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

Reusable magnetic alginate nanocomposite with immobilized Pseudozyma antarctica yeast cells offers the potential for bioremediation and detoxification of reactive black 5 dye

Azo dyes in wastewater of textile, paper and pulp, cosmetics, and leather tanning industries have toxicity and mutagenicity for all living organisms. The aim of the current research was the study of free and immobilized yeast cells of Pseudozyma antarctica on the beads of magnetic alginate nanocomposite to decolorize and detoxify Reactive Black 5 (RB5) as a representative of azo dyes. This yeast decolorized a high concentration of RB5 (2500 mg/L) with 82.30 % decolorization efficiency. The beads containing immobilized yeast cells were used for decolorization in consecutive cycles, and the decolorization efficiency of the beads after four cycles was more than 67 %. UV-visible and FTIR spectroscopy studies showed that the azo bond in RB5 was removed and destroyed by yeast activity. The azo bond of RB5 is destroyed in the biodegradation mechanism which confirms the decolorization of RB5 by P. antarctica via the biodegradation mechanism. According to the phytotoxicity results, RB5 decolorization by P. antarctica reduced the toxicity of the dye. This is the first study on the decolorizing and detoxifying potentials of P. antarctica and introduces a promising candidate for the treatment of wastewater containing azo dyes. Furthermore, its successful immobilization on magnetic alginate nanocomposite and its convenient consecutive uses make it more attractive for environmental applications.

Recent Strategies for the Remediation of Textile Dyes from Wastewater: A Systematic Review

The presence of dye in wastewater causes substantial threats to the environment, and has negative impacts not only on human health but also on the health of other organisms that are part of the ecosystem. Because of the increase in textile manufacturing, the inhabitants of the area, along with other species, are subjected to the potentially hazardous consequences of wastewater discharge from textile and industrial manufacturing. Different types of dyes emanating from textile wastewater have adverse effects on the aquatic environment. Various methods including physical, chemical, and biological strategies are applied in order to reduce the amount of dye pollution in the environment. The development of economical, ecologically acceptable, and efficient strategies for treating dye-containing wastewater is necessary. It has been shown that microbial communities have significant potential for the remediation of hazardous dyes in an environmentally friendly manner. In order to improve the efficacy of dye remediation, numerous cutting-edge strategies, including those based on nanotechnology, microbial biosorbents, bioreactor technology, microbial fuel cells, and genetic engineering, have been utilized. This article addresses the latest developments in physical, chemical, eco-friendly biological and advanced strategies for the efficient mitigation of dye pollution in the environment, along with the related challenges.

A novel N-arachidonoyl-l-alanine-catabolizing strain of Serratia marcescens for the bioremediation of Cd and Cr co-contamination

Cadmium (Cd) and chromium (Cr) are widespread contaminants with a high risk to the environment and humans. Herein we isolated a novel strain of Serratia marcescens, namely strain S27, from soil co-contaminated with Cd and Cr. This strain showed strong resistance to Cd as well as Cr. S27 cells demonstrated Cd adsorption rate of 45.8% and Cr reduction capacity of 84.4% under optimal growth conditions (i.e., 30 °C, 200 rpm, and pH 7.5). Microscopic characterization of S27 cells revealed the importance of the functional groups C-O-C, C-H-O, C-C, C-H, and -OH, and also indicated that Cr reduction occurred on bacterial cell membrane. Cd(II) and Cr(VI) bioaccumulation on S27 cell surface was mainly in the form of Cd(OH)₂ and Cr₂O₃, respectively. Further, metabolomic analyses revealed that N-arachidonoyl-l-alanine was the key metabolite that promoted Cd and Cr complexation by S27; it primarily promotes γ-linolenic acid (GLA) metabolism, producing siderophores and coordinating with organic acids to enhance metal bioavailability. To summarize, our results suggest that S27 is promising for the bioremediation of environments contaminated with Cd and Cr in tropical regions.

Secondary bond interface assembly of polyethyleneimine on zein microparticles for rapid adsorption of Reactive Black 5

Textile dye wastewater has the characteristics of high concentration, complex composition and changeable color degree and pH, which is difficult to be effectively and completely treated, and easy to cause environmental pollution. Here, a strategy of secondary bond interface assembly of polyethyleneimine on zein microparticles (PEI) (PEI@zein) was constructed to achieve rapid and efficient removal of Reactive Black 5 (RB5), which is one of the most widely used reactive dyes in the textile industry. Structural analysis indicated that the as-prepared PEI layer immobilized on zein microparticles was constructed based on the interface assembly dominated by hydrophobic interactions and electrostatic attraction between PEI molecules and zein chains. The novel interface showed excellent absorption performance for RB5 with an absorption capacity of 631.0 mg·g^-1, rapid adsorption in 2 min, wide pH range of 4-10. Mechanism analysis suggested the effective adsorption of RB5 by PEI@zein microparticles was mainly attributed to secondary bond interface such as electrostatic interaction and hydrogen bond between RB5 and PEI immobilized on the surface of zein microparticles. Moreover, due to the presence of secondary bond interface, RB5 adsorbed on microparticles can be easily desorbed by using 0.01 M NaOH. Therefore, the strategy of secondary bond interface assembly with polyethyleneimine on zein microparticles has high potential for practical application in the treatment of dye-containing wastewater.

Bacterial oxidoreductive enzymes as molecular weapons for the degradation and metabolism of the toxic azo dyes in wastewater: a review

Azo dyes are extremely toxic and pose significant environmental and health risks. Consequently, mineralization and conversion to simple compounds are required to avoid their hazardous effects. A variety of enzymes from the bacterial system are thought to be involved in the degradation and metabolism of azo dyes. Bioremediation, a cost effective and eco-friendly biotechnology, involving bacteria is powered by bacterial enzymes. As mentioned, several enzymes from the bacterial system serve as molecular weapons in the degradation of these dyes. Among these enzymes, azoreductase, oxidoreductase, and laccase are of great interest for the degradation and decolorization of azo dyes. Combination of the oxidative and reductive enzymes is used for the removal of azo dyes from water. The aim of this review article is to provide information on the importance of bacterial enzymes. The review also discusses the genetically modified microorganisms in the biodegradation of azo dyes in polluted water.

Biological Degradation of the Azo Dye Basic Orange 2 by Escherichia coli: A Sustainable and Ecofriendly Approach for the Treatment of Textile Wastewater

In this study, initially 11 different bacterial strains were tested for the degradation capabilities against Basic Orange 2 dye. In initial screening with 78.90% degradation activity, Escherichia coli emerged as the most promising strain to degrade the selected dye, and was then employed in subsequent experiments. For further enhancing the degradation capability of selected bacteria, the effects of various physicochemical parameters were also evaluated. Among the tested parameters, 20 ppm dye concentration, 1666 mg/L glucose concentration, a temperature of 40 °C, 666 mg/L sodium chloride concentration, pH 7, 1000 mg/L urea concentration, a 3-day incubation period and the use of sodium benzoate as a redox mediator (666 mg/L) were found to be ideal conditions to get the highest decolorization/degradation activities. Finally, all the mentioned parameters were combined in a single set of experiments, and the decolorization capacity of the bacteria was enhanced to 89.88%. The effect of pH, dye concentration, incubation time and temperature were found to be responsible for the optimum degradation of dye (p < 0.05), as predicted from the ANOVA (analysis of variance) of the response surface methodology. The metabolites were collected after completion of the process and characterized through Fourier transform irradiation (FTIR) and gas chromatography mass spectrometry (GC-MS). From the data obtained, a proposed mechanism was deduced where it was assumed that the azo bond of the dye was broken by the azoreductase enzyme of the bacteria, resulting in the formation of aniline and 3, 4-diaminobezeminium chloride. The aniline was then further converted to benzene by deamination by the action of the bacterial deaminase enzyme. The benzene ring, after subsequent methylation, was transformed into o-xylene, while 3, 4-diaminobezeminium chloride was converted to p-xylene by enzymatic action. These findings suggest that Escherichia coli is a capable strain to be used in the bioremediation of textile effluents containing azo dyes. However, the selected bacterial strain may need to be further investigated for other dyes as well.

Optimization of reactive black 5 decolorization by the newly isolated Saccharomyces cerevisiae X19G2 using response-surface methodology

In the current investigation, the capacity of different yeast strains to decolorize reactive black 5 (RB-5) was assessed. A comparative study between the different strains demonstrated that Saccharomyces cerevisiae X19G2 exhibited the highest decolorization rate (69.20 ± 1.16%) after 48 h of incubation. This strain was selected to optimize the medium components' concentrations for maximum RB-5 decolorization. Response-surface methodology (RSM) was tested for the most significant parameters (glucose, yeast extract and RB-5 dye concentrations) that were previously determined by Plackett-Burman design. A dye decolorization rate of 99.59 ± 0.24% was achieved within 48 h using a maximum RB-5 concentration (0.15 g/L) with glucose and yeast extract concentrations equalling to 10.5 g/L and 1 g/L, respectively. Experimental data results proved to fit well with the pseudo-second order kinetics model. The phytotoxicity assessment was carried out using Raphanus sativus seeds to determine the toxicity of RB-5 before and after treatment by S. cerevisiae. Results suggested that germination rate and the length of seeds radical irrigated with 0.15 g/L of RB-5 decreased by 30 and 53%, compared to those irrigated with treated solution. Therefore, metabolites derived from decolorization of RB-5 by S. cerevisiae X19G2 were significantly less toxic than the original dye.

Optimization of the Decolorization of the Reactive Black 5 by a Laccase-like Active Cell-Free Supernatant from Coriolopsis gallica

The textile industry generates huge volumes of colored wastewater that require multiple treatments to remove persistent toxic and carcinogenic dyes. Here we studied the decolorization of a recalcitrant azo dye, Reactive Black 5, using laccase-like active cell-free supernatant from Coriolopsis gallica. Decolorization was optimized in a 1 mL reaction mixture using the response surface methodology (RSM) to test the influence of five variables, i.e., laccase-like activity, dye concentration, redox mediator (HBT) concentration, pH, and temperature, on dye decolorization. Statistical tests were used to determine regression coefficients and the quality of the models used, as well as significant factors and/or factor interactions. Maximum decolorization was achieved at 120 min (82 ± 0.6%) with the optimized protocol, i.e., laccase-like activity at 0.5 U mL−1, dye at 25 mg L−1, HBT at 4.5 mM, pH at 4.2 and temperature at 55 °C. The model proved significant (ANOVA test with p < 0.001): coefficient of determination (R²) was 89.78%, adjusted coefficient of determination (R²A) was 87.85%, and root mean square error (RMSE) was 10.48%. The reaction conditions yielding maximum decolorization were tested in a larger volume of 500 mL reaction mixture. Under these conditions, the decolorization rate reached 77.6 ± 0.4%, which was in good agreement with the value found on the 1 mL scale. RB5 decolorization was further evaluated using the UV-visible spectra of the treated and untreated dyes.

Transport Behavior of RB5 Dye in Alluvial Soil in the Northeast of Brazil

The textile industry generates a large volume of chemically diversified effluents containing, among other compounds, dyes. Untreated wastes are contaminants to surface water, soil, and groundwater. In this aspect, various studies have explored the issue of contamination of alluvial soils in the Alto Capibaribe region, northeast of Brazil, due to local textile activity. This region, inserted into the Brazilian semiarid region, suffers from water scarcity, and there is a need for rural communities to use alluvial formations for water supply. The simulation of solute transport is a fundamental tool for understanding the environmental performance and risks associated with contamination by textile dyes. Transport parameters that directly influence pollutant dynamics in sedimentary environments are characterized. This study evaluated the retention and mobility of the dye Remazol Black 5 (RB5) in two superficial layers of alluvial soil from Alto Capibaribe to obtain transport parameters. In the laboratory, tests of mobility in soil columns with RB5 dye (concentration of the 25 mg L−1) and KBr tracer (concentration of the 35.7 g L−1) solutions were conducted. The CDE and two-region models were used to model the KBr experimental transport data, and the two-site model was used to model the RB5 experimental transport data. Physical non-equilibrium was found in the soils for KBr transport, and the two-region model adequately modeled the experimental breakthrough curves (BTCs). For the transport of RB5, the results showed a chemical non-equilibrium, and the two-site model was adequate to model the experimental BTCs. The results indicate that the surface layer is most responsible for the retention of RB5, where the RB5 solution was less mobile than in the lower layer. Both layers showed low retention and high mobility for RB5, indicating that the RB5 dye in the region may contaminate groundwater.

Treatment of textile wastewater containing mixed toxic azo dye and chromium (VI) BY haloalkaliphilic bacterial consortium

Scientific empowerment in this century created a positive and negative impact on the ecosystem's biotic and abiotic components. The current scenario of emerging recalcitrant pollutants in the environment is encountered using various remediation approaches are enforced and applied. The need for mineralization of the toxic pollutants to non - toxic forms accomplished the application of microbes (bacteria, fungi and algae) and plants individually or in a combined manner. The current research on the removal of pollutants from synthetic textile wastewater containing 1200 ppm concentration of mixed azo dyes -Reactive red (RR), Reactive Brown (RB) & Reactive Black (RBl) and 300 ppm Cr (VI) metal using haloalkaliphilic bacterial strains LBKVG1, LBKVG2, LBKVG3 & LBKVG4 in a Moving Bed Biofilm Reactor (MBBR), showed decolorization of 82 ± 0.5% of mixed azo dyes and degradation 56 ± 0.5% of Cr (VI) metal at 37 ^°C and pH 8.5 in the fifth day of the study. The isolated bacterial strains in the consortium were molecularly and morphologically characterized by 16SrRNA sequencing and SEM analysis. FT-IR and GC-MS analysis scrutinized the metabolites obtained. The findings suggest the degradation of hazardous pollutants even at higher concentrations and attempt to decolourize the mixed azo dyes simultaneously using the eco-friendly bacterial consortium.

Chemically induced oxidative stress improved bacterial laccase-mediated degradation and detoxification of the synthetic dyes

To alleviate the risk of textile effluent, the development of highly effective bioremediation strategies for synthetic dye removal is needed. Herein, we aimed to assess whether intensified bioactivity of Bacillus pumilus ZB1 by oxidative stress could improve the removal of textile dyes. Methyl methanesulfonate (MMS) induced oxidative stress significantly promoted laccase expression of B. pumilus ZB1. Both the level of hydrogen dioxide and superoxide anion showed a significant positive correlation with laccase activity (RSQ = 0.963 and 0.916, respectively) along with the change of MMS concentration. The regulation of laccase expression was closely related to oxidative stress. The overexpressed laccase in the supernatant improved the decolorization of synthetic dyes (16.43% for Congo Red, 54.05% for Crystal Violet, and 41.61% for Reactive Blue 4). Laccase was subsequently expressed in E. coli. Investigation of the potential of bacterial laccase in dye remediation using Congo Red showed that an effective degradation of azo dye could be achieved with laccase treatment. Laccase remediation alleviated the cytotoxicity of Congo Red to human hepatocytes. In silico study identified eight amino acid residues of laccase involved in binding with Congo Red. Overall, regulation of oxidative stress towards bacterium can be used as a promising approach for the improvement of bacterial bioactivity in synthetic dye remediation.

Biodegradation of Reactive Red 198 by textile effluent adapted microbial strains

A sustainable technology to eliminate the persistent reactive dyes from the textile effluents discharged indiscriminately in the environment is highly desirous given the explosive growth of textile industries. The present study investigated the potential of two different bacterial strains, Bacillus cereus SKB12 and Enterobacter hormaechei SKB16 isolated from the dye house effluent sludge in the biotransformation of Reactive Red 198 (RR 198). Process variables such as temperature, pH, shaking conditions and contact time were optimized for the successful decolourization of RR 198. Maximum decolourization of 80% and 85% of RR 198 was achieved at pH 6 and 7, and 40 °C in microaerophilic conditions on treatment with B. cereus and E. hormaechei, respectively. High-Performance Liquid Chromatography (HPLC), and Gas Chromatography-Mass Spectrometry (GC-MS) analyses conducted further affirmed that the decolourization of RR 198 was rather due to biodegradation than biosorption through shift in wavenumbers, retention time variations and the appearance of lesser molecular weight peaks. Degradative pathway for RR 198 predicted based on the enzyme assay data and dye degraded metabolite peaks acquired through GC-MS analysis highlighted the significance of azoreductase and laccase in the degradation of RR 198 into smaller non-toxic compounds. In addition, toxicity assessment through zootoxicological and phytotoxicological experiments using brine shrimp and Vigna radiata validated the detoxified status of the metabolites thus proving the promising potentials of the bacterial strains in the remediation of azo dyes.

Simultaneous sorption of heavy metals on Algerian Bentonite: mechanism study

Industrialization has induced tremendous environmental problems, particularly surface and underground water pollution by harmful heavy metals. In this work, we attempt to eliminate simultaneously iron and cadmium from aqueous solutions by adsorption on Algerian Bentonite. This abundant material was used without any modification. The sorption mechanism was investigated, and effects of pH, initial adsorbate and adsorbent concentrations were studied. The kinetics study revealed that equilibrium was reached after 120 min for both metals, and maximal adsorbed quantities of cadmium (76 mg/g) and iron (55 mg/g ) were obtained at pH = 10 and 8 respectively. Different kinetic models were tested, such as pseudo first-order, pseudo second-order, film and intraparticle diffusion models. The pseudo second-order model fits well the experimental data. Biot number values (2-39) show that the simultaneous sorption process is controlled by film diffusion due to electrostatic interactions between negatively charged surface and cations, then by the internal diffusion and formation of bonds between cations and adsorbent constituents. Also, compared to iron, the high and rapid sorption of cadmium reflects the selective nature of the sorption process. These results show that raw bentonite could be used without further treatment as an efficient sorbent for heavy metal mixtures.

Diversity of Synthetic Dyes from Textile Industries, Discharge Impacts and Treatment Methods

Natural dyes have been used from ancient times for multiple purposes, most importantly in the field of textile dying. The increasing demand and excessive costs of natural dye extraction engendered the discovery of synthetic dyes from petrochemical compounds. Nowadays, they are dominating the textile market, with nearly 8 × 105 tons produced per year due to their wide range of color pigments and consistent coloration. Textile industries consume huge amounts of water in the dyeing processes, making it hard to treat the enormous quantities of this hazardous wastewater. Thus, they have harmful impacts when discharged in non-treated or partially treated forms in the environment (air, soil, plants and water), causing several human diseases. In the present work we focused on synthetic dyes. We started by studying their classification which depended on the nature of the manufactured fiber (cellulose, protein and synthetic fiber dyes). Then, we mentioned the characteristics of synthetic dyes, however, we focused more on their negative impacts on the ecosystem (soil, plants, water and air) and on humans. Lastly, we discussed the applied physical, chemical and biological strategies solely or in combination for textile dye wastewater treatments. Additionally, we described the newly established nanotechnology which achieves complete discharge decontamination.

Preparation and Characterization of High-Efficiency Magnetic Heavy Metal Capture Flocculants

In this study, a high-efficiency magnetic heavy metal flocculant MF@AA was prepared based on carboxymethyl chitosan and magnetic Fe3O4. It was characterized by SEM, FTIR, XPS, XRD and VSM, and the Cu(II) removal rate was used as the evaluation basis for the preparation process. The effects of AMPS content, total monomer concentration, photoinitiator concentration and reaction time on the performance of MF@AA flocculation to remove Cu(II) were studied. The characterization results show that MF@AA has been successfully prepared and exhibits good magnetic induction characteristics. The synthesis results show that under the conditions of 10% AMPS content, 35% total monomer concentration, 0.04% photoinitiator concentration, and 1.5 h reaction time, the best yield of MF@AA is 77.69%. The best removal rate is 87.65%. In addition, the response surface optimization of the synthesis process of MF@AA was performed. The optimal synthesis ratio was finally determined as iron content 6.5%, CMFS: 29.5%, AM: 53.9%, AMPS: 10.1%. High-efficiency magnetic heavy metal flocculant MF@AA shows excellent flocculation performance in removing Cu(II). This research provides guidance and ideas for the development of efficient and low-cost flocculation technology to remove Cu(II) in wastewater.

Simultaneous removal of Cu(II) and reactive green 6 dye from wastewater using immobilized mixed fungal biomass and its recovery

Immobilized fungal biomass (Aspergillus niger and Aspergillus flavus) was prepared and analysed for the simultaneous removal of Cu(II) ion and Reactive Green 6 dye from aqueous phase. Different characterization analysis was utilized to exploit the adsorption characteristics of fungal biomass. Batch biosorption tests, performed to investigate the factors influencing biosorption process inferred optimal values of 25 mg/L of adsorbate with equilibrium time of 60 min, 2.5 g of immobilized fungal biomass, temperature of 303 K and pH of 5.0 for the maximal removal of pollutants. The obtained experimental data was utilized to evaluate the kinetic, thermodynamic and equilibrium models. Langmuir isotherm model has higher correlation coefficient [Cu(II) ion = 0.8625 and RG 6 dye = 0.8575] with small values of errors (RMSE = 3.746 and SSE = 56.12 for Cu(II) ion; RMSE = 4.872 and SSE = 11.87 for RG 6 dye). Kinetic studies performed to evaluate the adsorption rate mechanism of this present study indicated that pseudo-first order and pseudo-second order kinetics to be most fitting model for removal of Cu(II) ions and Reactive green dye respectively. Thermodynamic analysis inferred the spontaneous, random, and exothermic nature of the biosorption process based on ΔG^o, ΔH^o, and ΔS^o values respectively. The prepared biomass can be an alternative for the elimination of toxic pollutants from wastewater.

Recent Achievements in Dyes Removal Focused on Advanced Oxidation Processes Integrated with Biological Methods

In the last 3 years alone, over 10,000 publications have appeared on the topic of dye removal, including over 300 reviews. Thus, the topic is very relevant, although there are few articles on the practical applications on an industrial scale of the results obtained in research laboratories. Therefore, in this review, we focus on advanced oxidation methods integrated with biological methods, widely recognized as highly efficient treatments for recalcitrant wastewater, that have the best chance of industrial application. It is extremely important to know all the phenomena and mechanisms that occur during the process of removing dyestuffs and the products of their degradation from wastewater to prevent their penetration into drinking water sources. Therefore, particular attention is paid to understanding the mechanisms of both chemical and biological degradation of dyes, and the kinetics of these processes, which are important from a design point of view, as well as the performance and implementation of these operations on a larger scale.

Adsorption and Separation of Crystal Violet, Cerium(III) and Lead(II) by Means of a Multi-Step Strategy Based on K10-Montmorillonite

A multi-step procedure, based on the employment of K10-Montmorillonite, is proposed for the selective removal of metal ions and dyes from a multicomponent solution. The objective is twofold: decontaminate the effluents and separate and recover the valuable byproducts present in wastewaters. Three common contaminants, i.e., crystal violet dye (CV), Ce(III) and Pb(II) were chosen as “model” pollutants. The main factors affecting the pollutants’ sorption were investigated. The experimental data were correlated with adsorption isotherms and kinetic models to obtain a deeper insight into the adsorption processes. The affinity of the clay toward the pollutants is favored by an increasing pH and follows the order CV > Pb(II) > Ce(III). Whereas Ce(III) metal ions do not adsorb onto clay under strongly acidic conditions, both Pb(II) and CV can adsorb under all the investigated pH conditions. The analysis of isotherms and kinetic profiles revealed that CV adsorbs onto clay through a mechanism consisting of two parallel processes, namely cation exchange on the external mineral surface and in the interlayer and surface complexation at the edge sites, while metal ion uptake is due solely to cation exchange processes involving mineral surfaces. The time required for the complete removal of pollutants follows the order CV > Ce(III) >> Pb(II). The possibility to modulate the adsorption features by changing experimental conditions was successfully employed to propose the best strategy for the progressive removal of different components from aqueous solutions.