Microbial degradation of dyes: An overview

Biodegradation of synthetic dyes using different bacteria is becoming an accepted approach for treating Azo dye wastewater to mitigate many environmental problems. Azo dye has a negative impact on the environment by increasing biochemical oxygen demand (B.O.D.) and chemical oxygen demand (C.O.D.). The Biodegradation of azo dyes by different bacteria was evaluated. Biodegradation of synthetic dyes not only results in the decolorization of the dyes but also in the disintegration of the dye molecules into smaller and simpler parts. Decolorization of the dye arises when the chromophoric center of the dye is slashed. Various microorganisms, including fungi, bacteria, yeasts, and algae, have been used to decolorize and Degradation of synthetic dyes. Bacterial decolorization is usually faster than fungal decolourization. It is well known that bacteria degrade azo dyes reductively under anaerobic circumstances to colorless aromatic amines, which are carcinogenic compounds. These colorless aromatic amines must also be degraded because they may be toxic, mutagenic, and carcinogenic to humans and animals Bacteria are capable of removing dyes by adsorption and absorption. Biosorption rates are directly matched with the composition of heteropolysaccharides and the cell wall lipids. Dead cells are more useful in Biosorption than living cells because they do not need nutrients and can be stockpiled for a long time. The azoreductases are considered to be the most potent group of enzymes active in the Biodegradation of synthetic azo dyes. They accomplish the reductive cleavage of synthetic azo dyes bonds. Laccases enzymes become more interesting and have more focus recently due to their ability in generating much lower toxic aromatic amines. Laccases do not need other cofactors. Many factors affecting the process are temperature, pH, salinity, dye concentration, and Bioremediation in aerobic and anaerobic environments. Keywords: Biodegradation, azo dyes, biochemical oxygen demand (B.O.D.), chemical oxygen demand (C.O.D.), bacterial enzymes and Bacterial Laccases enzymes.

Azo dyes are extremely toxic and pose significant environmental and health risks. Consequently, mineralization and conversion to simple compounds are required to avoid their hazardous effects. A variety of enzymes from the bacterial system are thought to be involved in the degradation and metabolism of azo dyes. Bioremediation, a cost effective and eco-friendly biotechnology, involving bacteria is powered by bacterial enzymes. As mentioned, several enzymes from the bacterial system serve as molecular weapons in the degradation of these dyes. Among these enzymes, azoreductase, oxidoreductase, and laccase are of great interest for the degradation and decolorization of azo dyes. Combination of the oxidative and reductive enzymes is used for the removal of azo dyes from water. The aim of this review article is to provide information on the importance of bacterial enzymes. The review also discusses the genetically modified microorganisms in the biodegradation of azo dyes in polluted water.

Microbial fuel cells for azo dye degradation: A perspective review

Exploring docking and aerobic-microaerophilic biodegradation of textile azo dye by bacterial systems

This research article deals with biodegradation of azo dyes by a newly isolated bacterial strain from activated sludge. Azo dyes are recalcitrant to the conventional modes of treatment due to their complex structure. This article reports decolorization of azo dye by, Bacillus subtillis ETL-1979. Response surface methodology was used to optimize the important physical parameters screened by Placket–Burman design. Five physical parameters such as pH, temperature (°C), dye concentration (mg/L), inoculum size % (v/v) and time (h) were tested by using Placket–Burman design criterion and all five parameters showed significant effect (P < 0.05) on decolorization of azo dye orange using Bacillus subtillis ETL-1979. The values of parameters was optimized by applying central composite design (CCD) and the most suitable values for orange dye decolorization by Bacillus subtillis ETL-1979, as predicted by the statistical tool, was pH 6.9; temperature 37.0°C; dye concentration 517 mg/L, inoculum size, v/v, (%) 5.5 % and time 23.7 h. At these optimum levels of parameters, bacterial decolorization of orange dye by 94.48% was obtained under static conditions. Biodegradation and decolorization of azo dye, orange, was confirmed using UV-VIS spectrophotometry, thin layer chromatography (TLC) and fourier transform infrared spectroscopy (FTIR) and electron spray ionization mass spectrometry (ESI-MS) analysis.

The varieties of synthetic azo dyes are widely used in textile industries to generate range of color tones in the textile and paper industries. Such textile dyes are toxic for the animals, birds and human along with environment. It is needful to remove those dyes from the effluent. The degradation of such dyes is accompanied by the involvement of dye degradating microorganisms. The purpose of this research is to isolate, identify, and screen bacterial species capable of decolorizing reactive pink, congo red, and malachite green. Soil and water samples were collected from the dye contaminated area of Jetpur, Gujarat, India. Dye degradating bacteria were isolated and selected through primary and secondary screening. The effect of yeast extract amount on the dye degradation properties of bacteria was examined using a visible spectrophotometer.&#x0D; After secondary screening MD2, MD8, MD20, MD31, MD33 and MD34 were selected for further analysis. All isolated are able to degrade reactive pink, congo red, and malachite green after 120hrs of incubation at a 4mgl-1 concentration of yeast extract. Dye degradation remains constant for 4 mgl-1 and 2 mgl-1 but gets reduced in 1 mgl-1 of yeast extract concentration. Wheat germination rate in control was 65% compared to 96%, 88%, and 85% in MD2, MD8, MD20 respectively. Sorghum germination rate in control was 62% while in isolates no MD31, MD33, MD34 were 96%, 87%, 83% and 65%.

The high demand for dyes in the paper, cosmetic, clothing, leather, and food industries drives up the use of dyes as a result of industrialization. As a result, wastewater production from dye manufacturing activities will rise. The presence of dyes and their structural compounds in wastewater from industrial sources place humans, animals and plants lives at risk. Synthetic dyes are more challenging to decolorize because they are more resistant to chemical and physical remediation than natural dyes. Microbial degradation has been investigated and checked mainly to speed up dye degradation. This paper discusses types of textile dyes and its biodegradation from a scientific and technological standpoint. It also compiles data on the factors that influence dye(s) biodegradation, the role of microbial species in the dye(s) degradation process, and future research directions in this field.

Textile industry consumes a large proportion of available water and releases huge amounts of toxic azo dye effluents, leading to an inevitable situation of acute environmental pollution that has been a significant threat to mankind. Decolorization or detoxification of harmful azo dyes has become a global priority to overcome the disastrous consequences and salvage the ecosystem. Biodegradation of textile azo dyes by endophytes stands to be a lucrative and viable alternative over conventional physico-chemical methods, owing to their eco-friendliness, cost-competitive and non-toxic nature. Especially, plant endophytic microbes exhibit promising biodegradation potential which has wired up the effective removal of textile azo dyes, attributing to their ability to produce dye degrading enzymes, laccases, peroxidases and azoreductases. Although both bacterial and fungal endophytes have been tried for azo dye degradation, endophytic fungi find broader application over bacteria. Despite of the advancements made in microbe-mediated biodegradation, there is still a need to fill the gap in lab to in situ translation of biodegradation research. This review concisely accentuates the xenobiotics of textile azo dyes and microbial mechanisms of biodegradation of textile azo dyes, positing plant endophytic community, especially bacterial and fungal endophytes as the potential dye degraders, highlighting currently reported dye degrading endophytic species.

As dye demand continues to rapidly increase in the food, pharmaceutical, cosmetic, paper, textile, and leather industries, an industrialization increase is occurring. Meanwhile, the degradation and removal of azo dyes have raised broad concern regarding the hazards posed by these dyes to the ecological environment and human health. Physicochemical treatments have been applied but are hindered by high energy and economic costs, high sludge production, and chemicals handling. Comparatively, the bioremediation technique is an eco-friendly, removal-efficient, and cost-competitive method to resolve the problem. This paper provides scientific and technical information about recent advances in the biodegradation of azo dyes. It expands the biodegradation efficiency, characteristics, and mechanisms of various microorganisms containing bacteria, fungi, microalgae, and microbial consortia, which have been reported to biodegrade azo dyes. In addition, information about physicochemical factors affecting dye biodegradation has been compiled. Furthermore, this paper also sketches the recent development and characteristics of advanced bioreactors.

Decolorization and biodegradation of azo dye, reactive blue 59 by aerobic granules

Peroxidases are well known for their ability to biodegrade some recalcitrant organic pollutants like phenol and their derivatives resulting in a reduction in their toxicity. The present study was designed to extract, characterize, and evaluate the potential of partially purified peroxidase from discarded and decaying waste cabbage leaves in the biodegradation of phenol and some common synthetic azo dyes. This was done by first partially purifying the crude extract of waste cabbage peroxidase (WCP) using ammonium sulfate precipitation, dialysis, and gel filtration chromatography. Thereafter, the experimental determination of protein concentration, peroxidase activity, and biodegradation of phenol and azo dyes was done spectrophotometrically. The results showed a purification fold of 87.65 with a 34.92% yield. The partially purified peroxidase had its optimum activity at temperature 30 °C, pH 5.5 while showing broad substrate preference with ABTS been the substrate. The stability studies also showed that WCP was stable over a wide range of pH (4.0–7.0) and 41% of its original activity was retained at 80 °C indicating that it is a thermostable enzyme. The kinetic data of WCP showed Km values of 1.24, 17.89, and 19.24 mM and Vmax values of 1111.11, 909.09, and 588.24 mM /minutes for ABTS, guaiacol, and o-dianisidine respectively. Three metal ions, Hg2+, Cu2+, Ni2+, organic solvent (acetone), EDTA, and urea inhibited peroxidase activity; whereas Mn2+ and Zn2+ showed slight activation. The partially purified WCP exhibited high efficiency for the biodegradation of synthetic azo dyes and phenol at the lab-scale. After 48 h incubation, the waste cabbage peroxidase efficiently catalyzed the decolorization of tested azo dyes at varying degrees; azo blue 5, azo purple, azo yellow 6, and citrus red 2, with a percentage decolorization of 85.1, 69.1, 46.2 and 42.9%, respectively. The waste cabbage peroxidase also shows up to 91.1% efficiency for degradation of phenol in aqueous solution after 60 min. Findings from this study provide promising evidence on the possibility of utilizing/recycling a readily abundant waste cabbage to useful bioproducts like peroxidase enzyme with the ability to biodegrade azo dyes and phenol at a small scale in the laboratory. Moreover, the findings from this study increase the prospect of waste cabbage peroxidase for the treatment of industrial effluents containing dyes and phenolic pollutants. The approach of transforming waste from one source into a useful biocatalyst that can potentially be exploited to treat waste pollutants from a different source offers a chain of green technology.

Azo dyes constitute a major class of environmental pollutants accounting for 60 to 70% of all dyes and pigments used. These compounds are characterized by aromatic moieties linked together with azo groups (-N=N-). The release of azo dyes into the environment is a concern due to coloration of natural waters and due to the toxicity, mutagenicity and carcinogenicity of the dyes and their biotransformation products. Therefore, considerable attention has been given to evaluating the fate of azo dyes during wastewater treatment and in the natural environment. Azo dyes require an anaerobic and an aerobic phase for their complete biodegradation. Therefore, the aim of this thesis was to evaluate the mineralization of azo dyes under integrated and sequential anaerobic/aerobic conditions. These conditions were applied on three azo dyes, Mordant Orange 1 (MO1), 4-phenylazophenol (4-PAP) and Mordant Yellow 10 (MY10). Since many azo dyes are substituted with a sulfonic acid group, special attention was paid to the sulfonated azo dyes and their biodegradation products, the sulfonated aromatic amines.The first step in the biodegradation of azo dyes is the azo dye reduction resulting in the formation of the aromatic amines. The influence of oxygen on the azo dye reduction of MO1 was tested in order to evaluate the integrated anaerobic/aerobic conditions. The co-substrate ethanol was successfully applied as electron donor for azo dye reduction and also created anaerobic microniches to facilitate anaerobic azo dye reduction in the presence of oxygen. Increasing oxygen concentrations showed decreasing azo dye-reduction rates with ethanol as co-substrate. These rates were higher when applying acetate as co-substrate. Moreover, Nedalco granular sludge could withstand better with the applied integrated anaerobic/aerobic conditions than Shell granular sludge.Since none of the expected aromatic amines from MO1 was degraded, further research was conducted to evaluate the aerobic biodegradation of aromatic amines. MY10 and 4-PAP were tested under integrated anaerobic/aerobic conditions. All aromatic amines were removed if sufficient oxygen was present. Oxygen was primarily used to oxidize co-substrate and if sufficient oxygen was available the formed aromatic amines were further degraded. The removal of 4-aminobenzenesulfonic acid (4-ABS) was only possible after bioaugmentation of a 4-ABS-degrading enrichment culture. The results from the biodegradation study of 4-AP indicated that 4-aminophenol was removed due to autoxidation. Degradation of azo dyes is possible under integrated anaerobic/aerobic conditions if co-substrate and oxygen are in balance.In the sequential anaerobic/aerobic bioreactor, the azo dye MY10 was successfully mineralized. Its constituent aromatic amines, 5-aminosalicylic acid (5-ASA) and 4-ABS, were both recovered in the anaerobic stage and degraded in the aerobic stage. Biodegradation of the 4-ABS was only possible after bioaugmentation with a 4-ABS-degrading enrichment culture. High recovery of sulfate indicated mineralization of 4-ABS. After long-term exposure to 5-ASA, the anaerobic granular sludge showed the ability to degrade this compound.It was observed that the degradation of the sulfonated aromatic amine 4-ABS only proceeded after bioaugmentation of a specialized enrichment culture. Therefore, the ultimate biodegradability of the sulfonated aromatic amines is questionable. To investigate this matter, the fate of sulfonated aromatic amines with natural mixed cultures was evaluated in aerobic and anaerobic batch assays and bioreactor experiments. None of the ten tested compounds was degraded under anaerobic conditions and only 2-ABS and 4-ABS were aerobically mineralized. This was observed in batch as well as in bioreactor experiments. Degradation of the 2-ABS and 4-ABS was found with inoculum sources that were historically polluted with sulfonated aromatic compounds. At concentrations up to 1.0 g l -1 , none of the tested sulfonated aromatic amines showed any toxicity towards anaerobic and aerobic biomass.The results of this research demonstrated that azo dyes are mineralized under integrated and sequential anaerobic/aerobic conditions. Due the difficulties with balancing the supply of co-substrate and oxygen in integrated anaerobic/aerobic systems, the sequential anaerobic/aerobic conditions are recommended for the mineralization of azo dyes. However, during the degradation of sulfonated azo dyes, many different sulfonated aromatic amines will be formed and these compounds are not likely to be degraded aerobically. Therefore, special attention should be paid on the removal of these compounds

The effluent coming out from the textile, paper and food industries containing dye is strongly coloured and reveals very harmful effects on living beings. In order to reduce wastewater pollution, the degradation of dye into non-toxic form is desirable. The photo catalytic degradation of methylene blue is reported in the present study. The irradiation of aqueous solution of methylene blue dye in presence of photo catalyst and UV light was carried out in the batch photo reactor. Titanium dioxide TiO2 /CFAC was used as photo catalyst for the study. The rate of decolorisation was estimated from residual concentration spectrophotometrically. Effects of various operating parameters such as the irradiation time, initial pH and the amounts of catalyst on the degradation of the dyes were investigated. Results show that the degradation kinetics fitted well to pseudo second order rate law. The maximum decolorizing efficiency occurred in less than 50min with 50mg of TiO2 /CFAC catalyst dose.

Mycoremediation, a form of bioremediation facilitated by fungi, has been employed for the biodegradation of azo dyes, including congo red, acid red, and basic blue. In this study, four fungal isolates, namely Aspergillus niger, Aspergillus piperis, Penicillium oxalicum, and Penicillium chrysogenum, obtained from dye effluent were used. Four biodegradation methods were selected, including solid media dye accumulation, liquid media methods under stationary and shaking conditions at 28°C, and biosorption using dead biomass. For the first time, we report the involvement of the isolated fungal species A. piperis, derived from textile effluent, in the biodegradation of textile dyes. Comparative spectrophotometric analysis revealed more than 90% of dye decolourization in the fungus-inoculated medium supplemented with dyes, compared to control. Higher percentage of decolorization were obtained under shaking conditions compared to the stationary method. Dead fungal biomass exhibited effective dye absorption, resulting in a noticeable color change during dye degradation. The seed germination bioassay revealed that treated dye solutions promoted germination; however, untreated inhibited it. Further, untreated dye effluent hindered microbial growth. The excellent performance of A. piperis in the biodegradation of textile azo dyes with diverse chemical structures highlights and reinforces the bioremediation potential of these fungi for environmental decontamination.

Biodegradation and decolorization of trypan blue azo dye by marine bacteria Vibrio sp. JM-17