes coexistence. The ratio of 2H and 3R types in AgFeO₂ NPs were regulated by controlling the calcination temperature (300, 400, and 500 °C). Such AgFeO₂ NPs were used as heterogeneous catalysts to activate peroxymonosulfate (PMS) for the removal of Orange I (OI) in the water. External water conditions effects and the stability of AgFeO₂ NPs were investigated. The catalytic performance of AgFeO₂ NPs was found to be significantly enhanced with the increasing content of 2H-AgFeO₂. ¹O₂, O₂^•-, SO₄^•-, and •OH were identified as the dominating reactive oxygen species (ROSs) participated in the catalytic process. The electron transfer of Ag⁰/Ag⁺ and Fe²⁺/Fe³⁺ cycles facilitated the decomposition of PMS to generate ROSs. The surface hydroxyl groups (-OH) were regarded as the catalytic active sites. The higher 2H-AgFeO₂ content in AgFeO₂ NPs promoted the concentration of surface hydroxyl groups ( C_-OH) and the reactivity of AgFeO₂ NPs for PMS activation. Based on theoretical calculations, the 2H-AgFeO₂ (004) plane with more Fe sites was more conducive to binding with the -OH compared to the 3R-AgFeO₂ (012) plane, ascribed to the stronger adsorption energy and shorter Fe-O bond length between 2H-AgFeO₂ and -OH.

A perspective on biotechnological applications of thermophilic microalgae and cyanobacteria

The importance of expanding our knowledge on microorganisms derived from extreme environments stems from the development of novel and sustainable technologies for our health, food, and environment. Microalgae and cyanobacteria represent a group of diverse microorganisms that inhabit a wide range of environments, are capable of oxygenic photosynthesis, and form a thick microbial mat even at extreme environments. Studies of thermophilic microorganisms have shown a considerable biotechnological potential due to their optimum growth and metabolisms at high temperatures (≥50 °C), which is supported by their thermostable enzymes. Microalgal and cyanobacterial communities present in high-temperature ecosystems account for a large part of the total ecosystem biomass and productivity, and can be exploited to generate several value-added products of agricultural, pharmaceutical, nutraceutical, and industrial relevance. This review provides an overview on the current status of biotechnological applications of thermophilic microalgae and cyanobacteria, with an outlook on the challenges and future prospects.

Could the porous chitosan-based composite materials have a chance to a "NEW LIFE" after Cu(II) ion binding?

Currently, biosorption is considered a leading-edge environmentally-friendly method for the low-cost remediation of wastewaters contaminated with metal ions. However, the safe disposal of metal-loaded biosorbents is still a challenging issue. In this context, our major objective was to explore the possibility of "waste minimization" by reusing the metal-loaded biosorbents in further environmental applications, particularly into the oxidative catalysis of dyes. Thus, the decolourisation efficiency (DE) of Methyl Orange (MO) in aqueous solutions under ambient light using copper-imprinted chitosan-based composites in comparison to non-imprinted ones was investigated in this work. The MO degradation was established first in the absence of any co-catalyst, when a DE value of 95.3% was achieved by the ion-imprinted catalysts within 360 min of reaction, compared to only 67.4% attained by the non-imprinted ones. Under Fenton-like conditions, the apparent degradation rate constant was seventy times higher, the DE increasing within 40 min to about 98.6%, and 70.5% respectively, whereas the content of co-catalyst (H₂O₂) was significantly lowered compared to other reported studies. The straightforward preparation of copper-loaded composites, along with their excellent stability and high efficiency even after four consecutive reaction runs support our ion-imprinted systems as potential catalysts for dye removal by oxidative decolourisation treatments.

Bio-Removal of Methylene Blue from Aqueous Solution by Galactomyces geotrichum KL20A

The conventional treatments used to remove dyes produced as a result of different industrial activities are not completely effective. At times, some toxic by-products are generated, affecting aquatic ecosystems. In this article, an efficient use of microorganisms is presented as a biodegradation technique that is a safe environmental alternative for the benefit of aquatic life. A strain of the yeast Galactomyces geotrichum KL20A isolated from Kumis (a Colombian natural fermented milk) was used for Methylene Blue (MB) bioremoval. Two parameters of the bioremediation process were studied at three different levels: initial dye concentration and growth temperature. The maximum time of MB exposure to the yeast was 48 h. Finally, a pseudo-first-order model was used to simulate the kinetics of the process. The removal percentages of MB, by action of G. geotrichum KL20A were greater than 70% under the best operating conditions and in addition, the kinetic simulation of the experimental results indicated that the constant rate of the process was 2.2 × 10-2 h−1 with a half time for biotransformation of 31.2 h. The cytotoxicity test based on the hemolytic reaction indicated that by-products obtained after the bioremoval process reached a much lower percentage of hemolysis (22%) compared to the hemolytic activity of the negative control (100%). All of these results suggest that the strain has the capacity to remove significant amounts of MB from wastewater effluents.

Synthesis of coal fly ash zeolite for the catalytic wet peroxide oxidation of Orange II

Fly ash, a coal combustion residue produced by Termotasajero in Colombia, has been hydrothermally treated after an alkaline fusion to produce zeolite without addition of silicon or aluminum. The starting material was thoroughly mixed with NaOH, in a 1:1.2 mass ratio, to obtain a homogeneous mixture that was heated to 100 °C during different times (6, 8, and 10 h) and three zeolite samples were produced. The samples were characterized by XRD, SEM, XRF, Mössbauer spectroscopy, and N₂ physisorption. According to characterization results (high surface area and appropriate morphological properties including crystallinity) and synthesis time, zeolitic catalyst synthesized with 8 h of hydrothermal treatment was selected to perform further analysis. This sample consisted of a mixture of zeolite X and zeolite A of high surface area (301 m² g^-1) and a Fe content of 6% wt/wt. The zeolite was used as a catalyst for the Fenton oxidation of Orange II. Experiments were performed in a laboratory batch reactor at 70 °C and constant pH = 3, using different concentrations of H₂O₂. When the stoichiometric amount of H₂O₂ was used, good mineralization (X_TOC = 45%), complete discoloration, and oxidant consumption were obtained after 240 min of reaction. The sample retained activity after 16 h of usage. The presence of Fe in the reaction media was always detected and a homogeneous Fenton mechanism induced by surface-leached iron is suggested.

The preparation of organophosphorus ligand-modified SBA-15 for effective adsorption of Congo red and Reactive red 2

P,P-bis (2-oxooxazolidin-3-yl)-N-(3-(triethoxysilyl)propyl)phosphinic amide (APTES-BOP)-modified SBA-15 (SBA-15-BOP) was prepared by a post-synthesis grafting method for the removal of anionic azo dyes from aqueous solutions. The properties of the prepared adsorbent were characterized by PXRD, FT-IR, SEM, TEM, nitrogen sorption, and elemental analysis. Adsorption equilibrium and adsorption kinetic studies demonstrated that the experimental data fitted well with the Langmuir isotherm model and pseudo-second-order model. According to Langmuir fitting, SBA-15-BOP showed high adsorption capacity for CR and RR2 dyes, with the maximum adsorption capacities of 518.1 mg g⁻¹ and 253.8 mg g⁻¹, respectively. The thermodynamic study indicated that the adsorption processes of CR and RR2 dyes on SBA-15-BOP were spontaneous and exothermal. The prepared SBA-15-BOP can be a promising adsorbent for the removal of anionic dyes from aqueous solutions.

P,P-bis (2-oxooxazolidin-3-yl)-N-(3-(triethoxysilyl)propyl)phosphinic amide (APTES-BOP)-modified SBA-15 (SBA-15-BOP) was prepared by a post-synthesis grafting method for the removal of anionic azo dyes from aqueous solutions.

Preparation of Sulfonated Poly(arylene ether nitrile)-Based Adsorbent as a Highly Selective and Efficient Adsorbent for Cationic Dyes

In this work, a highly selective and efficient polymer adsorbent inspired by a water-soluble sulfonated poly(arylene ether nitrile) (SPEN) was successfully synthesized. Due to the distinct structure of functional carboxyl, sulfonic acid and rigid benzene rings, a facile aluminium (III) ions crosslinking method was employed to fabricate the SPEN-based adsorbents (SPEN-Al). Among the three adsorbents, SPEN-Al-2 exhibited superior adsorption capacities with uniform morphology. Subsequently, the SPEN-Al-2 was selected as the adsorbent for three cationic dyes (rhodamine B (Rh B), neutral red (NR), methylene blue (MB)) and three anionic dyes (orange G (OG), methyl orange (MO), acid fuchsin (AF)), respectively, demonstrating that the adsorbent possessing excellent selectivity toward cationic dyes. Moreover, the dye's adsorption selectivity of SPEN-Al-2 was further certificated in a binary cationic-anionic dyes mixtures (MB/OG and MB/MO) system. Taking MB as a dye model, a series of factors (contact time, concentration, temperature and pH) and adsorption models were systematically investigated in dye adsorption experiments. Results indicated that the adsorption was endothermic and the maximum adsorption capacity of SPEN-Al-2 could reach up to 877.5 mg/g; pseudo-second-model and Langmuir model were fitted to the adsorption kinetics and equilibrium isotherm, respectively, manifesting that SPEN-Al adsorbent was promising in the dyes removing field.