Biodecolorization of Reactive Black-5 by a metal and salt tolerant bacterial strain Pseudomonas sp. RA20 isolated from Paharang drain effluents in Pakistan

Comparing biofilm reactors inoculated with Shewanella for decolorization of Reactive Black 5 using different carrier materials

This study assessed the performance of biofilm reactors inoculated with azo dye degrading Shewanella for the decolorization of Reactive Black 5 (RB5), using three different carrier materials, namely almond shell biochar, moving bed biofilm reactor (MBBR), and polypropylene carrier (PPC). The reactors were fed with low-nutrient artificial wastewater containing RB5, and all three carriers showed good RB5 decolorization performance, with varying efficiencies. Liquid Chromatography-Mass Spectrometry analysis revealed distinct RB5 degradation pathways associated with each carrier, influenced by carrier materials and microbial communities. The MBBR carrier exhibited good stability due to its rough surface and microbial aggregates. Sequencing results highlighted differences in the microbial community structures among the carriers. Shewanella predominated the functional bacteria in the MBBR and PPC carriers, while the biochar carrier fostered highly efficient degrading microbial communities. The physicochemical properties of carrier materials significantly influenced the microbial community and RB5 degradation efficiency. These findings provide valuable insights for optimizing biofilm reactors for dye-containing wastewater treatment.

Encapsulation of Pseudomonas aeruginosa strain KBN12 decolourizes and bioremediates brilliant blue dye mediated toxicity in mung bean (Vigna radiata L.)

AIM

The aim of this study was to explore the decolourization and bioremediation ability of non-encapsulated and encapsulated Pseudomonas aeruginosa (strain KBN 12) against the azo dye brilliant blue (BB).

METHODS AND RESULTS

Six efficient BB dye-decolourizing bacteria were isolated from textile dye effluent. The most efficient free cells of P. aeruginosa KBN 12 along with the optimized conditions such as carbon source (maltose: 5 g L-1), and nitrogen source (ammonium chloride: 4 g L-1) at pH 6 at 37°C decolourized 72.69% of BB dye aerobically after 9 days of incubation under static conditions. Encapsulated (calcium alginate) P. aeruginosa KBN 12 decolourized 87.67% of BB dye aerobically after 9 days of incubation under the same optimized conditions. Fourier-transform infrared spectroscopy (FTIR) and gas chromatography (GC) analysis of the chemical structure of BB dye after decolourization found changes in functional and chemical groups. Phytotoxicity and soil respiration enzyme assays revealed that the decolourized dye or dye products were less toxic than the pure BB dye.

CONCLUSION

The encapsulation of P. aeruginosa KBN 12 proved to be an effective method for BB dye decolourization or remediation.

Biodegradation of Reactive Yellow-145 azo dye using bacterial consortium: A deterministic analysis based on degradable Metabolite, phytotoxicity and genotoxicity study

Azo dyes are used at larger-scale as coloring agent in the textile industry. It generates a huge amount of dye containing wastewater and its toxicity threatens all kinds of life and also impacts human beings. At present, more impetus is being given to the biological treatment of dye effluent because of its azoreductase enzyme action to break down azo bond which leads to decolorization and degradation of dye. Bacterial consortium of E. asburiae and E. cloacae (1:1 ratio) was used for degradation and decolorization of Reactive Yellow-145 (RY-145) dye. The optimization of dye concentration, temperature, pH, and media has been carried out to determine the conditions required for maximum degradation and decolorization. The mixed consortium (10%) has shown 98.78% decolorization of RY-145 dye under static condition at 500 mgL^-1 concentration, 35 °C and pH 7.0 at 12 h contact period. FTIR analysis showed formation of new functional groups in the treated dye, such as O-H stretch at 1361 cm^-1, C-H stretch at 890 cm^-1, N-H stretch at 1598 cm^-1 and aromatic C-H at 671 cm^-1 revealing degradation of dye. Biodegraded metabolites of RY-145 dye were identified through GC-MS analysis that includes 2-Cyclohexen-1-ol, 5-Nitroso-2, 4, 6-triaminopyrimidine, Octahydroquinoline-9-hydroxyperoxide, Tetramethyl-2-hexadecen-1-ol, 9-Octadecanoic acid, methyl ester and Hexadecanoic acid, methyl ester, respectively which have industrial applications. Cyclohexane was used in gasoline and adhesive while Octahydroquinoline-9-hydroxyperoxide and 5-Nitroso-2, 4, 6-triaminopyrimidine were used in manufacturing drugs. Tetramethyl-2-hexadecen-1-ol, 9-Octadecanoic acid, methyl ester and Hexadecanoic acid, methyl ester are antimicrobial and antioxidant. Phytotoxicity test also showed non-toxic effects of treated dye on germination of Cicer arietinum and Vigna radiata seeds. Similarly, genotoxicity study indicated less toxic effects of biodegraded dye products on Mitotic index (MI) and cell division of Allium cepa.

Decolorization of the benzidine-based azo dye Congo red by the new strain Shewanella xiamenensis G5-03

Shewanella xiamenensis G5-03 was observed to decolorize the azo dye Congo red in synthetic wastewater. The influence of some factors on the dye decolorization efficiency was evaluated. The optimal decolorization conditions were temperature 30-35 °C, pH 10.0, incubation time 10 h, and static condition. The kinetic of Congo red decolorization fitted to the Michaelis-Menten model (Vmax = 111.11 mg L-1 h-1 and Km = 448.3 mg L-1). The bacterium was also able to degrade benzidine, a product of azo bond breakage of the Congo red, which contributed to reduce the phytotoxicity. The ability of S. xiamenensis G5-03 for simultaneous decolorization and degradation of Congo red shows its potential application for the biological treatment of wastewaters containing azo dyes.

Decolourization of textile effluent using native microbial consortium enriched from textile industry effluent

A robust and efficient treatment process is required to address the problem of residual colour and avoid expensive post-treatment steps while dealing with textile effluents. In the present work, a novel microbial consortium enriched from textile effluent was used to optimize the process of decolourization under extreme conditions with minimum inputs. With PreTreatment Range (PTR) effluent as a carbon source and only 0.5 g/L yeast extract as external input, the process enabled 70-73% colour reduction (from 1910-1930 to 516-555 hazen) in dyeing unit wastewater. Unhindered performance at higher temperatures (30 °C-50 °C) and wide pH range (7-12) makes this process highly suitable for the treatment of warm and extremely alkaline textile effluents. No significant difference was observed in the decolourization efficiency for effluents from different batches (Colour: 1647-4307 hazen; pH-11.5-12.0) despite wide variation in nature and concentration of dyes employed. Long term (60 days) continuous mode performance monitoring at hydraulic retention time of 48 h in lab-scale bioreactor showed consistent colour (from 1734-1980 to 545-723 hazen) and chemical oxygen demand (1720-2170 to 669-844 mg/L) removal and consistently neutral pH of the treated water. Present study thus makes a significant contribution by uncovering the ability of native microbial consortium to reliably treat dye laden textile wastewater without any dilution or pre-treatment and with minimum external inputs. The results ensure easy applicability of this indigenously developed process at the industrial scale.

Optimization of methylene blue degradation by Aspergillus terreus YESM 3 using response surface methodology

Synthetic dyes released from many industries cause pollution problems in aquatic environments affecting public health. The present study aimed to explore the potentiality of Aspergillus terreus YESM 3 (accession number LM653117) for colour removal of three different dyes: methylene blue (MB), malachite green (MG) and safranin (S). Results showed that the tolerance index of the studied fungus against tested dyes decreased in the order: methylene blue, safranin and malachite green. Removal of methylene blue colour was improved by using Box-Behnken design. Optimum condition for methylene blue biodegradation in Czapek Dox broth was achieved at pH 6, of 31.41 mg/L dye concentration and an inoculum of 5.7778 × 10⁴ (conidia/mL) with biodegradation of 89.41%. Thus, a novel and eco-friendly system for the biodegradation of dyes using Box-Behnken design has been efficiently developed. Accordingly, A. terreus YESM 3 can be professionally used for bioremediation of methylene blue dye in wastewater and removal of environmental pollution.

Comparison between Allura Red dye discoloration by activated carbon and azo bacteria strain

Azo dyes are extensively used in different industries areas, such as Allura Red (R-40). Previous studies have proven its carcinogenic and mutagenic properties. For the removal of this type of emerging pollutant from effluents, tertiary treatment techniques such as activated charcoal are used. Alternatively, the use of bacteria is preferred because of its quick discoloration processes. The aim of the present investigation is to compare the efficiency removal of R-40 from aqueous media by a physicochemical process and a biological one. The sorption kinetics of 10 ppm of R-40 was carried out with the use of activated charcoal based on walnut shells in water. Moreover, Pseudomonas aeruginosa and Bacillus subtilis stains were used separately to decolorize nutrient broth media supplemented with 50 ppm of R-40. The activated carbon was capable to remove 99.87% of R-40 at 264 h, while the bacterial strains decolorized 92.13% (P. aeruginosa) and 88.21% (B. subtilis), respectively, under microaerophilic conditions after 168 h. Therefore, both process strategies, physicochemical and biological rapprochements, were able to remove the dye from aqueous media. R-40 was not cytotoxic to used strains, besides gram-positive either negative bacteria could be applied to turn over this azo dye in short term. Combination of both approaches may be implemented in tandem architecture.

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.

Performance of a Newly Isolated Salt-Tolerant Yeast Strain Sterigmatomyces halophilus SSA-1575 for Azo Dye Decolorization and Detoxification

The effective degradation of hazardous contaminants remains an intractable challenge in wastewater processing, especially for the high concentration of salty azo dye wastewater. However, some unique yeast symbionts identified from the termite gut system present an impressive function to deconstruct some aromatic compounds, which imply that they may be valued to work on the dye degradation for various textile effluents. In this investigation, a newly isolated and unique yeast strain, Sterigmatomyces halophilus SSA-1575, was identified from the gut system of a wood-feeding termite (WFT), Reticulitermes chinensis. Under the optimized ambient conditions, the yeast strain SSA-1575 showed a complete decolorization efficiency on Reactive Black 5 (RB5) within 24 h, where this azo dye solution had a concentration of a 50 mg/L RB5. NADH-dichlorophenol indophenol (NADH-DCIP) reductase and lignin peroxidase (LiP) were determined as the key reductase and oxidase of S. halophilus SSA-1575. Enhanced decolorization was recorded when the medium was supplemented with carbon and energy sources, including glucose, ammonium sulfate, and yeast extract. To understand a possible degradation pathway well, UV-Vis spectroscopy, FTIR and Mass Spectrometry analyses were employed to analyze the possible decolorization pathway by SSA-1575. Determination of relatively high NADH-DCIP reductase suggested that the asymmetric cleavage of RB5 azo bond was mainly catalyzed by NADH-DCIP reductase, and finally resulting in the formation of colorless aromatic amines devoid of any chromophores. The ecotoxicology assessment of RB5 after a decolorization processing by SSA-1575, was finally conducted to evaluate the safety of its metabolic intermediates from RB5. The results of Microtox assay indicate a capability of S. halophilus SSA-1575, in the detoxification of the toxic RB5 pollutant. This study revealed the effectiveness of halotolerant yeasts in the eco-friendly remediation of hazardous pollutants and dye wastewater processing for the textile industry.

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.

Bacillus firmus strain FSS2C ameliorated oxidative stress in wheat plants induced by azo dye (reactive black-5)

This study was conducted to determine the ability of a bacterial strain FSS2C to ameliorate growth of wheat plants grown under induced stress of reactive black-5 (RB-5). The strain was taxonomically identified as Bacillus firmus on the basis of its 16S rRNA gene sequence analysis. The B. firmus FSS2C was found physiologically potent in phosphate solubilization, indole-3-acetic acid production and ammonia synthesis in the presence of varying concentrations of azo dye RB-5. Moreover, it decolorized RB-5 in vitro with the maximum decolorization (%) found at pH 7 and 30 °C. Inoculation of wheat plants, growing under stress induced by RB-5 dye, with rifampicin-resistant derivatives of the strain FSS2C substantially reduced the cellular oxidative stress, thereby resulting in higher plant biomass as compared to non-inoculated plants. Similarly, the inoculated plants revealed higher nutrient content in shoots as compared to non-inoculated ones. It was concluded that B. firmus strain FSS2C alleviated the oxidative stress impairment caused by reactive black-5 in wheat plants. Therefore, the strain can be used as bio-inoculant in wastewater irrigated soils.

Fructose as an additional co-metabolite promotes refractory dye degradation: Performance and mechanism

In this work, the performance and mechanism for the boosting effects of fructose as an additional co-metabolite towards the biological treatment of reactive black 5 were systematically investigated. A decolorization efficiency of 98% was obtained in sample FRU200 (with 3 g/L fructose added based on 3 g/L yeast extract), which was 21% higher than that without fructose. Several intermediates with low molecular weight generated in sample FRU200 and different metabolic pathways were deduced. The bacterial community structure significantly changed due to fructose addition. Label-free quantitative proteomic approach suggested that several up-regulated proteins in sample FRU200 might play essential roles during the degradation. Furthermore, the mechanisms of RB5 degradation by proteins/enzymes of the dominant species in flora DDMZ1 were proposed. This work deepens our understanding of the molecular and ecological mechanism of fructose as co-metabolite enhancing the biodegradation of refractory organic pollutants by a natural bacterial flora.

Highly efficient biodegradation of reactive blue 19 under the activation of tea residue by a newly screened mixed bacterial flora DDMY2

In this study, a newly screened mixed bacterial flora DDMY2 had high decolorization capacity for anthraquinone dye reactive blue 19 (RB19) and the decolorization efficiency of 300 mg L⁻¹ RB19 could reach up to 98% within 48 h in the presence of tea residue. Results indicated that RB19 could be efficiently decolorized by flora DDMY2 in wide ranges of pH values (5.0–9.0), temperatures (30–40 °C) and initial dye concentrations (50–500 mg L⁻¹) under the activation of tea residue. Concentration of tea residue had been proved to significantly impact the decolorization performance. UV-vis spectrophotometry, Fourier transform infrared spectrometry and liquid chromatography/time-of-flight/mass spectrometry analysis showed three identified degradation products and the possible degradation pathway of RB19 was speculated. High-throughput sequencing analysis revealed the community structures of bacterial flora before and after domestication by tea residue. Based on the result, it was inferred that unclassified_o_Pseudomonadales, Brevibacillus, Stenotrophomonas and Bordetella activated by tea residue were responsible for the excellent decolorization performance. Results of this research deepen our understanding of the biodegradation process of anthraquinone dyes by bacterial flora and broaden the knowledge of utilizing tea residue as a bioactivator in biological treatment.

Tea residue promoted the decolorization of RB19 by activating flora DDMY2, revealing corresponding degradation pathways and functional genera in DDMY2.

Adsorption of heavy metal tolerance strains to Pb2+ and Cd2+ in wastewater

The functional strains with high tolerance to heavy metal Pb²⁺ and Cd²⁺ were screened from soil obtained in a heavy metal waste accumulation area. The immobilized biological adsorbent was made by embedding method and used for treatment of wastewater containing heavy metals. The effects of initial concentration of heavy metals, adsorption time, pH value of wastewater, and dosage of adsorbent on adsorption performance were investigated. The study showed (1) the strains tested were Brevibacterium and their maximum tolerable concentrations for Pb²⁺ and Cd²⁺ were 2200 and 700 mg/L, respectively; (2) the maximum adsorption rate for Pb²⁺ and Cd²⁺ was 87.77% and 57.50% respectively when the dosage of adsorbent was 10 g/L and the pH value of wastewater was 6; (3) Pb²⁺ and Cd²⁺ could be adsorbed in the equilibrium solution for 40 min and the maximum adsorption capacity reached 114.36 mg/g and 82.12 mg/g, respectively; and (4) when the initial pH value of the wastewater was 5-7, the adsorption rate decreased with the increase of the concentration, and the initial concentration of Pb²⁺ had a greater effect on the adsorption rate than Cd²⁺. Langmuir and Freundlich equation showed that the adsorption of Pb²⁺ and Cd²⁺ was mainly on the surface of monolayer. And the pseudo-second-order kinetic equation indicates that Cd²⁺ has a relatively greater adsorption rate than Pb²⁺ does.

Enzymatic detoxification of azo dyes by a multifarious Bacillus sp. strain MR-1/2-bearing plant growth-promoting characteristics

This study was conducted to elucidate the inherent potential of Bacillus sp. MR-1/2, which was isolated from root zone of maize crop grown on a textile wastewater-irrigated soil. The isolated strain was identified through its ribosomal RNA sequence. Under in vitro conditions, the strain demonstrated its tolerance for high concentrations of various heavy metal ions as determined by minimum inhibitory concentration. Moreover, the strain MR-1/2 exhibited many important phytobeneficial traits such as inorganic P solubilization and 1-aminocyclopropane-1-carboxylate (ACC) deaminase ability even under high metal and salt stress. Results showed that the strain proficiently decolorizes various azo dye compounds, e.g., reactive black-5, reactive red-120, and direct blue-1 and congo red, in broth culture. The bioremediation potential of the strain MR-1/2 was further confirmed by analyzing the retrieved azoreductase gene sequence through bioinformatics tools, whereby a subsequent prediction revealed that the azoreductase enzyme activity was involved in decolorization process. When mung bean seeds were grown in pots under various concentrations of decolorized and non-decolorized azo dye, the Bacillus sp. MR-1/2 not only alleviated the azo dye toxicity, but also increased the plant growth parameters. In conclusion, the strain MR-1/2 efficiently decolorized the azo dyes and helped in mung bean plant growth by alleviating azo dye toxicity.

Effect of Reactive Black 5 azo dye on soil processes related to C and N cycling

Azo dyes are one of the largest classes of synthetic dyes being used in textile industries. It has been reported that 15-50% of these dyes find their way into wastewater that is often used for irrigation purpose in developing countries. The effect of azo dyes contamination on soil nitrogen (N) has been studied previously. However, how does the azo dye contamination affect soil carbon (C) cycling is unknown. Therefore, we assessed the effect of azo dye contamination (Reactive Black 5, 30 mg kg^-1 dry soil), bacteria that decolorize this dye and dye + bacteria in the presence or absence of maize leaf litter on soil respiration, soil inorganic N and microbial biomass. We found that dye contamination did not induce any change in soil respiration, soil microbial biomass or soil inorganic N availability (P > 0.05). Litter evidently increased soil respiration. Our study concludes that the Reactive Black 5 azo dye (applied in low amount, i.e., 30 mg kg^-1 dry soil) contamination did not modify organic matter decomposition, N mineralization and microbial biomass in a silty loam soil.

Simultaneous decolorization of sulfonated azo dyes and reduction of hexavalent chromium under high salt condition by a newly isolated salt-tolerant strain Bacillus circulans BWL1061

The co-existence of dyes, Cr(VI) and high concentration of salt in dyeing wastewater causes serious and complex environmental problems. In this study, a salt-tolerant strain Bacillus circulans BWL1061 was reported to simultaneously remove 50mg/L methyl orange and 50mg/L Cr(VI) under the anaerobic condition with 60g/L NaCl. During the decolorization process, the Cr(VI) reduction occurred preferentially over the dye decolorization due to the dominate utilization of electron by Cr(VI). The analysis of enzyme activities suggested that azoreductase, NADH-DCIP reductase, and laccase were associated with decolorization of methyl orange. A possible degradation pathway was proposed based on the metabolites analysis. The decolorization of methyl orange is involved in the symmetric cleavage of azo bond, which formed N,N-dimethyl p-phenylenediamine and 4-amino sulfonic acid, or the asymmetric cleavage of azo bond, which formed 4-(dimethylamino) phenol and 4-diazenylbenzene sulfonic acid. Phytotoxicity assays showed that strain BWL1061 could decrease the toxicity of methyl orange to Triticum aestivum, Pogostemon cablin and Isatis indigotica Fort during the decolorization process. In this study, Bacillus circulans is reported for the first time that could simultaneously remove azo dyes and Cr (VI) under high salt condition.

Potential plant growth-promoting strain Bacillus sp. SR-2-1/1 decolorized azo dyes through NADH-ubiquinone:oxidoreductase activity

In this study, a bacterial strain SR-2-1/1 was isolated from textile wastewater-irrigated soil for its concurrent potential of plant growth promotion and azo-dye decolorization. Analysis of 16S rRNA gene sequence confirmed its identity as Bacillus sp. The strain tolerated high concentrations (i.e. up to 1000mgL^-1) of metals (Ni²⁺, Cd²⁺, Co²⁺, Zn²⁺, and Cr⁶⁺) and efficiently decolorized the azo dyes (i.e. reactive black-5, reactive red-120, direct blue-1 and congo red). It also demonstrated considerable in vitro phosphate solubilizing and 1-aminocyclopropane-1-carboxylic acid deaminase abilities at high metal and salt levels. Bioinformatics analysis of its 537bp azoreductase gene and deduced protein revealed that it decolorized azo dyes through NADH-ubiquinone:oxidoreductase enzyme activity. The deduced protein was predicted structurally and functionally different to those of its closely related database proteins. Thus, the strain SR-2-1/1 is a powerful bioinoculant for bioremediation of textile wastewater contaminated soils in addition to stimulation of plant growth.

Characterization of a salt resistant bacterial strain Proteus sp. NA6 capable of decolorizing reactive dyes in presence of multi-metal stress

Microbial biotechnologies for the decolorization of textile wastewaters have attracted worldwide attention because of their economic suitability and easiness in handling. However, the presence of high amounts of salts and metal ions in textile wastewaters adversely affects the decolorization efficiency of the microbial bioresources. In this regard, the present study was conducted to isolate salt tolerant bacterial strains which might have the potential to decolorize azo dyes even in the presence of multi-metal ion mixtures. Out of the tested 48 bacteria that were isolated from an effluent drain, the strain NA6 was found relatively more efficient in decolorizing the reactive yellow-2 (RY2) dye in the presence of 50 g L(-1) NaCl. Based on the similarity of its 16S rRNA gene sequence and its position in a phylogenetic tree, this strain was designated as Proteus sp. NA6. The strain NA6 showed efficient decolorization (>90 %) of RY2 at pH 7.5 in the presence of 50 g L(-1) NaCl under static incubation at 30 °C. This strain also had the potential to efficiently decolorize other structurally related azo dyes in the presence of 50 g L(-1) NaCl. Moreover, Proteus sp. NA6 was found to resist the presence of different metal ions (Co(+2), Cr(+6), Zn(+2), Pb(+2), Cu(+2), Cd(+2)) and was capable of decolorizing reactive dyes in the presence of different levels of the mixtures of these metal ions along with 50 g L(-1) NaCl. Based on the findings of this study, it can be suggested that Proteus sp. NA6 might serve as a potential bioresource for the biotechnologies involving bioremediation of textile wastewaters containing the metal ions and salts.

Use of RSM modeling for optimizing decolorization of simulated textile wastewater by Pseudomonas aeruginosa strain ZM130 capable of simultaneous removal of reactive dyes and hexavalent chromium

Remediation of colored wastewater loaded with dyes and metal ions is a matter of interest nowadays. In this study, 220 bacteria isolated from textile wastewater were tested for their potential to decolorize each of the four reactive dyes (reactive red-120, reactive black-5, reactive yellow-2, and reactive orange-16) in the presence of a mixture of four different heavy metals (Cr, Zn, Pb, Cd) commonly found in textile effluents. Among the tested bacteria, the isolate ZM130 was found to be the most efficient in decolorizing reactive dyes in the presence of the mixture of heavy metals and was identified as Pseudomonas aeruginosa strain ZM130 by 16S rRNA gene analysis. The strain ZM130 was highly effective in simultaneously removing hexavalent chromium (25 mg L(-1)) and the azo dyes (100 mg L(-1)) from the simulated wastewater even in the presence of other three heavy metals (Zn, Pb, Cd). Simultaneous removal of chromium and azo dyes ranged as 76.6-98.7 % and 51.9-91.1 %, respectively, after 180 h incubation. On the basis of quadratic polynomial equation and response surfaces given by the response surface methodology (RSM), optimal salt content, pH, carbon co-substrate content, and level of multi-metal mixtures for decolorization of reactive red-120 in a simulated textile wastewater by the strain ZM130 were predicted to be 19.8, 7.8, and 6.33 g L(-1) and a multi-metal mixture (Cr 13.10 mg L(-1), Pb 26.21 mg L(-1), Cd 13.10 mg L(-1), Zn 26.21 mg L(-1)), respectively. Moreover, the strain ZM130 also exhibited laccase and nicotinamide adenine dinucleotide (reduced)-dichlorophenolindophenol reductase (NADH-DCIP reductase) activity during the decolorization of reactive red-120. However, the laccase activity was found to be maximum in the presence of 300 mg L(-1) of the dye as compared to other concentrations. Hence, the isolation of this strain might serve as a potential bio-resource required for developing the strategies aiming at bioremediation of the wastewater contaminated with dyes and heavy metals.

Yeast extract promotes decolorization of azo dyes by stimulating azoreductase activity in Shewanella sp. strain IFN4

Biological treatment of azo dyes commonly requires a combined anaerobic-aerobic process in which initial decolorization is achieved by reductive cleavage of azo bonds on the parent molecule. The present study was conducted to examine the relative importance of co-substrates for driving reductive decolorization of azo dyes by Shewanella sp. strain IFN4 using whole cells and enzyme assays. Results showed that the dye decolorization by strain IFN4 was faster in medium containing 1gL(-1) yeast extract (YE) as compared to nine other co-substrates. Moreover, only YE stimulated azoreductase activity (increased from 1.32 to 4.19U/mg protein). Increasing the level of YE up to 8gL(-)(1) resulted into 81% decolorization of the dye in 1h along with an increase in azoreductase activity up to 6.16U/mg protein. Among the components of YE, only riboflavin stimulated the decolorization process as well as enzyme activity. Moreover, strain IFN4 demonstrated flavin reductase activity, and a significant correlation (r(2)=0.98) between flavin reduction and dye reduction by this strain emphasized the involvement of flavin compounds in the decolorization process. The results of this study show that YE serves both as a source of reducing equivalents and an electron shuttle for catalyzing dye reduction.

Photocatalytic degradation of methylene blue under UV light irradiation on prepared carbonaceous TiO2

This study involves the investigation of altering the photocatalytic activity of TiO2 using composite materials. Three different forms of modified TiO2, namely, TiO2/activated carbon (AC), TiO2/carbon (C), and TiO2/PANi, were compared. The TiO2/carbon composite was obtained by pyrolysis of TiO2/PANi prepared by in situ polymerization method, while the TiO2/activated carbon (TiO2/AC) was obtained after treating TiO2/carbon with 1.0 M KOH solution, followed by calcination at a temperature of 450°C. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TG-DTA), Brunauer-Emmet-Teller (BET), and UV-Vis spectroscopy were used to characterize and evaluate the prepared samples. The specific surface area was determined to be in the following order: TiO2/AC > TiO2/C > TiO2/PANi > TiO2 (179 > 134 > 54 > 9 m(2) g(-1)). The evaluation of photocatalytic performance for the degradation of methylene blue under UV light irradiation was also of the same order, with 98 > 84.7 > 69% conversion rate, which is likely to be attributed to the porosity and synergistic effect in the prepared samples.