Decolorization of azo dyes by Shewanella sp. under saline conditions

Wastewaters from textile processing and dye-stuff manufacture industries contain substantial amounts of salts in addition to azo dye residues. To examine salinity effects on dye-degrading bacteria, a study was carried out with four azo dyes in the presence of varying concentrations of NaCl (0-100 g l(-1)) with a previously isolated bacterium, Shewanella putrefaciens strain AS96. Under static, low oxygen conditions, the bacterium decolorized 100 mg dye l(-1) at salt concentrations up to 60 g NaCl l(-1). There was an inverse relationship between the velocity of the decolorization reaction and salt concentration over the range between 5 and 60 g NaCl l(-1) and at dye concentrations between 100 and 500 mg l(-1). The addition of either glucose (C source) or NH(4)NO(3) (N source) to the medium strongly inhibited the decolorization process, while yeast extract (4 g l(-1)) and Ca(H(2)PO(4))(2).H(2)O (1 g l(-1)) both enhanced decolorization rates. High-performance liquid chromatography analysis demonstrated the presence of 1-amino-2-naphthol, sulfanilic acid and nitroaniline as the major metabolic products of the azo dyes, which could be further degraded by a shift to aerobic conditions. These findings show that Shewanella could be effective for the treatment of dye-containing industrial effluents containing high concentrations of salt.     

Oxidative degradation of high molecular weight chlorolignin by manganese peroxidase of Phanerochaete chrysosporium

Phanerochaete chrysosporium was able to degrade high molecular weight chlorolignins (Mr greater than 30,000) from bleach plant effluents, although a direct contact between ligninolytic enzymes and chlorolignin was prevented by a dialysis tubing. In the absence of the enzymes, Mn3+ depolymerized chlorolignin when complexed with lactate causing the color, chemical oxygen demand (COD) and dry weight to decrease by 80%, 60% and 40%, respectively. Manganese peroxidase effectively catalyzed the depolymerization of chlorolignin in the presence of Mn2+ and H2O2. It can be concluded from these results that manganese peroxidase plays the major role in the initial breakdown and decolorization of high molecular weight chlorolignin in bleach plant effluents by P. chrysosporium in vivo.     

Decolorization of azo dyes by marine Shewanella strains under saline conditions

Azo dye decolorization was studied with Shewanella strains under saline conditions. Growing cells of Shewanella algae and Shewanella marisflavi isolated from marine environments demonstrated better azo dye decolorization capacities than the other three strains from non-saline sources. Cell suspensions of S. algae and S. marisflavi could decolorize single or mixed azo dyes with different structures. Decolorization kinetics were described with Michaelis–Menton equation, which indicated better decolorization performance of S. algae over S. marisflavi. Lactate and formate were identified as efficient electron donors for amaranth decolorization by the two strains. S. algae and S. marisflavi could decolorize amaranth at up to 100 g?L^?1 NaCl or Na₂SO₄. However, extremely low concentration of NaNO₃ exerted strong inhibition on decolorization. Both strains could remove the color and COD of textile effluent during sequential anaerobic–aerobic incubation. Lower concentrations of NaCl (20–30 g?L^?1) stimulated the activities of azoreductase, laccase, and NADH-DCIP reductase. The decolorization intermediates were identified by high-performance liquid chromatography and Fourier transform infrared spectroscopy. Decolorization metabolites of amaranth were less toxic than original dye. These findings improved our knowledge of azo-dye-decolorizing Shewanella species and provided efficient candidates for the treatment of dye-polluted saline wastewaters.     

Enhanced bio-decolorization of azo dyes by quinone-functionalized ceramsites under saline conditions

Anthraquinone-2-sulfonate was immobilized on ceramsites (AQS-ceramsites) using a novel adsorption/covalence coupling method and their effects on the anaerobic bio-decolorization rates of azo dyes by salt-tolerant AQS-reducing (STAR) community were investigated. The results showed that AQS-ceramsites mediated specific bio-decolorization rates of four azo dyes Acid Yellow 36, Reactive Red 2, Acid Red 27 and Acid Orange 7 increase 2.3–6.4 fold than those lacking ceramsites in the presence of 50 g/L NaCl. Moreover, repeated experiments with AQS-ceramsites showed that the decolorization efficiencies of azo dyes could remain over 98% of their original value. These results indicated that AQS-ceramsites functioning as redox mediators exhibited good catalytic activity and stability under saline conditions. The dynamics of the STAR community structure revealed by PCR-DGGE also showed that the presence of AQS-ceramsites made STAR bacteria keeping predominant in the catalytic system. Therefore, it can be concluded that this novel solid redox mediator is potentially useful for the treatment of saline dye wastewater.     

Microbial decolorization of reactive azo dyes under aerobic conditions

Summary Kodam et al. reported a 100% decolorization of the sulfonated azo dyes Reactive Red 2, Reactive Red 141, Reactive Orange 4, Reactive Orange 7 and Reactive Violet 5 by an unidentified bacterium, KMK 48. High effectiveness was attained within 36 h of incubation at room temperature and neutral pH. Optimum decolorization took place strictly under aerobic conditions, which is contrary to other well-documented reports. Thus, this microorganism seems to be potentially effective for bioremediation of textile-dyeing industry effluents.     

Rapid decolorization of azo dyes by crude manganese peroxidase from Schizophyllum sp. F17 in solid-state fermentation

The production of ligninolytic enzymes by the fungus Schizophyllum sp. F17 using a cost-effective medium comprised of agro-industrial residues in solid-state fermentation (SSF) was optimized. The maximum activities of the enzymes manganese peroxidase (MnP), laccase (Lac), and lignin peroxidases (LiP) were 1,200, 586, and 109 U/L, respectively, on day 5 of SSF. In vitro decolorization of three structurally different azo dyes by the extracellular enzymes was monitored to determine its decolorization capability. The results indicated that crude MnP, but not LiP and Lac, played a crucial role in the decolorization of azo dyes. After optimization of the dye decolorization system with crude MnP, the decolorization rates of Orange IV and Orange G, at an initial dye concentration of 50 mg/L, were enhanced to 76 and 57%, respectively, after 20 min of reaction at pH 4 and 35°C. However, only 8% decolorization of Congo red was observed. This enzymatic reaction system revealed a rapid decolorization of azo dyes with a low MnP activity of 24 U/L. Thus, this study could be the basis for the production and application of MnP on a larger scale using a low-cost substrate.     

Decolorization of reactive azo dyes by Cunninghamella elegans UCP 542 under co-metabolic conditions

The inappropriate disposal of dyes in wastewater constitutes an environmental problem and can cause damage to the ecosystem. Alternative treatments have been reported that fungi are particularly effective in the decolorization of textile effluents. The decolorization of dyes with different molecular structures by Cunninghamella elegans was evaluated under several media conditions. The decolorization procedures consisted of adding 72 h of mycelium into the culture medium containing either orange or reactive black or reactive red or a mixture of these dyes in the presence or absence of sucrose and/or peptone. The decolorization profile was highly dependent upon the incubation time, the molecular structure of the dye and presence or absence of co-substrates. The presence of sucrose or both sucrose and peptone significantly increased the decolorization of the solutions, however, the presence of only the nitrogen source suppressed it. The ultraviolet spectra of the solutions before and after decolorization suggested the occurrence of biodegradation in addition to the biosorption of the dyes. All tested dyes, except for the reactive black, caused inhibition of respiration of Escherichia coli, which suggested that toxic metabolites were produced.     

Bacterial decolorization and degradation of azo dyes

Azo compounds constitute the largest and the most diverse group of synthetic dyes and are widely used in a number of industries such as textile, food, cosmetics and paper printing. They are generally recalcitrant to biodegradation due to their xenobiotic nature. However microorganisms, being highly versatile, have developed enzyme systems for the decolorization and mineralization of azo dyes under certain environmental conditions. Several genera of Basidomycetes have been shown to mineralize azo dyes. Reductive cleavage of azo bond, leading to the formation of aromatic amines, is the initial reaction during the bacterial metabolism of azo dyes. Anaerobic/anoxic azo dye decolorization by several mixed and pure bacterial cultures have been reported. Under these conditions, this reaction is non-specific with respect to organisms as well as dyes. Various mechanisms, which include enzymatic as well as low molecular weight redox mediators, have been proposed for this non-specific reductive cleavage. Only few aerobic bacterial strains that can utilize azo dyes as growth substrates have been isolated. These organisms generally have a narrow substrate range. Degradation of aromatic amines depends on their chemical structure and the conditions. It is now known that simple aromatic amines can be mineralized under methanogenic conditions. Sulfonated aromatic amines, on the other hand, are resistant and require specialized aerobic microbial consortia for their mineralization. This review is focused on the bacterial decolorization of azo dyes and mineralization of aromatic amines, as well as the application of these processes for the treatment of azo-dye-containing wastewaters.     

Rapid decolourization of azo dyes by a new isolated higher manganese peroxidase producer: Phanerochaete sp. HSD

In the present paper, a strain of higher MnP producer, Phanerochaete sp. HSD, was screened and the important medium components influencing MnP production were optimized using fractional factorial design and central composite experimental design; statistical analysis suggested diammonium tartrate and Mn²⁺ were the important factors and under the optimum conditions, MnP activity reached 2613 ± 22 U/l, accorded with the predicted value from response surface analysis. The feasibility of using this fungus to decolourize azo dyes was examined too. Results indicated that crude enzyme solution of it could decolourize three azo dyes efficiently and speedily: for 120 and 350 mg/l of Congo red, 95% decolourization rate was observed at the 5th and 8th hour; for 200, 350 and 600 mg/l methyl orange, 95% decolourization rate was obtained at the 5th, 6th and 9th hour; furthermore, the decolourization rates of 150 and 300 mg/l of Eriochrome black T were up to 97.1% and 91.4% at the 7th and 13th hour, respectively. In addition, MnP played a crucial role in the decolourization process.     

Toxicity assessment and microbial degradation of azo dyes

Toxic effluents containing azo dyes are discharged from various industries and they adversely affect water resources, soil fertility, aquatic organisms and ecosystem integrity. They pose toxicity (lethal effect, genotoxicity, mutagenicity and carcinogenicity) to aquatic organisms (fish, algae, bacteria, etc.) as well as animals. They are not readily degradable under natural conditions and are typically not removed from waste water by conventional waste water treatment systems. Benzidine based dyes have long been recognized as a human urinary bladder carcinogen and tumorigenic in a variety of laboratory animals. Several microorganisms have been found to decolourize, transform and even to completely mineralize azo dyes. A mixed culture of two Pseudomonas strains efficiently degraded mixture of 3-chlorobenzoate (3-CBA) and phenol/cresols. Azoreductases of different microorganisms are useful for the development of biodegradation systems as they catalyze reductive cleavage of azo groups (-N=N-) under mild conditions. In this review, toxic impacts of dyeing factory effluents on plants, fishes, and environment, and plausible bioremediation strategies for removal of azo dyes have been discussed.     

The microbial degradation of azo dyes: minireview

The removal of dyes in wastewater treatment plants still involves physical or chemical processes. Yet numerous studies currently exist on degradation based on the use of microbes—which is a well-studied field. However progress in the use of biological methods to deal with this environmentally noxious waste is currently lacking. This review focuses on the largest dye class, that is azo dyes and their biodegradation. We summarize the bacteria identified thus far which have been implicated in dye decolorization and discuss the enzymes involved and mechanisms by which these colorants are broken down.     

Accelerated decolorization of reactive azo dyes under saline conditions by bacteria isolated from Arabian seawater sediment

Presence of huge amount of salts in the wastewater of textile dyeing industry is one of the major limiting factors in the development of an effective biotreatment system for the removal of azo dyes from textile effluents. Bacterial spp. capable of thriving under high salt conditions could be employed for the treatment of saline dye-contaminated textile wastewaters. The present study was aimed at isolating the most efficient bacterial strains capable of decolorizing azo dyes under high saline conditions. Fifty-eight bacterial strains were isolated from seawater, seawater sediment, and saline soil, using mineral salt medium enriched with 100?mg?l^?1 Reactive Black-5 azo dye and 50?g NaCl l^?1 salt concentration. Bacterial strains KS23 (Psychrobacter alimentarius) and KS26 (Staphylococcus equorum) isolated from seawater sediment were able to decolorize three reactive dyes including Reactive Black 5, Reactive Golden Ovifix, and Reactive Blue BRS very efficiently in liquid medium over a wide range of salt concentration (0–100?g NaCl l^?1). Time required for complete decolorization of 100?mg dye l^?1 varied with the type of dye and salt concentration. In general, there was an inverse linear relationship between the velocity of the decolorization reaction (V) and salt concentration. This study suggested that bacteria isolated from saline conditions such as seawater sediment could be used in designing a bioreactor for the treatment of textile effluent containing high concentration of salts.     

氧气对混合菌群脱色降解偶氮染料效果的影响

【背景】偶氮染料及其中间产物具有一定的环境毒性,利用混合菌群降解偶氮染料是一种环境友好型方法,但降解过程中氧气的存在起到至关重要的作用,可以促进或抑制偶氮染料的微生物降解作用。【目的】探讨氧气对偶氮染料微生物脱色液的影响,分析氧气对混合菌群脱色降解偶氮染料效果的影响。【方法】利用混合菌群DDMY1在3种培养条件(好氧、厌氧、兼氧)下,对7种偶氮染料进行脱色降解,探讨偶氮染料脱色液对氧气的响应情况,利用紫外可见分光光度法(ultraviolet visible spectrophotometry,UV-vis)和傅里叶变换红外光谱法(Fourier transform infrared spectroscopy,FTIR)对脱色产物进行分析。【结果】在兼氧和厌氧条件下反应48 h后的染料脱色液,与氧气充分接触后,部分偶氮染料微生物脱色液发生较为明显的复色现象,如活性黑5、直接黑38;UV-vis分析结果表明,这种复色现象是由于脱色液与氧气接触之后产生新物质所致;FTIR分析结果表明,混合菌群对发生复色反应的偶氮染料仍然具有一定脱色降解效果,但是脱色尚不够完全。【结论】兼氧和厌氧条件下,氧气对部分偶氮染料微生物脱色液具有较为明显的影响,从而影响混合菌群对偶氮染料的整体脱色效果,这可为今后研究偶氮染料彻底生物降解提供理论基础。     

Increasing manganese peroxidase production and biodecolorization of triphenylmethane dyes by novel fungal consortium

A fungal consortium-SR consisting of Trametes sp. SQ01 and Chaetomium sp. R01 was developed for decolorizing three kinds of triphenylmethane dyes, which were decolorized by individual fungi with low efficiencies. The fungal consortium-SR produced 1.3 U ml(-1) of manganese peroxidase, 5.5 times higher than that produced by the monoculture of Trametes sp. SQ01, and decolorized Crystal Violet, Coomassie Brilliant Blue G250 (CBB G250) and Cresol Red. The fungal consortium-SR had a decolorization rate of 63-96%, much higher than that of the monoculture of strain SQ01 (38-72%). In consortium-SR, the higher efficiencies of decolorization of Crystal Violet and CBB G250 were obtained when they added to the culture after 4d of mixed cultivation rather than at the beginning of cultivation. Cresol Red was the exception. It is suggested that the consortium-SR has great potential for decolorizing triphenylmethane dyes.     

Oxidative degradation of Remazol Turquoise Blue G 133 by soybean peroxidase

Reactive dyes are widely employed in textile industries and their removal from wastewaters is a relevant environmental problem. In addition to chemical and physical methods, several bioremediation approaches, involving intact micro-organisms or isolated enzymes, have been proposed to decolorize dye solutions. In this paper, we report the complete and fast decolourization of a Cu(II)-phthalocyanine based reactive dye (Remazol Turquoise Blue G 133) by means of the soybean peroxidase/H₂O₂ system. The oxidative degradation of the dye in aqueous solution at 25 °C was studied as function of pH, revealing a quantitative decolourization yield at acidic pH values with a maximum of activity at pH 3.3. The reaction products were identified and characterized by HPLC-diode array detector (DAD)-mass spectrometry (MS), ionic chromatography and EPR techniques. This analysis showed that the enzyme catalyses the breaking of the phthalocyanine ring producing sulfophthalimide as the main degradation product, and the release of stoichiometric amount of ammonium and Cu(II) ions.     

Horseradish peroxidase catalyzed degradation of industrially important dyes.

Horseradish peroxidase (HRP) is known to degrade certain recalcitrant organic compounds such as phenol and substituted phenols. Here, for the first time we have shown HRP to be effective in degrading and precipitating industrially important azo dyes. For Remazol blue, the enzyme activity was found to be far better at pH 2.5 than at neutral pH. In addition, Remazol blue acts as a strong competitive inhibitor of HRP at neutral pH. Horseradish peroxidase shows broad substrate specificity toward a variety of azo dyes. Kinetic constants (K(m)(app) and V(max)(app)) for two different dyes have been determined. In addition to providing a systematic analysis of the potential of HRP in degradation of dyes, this study opens up a new area on exploration of commercial dyes as inhibitors of enzymes. 2001 John Wiley & Sons, Inc.     

The new incorporation bio-treatment technology of bromoamine acid and azo dyes wastewaters under high-salt conditions

The accelerating effect of quinones has been studied in the bio-decolorization processes, but there are no literatures about the incorporation bio-treatment technology of the bromoamine acid (BA) wastewater and azo dyes wastewaters under high-salt conditions (NaCl, 15%, w/w). Here we described the BA wastewater as a redox mediator in the bio-decolorization of azo dye wastewaters. Decolorization of azo dyes was carried out experimentally using the salt-tolerant bacteria under the BA wastewater and high-salt conditions. The BA wastewater used as a redox mediator was able to increase the decolorization rate of wastewater containing azo dyes. The effects of various operating conditions such as dissolved oxygen, temperature, and pH on microbial decolorization were investigated experimentally. At the same time, BA was tested to assess the effects on the change of the Oxidation–Reduction Potential (ORP) values during the decolorization processes. The experiments explored a great improvement of the redox mediator application and the new bio-treatment concept.     

Basic and applied aspects in the microbial degradation of azo dyes

Azo dyes are the most important group of synthetic colorants. They are generally considered as xenobiotic compounds that are very recalcitrant against biodegradative processes. Nevertheless, during the last few years it has been demonstrated that several microorganisms are able, under certain environmental conditions, to transform azo dyes to non-colored products or even to completely mineralize them. Thus, various lignolytic fungi were shown to decolorize azo dyes using ligninases, manganese peroxidases or laccases. For some model dyes, the degradative pathways have been investigated and a true mineralization to carbon dioxide has been shown. The bacterial metabolism of azo dyes is initiated in most cases by a reductive cleavage of the azo bond, which results in the formation of (usually colorless) amines. These reductive processes have been described for some aerobic bacteria, which can grow with (rather simple) azo compounds. These specifically adapted microorganisms synthesize true azoreductases, which reductively cleave the azo group in the presence of molecular oxygen. Much more common is the reductive cleavage of azo dyes under anaerobic conditions. These reactions usually occur with rather low specific activities but are extremely unspecific with regard to the organisms involved and the dyes converted. In these unspecific anaerobic processes, low-molecular weight redox mediators (e.g. flavins or quinones) which are enzymatically reduced by the cells (or chemically by bulk reductants in the environment) are very often involved. These reduced mediator compounds reduce the azo group in a purely chemical reaction. The (sulfonated) amines that are formed in the course of these reactions may be degraded aerobically. Therefore, several (laboratory-scale) continuous anaerobic/aerobic processes for the treatment of wastewaters containing azo dyes have recently been described.     

Degradation of azo dyes by Trametes villosa laccase over long periods of oxidative conditions

Trametes villosa laccase was used for direct azo dye degradation, and the reaction products that accumulated after 72 h of incubation were analyzed. Liquid chromatography-mass spectrometry (LC-MS) analysis showed the formation of phenolic compounds during the dye oxidation process as well as a large amount of polymerized products that retain azo group integrity. The amino-phenol reactions were also investigated by 13C-nuclear magnetic resonance and LC-MS analysis, and the polymerization character of laccase was shown. This study highlights the fact that laccases polymerize the reaction products obtained during long-term batch decolorization processes with azo dyes. These polymerized products provide unacceptable color levels in effluents, limiting the application of laccases as bioremediation agents.