Detoxification of azo dyes in the context of environmental processes

Multiple adverse effects of textile effluents and reactive Red 239 dye to aquatic organisms

Textile dyeing consumes high volumes of water, generating proportional number of colored effluents which contain several hazardous chemical. These contaminants can implicate in significant changes in aquatic environmental, including several adverse effects to organisms in different trophic levels. The present study was developed to assess the ecotoxicological effects of textile effluent samples and reactive Red 239 dye (used in cotton dyeing) to aquatic organisms Vibrio fischeri bacteria, Daphnia similis crustacean, and Biomphalaria glabrata snail (adults and embryos). Chronic assays with lethal and sublethal effects for Daphnia similis were included and performed only for textile effluents samples. The mutagenicity was also evaluated with Salmonella/microsome assay (TA98, TA100, and YG1041 strains). V. fischeri bacteria was the most sensitive to reactive Red 239 dye (EC50 = 10.14 mg L^-1) followed by mollusk embryos at all stages (EC50 = 116.41 to 124.14 mg L^-1), D. similis (EC50= 389.42 mg L^-1), and less sensitive to adult snails (LC50= 517.19 mg L^-1). The textile effluent was toxic for all exposed organisms [E(L)C50 < 15%] and B. glabrata embryos showed different responses in the early stages of blastulae and gastrulae (EC50 = 7.60 and 7.08%) compared to advanced development stages trochophore and veliger (EC50 = 21.56 and 29.32%). Developmental and sublethal effects in B. glabrata embryos and D. similis were evidenced. In the chronic assay with effluent, the EC10/NOEC = 3% was obtained. Mutagenic effects were not detected for dye aqueous solutions neither for effluents samples. These data confirmed the importance of evaluating the effects in aquatic organisms from different trophic levels and reinforce the need for environmental aquatic protection.

Advances in the Application of Nanocatalysts in Photocatalytic Processes for the Treatment of Food Dyes: A Review

The use of food additives (such as dyes, which improve the appearance of the products) has become more prominent, due to the rapid population growth and the increase in demand for beverages and processed foods. The dyes are usually found in effluents that are discharged into the environment without previous treatment; this promotes mass contamination and alters the aquatic environment. In recent years, advanced oxidation processes (AOPs) have proven to be effective technologies used for wastewater treatment through the destruction of the total organic content of toxic contaminants, including food dyes. Studies have shown that the introduction of catalysts in AOPs improve treatment efficiency (i.e., complete decomposition without secondary contamination). The present review offers a quick reference for researchers, regarding the treatment of wastewater containing food dyes and the different types of AOPs, with different catalyst and nanocatalyst materials obtained from traditional and green chemical syntheses.

Managing water sustainability in textile industry through adaptive multiple stakeholder collaboration

Textile manufacturing poses pressing challenges on water sustainability characterized by intensive chemical consumption and waterborne pollution. Industrial clustering is a hallmark of textile industry development, featuring a two-stage wastewater treatment system consisting of in-plant and centralized treatment facilities. Driven by increasingly stringent wastewater discharge limits, three pillar stakeholders in textile industrial clusters, the local government, enterprises and environmental utility operators, seek for systematic countermeasures by balancing contradictory interests. This study presents a trilateral game model to uncover the economic and environmental tradeoffs among the three stakeholders targeting the optimization of wastewater systems. The model is solidified by a representative textile industrial cluster and is then extrapolated to 242 large-scale Chinese textile clusters to quantify the benefits. The key finds are (1) the in-use wastewater systems in many clusters function with low eco-efficiency; (2) the optimal paradigm is to adaptively leave room at half- to onefold for discharge limits from in-plant to centralized treatment facilities; (3) the environmental and economic benefits thereof are 24∼x223C61% and 6%, respectively, after retrofitting to the optimal paradigm for the Chinese textile clusters.

Phylogenetically diverse bacteria isolated from tattoo inks, an azo dye-rich environment, decolorize a wide range of azo dyes

Purpose

There has been an interest in the microbial azo dye degradation as an optional method for the treatment of azo dye-containing wastes. Tattoo ink is an extremely unique azo dye-rich environment, which have never been explored in terms of microorganisms capable of degrading azo dyes. Previously, we isolated 81 phylogenetically diverse bacteria, belonging to 18 genera and 52 species, contaminated in tattoo inks. In this study, we investigated if these bacteria, which can survive in the azo dye-rich environment, have an ability to degrade azo dyes.

Methods

We conducted a two-step azo dye degradation (or decolorization) assay. In step 1, a high-throughput degradability assay was done for 79 bacterial isolates using Methyl Red and Orange II. In step 2, a further degradation assay was done for 10 selected bacteria with a representative of 11 azo dyes, including 3 commercial tattoo ink azo dyes. Degradation of azo dyes were calculated from measuring optical absorbance of soluble dyes at specific wavelengths.

Results

The initial high-throughput azo dye assay (step 1) showed that 79 isolates had a complete or partial degradation of azo dyes; > 90% of Methyl Red and Orange II were degraded within 24 h, by 74 and 20 isolates, respectively. A further evaluation of azo dye degradability for 10 selected isolates in step 2 showed that the isolates, belonging to Bacillus, Brevibacillus, Paenibacillus, and Pseudomonas, exhibited an excellent decolorization ability for a wide range of azo dyes.

Conclusions

This study showed that phylogenetically diverse bacteria, isolated from azo dye-rich tattoo inks, is able to degrade a diverse range of azo dyes, including 3 azo dyes used in commercial tattoo inks. Some of the strains would be good candidates for future studies to provide a systematic understanding of azo dye degradation mechanisms.

Liquid metal assisted sonocatalytic degradation of organic azo dyes to solid carbon particles

Room temperature liquid metals are an emerging class of materials for a variety of heterogeneous catalytic reactions. In this work we explore the use of Ga based liquid metals as a sonochemical catalyst for the degradation of organic azo dyes such as methyl orange, congo red and eriochrome black T. Rapid degradation to non toxic solid carbon particles was achieved over a large dye concentration range to produce differently sized particles via both bath and probe sonication which could be repeated multiple times with the same catalyst.

Biotransformation of Reactive Red 141 by Paenibacillus terrigena KKW2-005 and Examination of Product Toxicity

A total of 37 bacterial isolates were obtained from dye-contaminated soil samples at a textile processing factory in Nakhon Ratchasima Province, Thailand, and the potential of the isolates to decolorize and biotransform azo dye Reactive Red 141 (RR141) was investigated. The most potent bacterium was identified as Paenibacillus terrigena KKW2-005, which showed the ability to decolorize 96.45% of RR141 (50 mg/l) within 20 h under static conditions at pH 8.0 and a broad temperature range of 30-40°C. The biotransformation products were analyzed by using UV-Vis spectrophotometry and Fourier-transform infrared spectroscopy. Gas chromatography-mass spectroscopy analysis revealed four metabolites generated from the reductive biodegradation, namely sodium 3-diazenylnaphthalene-1,5-disulfonate (I), sodium naphthalene-2-sufonate (II), 4-chloro-1,3,5-triazin-2-amine (III) and N¹-(1,3,5-triazin-2-yl) benzene-1,4-diamine (IV). Decolorization intermediates reduced phytotoxicity as compared with the untreated dye. However, they had phytotoxicity when compared with control, probably due to naphthalene and triazine derivatives. Moreover, genotoxicity testing by high annealing temperature-random amplified polymorphic DNA technique exhibited different DNA polymorphism bands in seedlings exposed to the metabolites. They compared to the bands found in seedlings subjected to the untreated dye or distilled water. The data from this study provide evidence that the biodegradation of Reactive Red 141 by P. terrigena KKW2-005 was genotoxic to the DNA seedlings.

Photodegradation of organic water pollutants under visible light using anatase F, N co-doped TiO2/SiO2 nanocomposite: Semi-pilot plant experiment and density functional theory calculations

Visible-light driven photocatalysts are of great importance in wastewater treatment. In this work, fluorine and nitrogen co-doped titanium dioxide/silica nanocomposite (F-N-TiO₂/SiO₂) was synthetized using a sol-gel approach. The as-developed nanocomposite was well characterized using different techniques. In particular, an anatase structure with high surface area (345.69 m²/g) and a band gap of 2.97 eV were observed for the as-synthesized nanocomposite, which makes it a potential candidate for photocatalytic applications under visible light. A systematic density functional theory calculation was performed to get more insight into the effect of dopant atoms on the band gap of TiO₂ nanoparticles. To enhance the reusability of the photocatalyst in semi-pilot scale, the as-developed nanocomposite was immobilized onto the glass beads by coupling dip-coating and heat attachment methods. A semi-pilot scale custom-designed fixed-bed photoreactor was used to evaluate the photocatalytic performance of the as-developed nanocomposite under both visible and solar irradiations. A mixture of three azo dyes (i.e., basic red 29, basic blue 41 and basic yellow 51) was used as the model industrial wastewater. The analysis of the wastewater showed that the complete removal of the pollutants under visible light and sunlight can occurred at pH of 3 and flow rate of 280 mL/min. The durability results demonstrated the successful degradation of the pollutants for five cycles. The results of this study show how careful controlling the operational parameters as well as using a highly photocatalytic nanomaterial can lead to successful decontamination of organic water pollutants. This approach might open up new windows to the future applications of photocatalytic nanomaterials for wastewater treatment.

Wasteful Azo Dyes as a Source of Biologically Active Building Blocks

In this work, an environment-friendly enzymatic strategy was developed for the valorisation of dye-containing wastewaters. We set up biocatalytic processes for the conversion of azo dyes representative of the main classes used in the textile industry into valuable aromatic compounds: aromatic amines, phenoxazinones, phenazines, and naphthoquinones. First, purified preparations of PpAzoR azoreductase efficiently reduced mordant, acid, reactive, and direct azo dyes into aromatic amines, and CotA-laccase oxidised these compounds into phenazines, phenoxazinones, and naphthoquinones. Second, whole cells containing the overproduced enzymes were utilised in the two-step enzymatic conversion of the model mordant black 9 dye into sodium 2-amino-3-oxo-3H-phenoxazine-8-sulphonate, allowing to overcome the drawbacks associated with the use of expensive purified enzymes, co-factors, or exquisite reaction conditions. Third, cells immobilised in sodium alginate allowed recycling the biocatalysts and achieving very good to excellent final phenoxazine product yields (up to 80%) in water and with less impurities in the final reaction mixtures. Finally, one-pot systems using recycled immobilised cells co-producing both enzymes resulted in the highest phenoxazinone yields (90%) through the sequential use of static and stirring conditions, controlling the oxygenation of reaction mixtures and the successive activity of azoreductase (anaerobic) and laccase (aerobic).

A Short Review on Electrochemical Sensing of Commercial Dyes in Real Samples Using Carbon Paste Electrodes

Synthetic dyes are commonly used in food products like soft drinks, vegetable sauces, jellies, etc. Most artificial dyes can cause cancer, therefore it is very important to develop sensors to detect them in food samples. Voltammetric methods with carbon paste electrodes (CPEs) are promising for this purpose. However, modification of CPEs is necessary to detect the commercial dyes in food samples in the presence of interferents. In the current review, we have discussed the different previous research in which detection of dyes is performed in real samples with good detection limits. The current review will be helpful for readers who are interested in developing low-cost electrodes for the effective determination of dyes in commercial products like soft drinks and vegetable sauces.

Current Trends in the Application of Nanomaterials for the Removal of Pollutants from Industrial Wastewater Treatment-A Review

In the recent decades, development of new and innovative technology resulted in a very high amount of effluents. Industrial wastewaters originating from various industries contribute as a major source of water pollution. The pollutants in the wastewater include organic and inorganic pollutants, heavy metals, and non-disintegrating materials. This pollutant poses a severe threat to the environment. Therefore, novel and innovative methods and technologies need to adapt for their removal. Recent years saw nanomaterials as a potential candidate for pollutants removal. Nowadays, a range of cost-effective nanomaterials are available with unique properties. In this context, nano-absorbents are excellent materials. Heavy metal contamination is widespread in underground and surface waters. Recently, various studies focused on the removal of heavy metals. The presented review article here focused on removal of contaminants originated from industrial wastewater utilizing nanomaterials.

Variation and comparison of biotoxicity during typical biological treatment of dyeing wastewater

In present study, dyeing wastewater samples were collected from three typical dyeing wastewater treatment plants in Wujiang, Shengze and Shanghai, China. Physicochemical properties and biotoxicity indicators (luminescent bacteria acute toxicity and umu genotoxicity) were tested and the relationships among them were analyzed. The results revealed that two biotoxicity indicators varied significantly among different treatment units of three plants. After treatment by plant A, luminescent bacteria acute toxicity of dyeing wastewater reduced effectively, while umu genotoxicity increased significantly. Two biotoxicity indicators exhibited decrease and increase trends during the treatment processes of plant B and plant C, respectively. Correlation analysis indicated that there was little correlation among biotoxicity indicators and physicochemical properties, meanwhile two kinds of biotoxicity indicators were relatively independent. Therefore, it was recommended that comprehensive evaluation of dyeing wastewater toxicity needs the combination of various biotoxicity indicators, and the relationship among biotoxicity indicators and physicochemical properties of dyeing wastewater should be established individually. The results of this study would offer a general understanding and evaluation of biotoxicity during actual dyeing wastewater treatment processes and provide database for toxicity reduction and management of dyeing wastewater.

Biodecolourisation of Reactive Red 120 as a Sole Carbon Source by a Bacterial Consortium-Toxicity Assessment and Statistical Optimisation

The application of microorganisms in azo dye remediation has gained significant attention, leading to various published studies reporting different methods for obtaining the best dye decolouriser. This paper investigates and compares the role of methods and media used in obtaining a bacterial consortium capable of decolourising azo dye as the sole carbon source, which is extremely rare to find. It was demonstrated that a prolonged acclimation under low substrate availability successfully isolated a novel consortium capable of utilising Reactive Red 120 dye as a sole carbon source in aerobic conditions. This consortium, known as JR3, consists of Pseudomonas aeruginosa strain MM01, Enterobacter sp. strain MM05 and Serratia marcescens strain MM06. Decolourised metabolites of consortium JR3 showed an improvement in mung bean's seed germination and shoot and root length. One-factor-at-time optimisation characterisation showed maximal of 82.9% decolourisation at 0.7 g/L ammonium sulphate, pH 8, 35 °C, and RR120 concentrations of 200 ppm. Decolourisation modelling utilising response surface methodology (RSM) successfully improved decolourisation even more. RSM resulted in maximal decolourisation of 92.79% using 0.645 g/L ammonium sulphate, pH 8.29, 34.5 °C and 200 ppm RR120.

Photocatalytic activity of G-TiO2@Fe3O4 with persulfate for degradation of alizarin red S under visible light

A composite photocatalyst combined with TiO₂, graphite (G) and Fe₃O₄ was prepared by co-precipitation method. Then the G-TiO₂@Fe₃O₄ was employed with persulfate (PS) to degrade alizarin red S (ARS) under visible light. The removal rate of ARS reached 100% after 60 min irradiation. The degradation rate constant of G-TiO₂@Fe₃O₄/PS exhibited 20.8, 9.0 and 3.1 times than that of TiO₂, G-TiO₂ and G-TiO₂@Fe₃O₄, respectively. The effects of photocatalyst dosage, mass ratios of graphite and Fe₃O₄ to TiO₂, PS dosage, initial pH and ARS concentration on the degradation efficiency were investigated. The optimal removal efficiency of ARS was obtained when G-TiO₂@Fe₃O₄ dosage was 0.25 g/L, G: TiO₂ = 0.005, Fe₃O₄: TiO₂ = 0.8, PS concentration was 6 mmol/L, initial pH = 3, and initial concentration of ARS was 100 mg/L. The SO₄·^- was demonstrated more important than O₂^- and·OH in the degradation of ARS. The intermediates and possible degradation pathways of ARS were discussed. Reuse and stability of G-TiO₂@Fe₃O₄ were also tested, and 88.3% photocatalytic activity was maintained after five cycles. Therefore, the proposed G-TiO₂@Fe₃O₄/PS not only had excellent photocatalytic activity, but also showed superior stability and reusability.

Partial purification and characterization of a thermophilic and alkali-stable laccase of Phoma herbarum isolate KU4 with dye-decolorization efficiency

Production of an extracellular thermophilic and alkali stable laccase from Phoma herbarum isolate KU4 was reported for the first time, both in submerged fermentation (SmF, highest 1590 U/mL) and solid state fermentation (SSF, highest 2014.21 U/mL) using agro-industrial residues. The laccase was partially purified to 7.93 fold with the apparent molecular weight of 298 kDa. The enzyme had pH optimum at 5.0 and temperature optimum at 50 °C, with maximum stability at pH 8.0. It showed activity towards various phenolic and non-phenolic compounds. The kinetic parameters, K_m, V_max and K_cat of the laccase for DMP were 0.216 mM, 270.27 U/mg and 506.69 s^-1, respectively. Laccase activity was inhibited by various metal ions and conventional inhibitors, however, it was slightly increased by Zn²⁺. The laccase showed good decolorization efficiency towards four industrial dyes, namely, methyl violet (75.66%), methyl green (65%), indigo carmine (58%) and neutral red (42%) within 24 h. FTIR analysis of the decolorized products confirmed the degradation of the dyes. The decolorization efficiency of the enzyme suggests that the partially purified laccase could be used to decolorize synthetic dyes present in industrial effluents and for waste water treatments. The thermophilic and alkali stable laccase may also have wider potential industrial applications.

iTRAQ-facilitated proteomic analysis of Bacillus cereus via degradation of malachite green

The wide use of malachite green (MG) as a dye has caused substantial concern owing to its toxicity. Bacillus cereus can against the toxic effect of MG and efficiently decolourise it. However, detailed information regarding its underlying adaptation and degradation mechanisms based on proteomic data is scarce. In this study, the isobaric tags for relative and absolute quantitation (iTRAQ)-facilitated quantitative method was applied to analyse the molecular mechanisms by which B. cereus degrades MG. Based on this analysis, 209 upregulated proteins and 198 downregulated proteins were identified with a false discovery rate of 1% or less during MG biodegradation. Gene ontology and KEGG analysis determined that the differentially expressed proteins were enriched in metabolic processes, catalytic activity, antioxidant activity, and responses to stimuli. Furthermore, real-time qPCR was utilised to further confirm the regulated proteins involved in benzoate degradation. The proteins BCE_4076 (Acetyl-CoA acetyltransferase), BCE_5143 (Acetyl-CoA acetyltransferase), BCE_5144 (3-hydroxyacyl-CoA dehydrogenase), BCE_4651 (Enoyl-CoA hydratase), and BCE_5474 (3-hydroxyacyl-CoA dehydrogenase) involved in the benzoate degradation pathway may play an important role in the biodegradation of MG by B. cereus. The results of this study not only provide a comprehensive view of proteomic changes in B. cereus upon MG loading but also shed light on the mechanism underlying MG biodegradation by B. cereus.

Development of photochemical integrated submerged membrane bioreactor for textile dyeing wastewater treatment

A pilot-scale photocatalytic membrane bioreactor (PMBR) was developed for the treatment of textile dyeing wastewater. The PMBR is made of mild steel rectangular reactor of photocatalytic unit and polyethersulphone submerged hollow fibre membrane bioreactor unit with the working volume of about 20 L. For easy recovery, the tungsten oxide (WO₃) and WO₃/1% graphene oxide (GO)-powdered photocatalyst were made into bead and immersed in photocatalytic reactor. Graphene oxide incorporation has shown better results in decolourisation and degradation when compared with WO₃ alginate alone. The incorporation of GO into WO₃ minimises the recombination of photogenerated electron-hole pairs. The operating conditions such as 3 h of contact time for photocatalysis reaction (WO₃/1% GO), 10 h hydraulic retention time for MBR and 100 kPa of transmembrane pressure were optimised. Chemical oxygen demand removal efficiency of 48% was attained with photocatalysis, and the removal efficiency was further increased up to 76% when integrated with MBR. The colour removal efficiency after photocatalysis was 25% further increased up to 70% with MBR. Complete total suspended solid removal has been achieved with this hybrid system.

Blue dye degradation in an aqueous medium by a combined photocatalytic and bacterial biodegradation process

This paper aimed at implementing a treatment system for polluted water with textile dyes, starting with a photocatalytic decomposition process using sunlight as a source of energy and continuing with a bacterial biodegradation process, in order to reach degradation percentages higher than those obtained using only one of the processes mentioned above. When water treatment with the dye in the combined system was over, an acute ecotoxicity test was performed to make sure that toxic metabolites were not produced due to biodegradation. Solophenyl Blue azoic dye, and Erionyl Blue and Terasil Blue anthraquinone dye-colored solutions were treated with the Pd/Al ₈₀ Ce ₁₀ Zr ₁₀ catalyst in a solar collector for the photocatalytic process. On the other hand, the waste dye, which was obtained from photocatalysis with a bacterial consortium from polluted areas by metals and hydrocarbons in aerobic conditions, was inoculated for biodegradation. Biodegradation was obtained for the dyes after both processes as 90.91% for the Solophenyl Blue azoic dye, and 87.80% and 87.94%, respectively, for the Erionyl Blue and Terasil Blue anthraquinone dyes. After the degradation processes, it was proven, via an ecotoxicity test with Daphnia magna , that toxic metabolites had not been produced.

Application potential of biogenically synthesized silver nanoparticles using Lythrum salicaria L. extracts as pharmaceuticals and catalysts for organic pollutant degradation

This study was designed to evaluate the optimal conditions for the eco-friendly synthesis of silver nanoparticles (AgNPs) using Lythrum salicaria L. (Lythraceae) aqueous extracts and their potential application and safe use. AgNPs synthesized using L. salicaria aerial parts (LSA-AgNPs) and root extract (LSR-AgNPs) were characterized by UV-Vis spectrophotometry, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM/EDS), and X-ray powder diffraction (XRPD). Dynamic light scattering (DLS) was used for the determination of the size distribution profiles of the obtained nanoparticles. Both L. salicaria extracts showed high phenolic content, while the flavone C-glucosides orientin, vitexin, and isovitexin were detected in extracts using HPLC. The synthesized AgNPs displayed growth inhibition of the tested bacteria and fungi in concentrations between 0.156 and 1.25 mg mL⁻¹. The studied nanoparticles also showed antioxidant potential and gained selectivity at different concentrations on different cancer cell lines. Concentrations of LSA-AgNPs were found to be 20.5 and 12 μg mL⁻¹ towards A431 and SVT2, respectively, while LSR-AgNPs were effective only against A431 cancer cells (62 μg mL⁻¹). The hemolytic activity of LSA-AgNPs in concentrations up to 150 μg mL⁻¹ was not observed, while LSR-AgNPs in the highest applied concentration hemolyzed 2.8% of erythrocytes. The degradation possibility of Congo red and 4-nitrophenol using LSA-AgNPs and LSR-AgNPs as catalysts was also proven. The results indicate that L. salicaria may be used for the eco-friendly synthesis of AgNPs with possible applications as antimicrobial and selective cytotoxic agents towards cancer cell lines, as well as in catalytic degradation of pollutants.

This study was designed to evaluate the optimal conditions for the eco-friendly synthesis of silver nanoparticles (AgNPs) using Lythrum salicaria L. (Lythraceae) aqueous extracts and their potential application and safe use.

A Methodology to Estimate the Sorption Parameters from Batch and Column Tests: The Case Study of Methylene Blue Sorption onto Banana Peels

In the present work, a methodology is presented where batch and fixed-bed column tests of dye sorption onto granular biosorbents are analyzed with properly selected models to estimate the parameters required for the rational design of pilot-scale units. The sorption of methylene blue (MB) onto banana peels (BP) was investigated as a case study. To identify the mechanisms of MB sorption onto BP, the pore structure and surface of BP were characterized with mercury intrusion porosimetry (MIP), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Batch tests were performed over the temperature range of 15–45 °C, and three models (Langmuir, Freundlich, Langmuir–Freundlich) were fitted to equilibrium and kinetic data for (i) estimating thermodynamic/kinetic parameters and (ii) choosing the model with the best goodness-of-fit. Sorption tests on fixed-bed columns were combined with a one-dimensional macroscopic convection/dispersion/sorption model to estimate the sorption parameters of BP beds. MB sorption onto BP was a purely exothermic (ΔH0~−20 kJ/mol), reversible, and monolayer chemisorption with high activation energy for the desorption step (Ed~29 kJ/mol) and low activation energy for the adsorption step (Ea~9 kJ/mol). The Langmuir isotherm (KL = 141.9 m3/kg, T = 25 °C) and Langmuir kinetic model (kd = 1.05 × 10−5 s−1) provided the best fitting to equilibrium and transient data of batch tests. The sorption capacity ~0.15–0.22 kg/kg and kinetic constant 0.3 × 10−5 s−1–4.0 × 10−5 s−1 estimated from tests on BP beds were comparable to those obtained from batch tests.

Fungal biosynthesis of lignin-modifying enzymes from pulp wash and Luffa cylindrica for azo dye RB5 biodecolorization using modeling by response surface methodology and artificial neural network

This study demonstrates the evaluation between the artificial neural network technique coupled to the genetic algorithm (ANN-GA) and the response surface methodology (RSM) for prediction of Reactive Black 5 (RB5) decolorization by crude enzyme from Pleurotus. sajor-caju. Fungal lignin-modifying enzymes (FLME) were synthesized using pulp wash (PW) as an inducing substrate, and L. cylindrica (L.C) for cell immobilization. When grown in PW, the fungus showed higher Lac activity (126.5 IU. mL^-1), whereas when immobilized a higher MnP activity was achieved (22.79 IU. mL^-1), but both methods were capable of decolorizing the dye in about 89.4 % and 75 %, respectively. This indicates applicability of PW as an alternative substrate for FLME induction and viability of immobilization for MnP synthesis. For RB5 decolorization, the action of the crude enzyme extract was considered as a function of pH, dye concentration, temperature, and reaction time. The models are well adjusted to predict the efficiency of biodecolorization, with no statistical difference between ANN-GA and RSM, which indicates potential for green enzymes prospecting application in bioprocess industry.

Mineralization of Methyl Orange azo dye by processes based on H2O2 electrogeneration at a 3D-like air-diffusion cathode

This work addresses the mineralization of the widely used Methyl Orange (MO) azo dye by technologies based on H₂O₂ electrogeneration at a 3D-like air-diffusion cathode. These include two Fe²⁺-catalyzed processes such as electro-Fenton (EF) and photoelectro-Fenton (PEF). Bulk electrolyses were performed in a recirculation flow plant, in which the Eco-Cell filter-press electrochemical reactor was connected in series with a UVA photoreactor. The former reactor was equipped with a Ti|Ir-Sn-Sb oxide plate anode alongside a 3D-like air-diffusion cathode made from graphite felt and hydrophobized carbon cloth, aimed at electrogenerating H₂O₂ on site. The influence of current density (j), volumetric flow rate (Q) and initial MO concentration was examined. The greatest oxidation power corresponded to PEF process. The best operation conditions to treat 30 mg L^-1 of total organic carbon of MO in a 50 mM Na₂SO₄ solution by PEF were found at 0.50 mM Fe²⁺, pH 3.0, j = 20 mA cm^-2 and Q = 2.0 L min^-1, obtaining 100% and 94% of color and TOC removals at 30 and 240-300 min, respectively. This accounted for 35% of mineralization current efficiency and 0.12 kWh (g TOC)^-1 of energy consumption at the end of the electrolysis. The oxidation power of EF and PEF was compared with that of anodic oxidation (AO), and the sequence obtained was: PEF > EF > AO. The dye was gradually degraded, yielding non-toxic short carboxylic acids, like maleic, fumaric, formic, oxalic and oxamic, whose Fe(III) complexes were rapidly photolyzed.

Development of standardized method for the quantification of azo dyes by UV-Vis in binary mixtures

The azo dyes, Yellow 5 (Y5), Red 2 (R2) and Blue 1 (B1), quantified in solutions and in mixtures of binary dyes, were studied by means of UV-Vis spectroscopy. In this work was used a CIE algorithm developed in Visual Basic for Applications (VBA). The CIE algorithm is based on the tristimulus chromaticity diagram, as an alternative to the shielding effect that arises in dye mixtures, and it can also be applied to complex quantification methods such as HPLC (High Performance Liquid Chromatography). The results obtained through of the algorithm, showed a higher accuracy from 97 to 99% in relation with similar UV-Vis quantification methods. In contrast, linear methods only managed to reach an accuracy from 78 to 98%. Additionally, the algorithm yielded significant similar values to the UHPLC reference method. The results showed that the method CIE algorithm was accessible and reliable to quantify binary mixtures of the dyes used which suggests the possibility to apply this method on other dyes, within the limits of quantification obtained in this study (0.076-24.56 mg/L) and the pH values from 2 to 10.

Augmented Biodegradation of Textile Azo Dye Effluents by Plant Endophytes: A Sustainable, Eco-Friendly Alternative

Textile industry consumes a large proportion of available water and releases huge amounts of toxic azo dye effluents, leading to an inevitable situation of acute environmental pollution that has been a significant threat to mankind. Decolorization or detoxification of harmful azo dyes has become a global priority to overcome the disastrous consequences and salvage the ecosystem. Biodegradation of textile azo dyes by endophytes stands to be a lucrative and viable alternative over conventional physico-chemical methods, owing to their eco-friendliness, cost-competitive and non-toxic nature. Especially, plant endophytic microbes exhibit promising biodegradation potential which has wired up the effective removal of textile azo dyes, attributing to their ability to produce dye degrading enzymes, laccases, peroxidases and azoreductases. Although both bacterial and fungal endophytes have been tried for azo dye degradation, endophytic fungi find broader application over bacteria. Despite of the advancements made in microbe-mediated biodegradation, there is still a need to fill the gap in lab to in situ translation of biodegradation research. This review concisely accentuates the xenobiotics of textile azo dyes and microbial mechanisms of biodegradation of textile azo dyes, positing plant endophytic community, especially bacterial and fungal endophytes as the potential dye degraders, highlighting currently reported dye degrading endophytic species.

Using Electrolytic Manganese Residue to prepare novel nanocomposite catalysts for efficient degradation of Azo Dyes in Fenton-like processes

In this study, Electrolytic Manganese Residue (EMR) was treated by EDTA-2Na/NaOH, ultrasonic etching, and hydrothermal reaction to obtain a novel nanocomposite catalyst (called N-EMR), which then was used, together with H₂O₂, to treat synthetic textile wastewater containing Reactive Red X-3B, Methyl Orange, Methylene blue and Acid Orange 7. Results indicated that the N-EMR had a nano-sheet structure in sizes of 100-200 nm; new iron and manganese oxides with high activity were produced. The mixture of a small amount of N-EMR (40 mg/L) and H₂O₂ (0.4 × 10^-3 M) could removal about 99% of azo dyes (at 100 mg/L in 100 mL) within 6-15 min, much faster than many advanced oxidation processes (AOPs) reported in the literature. The elucidation of the associated mechanism for azo dyes degradation indicates that azo dyes were attacked by superoxide radicals, hydroxyl radicals, and electron holes generated within system. N-EMR was found to be reusable and showed limited inhibition by co-existing anions and cations. Moreover, high removal efficiency of azo dyes could happen in the system with a wide range of pH (1-8.5) and temperatures (25-45 °C), indicating that the process developed in this study may have broad application potential in treatment of azo dyes contaminated wastewater.

Ecofriendly biodegradation of Reactive Black 5 by newly isolated Sterigmatomyces halophilus SSA1575, valued for textile azo dye wastewater processing and detoxification

A total of seven yeast strains from 18 xylanolytic and/or xylose-fermenting yeast species isolated from the wood-feeding termite Reticulitermes chinenesis could efficiently decolorize various azo dyes under high-salt conditions. Of these strains, a novel and unique azo-degrading and halotolerant yeast, Sterigmatomyces halophilus SSA1575, has been investigated in this study. This strain could significantly decolorize four combinations of a mixture of dyes. It showed a high capability for decolorizing Reactive Black 5 (RB5) even at 1,500 mg L⁻¹. The strain SSA1575 still showed a high capability for decolorizing a 50 mg L⁻¹ RB5 with a salt mixing at a NaCl concentration of up to 80 g L⁻¹. It also exhibited significant ability to decolorize repeated additions of dye aliquots, with a reduction in time of up to 18 h. Most of the tested carbon and nitrogen sources could significantly enhance a RB5 decolorization. However, this process was inhibited by the addition of sucrose and sodium nitrate. NADH-dichlorophenol indophenol (NADH-DCIP) reductase and lignin peroxidase were determined as the key reductase and oxidase of S. halophilus SSA1575. Finally, strain SSA1575, can effectively detoxify RB5 into non-toxic products. Overall, S. halophilus SSA1575, might be a promising halotolerant yeast valued for the treatment of various textile effluents with high salinity.

The Application of Modified Natural Polymers in Toxicant Dye Compounds Wastewater: A Review

The utilization of various types of natural and modified polymers for removing toxicant dyes in wastewater generated by the dye industry is reviewed in this article. Dye wastewater contains large amounts of metals, surfactants, and organic matter, which have adverse effects on human health, potentially causing skin diseases and respiratory problems. The removal of dyes from wastewaters through chemical and physical processes has been addressed by many researchers. Currently, the use of natural and modified polymers for the removal of dyes from wastewater is becoming more common. Although modified polymers are preferred for the removal of dyes, due to their biodegradability and non-toxic nature, large amounts of polymers are required, resulting in higher costs. Surface-modified polymers are more effective for the removal of dyes from the wastewater. A survey of 80 recently published papers demonstrates that modified polymers have outstanding dye removal capabilities, and thus have a high applicability in industrial wastewater treatment.

Evaluation of Polyethylene Glycol Crosslinked β-CD Polymers for the Removal of Methylene Blue

The environment is at the heart of global worldwide discussion. This study describes the synthesis of ecofriendly polymers by a crosslinking reaction between β-cyclodextrin as the monomer and polyethylene glycol diglycidyl ether (PEDGE) as well as ethylene diglycidyl ether (EDGE) as the crosslinking agents. The studied polymers were characterized by several techniques, such as SEM, FTIR, TGA-TDA and XRD. Their adsorption properties for methylene blue under various conditions of pH, contact time and initial concentration of dye were assessed in order to find the optimal conditions. The results indicate that the polymers are good nominates for methylene blue adsorption with adsorption capacities up to 15 mg/g. The adsorption mechanism was demonstrated to follow the Langmuir model. Finally, the regeneration of the polymers was investigated using Soxhlet extraction with ethanol. The absorption capacities of the adsorbent were stable after three cycles.

Chemical Characterization of Specific Micropollutants from Textile Industry Effluents in Fez City, Morocco

Textile industry is one of the most polluting industries in the world. It has a high importance in terms of its environment impact, since it consumes a considerably large amount of water and produces highly polluted discharge water. In this work, characterization of toxic organic compounds is proposed. Based on gas chromatography coupled to mass spectrometry (GC/MS) screening analysis, organic micropollutant diversity of textile effluents from a local textile processing factory was investigated. In the present work, physicochemical characterization of the studied textile effluents showed considerably high values of principal pollution parameters above the prescribed discharge water limits. Heavy metals like zinc (Zn), copper (Cu), iron (Fe), nickel (Ni), cadmium (Cd), chromium (Cr), and lead (Pb) were found to be present within the permissible limits. The results of GC/MS revealed the presence of various organic compounds belonging to a wide range of chemical classes. Main groups of chemical compounds detected in these effluents were aromatic carboxylic acids, alkanes, aromatic amines, phthalates, aliphatic carboxylic acids, and linear aliphatic alcohols. The results of this study allowed significant contributions to the chemical characterization of textile industry contaminants and identification of indicators that can be considered an important tool for assessment of the potential impact of textile activities to the contamination of aquatic environment and health hazard.

Modified multi-walled carbon nanotubes assisted foam fractionation for effective removal of acid orange 7 from the dyestuff wastewater

In this study, multi-walled carbon nanotubes (MWCNTs) had been used to strengthen the removal of acid orange 7 (AO7) from the dyestuff wastewater by using foam fractionation. First, the surface modification of MWCNTs was performed by introducing hypochlorite groups (-OCl). The modified MWCNTs were characterized by using SEM, XRD, FTIR and Raman spectroscopy. Subsequently, the potential of modified MWCNTs as a novel collector for AO7 adsorption was examined. The adsorption conditions of modified MWCNTs towards AO7 were optimized by using response surface methodology (RSM) with a central composite design (CCD). The adsorption capacity of modified MWCNTs towards AO7 could reach 47.72 ± 0.79 mg·g^-1 under the optimum conditions. The kinetics and the equilibrium adsorption data were analyzed by using different kinetic and isotherm models. According to the regression results, adsorption kinetics data were well described by pseudo-second order model, whereas adsorption isotherm data were best represented by Langmuir isotherm model. Finally, foam fractionation was performed with a batch mode. Under the suitable conditions of loading liquid volume 300 mL, modified MWCNTs dosage 180 mg, cetyltrimethylammonium bromide (CTAB) concentration 50 mg·L^-1, AO7 concentration 30 mg·L^-1, pore diameter of gas distributor 0.125 mm and air flow rate 100 mL·min^-1, the removal percentage and enrichment ratio of AO7 were 91.23% and 6.17, respectively. The decolourization ratio of solution after foam fractionation was found to be 98.66%.

Fast-changing life-styles and ecotoxicity of hair dyes drive the emergence of hidden toxicants threatening environmental sustainability in Asia

The practice of hair dyeing is a rapidly expanding industry on a global scale; however, it has become a major concern for Asian countries because they have been undergoing rapid transformations of their environment and lifestyles. While the socio-economic benefits and impacts of this globalization trend are widely understood, the environmental effects are largely unknown. In particular, commonly available oxidative dyes potentially pose specific environmental risks due to their use of a toxic aromatic amine p-Phenylenediamine (PPD). In investigating the environmental impacts of PPD chemicals, we first provide context to the study by setting out the socio-psychological drivers to industrial expansion in Asian countries along with an overview of research into its effects, to show that its environmental impacts are under-researched. We then investigate the environmental toxicity of PPD by focusing on the role of microbes in metabolizing waste products. Results show that Acinetobacter baumannii EB1 isolated from dye effluent prevents autoxidation of PPD under oxygen-enriched (shaking) or oxygen-deficient (static) conditions representing different environmental settings. Microbes transformed PPD into more toxic metabolites, which then significantly reduced plant growth, thereby having a direct bearing on ecosystem services. Based on the findings, we argue that stricter regulatory controls on hair dye wastewater are necessary, particularly in newly industrialising Asian countries where the expansion of commercial practice is most prevalent.

Phosphoric Acid Activated Carbon from Melia azedarach Waste Sawdust for Adsorptive Removal of Reactive Orange 16: Equilibrium Modelling and Thermodynamic Analysis

Waste wood biomass as precursor for manufacturing activated carbon (AC) can provide a solution to ever increasing global water quality concerns. In our current work, Melia azedarach derived phosphoric acid-treated AC (MA-AC400) was manufactured at a laboratory scale. This novel MA-AC400 was tested for RO16 dye removal performance as a function of contact time, adsorbent dosage, pH, temperature and initial dye concentration in a batch scale arrangement. MA-AC400 was characterized via scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering (DLS) and fluorescence spectroscopy. MA-AC400 is characterized as mesoporous with BET surface area of 293.13 m² g^-1 and average pore width of 20.33 Å. pH_PZC and Boehm titration confirm the acidic surface charges with dominance of phenolic functional groups. The average DLS particle size of MA-AC400 was found in the narrow range of 0.12 to 0.30 µm and this polydispersity was confirmed with multiple excitation fluorescence wavelengths. MA-AC400 showed equilibrium adsorption efficiency of 97.8% for RO16 dye at its initial concentration of 30 mg L^-1 and adsorbent dose of 1 g L^-1. Thermodynamic study endorsed the spontaneous, favorable, irreversible and exothermic process for RO16 adsorption onto MA-AC400. Equilibrium adsorption data was better explained by Langmuir with high goodness of fit (R², 0.9964) and this fitness was endorsed with lower error functions. The kinetics data was found well fitted to pseudo-second order (PSO), and intra-particle diffusion kinetic models. Increasing diffusion constant values confirm the intraparticle diffusion at higher RO16 initial concentration and reverse was true for PSO chemisorption kinetics. MA-AC400 exhibited low desorption with studied eluents and its cost was calculated to be $8.36/kg.

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.

Enzyme immobilization in highly ordered macro–microporous metal–organic frameworks for rapid biodegradation of hazardous dyes

HRP immobilized in highly ordered macro–microporous metal–organic frameworks for biodegradation of hazardous dyes selectively and rapidly.

Fractional factorial design modelling on degradation of Direct Red 81 dye by advanced oxidation process - ozonation: reaction kinetics

In the present work, the degradation of Direct Red 81 by ozonation was studied. The interactive effects of the influencing factors (dye concentration = 500-2,000 mg/L; time = 10-30 min; pH = 7.0-11.0) on degradation efficiency was critically examined through experimental design optimization by central composite design under the response surface methodology. The high correlation coefficients (R² = 0.976 & adjusted R² = 0.958) obtained by analysis of variance (ANOVA) demonstrated close fit between the experimental and the predicted values. Optimized conditions under specified cost-driven restraints were obtained for the highest desirability (i.e. degradation of 1,210.59 mg/L dye) at pH = 11.0, initial dye concentration = 2,000 mg/L and ozone exposure time of 27.16 min. The degradation of Direct Red 81 was confirmed through Fourier transform infrared spectroscopy (FTIR) analysis and UV-Vis spectrometry.

Decolorization of azo and anthraquinone dyes by crude laccase produced by Lentinus crinitus in solid state cultivation

White-rot basidiomycetes such as Lentinus crinitus produce laccases with potential use in dye biodegradation. However, high productivity and enzymes with specific properties are required in order to make viable laccase production. We aimed to produce laccase from Lentinus crinitus grown in sugarcane bagasse for dye decolorization. Solid state cultivation medium had sugarcane bagasse added with a nutrient solution of 10 g/L glucose, 1 g/L KH₂PO₄, 0.5 g/L MgSO₄, 0.001 g/L FeSO₄, 0.01 g/L ZnSO₄, and 0.01 g/L MnSO₄. The addition of different nitrogen sources (peptone, urea, or peptone plus urea) and different nitrogen concentrations (0, 0.4, 0.6, 0.8, 1.0, and 1.2 g/L) were evaluated. Enzymatic extract was used in the decolorization of azo dyes, reactive blue 220 (RB220) and reactive black 5 (RB5), and anthraquinone dye, Remazol brilliant blue R (RBBR). The greatest laccase activity (4800 U/g dry mass) occurred when the peptone and urea mixture was added to the solid state cultivation medium. When the nitrogen concentration was 1 g/L, the laccase activity increased to 6555 U/g dry mass. The laccase activity peak occurred on the 10th day, and the maximum decolorization within 24 h was observed with enzymatic extracts obtained on different cultivation days, i.e., 6th day for RB220, 10th day for RB5, and 9th day for RBBR. Manganese and lignin peroxidases were not produced when nitrogen was added to the cultivation medium. The crude enzymatic extract was more effective in the decolorization of azo dyes (RB220 and RB5), more than 90% of decolorization, than anthraquinone dye with 77% decolorization.

Azo dyes decolorization under high alkalinity and salinity conditions by Halomonas sp. in batch and packed bed reactor

Biodecolorization and biodegradation of azo dyes are a challenge due to their recalcitrance and the characteristics of textile effluents. This study presents the use of Halomonas sp. in the decolorization of azo dyes Reactive Black 5 (RB5), Remazol Brilliant Violet 5R (RV5), and Reactive Orange 16 (RO16) under high alkalinity and salinity conditions. Firstly, the effect of air supply, pH, salinity and dye concentration was evaluated. Halomonas sp. was able to remove above 84% of all dyes in a wide range of pH (6-11) and salt concentrations (2-10%). The decolorization efficiency of RB5, RV5, and RO16 was found to be ≥ 90% after 24, 13 and 3 h, respectively, at 50 mg L^-1 of dyes. The process was monitored by HPLC-DAD, finding a reduction of dyes along the time. Further, Halomonas sp. was immobilized in volcanic rocks and used in a packed bed reactor for 72 days, achieving a removal rate of 3.48, 5.73, and 8.52 mg L^-1 h^-1, for RB5, RV5 and RO16, respectively, at 11.8 h. The study has confirmed the potential of Halomonas sp. to decolorize azo dyes under high salinity and alkalinity conditions and opened a scope for future research in the treatment of textile effluents.

Decolorization and Detoxification of Synthetic Dyes by Mexican Strains of Trametes sp

Laccases have attracted a great deal of interest because of their remarkable ability for the degradation of synthetic dyes present in wastewaters. New laccase producing sources with robust operational and functional properties are being continuously explored. In this work, the potential for the decolorization and detoxification of synthetic dyes was evaluated in two Mexican strains of the genus Trametes. The decolorization capacity of Trametesmaxima LE130 and Trametes sp. LA1 was tested in solid and liquid media. The phytotoxicity of the degradation products was determined using Raphanussativus and Pisum sativum seeds. In solid media, both strains showed a higher decolorization capacity (p ≤ 0.05) than Phanerochaetechrysosporium ATCC 24725, which is known to be very efficient in lignin and dye-degradation. They produced laccase as the main ligninolytic enzyme; T. maxima LE130 secreted a single isoform of 43.9 kDa, while Trametes sp. LA1 produced three isoforms of 67.3, 58.6 and 52.7 kDa, respectively. Trametes sp. LA1 culture fluids were capable of decolorizing and detoxifying chemically diverse dyes (anthraquinonic dye Remazol Brilliant Blue R, azoic Reactive Black 5 and triphenylmethane Crystal Violet) without the addition of redox mediators. Therefore, this could be considered as a new laccase source which could be potentially competitive in the bioremediation of dye-containing wastewaters.