Role of brown-rot fungi in the bioremoval of azo dyes under different conditions

Decolorization of various dyes by microorganisms and green-synthesized nanoparticles: current and future perspective

Various types of colored pigments have been recovered naturally from biological sources including shells, flowers, insects, and so on in the past. At present, such natural colored substances (dyes) are replaced by manmade dyes. On the other hand, due to their continuous usage in various purpose, these artificial dyes or colored substances persist in the environmental surroundings. For example, industrial wastewater contains diverse pollutant substances including dyes. Several of these (artificial dyes) were found to be toxic to living organisms. In recent times, microbial-based removal of dye(s) has gained more attention. These methods were relatively inexpensive for eliminating such contaminants in the environmental system. Hence, various researchers were isolated microbes from environmental samples having the capability of decolorizing synthetic dyes from industrial wastewater. Furthermore, the microorganisms which are genetically engineered found higher degradative/decolorize capacity to target compounds in the natural environs. Very few reviews are available on specific dye treatment either by chemical treatments or by bacteria and/or fungal treatments. Here, we have enlightened literature reports on the removal of different dyes in microbes like bacteria (including anaerobic and aerobic), fungi, GEM, and microbial enzymes and also green-synthesized nanoparticles. This up-to-date literature survey will help environmental managements to co-up such contaminates in nature and will help in the decolorization of dyes.

Biodegradation and reduction of toxicity of Azo Trypan Blue dye by Amazonian strains of gasteroid fungi (Basidiomycota)

Amazonian strains of Cyathus spp. and Geastrum spp. were studied for the ability to discolor the trypan blue azo dye and reduce its toxicity. Discoloration of trypan blue dye (0.05%) was evaluated in solid and aqueous medium over different periods. The reduction of dye toxicity after treatment was assessed by seed germination and the development of lettuce seedlings (Lactuca sativa L.) and toxicity test in Artemia salina (L.) larvae. All evaluated strains showed the potential to reduce the color intensity of trypan blue dye. Cyathus strains reached 96% discoloration, and C. albinus and C. limbatus also reduced dye toxicity. Geastrum strains showed a high efficiency degree in color reduction, reaching 98% discoloration, however, the by-products generated during the process presented toxicity and require further investigation. For the first time, Amazonian strains of gasteroid fungi degrading trypan blue are reported, some even reducing its toxicity. Thus, making them promising sources of enzymes of interest to bioremediation scenarios involving synthetic dyes.

Azo dyes degradation by microorganisms - An efficient and sustainable approach

Synthetic aromatic compounds consisting of various functional groups are known as dyes. These colored compounds are often discharged in effluents, and they are very dangerous to aquatic life. Basically, the dye industry started by using natural plant and insect sources, and then suddenly turned into artificial manufacturing. Natural equilibrium of our environment gets changed by the reduction in photosynthetic activity due to the dyes. In China 900,000 tons of all kinds of dyes are usually produced, which are used in many industries like food, textile, food, paper and leather. Untreated wastewater contaminates aquatic bodies by causing eutrophication, change in water color, oxygen depletion which affect aquatic organisms to a great extent. Dye wastewater is now the key environmental pollution form. In recent eras an extensive study line has been developed to explore the dye decolorization and biodegradation under both aerobic as well as anaerobic conditions. In this review, the chemistry, toxicity and microbial biodegradation/decolorization are presented. Some recent studies along with the new techniques and methodologies of remediating the dye pollution are also discussed to provide the bases of their handling. Overall, efficient and high biodegradation potential make microbes an impending foundation for green chemistry to eradicate toxic dyes from industrial wastewater.

Recent advances in biodecolorization and biodegradation of environmental threatening textile finishing dyes

Organic nature of dyes and their commercially made products are widely utilized in many industries including paper, cosmetics, pharmaceuticals, photography, petroleum as well as in textile manufacturing. The textile industry being the top most consumer of a large variety of dyes during various unit processes operation generates substantial amount of wastewater; hence, nominated as "Major Polluter of Potable Water". The direct discharge of such effluents into environment poses serious threats to the functioning of biotic communities of natural ecosystems. The detection of these synthetic dyes is considered as relatively easy, however, it is extremely difficult to completely eliminate them from wastewater and freshwater ecosystems. Aromatic chemical structure seems to be the main reason behind low biodegradability of these dyes. Currently, various physiochemical and biological methods are employed for their remediation. Among them, microbial degradation has attracted greater attention due to its sustainability, high efficiency, cost effectiveness, and eco-friendly nature. The current review presents recent advances in biodegradation of industrial dyes towards a sustainable and tangible technological innovative solutions as an alternative to existing conventional physicochemical treatment processes.

Decolorization and detoxification of different azo dyes by Phanerochaete chrysosporium ME-446 under submerged fermentation

Azo dyes are widely used in the textile industry due to their resistance to light, moisture, and oxidants. They are also an important class of environmental contaminant because of the amount of dye that reaches natural water resources and because they can be toxic, mutagenic, and carcinogenic. Different technologies are used for the decolorization of wastewater containing dyes; among them, the biological processes are the most promising environmentally. The aim of this study was to evaluate the potential of Phanerochaete chrysosporium strain ME-446 to safely decolorize three azo dyes: Direct Yellow 27 (DY27), Reactive Black 5 (RB5), and Reactive Red 120 (RR120). Decolorization efficiency was determined by ultraviolet-visible spectrophotometry and the phytotoxicity of the solutions before and after the fungal treatment was analyzed using Lactuca sativa seeds. P. chrysosporium ME-446 was highly efficient in decolorizing DY27, RB5, and RR120 at 50 mg L-1, decreasing their colors by 82%, 89%, and 94% within 10 days. Removal of dyes was achieved through adsorption on the fungal mycelium as well as biodegradation, inferred by the changes in the dyes' spectral peaks. The intensive decolorization of DY27 and RB5 corresponded to a decrease in phytotoxicity. However, phytotoxicity increased during the removal of color for the dye RR120. The ecotoxicity tests showed that the absence of color does not necessarily translate to an absence of toxicity.

Biological Treatment of Real Textile Effluent Using Aspergillus flavus and Fusarium oxysporium and Their Consortium along with the Evaluation of Their Phytotoxicity

Twenty-one fungal strains were isolated from dye-contaminated soil; out of them, two fungal strains A2 and G2-1 showed the highest decolorization capacity for real textile effluent and were, hence, identified as Aspergillus flavus and Fusarium oxysporium based on morphological and molecular methods. The highest decolorization percentage of 78.12 ± 2.1% was attained in the biotreatment with fungal consortium followed by A. flavus and F. oxysporium separately with removal percentages of 54.68 ± 1.2% and 52.41 ± 1.0%, respectively. Additionally, ultraviolet-visible spectroscopy of the treated effluent showed that a maximum peak (λ_max) of 415 nm was reduced as compared with the control. The indicators of wastewater treatment efficacy, namely total dissolved solids, total suspended solids, conductivity, biological oxygen demand, and chemical oxygen demand with removal percentages of 78.2, 78.4, 58.2, 78.1, and 77.6%, respectively, demonstrated a considerable decrease in values due to fungal consortium treatment. The reduction in peak and mass area along with the appearance of new peaks in GC-MS confirms a successful biodegradation process. The toxicity of treated textile effluents on the seed germination of Vicia faba was decreased as compared with the control. The shoot length after irrigation with effluents treated by the fungal consortium was 15.12 ± 1.01 cm as compared with that treated by tap-water, which was 17.8 ± 0.7 cm. Finally, we recommended the decrease of excessive uses of synthetic dyes and utilized biological approaches for the treatment of real textile effluents to reuse in irrigation of uneaten plants especially with water scarcity worldwide.

Myco-decontamination of azo dyes: nano-augmentation technologies

Effluents of textile, paper, and related industries contain significant amounts of synthetic dyes which has serious environmental and health implications. Remediation of dyes through physical and chemical techniques has specific limitations. Augmented biological decontamination strategies 'microbial remediation' may involve ring-opening of dye molecules besides the reduction of constituent metal ions. Both bacterial and fungal genera are known to exhibit metabolic versatility which can be harnessed for effective bio-removal of the toxic dye contaminants. Ascomycetous/basidiomycetes fungi can effectively decontaminate azo dyes through laccase/peroxidase enzyme-mediated catalysis. The extent, efficacy, and range of fungal dye decontamination can be enhanced by the conjugated application of nanomaterials, including nanoparticles (NPs) and their composites. Fungal cell-enabled NP synthesis- 'myco-farmed NPs', is a low-cost strategy for scaled-up fabrication of a variety of metal, metal oxide, non-metal oxide NPs through oxidation/reduction of dissolved ions/molecules by extracellular biomolecules. Augmented and rapid decontamination of azo dyes at high concentrations can be achieved by the use of myco-farmed NPs, NPs adsorbed fungal biomass, and nano-immobilized fungi-derived bio-catalytical agents. This manuscript will explore the opportunities and benefits of mycoremediation and application of fungus-NP bionanoconjugate to remediate dye pollutants in wastewaters and land contaminated with the effluent of textile industries.

Bio-Removal of Methylene Blue from Aqueous Solution by Galactomyces geotrichum KL20A

The conventional treatments used to remove dyes produced as a result of different industrial activities are not completely effective. At times, some toxic by-products are generated, affecting aquatic ecosystems. In this article, an efficient use of microorganisms is presented as a biodegradation technique that is a safe environmental alternative for the benefit of aquatic life. A strain of the yeast Galactomyces geotrichum KL20A isolated from Kumis (a Colombian natural fermented milk) was used for Methylene Blue (MB) bioremoval. Two parameters of the bioremediation process were studied at three different levels: initial dye concentration and growth temperature. The maximum time of MB exposure to the yeast was 48 h. Finally, a pseudo-first-order model was used to simulate the kinetics of the process. The removal percentages of MB, by action of G. geotrichum KL20A were greater than 70% under the best operating conditions and in addition, the kinetic simulation of the experimental results indicated that the constant rate of the process was 2.2 × 10-2 h−1 with a half time for biotransformation of 31.2 h. The cytotoxicity test based on the hemolytic reaction indicated that by-products obtained after the bioremoval process reached a much lower percentage of hemolysis (22%) compared to the hemolytic activity of the negative control (100%). All of these results suggest that the strain has the capacity to remove significant amounts of MB from wastewater effluents.

Process parameters for decolorization and biodegradation of orange II (Acid Orange 7) in dye-simulated minimal salt medium and subsequent textile effluent treatment by Bacillus cereus (MTCC 9777) RMLAU1

In this study, Bacillus cereus isolate from tannery effluent was employed for orange II dye decolorization in simulated minimal salt broth and textile effluent. Most of the physicochemical parameters of textile effluent were above the permissible limits. The strain was highly tolerant to dye up to 500 mg l(-1). Increasing dye concentration exerted inhibitory effect on the bacterial growth and decolorization. The maximum decolorization of initial 100 mg dye l(-1) was achieved at optimum pH 8.0 and 33 °C under static culture conditions during 96-h incubation. Supplementation with optimized glucose (0.4%, w/v) and ammonium sulfate (0.1%, w/v) with 3.0% B. cereus inoculum further enhanced dye decolorization to highest 68.5% within 96-h incubation. A direct correlation was evident between bacterial growth and dye decolorization. Under above optimized conditions, 24.3% decolorization of unsterilized real textile effluent by native microflora was achieved. The effluent decolorization enhanced substantially to 37.1% with B. cereus augmentation and to 40.5% when supplemented with glucose and ammonium sulfate without augmentation. The maximum decolorization of 52.5% occurred when textile effluent was supplemented with optimized exogenous carbon and nitrogen sources along with B. cereus augmentation. Gas chromatography-mass spectrometry identified sulfanilic acid as orange II degradation product. Fourier transform infra red spectroscopy of metabolic products indicated the presence of amino and hydroxyl functional groups. This strain may be suitably employed for in situ decolorization of textile industrial effluent under broad environmental conditions.