Complete Decolorization Research Articles

Niobium Oxide Catalysts as Emerging Material for Textile Wastewater Reuse: Photocatalytic Decolorization of Azo Dyes

Niobium-based metal oxides are emerging semiconductor materials with barely explored properties for photocatalytic wastewater remediation. Brazil possesses the greatest reserves of niobium worldwide, being a natural resource that is barely exploited. Environmental applications of solar active niobium photocatalysts can provide opportunities in the developing areas of Northeast Brazil, which receives over 22 MJ m2 of natural sunlight irradiation annually. The application of photocatalytic treatment could incentivize water reuse practices in small and mid-sized textile businesses in the region. This work reports the facile synthesis of Nb2O5 catalysts and explores their performance for the treatment of colored azo dye effluents. The high photoactivity of this alternative photocatalyst makes it possible to quickly obtain complete decolorization, in less than 40 min of treatment. The optimal operational conditions are defined as 1.0 g L−1 Nb2O5 loading in slurry, 0.2 M of H2O2, pH 5.0 to treat up to 15 mg L−1 of methyl orange solution. To evaluate reutilization without photocatalytic activity loss, the Nb2O5 was recovered after the experience and reused, showing the same decolorization rate after several cycles. Therefore, Nb2O5 appears to be a promising photocatalytic material with potential applicability in wastewater treatment due to its innocuous character and high stability.

Heterogeneous Electro-Fenton catalysis with HKUST-1-derived Cu@C decorated in 3D graphene network.

Transition metal and nanocarbon-based composites with high activity and stability draw great attention in electro-Fenton system for organic pollutants removal. In this study, HKUST-1-derived Cu@C nanoparticles embedded within three-dimensional reduced graphene oxide (rGO) network (denoted as 3DG/Cu@C) is synthesized through a simple strategy. The prepared catalyst shows ordered 3D porous carbon structure and Cu@C NPs are uniformly dispersed in the matrix. The 3DG/Cu@C is used as heterogeneous electro-Fenton (hetero-EF) catalyst and shows outstanding performance in various persistent organic pollutants removal. High concentration Rhodamine B (RhB) (40mgL-1) can achieve a complete decolorization within 150min with 25mgL-1 3DG/Cu@C catalyst, which is one of the lowest catalyst dosages in hetero-EF for RhB removal. More importantly, the 3DG/Cu@C achieves high RhB mineralization efficiency of 81.5% and exhibits high catalytic performance in a wide pH window from 3 to 9. The 3DG/Cu@C also remains high efficiency after five successive reaction cycles. The working mechanism study shows that RhB is mainly oxidized by •OH and O2•- radicals through hetero-EF and anodic oxidation processes. The high stability and outstanding performance of 3DG/Cu@C provide new insights in organic pollutants removal by hetero-EF process with transition metal and nanocarbon-based catalysts.

Performance evaluation of a novel electrolytic reactor with rotating and non rotating bipolar disc electrodes for synthetic textile wastewater treatment

Textile industry is one of the leading polluters of surface water due to the presence of various types of dyes and other hazardous pollutants. In this study, a novel rotating bipolar disc electrolytic (RBDE) reactor was designed for the treatment of textile wastewater and the performance was evaluated. The turbulence created in the system and enhanced mass transport (coagulants/ions) improved the overall performance of electrolytic cell during rotation. The effect of various parameters like current density, electrical conductivity, pH, rotation speed, and pollutant concentration on the performance of the RBDE reactor was examined in terms of COD, colour and TSS removal. Complete decolorization was obtained in 2 min and 6 min of electrolysis time in rotating and non-rotating mode of operation. COD removal was 4.8 times more in rotating electrode system (230.4 mg/L to 14.05 mg/L, 93.9% removal) compared to static mode of electrodes (230.4 mg/L to 67.9 mg/L, 70.6% removal), in 10 min of electrolysis time. Profilometry analysis confirmed that the rotation increased the electrode dissolution (8.1 μm in static and 62.3 μm in rotating electrodes) and also decreased the thickness of oxide film formation on cathode surface compared to static electrodes (0.55 μm on rotating and 6.48 μm on static electrodes). Moreover, RBDE reduced the energy consumption (1.4 kW h/kg dye) compared to static (2.1 kW h/kg) electrodes system for the complete decolourization of Rhodamine B (RB) dye.

Synthesis of selenium–silver nanostructures with enhanced antibacterial, photocatalytic and antioxidant activities

The development of a durable and efficient composite material that could perform a long-life antibacterial activity and radical scavenging ability is highly needed. In this paper, selenium nanostructures of different morphologies were synthesized by a wet chemical method under mild experimental setup. Silver nanoparticles were doped on the surface of these nanostructures and successfully characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, and high-resolution transmission electron microscopy. The potential applications of the designed composite were investigated in multiple disciplines including antibacterial, antioxidant, and photocatalytic activities. The selenium silver (Se–Ag) nanocomposite was employed as an antibacterial agent against a Gram-positive bacterium and a Gram-negative bacterium, and our findings disclosed that the designed composite is an excellent material in inhibiting the challenged bacterial strains. The Se–Ag composite has shown excellent activity with 30-mm inhibition zone at 2 mg/ml concentration, and maintains significant antibacterial efficacy for 72 h, indicating its sustainable performance for a long-life period. Furthermore, Se–Ag nanocomposite also exhibited a significant radical scavenging property against 2,2-diphenyl-1-picrylhydrazyl free radical and an enhanced photocatalytic activity (90–95%) with complete dye decolorization in 70 min. The superior antibacterial activity (zone of inhibition 30 mm), photocatalytic (95%) and antioxidant performance (78%) of the nanocomposite are due to the combined antibacterial (17 mm), photocatalytic (~ 30%) and antioxidant potentials (15%) of the Ag and Se (16 mm, 40%, 25%), respectively.

Electrochemically-driven dosing of iron (II) for autonomous electro-Fenton processes with in situ generation of H2O2

Reliance of Fenton processes to hazardous chemicals diminishes the range of niche applications of this highly efficient advanced oxidation process due to risks associated to transport, storage, and handling of chemicals. In this work, an alternative approach towards independent Fenton systems integrating (1) per demand in situ production of H2O2 from oxygen cathodic reduction and (2) electrochemically-driven iron (II) dosing system is explored as a novel strategy. For this purpose, a dual-cell system was designed to fulfill individual current needs of both processes while avoiding excessive iron sludge production observed in peroxicoagulation treatments. Experimental results indicate high reproducibility and resilience of the proposed dual-cell electro-Fenton system, which attained complete organic methylene blue dye decolorization in 80 ​min of treatment and over 80% mineralization in only 120 ​min of electro-Fenton treatment. These results showcase a new approach that opens alternative pathways for possible implementation of low-physical footprint electro-Fenton systems as point-of-entry treatments or even to treat effluents of small and mid-sized industries.

MOF [NH2-MIL-101(Fe)] as a powerful and reusable Fenton-like catalyst

Several metal-organic frameworks (MOFs) were evaluated as a Fenton-like catalyst for water treatment in a screening process. Herein, we report hydrothermally prepared NH2-MIL-101(Fe) can offer a dual function of good adsorption and excellent Fenton-like catalytic performances for organic pollutant removal. To understand the mode of action of both –NH2 and Fe, MIL-101(Fe) and NH2-MIL-101(Al) were comparatively investigated. It was found that the adsorption followed Langmuir isotherm and correlated well with pseudo-second-order kinetic model. Pseudo-first-order model was used to describe the catalysis performance. A complete decoloration of a relatively high concentration of RhB (0.25 mmol/L) by was achieved within only 4–10 min at a wide range of pH, and attained a high degradation rate constant (K) of 0.66 min−1 and 1.09 min−1at pH 7.2 and pH 11, respectively. These results were comparatively high, and tackling the problem of strict pH value (3.1) of Fenton reaction, and even of most of the Fenton-like catalysts, which are active only in acidic or near natural pH. Moreover, that outstanding performance was maintained after five successive reuse cycles. More importantly, the material potential use in the real application was validated by RhB mineralization (97.7 % TOC removal in 20 min), and by treating real textile wastewater (83 % TOC removal in 30 min). That excellent performance is a result of the synergetic effect between the high adsorption, fast electron transfer, and sustainable Fe ions release. The possible degradation mechanism was proposed.

Comparison of the effects of various supporting electrolytes on the treatment of a dye solution by electrocoagulation process

Laboratory experiments were conducted to investigate the effect of some supporting electrolytes on the treatment of Reactive Black 5 (RB5) by electrocoagulation using aluminum and iron electrode couples. Electrolytes, which contain Cl−, SO42−, NO− anions and Na+, K+, NH4+ cations, were compared in terms of color removal efficiencies. The presence of SO42− led to poor performances with aluminum electrodes yielding a removal efficiency close to 45% at 8.33 A/m2. Similarly, the presence of NO3− when iron electrodes were used adversely affected the process performance. The removal efficiency with KNO3 was 49.1% at 8.33 A/m2. Overall Cl− containing electrolytes performed well achieving almost complete decolorization (99.9%) regardless of the electrode type. The performance of Al electrode considerably improved in the presence of NH4+, achieving 98.0% and 99.1% removal efficiencies at the current densities of 4.17 A/m2 and 8.33 A/m2, respectively in 10 min treatment duration.

Biodegradation of malachite green by a newly isolated Bacillus vietnamensis sp. MSB17 from continental slope of the Eastern Arabian Sea: Enzyme analysis, degradation pathway and toxicity studies

A marine bacterial isolate, Bacillus vietnamensis sp. MSB17 from the sediments collected from the continental slope of the eastern Arabian Sea exhibited good Malachite Green (MG) decolorization ability in mineral medium supplemented with glucose and yeast extract under static conditions. The complete decolorization of dye (50 mg/L) was attained within 4 h of incubation. The activities of enzymes such as tyrosinase (0.62 IU/ml), laccase (12.02 U/ml), and manganese peroxidase (6.23 U/ml) were observed during dye degradation. UV-VIS, FT-IR, and GC-MS analysis of dye samples extracted with ethyl acetate confirmed the biodegradation of MG into methanone, [4-(dimethylamino) phenyl] phenyl- and 2, 6-bis (1, 1-dimethylethyl) phenol. The metabolites obtained from B. vietnamensis sp. MSB17 mediated MG degradation did not exhibit any microbial toxicity and phytotoxicity. The present study indicated the efficiency of Bacillus vietnamensis sp. MSB17 to effectively degrade MG, revealing its potential to be further utilized for bioremediation purposes.

TiO2/Fe2O3: Type-I Heterostructures for Electrochemical Dye Degradation/Water Splitting Studies

In contemporary research, semiconductor composite materials, i.e., combination of different semiconductor materials, play an important role in extracting needful energy from existing renewable energy forms. For example, “heterostructure” composite assemblies facilitate faster charge carrier transport and therefore improve the efficiency of the electro-/photoelectrochemical processes/devices due to synergistic interaction and synchronized charge transport across material interfaces that have formed in composite assembly. Herein, we report type-I heterostructure consists of TiO2 and Fe2O3 for crystal violet dye degradation and water splitting studies via electrochemical route. The rationale in choosing the above materials (TiO2, Fe2O3) in the present study will not only account stability, nontoxicity, and high oxidation power but also facilitate the fast charge carrier movements due to proper band edge alignments. Synthesized TiO2, Fe2O3, and TiO2/Fe2O3 nanoparticle assemblies were fabricated as electrodes on titanium (Ti) and indium tin oxide (ITO) substrates and used as anode in electrochemical analysis. Complete decolorization was achieved with all the fabricated electrodes and higher rate of degradation was achieved with composite electrode (Ti/TiO2/Fe2O3) than individuals (bare Ti, Ti/TiO2, Ti/Fe2O3). Further, the same composite electrode shows better performance toward electrochemical water splitting in comparison with individual electrodes.

TiO2/anthill clay as a heterogeneous catalyst for solar photocatalytic degradation of textile wastewater: Catalyst characterization and optimization studies

This present study aims at revealing the activity of TiO2–anthill clay in photocatalytic degradation of textile effluent. It also aims to investigate the effects of parameters affecting the photocatalytic degradation process such as catalyst dose (0.5–25 wt.%), reaction time (1–3 h) and solution pH (2–10) through central composite design. The synthesized photocatalyst was characterized using BET, SEM, EDX, FTIR, and XRF techniques. The results obtained from the optimization studies revealed that there were good agreements between the predicted and observed values of photocatalytic degradation efficiency. The maximum decolorization efficiency of 70.92% was obtained under the optimum experimental conditions of 2.50 wt.% catalyst dose, 1.07 h reaction time, and dye solution pH of 2.0. The TiO2-anthill photocatalyst was found to be efficient for complete decolorization of dye solution as it was able to be reused for up to four cycles.

Green Approach for Decolorization and Detoxification of Textile Dye- CI Direct Blue 201 Using Native Bacterial Strains

One hundred and fifty six native bacterial strains with different morphological characters were isolated from water and soil samples collected from textile wastewater effluent sites, Sri Lanka. Three isolated bacterial strains were more effective on decolorization of CI Direct Blue 201 textile dye and 16s rRNA analysis reveals that the bacterial strains were Alcaligenes faecalis (MK166784), Micrococcus luteus (MK166783) and Staphylococcus warneri (MK256311). A. faecalis, M. luteus and S. warneri showed complete decolorization of CI Direct Blue 201 textile dye within 60, 64, and 72 h of incubation time respectively under the static conditions at 28 oC. Decolorization was effective at a temperature range from 24 oC to 40 oC and pH range from 7 to 9. The presence of tryptone, peptone or yeast in the Mineral Salt Medium enhanced the decolorization of the dye. Phytotoxicity assay based on the seed germination percentages of Oryza sativa and Vigna radiate showed that the detoxification of CI Direct Blue 201 textile dye after the bacterial treatment was effective signifying the potential applicability of the A. faecalis, M. luteus and S. warneri to develop a green application to treat textile wastewater.

Comparative evaluation of Pseudomonas species in single chamber microbial fuel cell with manganese coated cathode for reactive azo dye removal

Microbial fuel cell (MFCs), distinguished by different strains of Pseudomonas species; Pseudomonas aeruginosa (MPEM-MFC I) and Pseudomonas fluorescens (MPEM-MFC II), was analyzed. Results have shown that, over a period of 360 h in the presence of 0.5 mM of model dye, MPEM MFC I produced the maximum power density of 2887 ± 13 μW m−2 (RO-16) and 1906 ± 7 μW m−2 (RB-5) compared with MPEM-MFC II with 1896 ± 15 μW m−2 (RO-16) and 1028 ± 9 μW m−2 (RB-5). Decolorization efficiency of MPEM-MFC I was 98 ± 1.2% (RO-16) and 95 ± 2% (RB-5). Total phenazine production in MPEM-MFC I was 12.3 ± 0.5 μg mL−1 higher than that of 8.9 ± 0.05 μg mL−1 (MPEM-MFC II) and its production have positive influence of electron shuttling that brought out high power output. Addition of phenazine externally reduced the dye degradation. Bioadhesion capability of P. aeruginosa on the anode reduced the internal resistance in MFCs. Thus the implementation of MFC is a most promising technology for the complete decolorization of reactive azo dyes and it has potential economic benefits in real-life industrial application.

Heterogeneous activation of peroxymonosulfate via nanocomposite CeO2-Fe3O4 for organic pollutants removal: The effect of UV and US irradiation and application for real wastewater

In this work, CeO2-Fe3O4 nano-composite (CeFe) was synthesized and applied to activate peroxymonosulfate (PMS) for degradation of synthetic dye Direct red 16 (DR16). X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), vibrating sample magnetometery (VSM), Brunauer–Emmett–Teller (BET) specific surface area and energy dispersive spectroscopy (EDS) were used to characterize CeFe. Operational parameters of pH, PMS and CeFe dosages were studied. Complete decolorization was obtained at pH = 7.0, 1.5 mM PMS and 0.3 g/L catalyst dosage and 25 min reaction time. Reusability and leaching experiments showed that CeFe nano-composite was a stable and recoverable catalyst for four cycles. Ultraviolet (UV) and ultrasound (US) irradiation improved the rate constant considerably. Fulvic acid, bicarbonate ions and sodium dodecyl sulfate exhibited the inhibitory effect on decolorization in CeFe/PMS. CeFe was effective to activate other chemical oxidants such as persulfate, hydrogen peroxide and percarbonate. Sulfate radical was found as dominant radical in CeFe/PMS while hydroxyl radicals also contributed in DR16 degradation in CeFe/PMS/UVA-LED and CeFe/PMS/US. The performance of CeFe/PMS was also studied on several organic pollutants (direct orange 26, bisphenol A, 2,4,6-trichlorophenol and benzotriazole) and real wastewater.

Optimization of complete RB-5 azo dye decolorization using novel cold-adapted and mesophilic bacterial consortia

Azo dyes are an important group of recalcitrant xenobiotics, which are difficult to degrade and deteriorate in cold environments. In this study, two microbial consortia consisting of cold-adapted and mesophilic bacteria were developed for effective decolorization of Reactive Black-5 azo dye. These bacteria were isolated from textile wastewater and soil of a cold region. Identification of bacterial isolates using 16s rRNA gene analysis revealed that they belong to genus Pseudoarthrobacter, Gordonia, Stenotrophomonas, and Sphingomonas. Decolorization assay was performed for every strain at dye concentrations of 25, 50 and 100 mg/L and the consortia PsGo consisting of mesophilic bacteria and StSp consisting of cold-adapted bacteria were constructed accordingly. Results showed that the consortia PsGo and StSp were able to decolorize 54 and 34 percent of RB-5 (50 mg/L) during 7 days. To improve the dye removal efficiency of the consortia, several parameters including temperature, pH, carbon and nitrogen sources were optimized. Over longer periods, StSp consortium managed to completely decolorize RB-5 (50 mg/L) at optimized conditions of 25–30 °C, pH 9, and using glucose and NH4H2PO4 as carbon and nitrogen source respectively, whereas PsGo consortium decolorized RB-5 (50 mg/mL) completely at 37 °C, pH 11, and with lactose and NH4H2PO4 used as carbon and nitrogen sources. Kinetic of reactions for StSp and PsGo consortia were found to be 0.05 and 0.13 day−1 respectively, but became 0.71 and 0.9 day−1 after optimization. In general, cold ecosystems are good sources for the isolation of novel bacterial strains with a potential application, especially when used as consortia, in environmental biotechnology such as decolorization of RB-5.

Zinc Oxide Nanoparticles Obtained by Supercritical Antisolvent Precipitation for the Photocatalytic Degradation of Crystal Violet Dye

In this work, the synthesis of zinc oxide (ZnO) photocatalyst from thermal decomposition of zinc acetate (ZnAc) nanoparticles obtained by supercritical antisolvent (SAS) precipitation was investigated. The optimization of calcination conditions of the SAS ZnAc was carried out, studying the effect of temperature (in the range 300–600 °C) on the production of ZnO nanoparticles. In particular, it was demonstrated that the organic residues in ZnO and its particle size, thus the specific surface area, strongly affect the photocatalytic performances. SAS micronization of ZnAc produces regular nanoparticles with a mean diameter of about 54.5 ± 11.5 nm, whereas unprocessed ZnAc is characterized by very large crystals. The experimental results evidenced that ZnAc prepared by SAS process calcined at 500 °C showed a regular nanometric structure (mean diameter: 65.0 ± 14.5 nm) and was revealed to be the best choice for the photocatalytic removal of crystal violet dye (CV). In fact, the photocatalytic activity performances of ZnO nanoparticles prepared by this route were higher with respect to that of ZnO from unprocessed ZnAc calcined at 500 °C (which is characterized by irregular tetrapods with mean size 181.1 ± 65.5 nm). The optimized photocatalyst was able to assure the complete CV decolorization in 60 min of UV irradiation time and a mineralization degree higher than 90% after 120 min of treatment time.

Entrapment of TiO2 and ZnO powders in alginate beads: Photocatalytic and reuse efficiencies for dye solutions and toxicity effect for DNA damage

Abstract Semiconductor photocatalysts; zinc oxide (ZnO) and titanium dioxide (TiO2) were used to entrap in calcium alginate (Ca-Alg) beads for photocatalytic oxidation of azo dye solutions. The decolorization of two textile dyes, Basic Red 18 (BR18) and Reactive Red 180 (RR180), was investigated in this study. The effect of catalyst loading and initial dye concentration were systematically evaluated. Complete decolorization (100%) of RR180 was obtained by ZnO/Ca-Alg beads at 10 g/L loading and 25 mg/L initial dye concentration for 180 min. However, at the same conditions, decolorization of 45.6% of RR180 was determined by TiO2/Ca-Alg beads. The results also showed that the highest BR18 decolorization levels were 98.4% at 10 g/L loading and 25 mg/L initial dye concentration for 180 min when ZnO/Ca-Alg beads were used as an entrapping matrix. However, a maximum decolorization of 87.1% of BR18 was obtained by TiO2/Ca-Alg beads at similar conditions for 180 min. Catalyst reusability was also tested during ten cycles and ZnO/Ca-Alg beads showed good stability compared to TiO2/Ca-Alg beads. Photocatalytic decolorization efficiency of ZnO/Ca-Alg beads was better than TiO2/Ca-Alg beads for both dyes. Using the comet assay for the genotoxic effect induced on Saccharomyces cerevisiae was also evaluated by entrapped ZnO and TiO 2 powders in Ca-Alg beads. Genotoxicity study showed that the proportion of damaged cells and the genetic damage index (GDI) increased after exposed to entrapped beads in the light phase.

BIODEGRADATION OF CRUDE OIL AND LIGNIN-MODIFYING ENZYME ACTIVITY OF WHITE ROT BASIDIOMYCETES

In the present study, the ability of eighteen white-rot basidiomycetes was evaluated for crude oil biodegradation. Cerrena unicolor strains, Panus tigrinus 433, P. lecometei 903, Pleurotus ostreatus 70, Trametes maxima 403, and T. versicolor 159 showed especially abundant mycelial growth on the surface of agar covered with droplets of crude oil. In the submerged cultivation in the glucose (3 g/L) containing medium, complete decolorization of indicator Resazurin was observed during two weeks in the presence of Bjerkandera adusta 139, C. unicolor 303, Coriolopsis gallica 142, P. ostreatus 70, P. pulmonarius 148, and T. versicolor 159. When artificially oil-polluted soil was inoculated with fungal mycelium pre-grown on a mixture of wheat straw and mandarin peels the maximum degradation rate (65%) was obtained when C. unicolor 305 was incubated in the 1% oil-containing soil for 28 days. At the same cultivation conditions, P. ostreatus 2175 eliminated 43.9% of initial oil when its concentration in the soil was increased to 2%. In the lignocellulose-containing soil, neither glucose nor yeast extract enhanced oil degradation, but wetting of soil with the distilled water to maintain its humidity favored oil elimination. The tested WRB secreted lignin-modifying enzymes in the presence of petroleum hydrocarbons; the higher was the concentration of lignocellulosic substrate in the soil the higher was the fungi enzyme activity. However, the data received did not show any direct relationship between the fungi enzyme activity and the degree of oil elimination. Key words: mycoremediation, crude oil, basidiomycetes, cultivation conditions, lignin-modifying enzymes

Photocatalytic oxidation of azo dye solutions by impregnation of ZnO on fungi

In this study, the semiconductor photocatalyst zinc oxide (ZnO) was used to impregnate on Aspergillus carbonarius (AC) and Penicillium glabrum (PG) fungi for photocatalytic oxidation of azo dye solutions. The photocatalytic decolorization of two textile dyes, Basic Red 18 (BR18) and Reactive Red 180 (RR180), was investigated and the impact of catalyst loading as well as initial dye concentration was systematically examined. Complete decolorization of BR18 was obtained by ZnO impregnated Aspergillus carbonarius (ZnO/AC) and Penicillium glabrum (ZnO/PG). The results also showed that the highest RR180 decolorization levels were 76.2% and 73.7% for ZnO/AC and ZnO/PG, respectively. The optimum catalyst loading was found to be 2 g/L. Catalyst reusability was also tested during five cycles and the bio-sorbent matrix (dead fungus) showed good stability after five reuse cycles. Photocatalytic decolorization of BR18 dye was much faster than RR180 dye, which we attributed to the electrostatic charge interaction between catalyst surface and dye molecules.

Decolorization and degradation of methyl orange by Bacillus stratosphericus SCA1007

Abstract The present study deals with complete decolorization and degradation of sulfonated azo dye (Methyl orange) by Bacillus stratosphericus SCA1007. These classes of dyes are difficult to degrade by conventional treatment methods. To overcome this problem, an environment friendly and efficient method was developed to degrade this recalcitrant dye. Bacillus stratosphericus SCA1007 could carry out complete decolorization of Methyl orange in a wide range up to 150 mg/L of dye concentration, at temperature 35 °C and pH 7 under static condition along with yeast extract in minimal salt media. This is the first study demonstrating complete decolorization of Methyl orange by Bacillus stratosphericus SCA1007 under optimized conditions within 12 h of incubation. The degradation of dye was studied by UV-vis and FTIR. Toxicity studies were performed on Escherichia coli and Vigna radiata to confirm the non-toxic nature of the degraded products.

Efficient decolorization and detoxification of sulphonated azo dye Ponceau 4R by using single and mixed bacterial consortia

The decolorization of toxic azo dye Ponceau 4R by three strains of bacteria Bacillus sp. strain AK1, Lysinibacillus sp. strain AK2 and Kerstersia sp. strain VKY1 individually and in consortia was studied. At optimal conditions, up to 95%, 93% and 87% of the dye was decolorized by the strains AK1, AK2 and VKY1, respectively, in 24 h at 200 mg/L of the dye. Decolorization of the dye was optimized for different parameters such as the concentration of dye, pH, temperature and NaCl concentration. These strains were able to decolorize Ponceau 4R up to an initial concentration of 800 mg/L in the pH range of 5–10, temperature 25–55 °C and NaCl concentration up to 30 g/L. The dye decolorization efficiency of these strains was further enhanced by using different consortia of AK1, AK2 and VKY1 in various combinations. The complete decolorization of the dye by a consortium was achieved within 18 h at 200 mg/L. The cell-free extract of these strains grown on this dye exhibited a remarkable activity of azoreductase which is involved in the breakage of the azo bond. The steady-state kinetics of azoreductase, validated the ping pong Bi-Bi mechanism of enzyme action. UV–Vis spectra, HPLC, FTIR and LC-MS analysis of the dye decolorized samples showed the formation of 4-aminonaphthalene-1-sulphonic acid and 5-amino-6-hydroxynaphthalene-2, 4-disulphonic acid as the products of azo bond breakage. The phytotoxicity test of decolorized sample revealed a considerable reduction in the toxicity in comparison with the parent dye.