Ecotoxic potential of a presumably non-toxic azo dye

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

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

Investigation of occurrence of aromatic amines in municipal wastewaters using passive sampling

Aromatic amines (AAs) are human-made compounds known for their mutagenic properties, entering surface waters from various sources, often originating as transformation products of dyes or pesticides. Despite their low concentrations in surface waters, AAs can exhibit mutagenicity. Our study focused on evaluating three passive samplers (PSs) for enriching these compounds from influent and effluent of a wastewater treatment plant (WWTP) in Brno, Czech Republic. The PSs tested included variants containing AttractSPE™ SDB-RPS sorbent disk, one with and one without a diffusive agarose hydrogel layer, and a modified Speedisk (Bakerbond Speedisk® H2O-Philic). PSs were deployed in wastewater (WW) for one to four weeks in various overlapping combinations, and the uptake of AAs to PSs was compared to their concentrations in 24-hour composite water samples. A targeted LC/MS analysis covered 42 amines, detecting 11 and 13 AAs in daily composite influent and effluent samples, respectively. In the influent, AAs ranged from 1.5 ng L-1 for 1-anilinonaphthalene to 1.0 μg L-1 for aniline, and the highest concentration among all measured amines was observed for cyclohexylamine at 2.9 μg L-1. In the effluent, concentrations ranged from 0.5 ng L-1 for 1-anilinonaphthalene to 88 ng L-1 for o-anisidine. PSs demonstrated comparable accumulation of amines, with integrative uptake up to 28 days in both influent and effluent and detection of up to 23 and 27 amines in influent and effluent, respectively; altogether 34 compounds were detected in the study. Sampling rates (Rs) were estimated for compounds present in at least 50 % of the samples and showing <40 % aqueous concentration variability, with robustness evaluated by comparing values for compounds in WWTP influent and effluent. Although all devices performed similarly, hydrogel-based PS exhibited superior performance in several criteria, including time integration and robustness of sampling rates, making it a suitable monitoring tool for AAs in WW.

Deciphering the ecological impact of azo dye pollution through microbial community analysis in water-sediment microcosms

The uncontrolled release of untreated dyeing wastewater into aquatic ecosystems poses global environmental risks. It alters native microbial communities and associated ecological processes, often going unnoticed. Therefore, the influence of acid orange 7 dye (AO7) contamination on the natural microbial community was investigated using a water-sediment microcosm. Compared to sterile microcosms, complete dye decolourization in natural microcosms showed microbial communities' significance in combating xenobiotic contamination. Proteobacteria dominated the water community, whereas Firmicutes dominated the sediment. AO7 exposure induced notable shifts in the structural composition of the bacterial community in both water and sediment. Niveispirillum exhibited a marked decrease, and Pseudomonas demonstrated a notable increase. The - 9.0 log2FC in Niveispirillum, a nitrogen-fixing bacterium, from 24.4% in the control to 0.1% post-treatment, may disrupt nutrient balance, plant growth, and ecosystem productivity. Conversely, elevated levels of Pseudomonas sp. resulting from azo dye exposure demonstrate its ability to tolerate and bioremediate organic pollutants, highlighting its resilience. Functional profiling via KEGG pathway analysis revealed differential expression patterns under AO7 stress. Specifically, valine, leucine, and isoleucine degradation pathways in water decreased by 52.2%, and cysteine and methionine metabolism ceased expression entirely, indicating reduced protein metabolism and nutrient bioavailability under dye exposure. Furthermore, in sediment, glutathione metabolism ceased, indicating increased oxidative stress following AO7 infusion. However, C5-branched dibasic acid metabolism and limonene and pinene degradation were uniquely expressed in sediment. Decreased methane metabolism exacerbates the effects of global warming on aquatic ecosystems. Further, ceased-butanoate metabolic pathways reflect the textile dye wastewater-induced adverse impact on ecological processes, such as organic matter decomposition, energy flow, nutrient cycling, and community dynamics that help maintain self-purification and ecological balance in river ecosystems. These findings underscore the critical need for more comprehensive environmental monitoring and management strategies to mitigate ecological risks posed by textile dyes in aquatic ecosystems, which remain unnoticed.

A feasible approach for azo-dye (methyl orange) degradation by textile effluent isolate Serratia marcescens ED1 strain for water sustainability: AST identification, degradation optimization and pathway hypothesis

Methyl orange (MO) is a dye commonly used in the textile industry that harms aquatic life, soil and human health due to its potential as an environmental pollutant. The present study describes the dye degradation ability of Serratia marcescens strain ED1 isolated from textile effluent and characterized by 16S rRNA gene sequence analysis. The laccase property of bacterial isolate was confirmed qualitatively. The effects of various factors (pH, temperature, incubation time, and dye concentration) were evaluated using Response Surface Methodology (RSM). The maximum dye (MO) degradation was 81.02 % achieved at 37 °C temperature and 7.0 pH with 200 mg/L dye concentration after 48 h of incubation. The beef extract, ammonium nitrate and fructose supplementation showed better response during bioremediation among the different carbon and nitrogen sources. The degree of pathogenicity was confirmed through the simple plate-based method, and an antibiotic resistance profile was used to check the low-risk rate of antibiotic resistance. However, the fate and extinct of degraded MO products were analysed through UV-Vis spectroscopy, FT-IR, and GC-MS analysis to confirm the biodegradation potential of the bacterial strain ED1 and intermediate metabolites were identified to propose metabolic pathway. The phytotoxicity study on Vigna radiata L. seeds confirmed nontoxic effect of degraded MO metabolites and indicates promising degradation potential of S. marcescens strain ED1 to successfully remediate MO dye ecologically sustainably.

Omics-Based Approaches in Research on Textile Dye Microbial Decolorization

The development of the textile industry has negative effects on the natural environment. Cotton cultivation, dyeing fabrics, washing, and finishing require a lot of water and energy and use many chemicals. One of the most dangerous pollutants generated by the textile industry is dyes. Most of them are characterized by a complex chemical structure and an unfavorable impact on the environment. Especially azo dyes, whose decomposition by bacteria may lead to the formation of carcinogenic aromatic amines and raise a lot of concern. Using the metabolic potential of microorganisms that biodegrade dyes seems to be a promising solution for their elimination from contaminated environments. The development of omics sciences such as genomics, transcriptomics, proteomics, and metabolomics has allowed for a comprehensive approach to the processes occurring in cells. Especially multi-omics, which combines data from different biomolecular levels, providing an integrative understanding of the whole biodegradation process. Thanks to this, it is possible to elucidate the molecular basis of the mechanisms of dye biodegradation and to develop effective methods of bioremediation of dye-contaminated environments.

Ecotoxicity, Health Risks and Contact Allergy Due to p-Phenylenediamine in Hair Dyes and Tattoos: Female Students' Perspectives

While the financial advantages of hair coloring and tattooing are widely acknowledged, environmental hazards and health risks linked to this trend due to their p-phenylenediamine (PPD) content have received less attention. Health education on hair-dying products is warranted to enhance the public's awareness of hair-dying ingredients and their side effects.  A cross-sectional study was therefore conducted with 319 students to assess knowledge of ecotoxicity, health risks, and practices of hair dyeing and tattooing among undergraduate students. A random sample of 59 students was checked for any allergic morphology in the scalp and exposed areas of skin near the neck, ears, palms, and nails. Responses collected were used for data analyses using IBM SPSS Statistics for Windows, Version 17 (Released 2008; IBM Corp., Armonk, New York, United States). Use of hair dye was significantly high among study participants 58.5% (n=187; p<0.05). However, their knowledge regarding the presence of PPD in hair dyes and associated environmental toxicity (37.8%, n=121) was very limited. The majority of participants did not do any allergy tests before applying hair dye (88.9%, n=283). The study revealed that the main reason for hair coloring was as a fashion statement (93.7%, n=299). Regarding tattooing practices, 96.9% (n=309) of study participants had never practiced tattoos, and hence, the prevalence of tattooing was 3.9% (n=12). These data confirmed that the practice of hair dyeing as a style statement was high among students. However, the majority were unaware of their PPD contents and their potential ecotoxicity and health risks.

Optimized decolorization of two poly azo dyes Sirius Red and Sirius Blue using laccase-mediator system

Factors, namely pH, laccase-like activity, dyes concentration as well as 1-Hydroxybenzotriazole (HBT) concentration was examined. The results indicated that the maximum decolorization yield and rate reached 98.30 ± 0.10% and 5.84 ± 0.01%/min, respectively for Sirius Blue, and 99.34 ± 0.47% and 5.85 ± 0.12%/min, respectively for Sirius Red after 4 h. The presence of the redox mediator 1-hydroxybenzotriazole (HBT) greatly improved the decolorization levels. The optimum concentrations of HBT, dyes, and laccase were 0.62 mM, 50 mg/L, and 0.89 U/mL respectively at pH 4.58 for both dyes. Phytotoxicity tests using treated and untreated dyes proved that the applied treatment slightly decreased the toxicity of the by-products. However, the germination index (GI) increased from 14.6 to 36.08% and from 31.6 to 36.96% for Sirius Red and Sirius Blue, respectively. The present study focused on the treatment of two recalcitrant azo dyes, namely: Sirius Blue (Direct Blue 71) and Sirius Red (Direct Red 80). The decolorization was performed using cell-free supernatant from Coriolopsis gallica culture with high laccase activity. Response surface methodology (RSM) and Box-Behnken design were applied to optimize the decolorization of the two tested dyes. The effect of four.

Microbial communities drive flux of acid orange 7 and crystal violet dyes in water-sediment system

Unchecked dye effluent discharge poses escalating environmental and economic concerns, especially in developing nations. While dyes are well-recognized water pollutants, the mechanisms of their environmental spread are least understood. Therefore, the present study examines the partitioning of Acid Orange 7 (AO7) and Crystal Violet (CV) dyes using water-sediment microcosms and reports that native microbes significantly affect AO7 decolorization and transfer. Both dyes transition from infused to pristine matrices, reaching equilibrium in a fortnight. While microbes influence CV partitioning, their role in decolorization is minimal, emphasizing their varied impact on the environmental fate of dyes. Metagenomic analyses reveal contrasting microbial composition between control and AO7-infused samples. Control water samples displayed a dominance of Proteobacteria (62%), Firmicutes (24%), and Bacteroidetes (9%). However, AO7 exposure led to Proteobacteria reducing to 57% and Bacteroidetes to 3%, with Firmicutes increasing to 34%. Sediment samples, primarily comprising Firmicutes (47%) and Proteobacteria (39%), shifted post-AO7 exposure: Proteobacteria increased to 53%, and Firmicutes dropped to 38%. At the genus level, water samples dominated by Niveispirillum (34%) declined after AO7 exposure, while Bacillus and Pseudomonas increased. Notably, Serratia and Sphingomonas, known for azo dye degradation, rose post-exposure, hinting at their role in AO7 decolorization. Conversely, sediment samples showed a decrease in the growth of Bacillus and an increase in that of Pseudomonas and Serratia. These findings emphasize the significant role of microbial communities in determining the environmental fate of dyes, providing insights on its environmental implications and management.

Do zebrafish become blind or is it too much red dye in water? Distinguishing the embryo-larval development and physiology effects of DR 60, 73, and 78

Some dyes currently used by the textile, pharmaceutical, food, cosmetic, and photographic industries have been shown to be toxic and/or mutagenic to aquatic life. Most of these dyes resist degradation processes available for treating wastewater, and these processes might generate even more toxic by-products. Despite the large number of available dyes and the large quantity of dyes released into the environment, studies on their toxicity are still scarce. We evaluated and compared the effects in the animal model Danio rerio (zebrafish) of environmentally relevant concentrations of Disperse Red 60 (DR 60), 73 (DR 73), and 78 (DR 78) using the fish embryo acute toxicity (FET) test, morphometric analysis, immunofluorescence imaging, and behavioral parameters. DR 60 caused ocular modifications, while the DR 73 caused non-inflation of the swim bladder (NISB), pericardial edema (PE), scoliosis (S) and abnormal yolk sac (AYS) from at 0.125 mg/L. In behavioral tests, all the dyes induced changes in velocity and time spent swimming of exposed larvae. However, these alterations in behavior seem to be caused by different factors dependent on the dye and its concentration. Nevertheless, behavior seems to add valuable information concerning the hazards analysis of dyes, since it reveals to be the most sensitive group of parameters tested in the current study. In conclusion, of the behavioral and developmental alterations caused by these dyes should be interpreted as an alert for greater attention when registering new dyes and releasing them into the environment. In the particular case of DR 60 the possibility that directly affects the eye of larvae is of great environmental concern, but also from the human health perspective.

Investigating sensitization activity of azobenzene disperse dyes via the Direct Peptide Reactivity Assay (DPRA)

Azobenzene disperse dyes are the fastest-growing category of commercial dyestuffs and have been found in indoor house dust and in children's polyester apparel. Azobenzene disperse dyes are implicated as potentially allergenic; however, little experimental data is available on allergenicity of these dyes. Here, we examine the binding of azobenzene disperse dyes to nucleophilic peptide residues as a proxy for their potential reactivity as electrophilic allergenic sensitizers. The Direct Peptide Reactivity Assay (DPRA) was utilized via both a spectrophotometric method and a high-performance liquid chromatography (HPLC) method. We tested dyes purified from commercial dyestuffs as well as several known transformation products. All dyes were found to react with nucleophilic peptides in a dose-dependent manner with pseudo-first order kinetics (rate constants as high as 0.04 h-1). Rates of binding reactivity were also found to correlate to electrophilic properties of dyes as measured by Hammett constants and electrophilicity indices. Reactivities of polyester shirt extracts were also tested for DPRA activity and the shirt extracts with high measured abundances of azobenzene disperse dyes were observed to induce greater peptide reactivity. Results suggest that azobenzene disperse dyes may function as immune sensitizers, and that clothing containing these dyes may pose risks for skin sensitization.

Decolorization of reactive azo dye using novel halotolerant yeast consortium HYC and proposed degradation pathway

The presence of high salinity levels in textile wastewater poses a significant obstacle to the process of decolorizing azo dyes. The present study involved the construction of a yeast consortium HYC, which is halotolerant and was recently isolated from wood-feeding termites. The consortium HYC was mainly comprised of Sterigmatomyces halophilus SSA-1575 and Meyerozyma guilliermondii SSA-1547. The developed consortium demonstrated a decolourization efficiency of 96.1% when exposed to a concentration of 50 mg/l of Reactive Black 5 (RB5). The HYC consortium significantly decolorized RB5 up to concentrations of 400 mg/l and in the presence of NaCl up to 50 g/l. The effects of physicochemical factors and the degradation pathway were systematically investigated. The optimal pH, salinity, temperature, and initial dye concentration were 7.0, 3%, 35 °C and 50 mg/l, respectively. The co-carbon source was found to be essential, and the addition of glucose resulted in a 93% decolorization of 50 mg/l RB5. The enzymatic activity of various oxido-reductases was assessed, revealing that NADH-DCIP reductase and azo reductase exhibited greater activity in comparison to other enzymes. UV-Visible (UV-vis) spectrophotometry, Fourier-transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC), and gas chromatography-mass spectrometry (GC-MS) were utilized to identify the metabolites generated during the degradation of RB5. Subsequently, a metabolic pathway was proposed. The confirmation of degradation was established through alterations in the functional groups and modifications in molecular weight. The findings indicate that this halotolerant yeast consortium exhibits promising potential of degrading dye compounds. The results of this study offer significant theoretical basis and crucial perspectives for the implementation of halotolerant yeast consortia in the bioremediation of textile and hypersaline wastewater. This approach is particularly noteworthy as it does not produce aromatic amines.

Identification of key degraders for controlling toxicity risks of disguised toxic pollutants with division of labor mechanisms in activated sludge microbiomes: Using nonylphenol ethoxylate as an example

Efficient management of disguised toxic pollutants (DTPs), which can undergo microbial degradation and convert into more toxic substances, necessitates the collaboration of diverse microbial populations in wastewater treatment plants. However, the identification of key bacterial degraders capable of controlling the toxicity risks of DTPs through division of labor mechanisms in activated sludge microbiomes has received limited attention. In this study, we investigated the key degraders capable of controlling the risk of estrogenicity associated with nonylphenol ethoxylate (NPEO), a representative DTP, in textile activated sludge microbiomes. The results of our batch experiments revealed that the transformation of NPEO into NP and subsequent NP degradation were the rate-limiting processes for controlling the risk of estrogenicity, resulting in an inverted V-shaped curve of estrogenicity in water samples during the biodegradation of NPEO by textile activated sludge. By utilizing enrichment sludge microbiomes treated with NPEO or NP as the sole carbon and energy source, a total of 15 bacterial degraders, including Sphingbium, Pseudomonas, Dokdonella, Comamonas, and Hyphomicrobium, were identified as capable of participating in these processes, Among them, Sphingobium and Pseudomonas were the two key degraders that could cooperatively interact in the degradation of NPEO with division of labor mechanisms. Co-culturing Sphingobium and Pseudomonas isolates exhibited a synergistic effect in degrading NPEO and reducing estrogenicity. Our study underscores the potential of the identified functional bacteria for controlling estrogenicity associated with NPEO and provides a methodological framework for identifying key cooperators engaged in labor division, contributing to the management of risks associated with DTPs by leveraging intrinsic microbial metabolic interactions.

A microfluidics vapor-membrane-valve generated by laser irradiation on carbon nanocoils

We have investigated a micro vapor membrane valve (MVMV) for closing the microfluidic channels by laser irradiation on carbon nanocoils (CNCs) attached to the inner wall of the microchannels. The microchannel with MVMVs was found to exhibit a "closed" state without the supply of laser energy, which is explained on the basis of the theory of heat and mass transfer. Multiple MVMVs for sealing the channels can be generated in sequence and exist simultaneously at different irradiation sites, independently. The significant advantages of the MVMV generated by the laser irradiation on CNCs are the elimination of extrinsic energy required to maintain the microfluidic channel "closed" state and the simplification of the structure integrated into the microfluidic channels and fluid control circuitries. The CNC-based MVMV is a powerful tool for the investigations of the functions of microchannel switching and sealing on microfluidic chips in biomedicine, chemical analysis and other fields. The study of MVMVs will have great significance for biochemical and cytological analysis.

Enhancing Photocatalytic Efficiency of Spent Tea Leaf Powder on ZnIn2S4 Incorporation: Role of Surface Charge on Dye Degradation

Photocatalytic degradation of dye contaminants using nanocomposite adsorbents has emerged as a promising solution for wastewater treatment. Owing to its abundant availability, eco-friendly composition, biocompatibility, and strong adsorption activity, spent tea leaf (STL) powder has been extensively explored as a viable dye-adsorbent material. In this work, we report spectacular enhancement in the dye-degradation properties of STL powder on incorporation of ZnIn₂S₄ (ZIS). The STL/ZIS composite was synthesized using a novel, benign, and scalable aqueous chemical solution method. Comparative degradation and reaction kinetics studies were performed onto an anionic dye, Congo red (CR), and two cationic dyes, Methylene blue (MB) and Crystal violet (CV). The degradation efficiencies of CR, MB, and CV dyes were obtained to be 77.18, 91.29, and 85.36%, respectively, using the STL/ZIS (30%) composite sample after the 120 min experiment. The spectacular improvement in the degradation efficiency of the composite was attributed to its slower charge transfer resistance (as concluded by the EIS study) and optimized surface charge (as concluded by ζ potential study). Scavenger tests and reusability tests deciphered the active species (^•O₂^-) and reusability of the composite samples, respectively. To the best of our knowledge, this is the first report to demonstrate improvement in the degradation efficiency of STL powder on ZIS incorporation.

Investigating Bio-Inspired Degradation of Toxic Dyes Using Potential Multi-Enzyme Producing Extremophiles

Biological treatment methods overcome many of the drawbacks of physicochemical strategies and play a significant role in removing dye contamination for environmental sustainability. Numerous microorganisms have been investigated as promising dye-degrading candidates because of their high metabolic potential. However, few can be applied on a large scale because of the extremely harsh conditions in effluents polluted with multiple dyes, such as alkaline pH, high salinity/heavy metals/dye concentration, high temperature, and oxidative stress. Therefore, extremophilic microorganisms offer enormous opportunities for practical biodegradation processes as they are naturally adapted to multi-stress conditions due to the special structure of their cell wall, capsule, S-layer proteins, extracellular polymer substances (EPS), and siderophores structural and functional properties such as poly-enzymes produced. This review provides scientific information for a broader understanding of general dyes, their toxicity, and their harmful effects. The advantages and disadvantages of physicochemical methods are also highlighted and compared to those of microbial strategies. New techniques and methodologies used in recent studies are briefly summarized and discussed. In particular, this study addresses the key adaptation mechanisms, whole-cell, enzymatic degradation, and non-enzymatic pathways in aerobic, anaerobic, and combination conditions of extremophiles in dye degradation and decolorization. Furthermore, they have special metabolic pathways and protein frameworks that contribute significantly to the complete mineralization and decolorization of the dye when all functions are turned on. The high potential efficiency of microbial degradation by unculturable and multi-enzyme-producing extremophiles remains a question that needs to be answered in practical research.

The Role of Fungal Fuel Cells in Energy Production and the Removal of Pollutants from Wastewater

Pure water, i.e., a sign of life, continuously circulates and is contaminated by different discharges. This emerging environmental problem has been attracting the attention of scientists searching for methods for the treatment of wastewater contaminated by multiple recalcitrant compounds. Various physical and chemical methods are used to degrade contaminants from water bodies. Traditional methods have certain limitations and complexities for bioenergy production, which motivates the search for new ways of sustainable bioenergy production and wastewater treatment. Biological strategies have opened new avenues to the treatment of wastewater using oxidoreductase enzymes for the degradation of pollutants. Fungal-based fuel cells (FFCs), with their catalysts, have gained considerable attention among scientists worldwide. They are a new, ecofriendly, and alternative approach to nonchemical methods due to easy handling. FFCs are efficiently used in wastewater treatment and the production of electricity for power generation. This article also highlights the construction of fungal catalytic cells and the enzymatic performance of different fungal species in energy production and the treatment of wastewater.

One-pot green synthesis of silver nanoparticles using brittle star Ophiocoma scolopendrina: Assessing biological potentialities of antibacterial, antioxidant, anti-diabetic and catalytic degradation of organic dyes

In the current study, aqueous extract of O. scolopendrina (OSE) was used to synthesize AgNPs in a simple and environmentally friendly manner. The biosynthesized OSE-AgNPs were also assessed for its catalytic, antibacterial, anti-diabetic, antioxidant and dye degradation properties. The techniques like UV-visible spectroscopic examinations, TEM, SEM, TGA, zeta potential and FT-IR were used in the characterization investigations. The bioproduction of OSE-AgNPs was preliminary confirmed by UV-visible spectroscopic based investigation followed by microscopic visualization. The synthesized OSE-AgNPs exhibited a reddish brown colour and nearly spherical forms with sizes between 5 and 50 nm quantified by TEM and SEM. The attendance of functional groups like -OH and -NH present in OSE caps on the AgNPs surface was confirmed by FTIR analysis. Interestingly, in the presence of OSE-AgNPs, the degradation of dyes (CV, 95% and EY, 96% in 15 min) were noticeably accelerated. Further, OSE-AgNPs demonstrated substantial antibacterial activity; robust antioxidant properties andnotable anti-diabetic activities. This is the first account on the biosynthetic process of AgNPs using the aqueous extract of O. scolopendrina.

Decolorization of Reactive Red 120 by a novel bacterial consortium: Kinetics and heavy metal inhibition study

<abstract><p>Juru River is one of the most polluted rivers in Malaysia. A dye-degrading bacterial consortium has been isolated from the river's sediment. This consortium JR3 consists of <italic>Pseudomonas aeruginosa</italic> MM01, <italic>Enterobacter</italic> sp. MM05 and <italic>Serratia marcescens</italic> MM06, which were able to decolorize up to 700 ppm of the Reactive Red 120 (RR120) dye under optimal conditions with limited substrate available. Substrate inhibition kinetics were investigated, and, based on the best model, Aiba, the maximum growth rate was 0.795 h^–1, while the saturation constant and inhibitory constant were 0.185% and 0.14%, respectively. In addition, the influence of various metal ions on the growth and decolorization rate of this bacterial consortium on RR120 was investigated. Chromium showed the weakest effect on the decolorization of 200 ppm RR120, with 73.5% removal and bacterial growth of 11.461 log CFU mL^–1. Zinc yielded the second weakest effect, followed by silver and lead, with percentages of RR120 decolorization of 63.8%, 54.6% and 50.5%, respectively. Meanwhile, cadmium, arsenic and copper reduced the decolorization of RR120 in consortium JR3 by half. Mercury strongly inhibited decolorization by 32.5%. Based on the least inhibited heavy metal in RR120 decolorization activity of consortium JR3, the best inhibitory kinetic model was Levenspiel, with a maximum growth rate of 0.632 h^–1, while the saturation constant and inhibitory constants were 15.08% and 0.5783%, respectively. The metal-tolerant azo dye-degrading bacterial consortium will be very useful in dye remediation in metal-laden polluted environments.</p></abstract>

Taguchi L16 (44) orthogonal array-based study and thermodynamics analysis for electro-Fenton process treatment of textile industrial dye

Reactive orange 16 (RO16) is the most widely used azo dye in Textile industry. Complex aromatic structures and resistivity to biological decay caused the dye pollutants incompletely treated by the conventional oxidative methods. The current study presents the electro-Fenton-based advanced oxidation treatment of RO16 dye and the process optimization by Taguchi-based design of experiment (DOE). Using a 500 mL volume lab-scale experimental setup, the process was first studied for the principal operational parameters (initial dye concentration (q); [H2O2]/[Fe+2] (R); current density (ρ); and temperature (T)) effect on decolourization (D R ) and COD removal (C R ). Then, by means of the L16 (44) orthogonal array (OA) formation, standard mean and signal-to-noise (S/N) ratio, the process was optimized for the response variables. The result showed the optimized result at q = 100 mg/L, R = 100, ρ = 8 mA/cm2, and T = 32 °C; with D R and C R as 90.023 and 84.344%, respectively. It was found that the current density affects the process most, followed by [H2O2]/[Fe+2] ratio, initial dye concentration, and temperature i.e., ρ > R > q > T. Also, with the analysis of variance (ANOVA), model equations for D R and C R were developed and its accuracy was verified for experimental results. At optimized conditions, the first order removal rate constants (k a ) were found from batch results. Additionally, the thermodynamic constants (ΔH e , ΔS e , and ΔG b ) were also calculated for the nature of heat-energy involved and temperature effect study on dye degradation. The results showed that the process was thermodynamically feasible, endothermic, and non-spontaneous with a lower energy barrier (E A  = 46.7 kJ mol−1).

Azo dyes degradation by microorganisms - An efficient and sustainable approach

Synthetic aromatic compounds consisting of various functional groups are known as dyes. These colored compounds are often discharged in effluents, and they are very dangerous to aquatic life. Basically, the dye industry started by using natural plant and insect sources, and then suddenly turned into artificial manufacturing. Natural equilibrium of our environment gets changed by the reduction in photosynthetic activity due to the dyes. In China 900,000 tons of all kinds of dyes are usually produced, which are used in many industries like food, textile, food, paper and leather. Untreated wastewater contaminates aquatic bodies by causing eutrophication, change in water color, oxygen depletion which affect aquatic organisms to a great extent. Dye wastewater is now the key environmental pollution form. In recent eras an extensive study line has been developed to explore the dye decolorization and biodegradation under both aerobic as well as anaerobic conditions. In this review, the chemistry, toxicity and microbial biodegradation/decolorization are presented. Some recent studies along with the new techniques and methodologies of remediating the dye pollution are also discussed to provide the bases of their handling. Overall, efficient and high biodegradation potential make microbes an impending foundation for green chemistry to eradicate toxic dyes from industrial wastewater.

Iron-dependent mutualism between Chlorella sorokiniana and Ralstonia pickettii forms the basis for a sustainable bioremediation system

Phototrophic communities of autotrophic microalgae and heterotrophic bacteria perform complex tasks of nutrient acquisition and tackling environmental stress but remain underexplored as a basis for the bioremediation of emerging pollutants. In industrial monoculture designs, poor iron uptake by microalgae limits their productivity and biotechnological efficacy. Iron supplementation is expensive and ineffective because iron remains insoluble in an aqueous medium and is biologically unavailable. However, microalgae develop complex interkingdom associations with siderophore-producing bacteria that help solubilize iron and increase its bioavailability. Using dye degradation as a model, we combined environmental isolations and synthetic ecology as a workflow to design a simplified microbial community based on iron and carbon exchange. We established a mutualism between the previously non-associated alga Chlorella sorokiniana and siderophore-producing bacterium Ralstonia pickettii. Siderophore-mediated increase in iron bioavailability alleviated Fe stress for algae and increased the reductive iron uptake mechanism and bioremediation potential. In exchange, C. sorokiniana produced galactose, glucose, and mannose as major extracellular monosaccharides, supporting bacterial growth. We propose that extracellular iron reduction by ferrireductase is crucial for azoreductase-mediated dye degradation in microalgae. These results demonstrate that iron bioavailability, often overlooked in cultivation, governs microalgal growth, enzymatic processes, and bioremediation potential. Our results suggest that phototrophic communities with an active association for iron and carbon exchange have the potential to overcome challenges associated with micronutrient availability, while scaling up bioremediation designs.

TiO2-modified g-C3N4 nanocomposite for photocatalytic degradation of organic dyes in aqueous solution

In the current study, a direct S-scheme titanium dioxide/graphitic carbon nitride (TiO₂/g-C₃N₄) heterojunction structure was fabricated via simultaneous calcination of TiO₂ precursors and g-C₃N₄. Guava leaf extract was utilized as a reductant for TiO₂ production through a green synthetic method, and g-C₃N₄ was prepared by thermal decomposition of melamine. The pristine and nanocomposite photocatalysts were characterized by XRD, FTIR, BET, TGA, HRTEM, UV-vis DRS, and PL to elucidate their physicochemical properties. The photocatalytic activity of synthesized photocatalysts was examined through the degradation of rhodamine B (RhB) and methylene blue (MB) dyes under simulated solar light irradiation. The nanocomposite exhibited commendable photocatalytic performances with 96% degradation efficiency of RhB attained in 120 min and 95% degradation efficiency of MB achieved in 150 min. The enhanced photocatalytic activities were attributable to visible light-harvesting characteristics and the formation of an S-scheme heterojunction system between two catalysts which promotes interfacial charge separation efficiency and longer charge carrier lifespan. After 4 consecutive cycles, the degradation efficiencies of both RhB and MB remained above 85%. According to the trapping experiments, OH^• and O₂ ^•- radicals were critical in the degradation of RhB, while h⁺ and O₂ ^•- radicals were dominant in the degradation of MB. The nanocomposite was also tested for elution of actual water pollutants by combining two dyes, and above 90% degradation efficiencies were achieved for both dyes after 240 min.

Bach-Type Polycondensation with the Aid of Hemoglobin as an Oxygen Supplier, and Synthetic/Bio-Composite

We developed a new Bach-type reaction in the presence of oxy-hemoglobin as an oxygen supplier to synthesize polyazobenzene by traditional Bach reaction. The resultant product is a form of polymeric dye/hemoglobin copolymer. The advantage of this research is that it involves a new reaction using the function of biomolecules, as well as the formation of plastics and biomaterials. The bio-based material may have good affinity with life forms, which may lead to applications in medical science.

Microbial fuel cells for mineralization and decolorization of azo dyes: Recent advances in design and materials

Microbial fuel cells (MFCs) exhibit tremendous potential in the sustainable management of dye wastewater via degrading azo dyes while generating electricity. The past decade has witnessed advances in MFC configurations and materials; however, comprehensive analyses of design and material and its association with dye degradation and electricity generation are required for their industrial application. MFC models with high efficiency of dye decolorization (96-100%) and a wide variation in power generation (29.4-940 mW/m²) have been reported. However, only 28 out of 104 studies analyzed dye mineralization - a prerequisite to obviate dye toxicity. Consequently, the current review aims to provide an in-depth analysis of MFCs potential in dye degradation and mineralization and evaluates materials and designs as crucial factors. Also, structural and operation parameters critical to large-scale applicability and complete mineralization of azo dye were evaluated. Choice of materials, i.e., bacteria, anode, cathode, cathode catalyst, membrane, and substrate and their effects on power density and dye decolorization efficiency presented in review will help in economic feasibility and MFCs scalability to develop a self-sustainable solution for treating azo dye wastewater.

Recent progress in treatment of dyes wastewater using microbial-electro-Fenton technology

Globally, textile dyeing and manufacturing are one of the largest industrial units releasing huge amount of wastewater (WW) with refractory compounds such as dyes and pigments. Currently, wastewater treatment has been viewed as an industrial opportunity for rejuvenating fresh water resources and it is highly required in water stressed countries. This comprehensive review highlights an overall concept and in-depth knowledge on integrated, cost-effective cross-disciplinary solutions for domestic and industrial (textile dyes) WW and for harnessing renewable energy. This basic concept entails parallel or sequential modes of treating two chemically different WW i.e., domestic and industrial in the same system. In this case, contemporary advancement in MFC/MEC (METs) based systems towards Microbial-Electro-Fenton Technology (MEFT) revealed a substantial emerging scope and opportunity. Principally the said technology is based upon previously established anaerobic digestion and electro-chemical (photo/UV/Fenton) processes in the disciplines of microbial biotechnology and electro-chemistry. It holds an added advantage to all previously establish technologies in terms of treatment and energy efficiency, minimal toxicity and sludge waste, and environmental sustainable. This review typically described different dyes and their ultimate fate in environment and recently developed hierarchy of MEFS. It revealed detail mechanisms and degradation rate of dyes typically in cathodic Fenton system under batch and continuous modes of different MEF reactors. Moreover, it described cost-effectiveness of the said technology in terms of energy budget (production and consumption), and the limitations related to reactor fabrication cost and design for future upgradation to large scale application.

Synthesis, characterization and application of new adsorbent composites based on sol-gel/chitosan for the removal of soluble substance in water

In this work, new adsorbent composites from the silica precursor tetraethyl orthosilicate (TEOS) and chitosan have been successfully synthesized, denominated 20%Chi, 30%Chi and 40%Chi. The composites presented enhanced chemical and physical characteristics, with emphasis on the high surface areas between 374.94 m²/g to 886.31 m²/g. The application of the composites in the model system (TY - Tartrazine yellow dye), presented adsorption capacities dependent on the amount of chitosan in the composite (40%Chi > 30%Chi > 20%Chi). However, from the experimental data of the constituent materials, 30%Chi provided the greatest increase in the adsorption capacity in the monolayer, with values of 36%. This demonstrates that the amount of chitosan in the compound alters the arrangement of adsorption sites. The 30%Chi composite presented life cycle superior to 10 reuse cycles.

•

The addition of silica provided better physical and chemical properties to the developed composites.

•

The synthesis of the 30%Chi composite enabled an increase in the adsorption capacity of the TY dye.

•

The 30%Chi composite obtained a surface area of 886.31 m²/g.

•

The 30%Chi composite was useful for more than 10 adsorption and desorption cycles.

Visible-Light-Driven AO7 Photocatalytic Degradation and Toxicity Removal at Bi-Doped SrTiO3

In this study, Bi-doped SrTiO3 perovskites (Sr1−xBixTiO3, x = 0, 0.03, 0.05, 0.07 and 0.1) were synthesized using the solid-state method, characterized, and tested as photocatalysts in the degradation of the azo dye acid orange 7 (AO7) under visible light. The perovskites were successfully synthesized, and XRD data showed a predominant, well-crystallized phase, belonging to the cubic perovskite symmetry. For the doped samples, a minority phase, identified as bismuth titanate, was detected. All doped samples exhibited improved photocatalytic activity under visible light, on the degradation of AO7 (10 mg L−1), when compared with the undoped SrTiO3, with an increase in relative Abs484 nm decay from 3.7% to ≥67.8% after 1 h, for a powder suspension of 0.2 g L−1. The best photocatalytic activity was exhibited by the Sr0.95Bi0.05TiO3 perovskite. Reusability studies showed no significant loss in photocatalytic activity under visible light. The final solutions showed no toxicity towards D. magna, proving the efficiency of Sr0.95Bi0.05TiO3 as a visible-light-driven photocatalyst to degrade both the AO7 dye as well as its toxic by-products. A degradation mechanism is proposed.

A critical review on the treatment of dye-containing wastewater: Ecotoxicological and health concerns of textile dyes and possible remediation approaches for environmental safety

The synthetic dyes used in the textile industry pollute a large amount of water. Textile dyes do not bind tightly to the fabric and are discharged as effluent into the aquatic environment. As a result, the continuous discharge of wastewater from a large number of textile industries without prior treatment has significant negative consequences on the environment and human health. Textile dyes contaminate aquatic habitats and have the potential to be toxic to aquatic organisms, which may enter the food chain. This review will discuss the effects of textile dyes on water bodies, aquatic flora, and human health. Textile dyes degrade the esthetic quality of bodies of water by increasing biochemical and chemical oxygen demand, impairing photosynthesis, inhibiting plant growth, entering the food chain, providing recalcitrance and bioaccumulation, and potentially promoting toxicity, mutagenicity, and carcinogenicity. Therefore, dye-containing wastewater should be effectively treated using eco-friendly technologies to avoid negative effects on the environment, human health, and natural water resources. This review compares the most recent technologies which are commonly used to remove dye from textile wastewater, with a focus on the advantages and drawbacks of these various approaches. This review is expected to spark great interest among the research community who wish to combat the widespread risk of toxic organic pollutants generated by the textile industries.

Degradation of Azo Dyes: Bacterial Potential for Bioremediation

The use of dyes dates to ancient times and has increased due to population and industrial growth, leading to the rise of synthetic dyes. These pollutants are of great environmental impact and azo dyes deserve special attention due their widespread use and challenging degradation. Among the biological solutions developed to mitigate this issue, bacteria are highlighted for being versatile organisms, which can be applied as single organism cultures, microbial consortia, in bioreactors, acting in the detoxification of azo dyes breakage by-products and have the potential to combine biodegradation with the production of products of economic interest. These characteristics go hand in hand with the ability of various strains to act under various chemical and physical parameters, such as a wide range of pH, salinity, and temperature, with good performance under industry, and environmental, relevant conditions. This review encompasses studies with promising results related to the use of bacteria in the bioremediation of environments contaminated with azo dyes in the most diverse techniques and parameters, both in environmental and laboratory samples, also addressing their mechanisms and the legislation involving these dyes around the world, showcasing the importance of bacterial bioremediation, specialty in a scenario in an ever-increasing pursuit for sustainable production.

Decolorization of textile wastewater by electrooxidation process using different anode materials: Statistical optimization

The presence of reactive dyes in textile wastewater is a serious environmental concern due to their associated mutagenic and carcinogenic effects. The present study aims to analyze the effect of different anodic materials on the decolorization of a real textile wastewater effluent. For this purpose, four different anodic materials-TiO2-coated platine, TiO2-coated ruthenium dioxide (RuO2) (viz., RuO2), titanium dioxide (TiO2), and graphite-were connected, respectively, to titanium dioxide (TiO2) used as a cathode electrode. Color and cost optimization studies were performed using the response surface methodology and the Box-Behnken experimental design (BBD). According to ANOVA results, the R2 values for Pt/TiO2, RuO2/TiO2, TiO2/TiO2, and graphite/TiO2 electrode pairs were found to be 97.4%, 93.8%, 92.44%, and 92.2%, respectively, indicating a good compatibility as it is close to one. The results show that color removal efficiencies at the optimal conditions were 86.3%, 90.8%, 91.5%, and 93.6% for Pt/TiO2, graphite/TiO2, TiO2/TiO2, and RuO2/TiO2, respectively. Furthermore, energy consumption cost at the optimum conditions was also evaluated, and the results were as follows: Pt/TiO2 (0.95 €/m3), graphite/TiO2 (0.74 €/m3), TiO2/TiO2 (0.31 €/m3), and RuO2/TiO2 (0.26 €/m3). Consequently, this research paper shows that all of the tested anodic materials give satisfactory color removal efficiencies higher than 86%. When energy consumption and color removal are considered together, the use of TiO2/TiO2 and RuO2/TiO2 pairs would be preferred. PRACTITIONER POINTS: Anodic contribution was investigated for decolorization of textile wastewater by electrooxidation process. Graphite, TiO2-coated Pt, TiO2-coated RuO2, and TiO2 were used as anode materials. Highest color removal with lowest energy consumption was achieved with TiO2-coated RuO2 anode material (93.6%).

Modification of cyclodextrin and use in environmental applications

Water pollution, which has become a global problem in parallel with environmental pollution, is a problem that needs to be solved urgently, considering the gradual depletion of water resources. The inadequacy of the water treatment methods and the materials used somehow directed the researchers to look for dual character structures such as biocompatible and biodegradable β-cyclodextrin (β-CD). β-CD, which is normally insoluble in water, is used in demanding wastewater applications by being modified with the help of different agents to be water soluble or transformed into polymeric adsorbents as a result of co-polymerization via cross-linkers. In this way, in addition to the host-guest interactions offered by β-CD, secondary forces arising from these interactions provide advantages in terms of regeneration and reusability. However, the adsorption efficiency and synthesis steps need to be improved. Based on the current studies presented in this review, in which cross-linkers and modification methods are also mentioned, suggestions for novel synthesis methods of new-generation β-CD-based materials, criticisms, and recent methods of removal of micropollutants such as heavy metals, industrial dyes, harmful biomolecules, and pharmaceutics wastes are mentioned.

Characterizing azobenzene disperse dyes in commercial mixtures and children's polyester clothing

Azobenzene disperse dyes are the fastest-growing class of dyestuffs, yet little is known about dye occurrences, sources, and transformations; azo dyes are also underrepresented in chemical standard catalogs, molecular databases, and mass spectral libraries. Many azo dyes are known to have sensitization, mutagenic, and carcinogenic properties. To fill these knowledge gaps, azo dyes were purified from dyestuffs by Soxhlet extraction and flash chromatography and characterized using ultra-high-performance liquid chromatography (UHPLC) coupled to a high resolution Orbitrap Fusion Lumos mass spectrometer operated in positive electrospray ionization mode, as well as by ¹H and ¹³C NMR. Data were analyzed to identify likely chemical formulas and structures using a weight-of-evidence approach with multiple open-source, in silico computational mass spectrometry tools. Nineteen total azobenzene dyes were detected in dyestuffs via a non-targeted analysis approach; the azobenzene dyes Disperse Blue 79:1, Disperse Blue 183:1, Disperse Orange 44, Disperse Orange 73, Disperse Red 50, Disperse Red 73, and Disperse Red 354 were purified from raw dyestuffs. Samples of children's polyester clothing were then analyzed likewise. In clothing, 21 azobenzene disperse dyes were detected, 12 of which were confirmed and quantified via reference standards. Individual dyes in apparel were quantified at concentrations up to 9230 μg dye/g shirt, with geometric means ranging 7.91-300 μg dye/g shirt. Total dye load in apparel was quantified at up to 11,430 μg dye/g shirt. This research supported the development of reference standards and library mass spectra for azobenzene disperse dyes previously absent from standard and spectral libraries. By analyzing the scope and quantities of azo dyes in children's polyester apparel, this study will facilitate a more robust understanding of sources of these potentially allergenic and mutagenic compounds.

Mutagenicity of a novel 2-phenylbenzotriazole (non-chlorinated 2-phenylbenzotriazole-9) in mice

Dinitrophenylazo dyes can form 2-phenylbenzotriazoles (PBTAs) in the textile dyeing process upon the addition of chemical reducing agents. Some dinitrophenylazo dyes, as well as their respective reduced (non-chlorinated) and chlorinated PBTAs, are now found in rivers owing to wastewater from textile plants. This study aimed to investigate the genotoxicity of a new PBTA derived from C.I. Disperse Violet 93 azo dye, namely non-Cl PBTA-9. Primary DNA damage in the blood, liver, and colon cells, micronucleated cells in the bone marrow, and gene expression (NAT2, CYP1A1, TRP53, and CDKN1A) in liver cells were observed in mice, at acute oral exposure (gavage) doses of 5, 50, and 500 μg/kg body weight (b.w.). The non-chlorinated PBTA-9 caused DNA damage in the blood and liver (at 500 μg/kg b.w.) and in colon cells (at 5, 50, and 500 μg/kg), and increased the frequency of micronucleated cells in the bone marrow (at 5 and 50 μg/kg). No histological alterations or gene expression changes were observed. In conclusion, in vivo exposure to non-chlorinated PBTA-9 induced genetic damage in various rodent tissues, corroborating results previously obtained from the Ames test. Because this compound has been detected in rivers, exposure to humans and biota is a major concern.

Galvano-Fenton Engineering Solution with Spontaneous Catalyst's Generation from Waste: Experimental Efficiency, Parametric Analysis and Modeling Interpretation Applied to a Clean Technology for Dyes Degradation in Water

In this paper, the degradation of the diazo dye naphthol blue black (NBB) using the Galvano-Fenton process is studied experimentally and numerically. The simulations are carried out based on the anodic, cathodic, and 34 elementary reactions evolving in the electrolyte, in addition to the oxidative attack of NBB by HO• at a constant rate of 3.35×107 mol-1·m3·s-1 during the initiation stage of the chain reactions. The selection of the operating conditions including the pH of the electrolyte, the stirring speed, and the electrodes disposition is performed by assessing the kinetics of NBB degradation; these parameters are set to 3, 350 rpm and a parallel disposition with a 3 cm inter-electrode distance, respectively. The kinetics of Fe(III) in the electrolyte were monitored using the principles of Fricke dosimetry and simulated numerically. The model showed more than a 96% correlation with the experimental results in both the blank test and the presence of the dye. The effects of H2O2 and NBB concentrations on the degradation of the dye were examined jointly with the evolution of the simulated H2O2, Fe2+, and HO• concentrations in the electrolyte. The model demonstrated a good correlation with the experimental results in terms of the initial degradation rates, with correlation coefficients exceeding 98%.

Synergistic effect of the activated carbon addition from leather wastes in chitosan/alginate-based composites

In this work, chitosan/alginate composites were developed by the gelation method with the addition of different amounts of activated carbon produced from tannery waste (ACTW). The performance of these composites was verified through the adsorption of the textile dye Remazol Brilliant Blue R (RBBR). A synergistic effect was observed by the addition of ACTW; with a specific surface area up to 45.584 m²/g, the maximum adsorption capacity was 300.96 mg/g. The synergy was due to the reduction in steric hindrance, with the adsorption capacity 1.2 times higher than expected. The material was regenerated with sodium hydroxide for 10 cycles. The composite containing 30% ACTW (AC30) was applied in the treatment of real textile effluent, with 30% reductions in the biochemical oxygen demand (BOD), 39% in the chemical oxygen demand (COD), 78% in turbidity, and 67% in color.

Electrodegradation of Acid Mixture Dye through the Employment of Cu/Fe Macro-Corrosion Galvanic Cell in Na2SO4 Synthetic Wastewater

Traditional wastewater purification processes are based on a combination of physical, chemical, and biological methods; however, typical electrochemical techniques for removing pollutants require large amounts of electrical energy. In this study, we report on a process of wastewater purification, through continuous anodic dissolution of iron anode for aerated Cu/Fe galvanic cell in synthetic Na₂SO₄ wastewater solution. Electrochemical experiments were conducted by means of a laboratory size electrolyzer, where electrocoagulation along with electrooxidation phenomena were examined for wastewater containing Acid Mixture dye. The above was visualized through the employment of electrochemical (cyclic voltammetry and ac impedance spectroscopy techniques) along with instrumental spectroscopy analyses.

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.

Bibliometric analysis of advanced oxidation processes (AOPs) in wastewater treatment: global and Ibero-American research trends

Advanced oxidation processes (AOPs) constitute a developing area of particular interest for researchers in different fields due to their broad range of applications. However, there are few studies dedicated to the bibliometric analysis of AOPs. Hence, a systematic literature review of research publications (research articles, review articles, and book chapters) from 1980 to 2018 was carried out to visualize and evaluate research trends on AOPs around the world and, especially in Ibero-America (IA), on the field of wastewater treatment. Using the most extensive databases in literature search, Scopus and Web of Science (WoS), which encompass 95% of the publications in the world, a total of 18,751 records were retrieved by limiting the search results to words associated with AOPs in the titles, keyword, and abstracts. Raw data were manually organized and filtered, standardizing authors and institution names, publication titles, and keywords for the purpose of eliminating double-counted entries. Similarly, homonymous authors and institutions were identified for all records retrieved. The bibliometric dataset was processed using the VantagePoint software. The research trends visualized about AOPs were as follows: number of publications per triennium, publications by country, participation by continent, most important journals and authors, most referenced institutions, global network of co-authors, and keywords network visualization, highlighting the Ibero-American contribution to global research.

Franconibacter sp., 1MS: A New Strain in Decolorization and Degradation of Azo Dyes Ponceau S Red and Methyl Orange

The aim of the present study is focused on the decolorization and degradation of azo dyes Ponceau S Red and Methyl Orange by a bacterial strain isolated from the gold mining district of San Martin de Loba, South of Bolivar (Colombia) sediment samples and identified as Franconibacter sp. 1MS (GenBank: MT568543) based on phenotypic and genotypic methods. A higher percentage of decolorization at 100 mg/L concentration, 37 °C, and pH 7 was recorded at 120 h of incubation period for both dyes. The UV-vis, Fourier transform infrared spectroscopy, and gas chromatography-mass spectrometry analysis of the original dyes and their degraded metabolites confirmed that the decolorization was due to degradation. The proposed metabolic pathways for biodegradation of both dyes have been elucidated, which showed the formation of five intermediate metabolites, namely, N,N-dimethylbenzyl-1,4-diamine, sulfonamide, 1,4-diaminobenzene, 2,5-diaminobenzenesulfonic acid, and 1-amino-2-naphthol, which are not only highly toxic but also be able to be converted through metabolic activation into mutagenic, carcinogenic, and/or teratogenic species. The phytotoxicity studies of the original dye and degraded metabolites were tested on Phaseolus vulgaris and divulged that the degraded metabolites have toxic effects. An effective phytostimulation was observed in Ponceau S Red, which could be attributed to its capacity for enrichment of the culture medium with essential nutrients, a favorable environment for the growth of the plant.

Application of sonochemically synthesized SnS and SnS2 in the electro-Fenton process: Kinetics and enhanced decolorization

SnS and SnS₂ powders were synthesized with the use of ultrasound. The indirect sonication was applied with ultrasound frequency 40 kHz and acoustic power 38 W/L. Products of syntheses were examined with PXRD, TEM, EDX, XPS, and UV-Vis (the Tauc method) investigations. The resulting microparticles were used for tip coating of copper cathodes. These electrodes were used in the degradation of model azo-dye Metanil Yellow by the electro-Fenton process. The efficiencies of degradation using copper, SnS-coated copper, and SnS₂-coated copper cathodes are compared. Kinetics of degradation of Metanil Yellow in the electro-Fenton process with the application of three different cathodes is also investigated. It was found that the degradation follows pseudo-first-order and that SnS-coated copper cathode improves the efficiency of degradation, while SnS₂-coated copper cathode decreases the efficiency of degradation.

Myco-decontamination of azo dyes: nano-augmentation technologies

Effluents of textile, paper, and related industries contain significant amounts of synthetic dyes which has serious environmental and health implications. Remediation of dyes through physical and chemical techniques has specific limitations. Augmented biological decontamination strategies 'microbial remediation' may involve ring-opening of dye molecules besides the reduction of constituent metal ions. Both bacterial and fungal genera are known to exhibit metabolic versatility which can be harnessed for effective bio-removal of the toxic dye contaminants. Ascomycetous/basidiomycetes fungi can effectively decontaminate azo dyes through laccase/peroxidase enzyme-mediated catalysis. The extent, efficacy, and range of fungal dye decontamination can be enhanced by the conjugated application of nanomaterials, including nanoparticles (NPs) and their composites. Fungal cell-enabled NP synthesis- 'myco-farmed NPs', is a low-cost strategy for scaled-up fabrication of a variety of metal, metal oxide, non-metal oxide NPs through oxidation/reduction of dissolved ions/molecules by extracellular biomolecules. Augmented and rapid decontamination of azo dyes at high concentrations can be achieved by the use of myco-farmed NPs, NPs adsorbed fungal biomass, and nano-immobilized fungi-derived bio-catalytical agents. This manuscript will explore the opportunities and benefits of mycoremediation and application of fungus-NP bionanoconjugate to remediate dye pollutants in wastewaters and land contaminated with the effluent of textile industries.