Decolorization of sulfonated azo dye Metanil Yellow by newly isolated bacterial strains: Bacillus sp. strain AK1 and Lysinibacillus sp. strain AK2

Exploring the decolorization efficiency and biodegradation mechanisms of different functional textile azo dyes by Streptomyces albidoflavus 3MGH

Efficiently mitigating and managing environmental pollution caused by the improper disposal of dyes and effluents from the textile industry is of great importance. This study evaluated the effectiveness of Streptomyces albidoflavus 3MGH in decolorizing and degrading three different azo dyes, namely Reactive Orange 122 (RO 122), Direct Blue 15 (DB 15), and Direct Black 38 (DB 38). Various analytical techniques, such as Fourier Transform Infrared (FTIR) spectroscopy, High-Performance Liquid Chromatography (HPLC), and Gas Chromatography-Mass Spectrometry (GC-MS) were used to analyze the degraded byproducts of the dyes. S. albidoflavus 3MGH demonstrated a strong capability to decolorize RO 122, DB 15, and DB 38, achieving up to 60.74%, 61.38%, and 53.43% decolorization within 5 days at a concentration of 0.3 g/L, respectively. The optimal conditions for the maximum decolorization of these azo dyes were found to be a temperature of 35 °C, a pH of 6, sucrose as a carbon source, and beef extract as a nitrogen source. Additionally, after optimization of the decolorization process, treatment with S. albidoflavus 3MGH resulted in significant reductions of 94.4%, 86.3%, and 68.2% in the total organic carbon of RO 122, DB 15, and DB 38, respectively. After the treatment process, we found the specific activity of the laccase enzyme, one of the mediating enzymes of the degradation mechanism, to be 5.96 U/mg. FT-IR spectroscopy analysis of the degraded metabolites showed specific changes and shifts in peaks compared to the control samples. GC-MS analysis revealed the presence of metabolites such as benzene, biphenyl, and naphthalene derivatives. Overall, this study demonstrated the potential of S. albidoflavus 3MGH for the effective decolorization and degradation of different azo dyes. The findings were validated through various analytical techniques, shedding light on the biodegradation mechanism employed by this strain.

Olive stone as an eco-friendly bio-adsorbent for elimination of methylene blue dye from industrial wastewater

Adsorbents synthesized by activation and nanoparticle surface modifications are expensive and might pose health and ecological risks. Therefore, the interest in raw waste biomass materials as adsorbents is growing. In batch studies, an inexpensive and effective adsorbent is developed from raw olive stone (OS) to remove methylene blue (MB) from an aqueous solution. The OS adsorbent is characterized using scanning electron microscopy (SEM), Fourier Transform Infra-Red (FTIR), and Brunauer-Emmett-Teller (BET) surface area. Four isotherms are used to fit equilibrium adsorption data, and four kinetic models are used to simulate kinetic adsorption behavior. The obtained BET surface area is 0.9 m2 g-1, and the SEM analysis reveals significant pores in the OS sample that might facilitate the uptake of heavy compounds. The Langmuir and Temkin isotherm models best represent the adsorbtion of MB on the OS, with a maximum monolayer adsorption capacity of 44.5 mg g-1. The best dye color removal efficiency by the OS is 93.65% from an aqueous solution of 20 ppm at the OS doses of 0.2 g for 90 min contact time. The OS adsorbent serves in five successive adsorption cycles after a simple filtration-washing-drying process, maintaining MB removal efficiency of 91, 85, 80, and 78% in cycles 2, 3, 4, and 5, respectively. The pseudo second-order model is the best model to represent the adsorption process dynamics. Indeed, the pseudo second-order and the Elovich models are the most appropriate kinetic models, according to the correlation coefficient (R2) values (1.0 and 0.935, respectively) derived from the four kinetic models. The parameters of the surface adsorption are also predicted based on the mass transfer models of intra-particle diffusion and Bangham and Burt. According to the thermodynamic analysis, dye adsorption by the OS is endothermic and spontaneous. As a result, the OS material offers an efficient adsorbent for MB removal from wastewater that is less expensive, more ecologically friendly, and economically viable.

Eco-toxicological effect of a commercial dye Rhodamine B on freshwater microalgae Chlorella vulgaris

In this study, the acute toxicity effects of a fluorescent xanthene dye, Rhodamine B (RhB), widely used in textile, paper, and leather industries was investigated on a freshwater microalgae Chlorella vulgaris. The acute toxicity of RhB on C. vulgaris was determined by examining the growth, cell morphology, pigment production, protein content, and the activities of oxidative stress enzymes. Based on the results of the toxicity study of 24-96 h, the median inhibitory concentration (IC₅₀) values ranged from 69.94 to 31.29 mg L^-1. The growth of C. vulgaris was conspicuously inhibited by RhB exposure, and the cell surfaces appeared to be seriously shrunk in SEM analysis. The growth of C. vulgaris was hindered after exposure to graded concentrations (10-50 mg L^-1) of RhB. A significant reduction in growth rate, pigment synthesis (chlorophyll a, chlorophyll b, and carotenoid), and protein content was recorded in a dose-dependent manner. After 96 h exposure of C. vulgaris to 50 mg L^-1 RhB, chlorophyll a, chlorophyll b, carotenoids, and protein contents were reduced by 71.59, 74.90, 65.84, and 74.20%, respectively. The activities of the antioxidant enzymes peroxidase (POD), and catalase (CAT) also increased markedly in the presence of RhB. A notable effect was observed on oxidative enzymes catalase and peroxidase, indicating that oxidative stress may be the primary factor in the inhibition of growth and pigment synthesis. Consequently, the experimental acute toxicity data were compared to the QSAR prediction made by the ECOSAR programme. Results showed that the experimental acute toxicity values were 67.74-fold lower than the ECOSAR predicted values. The study provides convincing evidence for the metabolic disruption in the ubiquitous microalgae C. vulgaris due to the RhB dye toxicity.

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

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

Monitoring and assessment of Dracaena-based constructed vertical flow wetlands treating textile dye wastewater

The monitoring and assessment of multiple constructed vertical flow wetlands (CVFWs) treating textile dye wastewater (metanil yellow as dye) are studied covering three seasons. Three CVFWs (CVFW-1, dye-5 mg/l; CVFW-2, dye-50 mg/l; and CVFW-3, dye-100 mg/l) and a control (dye-5 mg/l) were used. The CVFWs with Dracaena (an ornamental plant) efficiently removed contaminants like dye, COD, NH4+-N, and PO43--P from the wastewater under varying inlet dye concentrations, indicating its dependence on meteorological conditions. Substantial dye removal was observed to be maximum in summer (control, 44.3%; CVFW-1, 75.1%; CVFW-2, 76.1%; CVFW-3, 46%), but lesser in winter (control, 45%; CVFW-1, 73.1%; CVFW-2, 76.8%; CVFW-3, 42.6%) and minimum in monsoon (control, 40.8%; CVFW-1, 63.5%; CVFW-2, 51.6%; CVFW-3, 37.1%), respectively. Efficiency was less in CVFW-3 as it observed plant stress due to higher inlet dye concentration. COD removal was higher in winter, followed by summer and monsoon. A first-order kinetic model was used to investigate the efficiency of the CVFW system w.r.t. contaminant removal. Various functional groups were characterized using Fourier transform infrared spectroscopy (FTIR) from the inlet and outlet water samples of different CVFWs. The Dracaena accumulated various elements and oxides during the treatment with no stress on its health. No effects on plant health highlight the suitability of Dracaena for textile wastewater treatment. The results were validated using statistical tools like the Mann-Whitney U test and principal component analysis (PCA).

Biodegradation of Azo Dye Methyl Red by Pseudomonas aeruginosa: Optimization of Process Conditions

Water pollution due to textile dyes is a serious threat to every life form. Bacteria can degrade and detoxify toxic dyes present in textile effluents and wastewater. The present study aimed to evaluate the degradation potential of eleven bacterial strains for azo dye methyl red. The optimum degradation efficiency was obtained using P. aeruginosa. It was found from initial screening results that P. aeruginosa is the most potent strain with 81.49% degradation activity and hence it was subsequently used in other degradation experiments. To optimize the degradation conditions, a number of experiments were conducted where only one variable was varied at a time and where maximum degradation was observed at 20 ppm dye concentration, 1666.67 mg/L glucose concentration, 666.66 mg/L sodium chloride concentration, pH 9, temperature 40 °C, 1000 mg/L urea concentration, 3 days incubation period, and 66.66 mg/L hydroquinone (redox mediator). The interactive effect of pH, incubation time, temperature, and dye concentration in a second-order quadratic optimization of process conditions was found to further enhance the biodegradation efficiency of P. aeruginosa by 88.37%. The metabolites of the aliquot mixture of the optimized conditions were analyzed using Fourier transform infrared (FTIR), GC-MS, proton, and carbon 13 Nuclear Magnetic Resonance (NMR) spectroscopic techniques. FTIR results confirmed the reduction of the azo bond of methyl red. The Gas Chromatography-Mass Spectrometry (GC-MS) results revealed that the degraded dye contains benzoic acid and o-xylene as the predominant constituents. Even benzoic acid was isolated from the silica gel column and identified by ¹H and ¹³C NMR spectroscopy. These results indicated that P. aeruginosa can be utilized as an efficient strain for the detoxification and remediation of industrial wastewater containing methyl red and other azo dyes.

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.

Synthetic azo dye bio-decolorization by Priestia sp. RA1: process optimization and phytotoxicity assessment

Azo compounds represent the most diverse group of colorants widely employed in industrial sectors. Being highly toxic and recalcitrant compound, azo dyes pose a threat to plants, animals, and humans. In the present report, bio-decolorization of azo dye, reactive black 5, was evaluated by newly isolated Priestia sp. RA1. Strain RA1 was able to decolorize 97% of 100 ppm reactive black 5 in 60 h. Specific activity of dye decolorization was found to be 0.233 μmol min^-1 g^-1 dry cells. Successful decolorization over a broad range of pH, salinity, temperature, and initial dye concentration was observed. Phytotoxicity assay on agriculturally important crops showed considerable difference in percentage seed germination and growth when treated with original and bio-decolorized dye samples. Bio-decolorization at high dye concentrations, promising decolorization rate, and non-toxic nature of treated products suggest the potential of strain RA1 for bioremediation of dye-contaminated water and its re-use in the industries.

Microbial Degradation of Azo Dyes: Approaches and Prospects for a Hazard-Free Conversion by Microorganisms

Azo dyes have become a staple in various industries, as colors play an important role in consumer choices. However, these dyes pose various health and environmental risks. Although different wastewater treatments are available, the search for more eco-friendly options persists. Bioremediation utilizing microorganisms has been of great interest to researchers and industries, as the transition toward greener solutions has become more in demand through the years. This review tackles the health and environmental repercussions of azo dyes and its metabolites, available biological approaches to eliminate such dyes from the environment with a focus on the use of different microorganisms, enzymes that are involved in the degradation of azo dyes, and recent trends that could be applied for the treatment of azo dyes.

In vitro and in silico analysis of Brilliant Black degradation by Actinobacteria and a Paraburkholderia sp

The soil bacteria isolated in this study, including three strains of actinobacteria and one Paraburkholderia sp., showed decolorization activity of azo dyes in the resting cell assay and were shown to use methyl red as the sole carbon source to proliferate. Therefore, their ability to degrade, bioabsorb, or a combination of both was investigated using the substrate brilliant black. The strains DP-A9 and DP-L11, within 24 h of incubation, showed complete biodegradation of 173.54 mg/L brilliant black and the strains DP-D10 and DP-P12 showed partial decolorization of 83.3 mg/L and 36.4 mg/L, respectively, by both biosorption and biodegradation. In addition, the shotgun assembled genome of strains studied included a highly diverse set of genes encoding for candidate dye degrading enzymes, providing avenues to study azo dye metabolism in more detail.

Decolorization of textile azo dye Novacron Red using bacterial monoculture and consortium: Response surface methodology optimization

The present study was intended toward the optimization of a textile dye Novacron Red decolorization by single and mixed culture of Bacillus strains namely, B. firmus, B. filamentosus and B. subterraneus. Optimization of dye decolorization using Bacillus monocultures was conducted using central composite design. The maximum dye decolorization achieved under optimized conditions for B. firmus, B. filamentosus and B. subterraneus was 89.24%, 88.28% and 88.45%, respectively. The effect of various consortia of selected Bacillus strains on dye removal was evaluated by applying a mixture design. The best dye (100 mg/L) decolorization yield (84%) was achieved using the consortium of B. filamentosus and B. subetrraneus.The Fourier Transform Infrared Spectroscopy analyses confirmed biodegradation potential of the two Bacillus strains. The results highlighted the potential of mono- and co-cultures of Bacillus strains for application in textile wastewater treatment. PRACTITIONER POINTS: Novel dye-decolorizing Bacillus strains were isolated from marine sediment. Optimization of decolorization was conducted using response surface methodology. Efficient decolorization of textile dye by Bacillus strains on mono- and co-cultures. The efficiency of the consortium B. filamentosus and B. subetrraneus on dye removal.

Cellulose Acetate Hollow Fiber Membranes from Banana Stem Fibers Coated by TiO2 for Degradation of Waste Textile Dye

Cellulose acetate hollow fiber membrane from banana stem fibers coated by TiO2 (CAHFMT) was prepared and characterized as an alternative material for degradation of waste textile dye. Its applicability was demonstrated by mechanical properties, FTIR, SEM, thermal resistance, performance, and degradation efficiency. Cellulose acetate (CA) was synthesized from banana stem fibers by swelling stage, acetylation reaction, and hydrolysis reaction. CA was modified using TiO2 of various concentrations. CAHFMT with 22 % w/v dope concentration has the optimum mechanical properties (stress, strain and Young’s modulus), as well as hydrophilic properties. The performances of CAHFMT with Congo red were determined. The SEM results showed that the membrane had rigid pores. Moreover, this research stated that CAHFMT could be a solution to overcome economical and effective problems.

Dye-decolorization of a newly isolated strain Bacillus amyloliquefaciens W36

Dye-decolorization is one of the most important steps in dye-polluted wastewater treatment. The dye-decolorization bacteria were isolated from active sludge collected from wastewater treating pond of a dyeing and printing plant using serial dilution method. Among the 44 bacteria isolates from the active sludge, the strain Bacillus amyloliquefaciens W36 was found to have strong ability in dye-decolorization. The effects of carbon source, nitrogen sources, C/N, metal ions, temperature, pH, and rotation speed for dye-decolorization were investigated. The optimum decolorization conditions were that the strain was grown in enriched mineral salt medium (EMSM) using maltose 1 g/L, (NH₄)₂SO₄ 1 g/L as carbon and nitrogen source respectively, supplemented with 100 mg/L different dyes (pH 6.0), at 30 °C, 200 rpm from 48 to 96 h. The bacteria could aerobically decolorize dyes, such as Coomassie brilliant blue (95.42%), Bromcresol purple (93.34%), Congo red (72.37%) and Sarranine (61.7%), within 96 h. The dyes decolorization products were analyzed by ultra-violet and visible (UV-vis) spectroscopy before and after decolorization, which indicated that the four dyes were significantly degraded by the strain. The results indicated that the bacteria Bacillus amyloliquefaciens W36 could be used in dye-polluted wastewater treatment.

A critical review on advances in the practices and perspectives for the treatment of dye industry wastewater

Rapid industrialization has provided comforts to mankind but has also impacted the environment harmfully. There has been severe increase in the pollution due to several industries, in particular due to dye industry, which generate huge quantities of wastewater containing hazardous chemicals. Although tremendous developments have taken place for the treatment and management of such wastewater through chemical or biological processes, there is an emerging shift in the approach, with focus shifting on resource recovery from such wastewater and also their management in sustainable manner. This review article aims to present and discuss the most advanced and state-of-art technical and scientific developments about the treatment of dye industry wastewater, which include advanced oxidation process, membrane filtration technique, microbial technologies, bio-electrochemical degradation, photocatalytic degradation, etc. Among these technologies, microbial degradation seems highly promising for resource recovery and sustainability and has been discussed in detail as a promising approach. This paper also covers the challenges and future perspectives in this field.

Biostimulation of Microbial Communities from Malaysian Agricultural Soil for Detoxification of Metanil Yellow Dye; a Response Surface Methodological Approach

In the present study, a mixed culture from a local agricultural soil sample was isolated for Metanil Yellow (MY) dye decolorization. The metagenomic analysis confirmed that 42.6% has been dominated by genus Bacillus, while Acinetobacter (14.0%) is present in the microbial communities of the mixed culture. For fungi diversity analysis, around 97.0% was “unclassified” fungi and 3% was Candida. The preliminary investigation in minimal salt media (MSM) showed that 100% decolorization was achieved after 24 h of incubation. Response surface methodology (RSM) was successfully applied using Box-Behnken design (BBD) to study the effect of four independent parameters—MY dye concentration, glucose concentration, ammonium sulfate concentration, and pH—on MY dye decolorization by the mixed bacterial culture. The optimal conditions predicted by the desirability function were 73 mg/L of MY, 1.934% glucose, 0.433 g/L of ammonium sulfate, and a pH of 7.097, with 97.551% decolorization The correlation coefficients (R2 and R2 adj) of 0.913 and 0.825 indicate that the established model is suitable to predict the effectiveness of dye decolorization under the investigated condition. The MY decolorization of the mixed bacterial culture was not affected by the addition of heavy metals in the growth media. Among the 10 heavy metals tested, only copper gave 56.19% MY decolorization, whereas the others gave almost 100% decolorization. The decolorization potential of the mixed bacterial culture indicates that it could be effective for future bioremediation of soil-contaminated sites and treatment solutions of water bodies polluted with the MY dye.

Immobilization of Metanil Yellow Decolorizing Mixed Culture FN3 Using Gelling Gum as Matrix for Bioremediation Application

In this study, the Metanil Yellow (MY) decolorizing mixed culture, namely FN3, has been isolated from agriculture soil. The mixed culture was immobilized using gellan gum. In order to optimize the immobilization process for maximal dye decolorization, Response Surface Methodology (RSM) was performed. The optimal conditions for immobilization predicted by desirability function are 130 mg/L of MY dye concentration, 1.478% of gellan gum concentration, 50 beads and 0.6 cm of beads size with the percentage of decolorization of 90.378%. The correlation coefficients of the model (R2 and R2 adj) are 0.9767 and 0.9533, respectively. This indicates that the established model is suitable to predict the effectiveness of dye decolorization under the investigated condition. The immobilized beads of mixed culture FN3 were able to be reused up to 15 batches of decolorization. The immobilized cells also have high tolerance towards heavy metals. This was proven by higher dye decolorization rate by the immobilized cells even with the addition of heavy metals in the media. The decolorization potential of the mixed culture indicates that it could be useful for future bioremediation of soil contaminated sites and treatment solutions of water bodies polluted with MY dye.

Synthesis and characterization of hexagonal boron nitride used for comparison of removal of anionic and cationic hazardous azo-dye: kinetics and equilibrium studies

The purpose of this study was to compare the adsorption behavior of cationic and anionic dyes onto a hexagonal boron nitride (hBN) nanostructure that was rich in a negative charge. Herein, the hBN nanostructure was synthesized using boric acid as a precursor material. The characteristic peaks of the hBN nanostructure were performed using Fourier transform infrared (FT-IR) and Raman spectroscopies. The morphology and the particle size of hBN nanostructure were determined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). During the studies, various essential adsorption parameters were investigated, such as the initial dye concentration, pH of the dye solution, adsorbent dose, and contact time. Under optimal conditions, the removal of 42.6% Metanil yellow (MY) and 90% Victoria blue B (VBB) from aqueous solution was performed using a 10-mg hBN nanostructure. Furthermore, the equilibrium studies showed that the Freundlich isotherm model fitted well for the removal of MY. However, the Langmuir isotherm model fitted well for the removal of VBB. Moreover, according to the results obtained from the kinetic studies, while the first-order kinetic model was suited for the adsorption of the MY, the second-order kinetic model was found to well fit for the adsorption of VBB.

Bacilli-Mediated Degradation of Xenobiotic Compounds and Heavy Metals

Xenobiotic compounds are man-made compounds and widely used in dyes, drugs, pesticides, herbicides, insecticides, explosives, and other industrial chemicals. These compounds have been released into our soil and water due to anthropogenic activities and improper waste disposal practices and cause serious damage to aquatic and terrestrial ecosystems due to their toxic nature. The United States Environmental Protection Agency (USEPA) has listed several toxic substances as priority pollutants. Bacterial remediation is identified as an emerging technique to remove these substances from the environment. Many bacterial genera are actively involved in the degradation of toxic substances. Among the bacterial genera, the members of the genus Bacillus have a great potential to degrade or transform various toxic substances. Many Bacilli have been isolated and characterized by their ability to degrade or transform a wide range of compounds including both naturally occurring substances and xenobiotic compounds. This review describes the biodegradation potentials of Bacilli toward various toxic substances, including 4-chloro-2-nitrophenol, insecticides, pesticides, herbicides, explosives, drugs, polycyclic aromatic compounds, heavy metals, azo dyes, and aromatic acids. Besides, the advanced technologies used for bioremediation of environmental pollutants using Bacilli are also briefly described. This review will increase our understanding of Bacilli-mediated degradation of xenobiotic compounds and heavy metals.

Heterologous expression of azoreductase-encoding gene azrS of Bacillus sp. MR-1/2 for enhanced azo dye decolorization and wastewater treatment

In Pakistan, 55% of textile exports are contributed by textile-units of Faisalabad. The effluents of these textile units, being discharged without any treatment, contain the contamination of a huge amount of synthetic azo dyes. The objective of the current research was to evaluate the contribution of an azoreductase-encoding gene (azrS) from a pre-characterized azo dye decolorizing bacterial strain Bacillus sp. MR-1/2 in a high copy number host system (pUC19-T7-Top-T) of Escherichia coli strain DH5α followed by in-silico prediction of azoreductase enzyme (AzrS) function. The recombinant cells that contained azrS had a significantly higher rate of color removal in congo red and reactive black-5 dyes when compared to wild-type MR-1/2 and E. coli DH5α after 72 h of incubation. Moreover, we were able to show that the recombinant strain significantly reduced the values of all tested parameters (pH, EC, turbidity, TSS, and COD) in actual wastewater. In support of our results, it was also predicted through bioinformatics analysis that the deduced azoreductase protein of strain MR-1/2 is linked with the dye decolorization ability of the strain through NAD(P)H-ubiquinone: oxidoreductase activity. Furthermore, we also found that the deduced protein resembled closely related proteins of protein databank in many features, yet some unique features were predicted in the enzyme activity of strain MR-1/2. It was concluded that the recombinant strain could be examined in pilot-scale experiments for textile wastewater treatment.

Utilization of nano-olive stones in environmental remediation of methylene blue from water

BACKGROUND

The use of agricultural waste as a low-cost adsorbent for the removal of hazardous methylene blue (MB) from aqueous solution was investigated. In this research, the potentiality of using black nano olive stones (black NOS) and green nano olive stones (green NOS) for MB adsorption was conducted.

METHODS

Various remediation parameters such as initial MB concentration, pH, and temperature were investigated. Thermodynamic study was carried out to determine the homogeneity of the adsorbent and spontaneity of the adsorption process. Different physical and chemical characterizations were studied using scanning electron microscopy (SEM), Fourier transform infrared (FTIR), Brunauer-Emmett-Teller (BET) surface area, pore radius and pore volume.

RESULTS

It was found that NOS exhibits an acidic nature, however the highest MB removal efficiency was recorded at pH 10; reaching up to 71%. The negative value of the heat of the adsorption process (∆H ° ) indicated the reaction followed an exothermic pathway while the negative value of Gibbs adsorption (∆G ° ) further suggested its spontaneous nature. The results indicated that the Freundlich model described well the adsorption process with 99.5% correlation coefficient for green NOS. FTIR was used to analyze functional groups on the adsorbents' surfaces that could play vital roles in the remediation process. SEM analysis revealed that the adsorbents comprised of abundant spherical deep cavities and porous nature.

CONCLUSION

The result obtained successfully demonstrated the potential of using black and green NOS as suitable adsorbents for the removal of MB from water.

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

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

A study on the utility of immobilized cells of indigenous bacteria for biodegradation of reactive azo dyes

Azo dyes are recalcitrant compounds used as a colorant in various industries. The pollution caused by their extensive usage has adversely affected the environment for years. The existing physicochemical methods for dye pollution remediation are rather inefficient and hence there is a dearth of low-cost, potential systems capable of dye degradation. The current research studies the biodegradation potential of immobilized bacterial cells against azo dyes Reactive Orange 16 (RO-16) and Reactive Blue 250 (RB-250). Two indigenous dye degrading bacteria Bacillus sp. VITAKB20 and Lysinibacillus sp. KPB6 was isolated from textile sludge sample. Free cells of Bacillus. sp. VITAKB20 degraded 92.38% of RO-16 and that of Lysinibacillus sp. KPB6 degraded 95.36% of RB-250 within 72 h under static conditions. Upon immobilization with calcium alginate, dye degradation occurred rapidly. Bacillus. sp. VITAKB20 degraded 97.5% of RO-16 and Lysinibacillus sp. KPB6 degraded 98.2% of RB-250 within 48 h under shaking conditions. Further, the nature of dye decolorization was biodegradation as evident by high-performance liquid chromatography (HPLC), and Fourier-transform infrared spectroscopy (FTIR) results. Phytotoxicity and biotoxicity assays revealed that the degraded dye products were less toxic in nature than the pure dyes. Thus, immobilization proved to be a highly likely alternative treatment for dye removal.

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

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

Application of docking and active site analysis for enzyme linked biodegradation of textile dyes

Growth of textile industries led to production of enormous dye varieties. These textile dyes are largely used, chemically stable and easy to synthesize. But they are recalcitrant and persist as less biodegradable pollutants when discharged into waterbodies. Potential use of enzyme-linked bioremediation of textile dyes will control their toxicity in waterbodies. Bioinformatics and Molecular docking tool provides an insight into remediation mechanism by predicting susceptibility of dye degradation using oxidoreductive enzymes. In this study, six dyes, Reactive Red F3B, Remazol Red RGB, Joyfix Red RB, Joyfix Yellow MR, Remazol Blue RGB and Turquoise CL-5B of azo, anthraquinone and phthalocyanine molecular class were identified as potential targets for degradation by laccase and azoreductase of Aeromonas hydrophila in addition to Lysinibacillus sphaericus through in silico docking tool BioSolveIT-FlexX. Azoreductase breaks azo bonds by ping-pong mechanism whereas laccase decolorizes dyes by free radical mechanism which is not specific in nature. Results were analyzed based on parameters like stability, catalytic action and selectivity for enzyme-dye interactions. Amino acids of enzymes interacted with several dyes substantiating variations in active site for enzyme-ligand binding affinity. This suggests the role of enzymes in decolorizing an extensive variety of textile dyes, thereby, aiding in understanding the enzyme mechanisms in Bioremediation.

Ice-templated graphene oxide/chitosan aerogel as an effective adsorbent for sequestration of metanil yellow dye

Graphene oxide/chitosan aerogel (GOCA) was prepared by a facile ice-templating technique without using any cross-linking reagent for metanil yellow dye sequestration. The adsorption performance of GOCA was investigated by varying the adsorbent mass, shaking speed, initial pH, contact time, concentration and temperature. The combined effects of adsorption parameters and the optimum conditions for dye removal were determined by response surface methodology. GOCA exhibited large removal efficiencies (91.5-96.4%) over a wide pH range (3-8) and a high adsorption capacity of 430.99 mg/g at 8 mg adsorbent mass, 400 mg/L concentration, 35.19 min contact time and 175 rpm shaking speed. The adsorption equilibrium was best represented by the Langmuir model. GOCA could be easily separated after adsorption and regenerated for re-use in 5 adsorption-desorption cycles thereby maintaining 80% of its adsorption capability. The relatively high adsorption and regeneration capabilities of GOCA render it an attractive adsorbent for treatment of azo dye-polluted water.

Biodegradation of metal complex Naphthol Green B and formation of iron-sulfur nanoparticles by marine bacterium Pseudoalteromonas sp CF10-13

Treatment of metal complex dye wastewater has attracted growing attention due to the degradation-resistant, high cost and potential hazards of current techniques. This study reported a marine bacterium (Pseudoalteromonas sp CF10-13) with potential performance in decolorization and degradation of a metal complex dye-Naphthol Green B (NGB) at wide ranges of salinity, dye concentration and alkalinity under anaerobic conditions. It was inferred that the secretion of electron mediators in soluble extracellular metabolites by P. sp CF10-13 played important roles in NGB decolorization and degradation through extracellular electron transfer. Naphthalenesulfonate, the major structure in NGB molecule, was further degraded into low-toxic benzamide. Black stable iron-sulfur nanoparticles were formed endogenously avoiding H₂S releasing, exogenous sulfur addition and metal sludge in accumulation. Accordingly, this study provided a cost-effective and eco-friendly biodegradation method to refractory NGB, further promoting the understanding of dye resources recovery.

Biodecolorization of textile azo dye using Bacillus sp. strain CH12 isolated from alkaline lake

Textile azo dye decolorizing bacteria were isolated from alkaline Lakes Abaya and Chamo using Reactive Red 239 (RR239) dye. Through subsequent screening process, strain CH12 was selected to investigate the effects of nutrient supplement, DO, pH, temperature, dye concentration and types on decolorization. Based on 16S rRNA gene sequence analysis, strain CH12 was identified as Bacillus sp. Decolorization efficiencies were significantly enhanced with carbon (≥98%) and organic nitrogen (∼100%) supplements. Complete decolorization was also observed under anoxic and anaerobic conditions, and at the temperature of 30 °C and the pH of 10. However, the azo dye decolorization efficiency of strain CH12 was significantly reduced when NaNO₃ (1-8%) was supplemented or under aerobic culturing condition (≤6%), indicating that RR239 was less preferred electron acceptor. Overall, strain CH12 can be a promising candidate for decolorization applications due to its potential to effectively decolorize higher RR239 concentrations (50-250 mg/L) and six additional dyes.

Isolation and Characterisation of a Molybdenum-reducing and Metanil Yellow Dye-decolourising Bacillus sp. strain Neni-10 in Soils from West Sumatera, Indonesia

A molybdenum reducing bacterium with the novel ability to decolorise the azo dye Metanil Yellow is reported. Optimal conditions for molybdenum reduction were pH 6.3 and at 34°C. Glucose was the best electron donor. Another requirement includes a narrow phosphate concentration between 2.5 and 7.5 mM. A time profile of Mo-blue production shows a lag period of approximately 12 hours, a maximum amount of Mo-blue produced at a molybdate concentration of 20 mM, and a peak production at 52 h of incubation. The heavy metals mercury, silver, copper and chromium inhibited reduction by 91.9, 82.7, 45.5 and 17.4%, respectively. A complete decolourisation of the dye Metanil Yellow at 100 and 150 mg/L occurred at day three and day six of incubations, respectively. Higher concentrations show partial degradation, with an approximately 20% decolourisation observed at 400 mg/L. The bacterium is partially identified based on biochemical analysis as Bacillus sp. strain Neni-10. The absorption spectrum of the Mo-blue suggested the compound is a reduced phosphomolybdate. The isolation of this bacterium, which shows heavy metal reduction and dye-decolorising ability, is sought after, particularly for bioremediation.

A critical review on textile wastewater treatments: Possible approaches

Waste water is a major environmental impediment for the growth of the textile industry besides the other minor issues like solid waste and resource waste management. Textile industry uses many kinds of synthetic dyes and discharge large amounts of highly colored wastewater as the uptake of these dyes by fabrics is very poor. This highly colored textile wastewater severely affects photosynthetic function in plant. It also has an impact on aquatic life due to low light penetration and oxygen consumption. It may also be lethal to certain forms of marine life due to the occurrence of component metals and chlorine present in the synthetic dyes. So, this textile wastewater must be treated before their discharge. In this article, different treatment methods to treat the textile wastewater have been presented along with cost per unit volume of treated water. Treatment methods discussed in this paper involve oxidation methods (cavitation, photocatalytic oxidation, ozone, H2O2, fentons process), physical methods (adsorption and filtration), biological methods (fungi, algae, bacteria, microbial fuel cell). This review article will also recommend the possible remedial measures to treat different types of effluent generated from each textile operation.

A novel recombinant AzrC protein proposed by molecular docking and in silico analyses to improve azo dye's binding affinity

Azo dyes are broadly used in different industries through their chemical stability and ease of synthesis. These dyes are usually identified as critical environmental pollutants and many attentions were performed to degradation of azo dyes using biological systems. In this study, the interactions of an azoreductase from mesophilic gram-positive Bacillus sp. B29, AzrC, with four common azo dyes (orange I, orange II, orange G and acid red 88) were investigated. Fifteen points, double, triple and quadruple mutant forms of AzrC were made using Molegro Virtual Docker 6.0 in order to improve the binding affinity of azo dyes to AzrC. The impact of 15 different mutations on azo dye affinity potency of AzrC was computationally analyzed using AzrC-azo dye molecular docking, and each interaction was scored based on AutoDock 4.2 free binding energy. Our results have indicated that Asn 104 (A), Asn 187 (B), and Tyr 151 (A) make stable hydrogen bond between AzrC and azo dyes. The hydrophobic amino acids like Phe105 (A), Phe 125 (B), and Phe 172 (B) in wild type form make hydrophobic interactions. In addition, the presence of more hydrophobic residues F60 (B), I119 (B), I121 (B) and F132 (B) in mutant forms made more powerful hydrophobic pocket in the active site. In conclusion, recombinant AzrC with quadruple mutations was suggested in order to increase the biodegradation capacity of AzrC through improving its affinity to four studied azo dyes. This study would be promising for future experimental analyses in order to produce recombinant form of AzrC.

Detoxification and color removal of Congo red by a novel Dietzia sp. (DTS26) - a microcosm approach

The present study deals with the decolorization and detoxification of Congo red (CR) by a novel marine bacterium Dietzia sp. (DTS26) isolated from Divar Island, Goa, India. The maximum decolorization of 94.5% (100 mg L(-1)) was observed under static condition within 30 h at pH 8 and temperature 32±2°C. Bacterially treated samples could enhance the light intensity by 38% and the primary production levels 5 times higher than the untreated. The strain was also able to reduce COD by 86.4% within 30 h at 100 mg L(-1) of CR dye. The degraded metabolites of CR dye were analyzed by FTIR, HPLC, GC-MS and the end product closely matches with 4-amino-3-naphthol-1-sulfonate which is comparatively less toxic than CR. Bioassay experiments conducted in treated samples for Artemia franciscana showed better survival rates (after 72 h) at higher concentration of CR (500 mg L(-1)). This work suggests the potential application of DTS26 in bioremediation of dye wastes and its safe disposal into coastal environment.

Removal of a reactive dye and hexavalent chromium by a reusable bacteria attached electrospun nanofibrous web

Bacteria have been immobilized onto a polysulfone nanofibrous web and used for the removal of reactive dye and heavy metal.

Highly effective bacterial agents against Cimbex quadrimaculatus (Hymenoptera: Cimbicidae): isolation of bacteria and their insecticidal activities

Cimbex quadrimaculatus (Hymenoptera: Cimbicidae) is one of the serious pests of almonds in Turkey and worldwide. Since there is no effective control application against this pest, it has been a serious problem up to now. Therefore, we aimed to find an effective bacterium that can be utilized as a biocontrol agent against C. quadrimaculatus in pest management. We isolated seven bacteria from dead and live C. quadrimaculatus larvae, and evaluated the larvicidal potency of all isolates on the respective pest. Based on the morphological, physiological, biochemical and molecular properties (partial sequence of 16S rRNA gene), the isolates were identified to be Bacillus safensis (CQ1), Bacillus subtilis (CQ2), Bacillus tequilensis (CQ3), Enterobacter sp. (CQ4), Kurthia gibsonii (CQ5), Staphylococcus sp. (CQ6) and Staphylococcus sciuri (CQ7). The results of the larvicidal activities of these isolates indicated that the mortality value obtained from all treatments changed from 58 to 100 %, and reached 100 % with B. safensis (CQ1) and B. subtilis (CQ2) on the 3rd instar larvae within 10 days of application of 1.89 × 10(9) cfu/mL bacterial concentration at 25 °C under laboratory conditions. Findings from this study indicate that these isolates appear to be a promising biocontrol agent for C. quadrimaculatus.

Effect of NaCl and Na2SO4 on the biodecolourization of K-2BP by Halomonas sp. GYW

In this paper, the effect of NaCl and Na₂SO₄ on the biodecolourization of reactive brilliant red K-2BP by a Halomonas sp. GYW (EF188281) was investigated in details. The decolourisation efficiency and the oxidation-reduction potential (ORP) change were explored during the decolourization process. The results from sequencing batch tests showed that Na₂SO₄ influenced the decolourization efficiency more slightly than NaCl in different synthetic dye solutions with different mixtures of Na₂SO₄ and NaCl. In the dye solutions with the same salt concentration or the same Na⁺ concentration, high Na₂SO₄ concentration did not inhibit the decolourization process and even stimulated the decolourization efficiency of reactive brilliant red K-2BP. Compared to NaCl system, the addition of Na₂SO₄ increased the ORP values about 35 mV, which agreed with the theoretic analysis of Gibbs function. This study improved our knowledge of azo dye decolourization under high salinity conditions and provided efficient option for the treatment of azo dye wastewater.

Decolorization and detoxification of sulfonated toxic diazo dye C.I. Direct Red 81 by Enterococcus faecalis YZ 66

Isolated Enterococcus faecalis YZ 66 strain shows ability to decolorize various industrial dyes among which, it showed complete decolorization and degradation of toxic, sulfonated recalcitrant diazo dye Direct Red 81 (50 mg/L) within 1.5 h of incubation under static anoxic condition. The optimum pH and temperature for decolorization was 7.0 and 40°C, respectively. Significant induction in the activity of intracellular oxidoreductive enzymes suggested its involvement in the decolorization of Direct Red 81. The biodegradation of Direct Red 81 was monitored by UV-Visible, FT-IR spectroscopy and HPLC. The final products were characterized by GC-MS and possible pathway of the degradation of the dye was proposed. The phytotoxicity assay (with respect to plants Sorghum vulgare and Phaseolus mungo) revealed that the degradation of Direct Red 81 produced nontoxic metabolites. Finally E. faecalis was employed to decolorize actual industrial effluent showing decolorization (in terms of ADMI value) with moderate COD and BOD reduction. Moreover the result increases the applicability of the strain for the treatment of industrial wastewaters containing dye pollutants.

Biodecolorization of a food azo dye by the deep sea Dermacoccus abyssi MT1.1(T) strain from the Mariana Trench

This study reports the characterization of the ability of Dermacoccus spp. isolated from the deepest point of the world's oceans for azo dye decolorization. A detailed investigation of Dermacoccus abyssi MT1.1(T) with respect to the azoreductase activity and enzymatic mechanism as well as the potential role of the bacterial strain for biocleaning of industrial dye baths is reported. Resting cells with oxygen-insensitive azoreductase resulted in the rapid decolorization of the polysulfonated dye Brilliant Black BN (BBN) which is a common food colorant. The highest specific decolorization rate (vs) was found at 50 °C with a moderately thermal tolerance for over 1 h. Kinetic analysis showed the high rates and strong affinity of the enzymatic system for the dye with a Vmax = 137 mg/g cell/h and a Km = 19 mg/L. The degradation of BBN produces an initial orange intermediate, 8-amino-5-((4-sulfonatophenyl)diazenyl)naphthalene-2-sulfonic acid, identified by mass spectrometry which is later converted to 4-aminobenzene sulfonic acid. Nearly 80% of the maximum vs is possible achieved in resting cell treatment with the salinity increased up to 5.0% NaCl in reaction media. Therefore, this bacterial system has potential for dye decolorization bioprocesses occurring at high temperature and salt concentrations e.g. for cleaning dye-containing saline wastewaters.