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BACKGROUND: Synthetic dyes are one of the main pollutants in the textile industry and bioremediation is considered as an environmentally friendly method to degrade them. Soil microbial consortia (MCs) are reported having the potential of decolorizing most of textile dyes. This study aimed at evaluating dye-degrading ability of MCs developed from fungi and bacteria. METHODS AND RESULTS: Fungi and bacteria were isolated from the soil samples obtained from textile waste dumping site at Horana industrial zone, Sri Lanka and were screened for crystal violet (CV) and congo red (CR) dyes to develop MCs. Decolorization assay was performed for MCs along with individual isolates under variable pH levels. Metabolized products were characterized to confirm the biodegradation. A. tamari (F5) and P. putida (B3) significantly (P < 0.05) decolorized both dyes. All the MCs showed higher decolorization percentages over the individual microorganisms. Neutral pH (pH 7) was the optimum pH for the decolorization of both dyes by individual isolates and the percentages were significantly changed under the acidic and basic pH levels. However, decolorization ability by all MCs was not significantly changed with pH. Consortium with A. tamari - P. putida significantly (P < 0.05) decolourized both dyes under optimum pH 7. CONCLUSION: All MCs showed better pH tolerance in degrading CV and CR. Thus, it can be concluded that the selected MC with A. tamari - P. putida can degrade CV and CR textile dyes efficiently into non-toxic compounds against plants under neutral pH. Degradation and decolorization of textile azo dyes by effective fungal-bacterial consortium.

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Zinc oxide nanoparticles (ZnONPs), which are produced on a large scale, pose a potential threat to various environments because they can interact with the microbial populations found in them. Bacteria that are widespread in soil, water, and plant material include the Bacillus cereus group, which plays an important role in biodegradation and the nutrient cycle and is a major factor determining ecological balance. This group includes, among others, the foodborne pathogen B. cereus sensu stricto (herein referred to as B. cereus). The aim of this study was a comprehensive assessment of the effects of commercially available ZnONPs on B. cereus. The MIC (minimum inhibitory concentration) for B. cereus was 1.6 mg/mL, and the MBC (minimum bactericidal concentration) was 1.8 mg/mL. Growth of B. cereus was inhibited by a concentration of ZnONPs lower than or equal to MIC50. Concentrations from 0.2 to 0.8 mg/mL inhibited the growth of these bacteria in liquid media, induced symptoms of oxidative stress, and stimulated an environmental stress response in the form of biofilm and endospore formation. In addition, ZnONPs negatively affected the ability of the bacteria to break down the azo dye Evans Blue but enhanced the antimicrobial properties of phenolic compounds. Sublethal concentrations of ZnONPs generally decreased the activity of B. cereus cells, especially in the presence of phenolics, which indicates their potential toxicological impact, but at the same time they induced universal defence responses in these cells, which in the case of potential pathogens can hinder their removal.

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In this work, at 15 °C and 25 °C, authors study the decolouration reactions (or degradation reactions or oxidation reactions) of 0.10 mM azo dyes (methyl orange and congo red) by (1) K2S2O8 and (2) Co2+/K2S2O8, expounding the roles of K2S2O8 and Co2+: K2S2O8 can oxidize azo dyes automatically in water by radicals; Co2+ has catalysis for oxidation of K2S2O8, whether Co2+ is from CoSO4 or Co(NO3)2, CoCl2, CoAc2. The decolouration degree of azo dyes in all systems quickens with the increase of the initial concentration of K2S2O8 and the reaction temperature. In the presence and absence of Co2+, comparative experiments are done between the oxidation of K2S2O8 and oxone, K2S2O8 shows weaker oxidation than oxone. The decolouration reaction of methyl orange (MO) in the system of (0.10 mM MO + 2.00 mM K2S2O8) accords with the second order reaction, the reaction rate constants are 4.789 M-1 min-1 at 15 °C and 5.894 M-1 min-1 at 25 °C respectively, the activation energy Ea is 14813 J/mol, and Arrhenius equation is k = 2.328 exp[-14813/(RT)].

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Modification of cellulosic-rich materials for the production of cellulose-based polyelectrolytes (PELs) can bring several benefits, such as high biodegradability and low or no toxicity, for numerous applications, when compared with the use of traditional, synthetic PELs. Moreover, cellulose-based PELs originating from wood wastes, contribute to the valorisation of such wastes. In this work, Eucalyptus pulps with diverse lignin contents, extracted from Eucalyptus wood wastes, were anionized by a two-step reaction procedure (periodate oxidation followed by sulfonation). Applying different reaction times (24-144 h) in the sulfonation step allowed for producing a range of cellulose-based anionic polyelectrolytes with different characteristics. PELs obtained after 24 and 72 h of sulfonation were thoroughly characterized (Fourier transform infrared and 1H nuclear magnetic resonance spectroscopies, zeta potential and degree of substitution (elemental analysis) and hydrodynamic diameter (dynamic light scattering)) and subsequently evaluated as flocculants in decolouration processes of model effluents (Methylene Blue and Crystal Violet) and an industrial effluent from a textile industry. Furthermore, possible flocculation mechanisms induced by the use of the various PELs are discussed. Results are compared with those obtained with a commonly applied, synthetic flocculant (polyacrylamide). It is demonstrated that it was possible to obtain water-soluble lignocellulosic PELs starting from raw materials with different degrees of purity and that those PELs are promising eco-friendly alternative flocculation agents for the decolouration of effluents.

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The development of durable photocatalytic supports resistant in harsh environment has become challenging in advanced oxidation processes (AOPs) focusing on water and wastewater remediation. In this study, stainless steel (SS), SS/Ti (N,O) and SS/Cr-N/Cr (N,O) anticorrosion layers on SS meshes were dip-coated with sol gel synthesised C-N-TiO2 photo catalysts pyrolysed at 350 °C for 105 min, using a heating rate of 50 °C/min under N2 gas. The supported C-N-TiO2 films were characterised by scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Raman spectroscopy. The results showed that C-N-TiO2 was successfully deposited on anticorrosion coated SS supports and had different morphologies. The amorphous C and TiO2 were predominant in C-N-TiO2 over anatase and rutile phases on the surface of SS and anticorrosion supports. The C-N-TiO2 coated films showed enhanced photocatalytic activity for the decolouration of O.II dye under both solar and UV radiation. The fabricated C-N-TiO2 films showed significant antibacterial activities in the dark as well as in visible light. Herein, we demonstrate that SS/Ti(N,O) and SS/Cr-N/Cr(N,O) anticorrosion coatings are adequate photocatalytic and corrosion resistant supports. The C-N-TiO2 photo catalytic coatings can be used for water and wastewater decontamination of pollutants and microbes.

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In wastewater treatment, flocculation is a widely used solid/liquid separation technique, which typically employs a charged polymer, a polyelectrolyte (PEL). Polyelectrolytes features, such as charge type, charge density and molecular weight, are essential parameters affecting the mechanism of flocculation and subsequent floc sedimentation. The effectiveness of the process is also influenced by the characteristics of the system (e.g., type, size, and available surface area of suspended particles, pH of the medium, charge of suspended particles). Thus, a good understanding of the flocculation kinetics, involved mechanisms and flocs structure is essential in identifying the most adequate treatment conditions, having also into consideration possible subsequent treatments. In this study, Eucalyptus bleached pulp and a cellulosic pulp with high lignin content (~4.5 wt%) obtained from Eucalyptus wood waste were used for bio-PELs production. Firstly, a pre-treatment with sodium periodate increased the pulps reactivity. To produce cationic cellulose the oxidation step was followed by the introduction of cationic groups in the cellulose chains, through reaction with Girard's reagent T. Applying different molar ratios (0.975 and 3.9) of Girard's reagent T to aldehyde groups led to cationic PELs with diverse charge density. On the other hand, to obtain anionic cellulose a sulfonation reaction with sodium metabisulfite was applied to the intermediate dialdehyde cellulose-based products, during 24 or 72 h, and anionic-PELs with diverse features were obtained. The developed water soluble, anionic and cationic bio-PELs were characterized and tested as flocculation agents for a textile industry effluent treatment. Initially, jar-tests were used to tune the most effective flocculation procedure (pH, flocculant dosage, etc.). Flocculation using these conditions was then monitored continuously, over time, using laser diffraction spectroscopy (LDS). Due to the small size of the dyes molecules, a dual system with an inorganic complexation agent (bentonite) was essential for effective decolouration of the effluent. Performance in the treatment was monitored first by turbidity removal evaluation (75-88% with cationic-PELs, 75-81% with anionic-PELs) and COD reduction evaluation (79-81% with cationic-PELs, 63-77% with anionic-PELs) in the jar tests. Additionally, the evolution of flocs characteristics (structure and size) during their growth and the flocculation kinetics, were studied using the LDS technique, applying the different PELs produced and for a range of PEL concentration. The results obtained through this monitoring procedure allowed to discuss the possible flocculation mechanisms involved in the process. The results obtained with the bio-PELs were compared with those obtained using synthetic PELs, commonly applied in effluents treatment, polyacrylamides. The developed bio-PELs can be competitive, eco-friendly flocculation agents for effluents treatment from several industries, when compared to traditional synthetic flocculants with a significant environmental footprint. Moreover, LDS proved to be a feasible technique to monitor flocculation processes, even when a real industrial effluent is being tested.

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The aim of this study was to assess the effect of sodium nitrate concentration on the decolouration of laboratory dyes (bromothymol blue, crystal violet, eosin blue, eosin yellow and methylene blue), by alginate immobilized cells of Pseudomonas aeruginosa and Bacillus subtilis. The sodium nitrate concentrations used in the study were 5, 10, 15 and 20 g/L. A control setup that contained no sodium nitrate was also studied. During incubation, aliquot samples were withdrawn from each flask every 24 for 144 h duration for the estimation of decolouration rate of the dyes, using standard procedures. The results revealed remarkable decolouration of the bromothymol blue and crystal violet in presence of the P. aeruginosa occurring at sodium nitrate concentrations of 10 and 15 g/L, respectively. In the case of media that was inoculated with the B. subtilis cells, although no remarkable decolouration of the bromothymol blue and crystal violet was observed throughout the period of incubation, highest decolouration were observed at sodium nitrate concentration of 5 and 10 g/L, respectively. For the eosin blue and methylene dyes, no remarkable decolouration were observed in presence of the test bacterial species at the respective sodium nitrate concentrations. Highest decolouration of the eosin yellow was however observed in media with sodium nitrate concentration of 5 g/L. The results of this study could be applied in scale up studies and continuous process, for implementation in biological decolouration of dye effluents.

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Several species of white-rot fungi were investigated for their utility in prolonged decolouration of the recalcitrant sulfonated azo dye, amaranth. Trametes pubescens, T. multicolor, T. meyenii and T. versicolor decoloured amaranth azo-dye best on low-nitrogen agar-solidified media whereas Bjerkandera adusta and Phlebia radiata were most effective in low nitrogen medium supplemented with manganese. Trametes cotonea did not decolour effectively under any condition. The decolouring Trametes species were also effective in liquid culture whereas B. adusta and P. radiata were not. Trametes meyenii, T. pubescens and T. multicolor were equal to or better than commonly employed T. versicolor at decolouring amaranth. This is the first study to show the dye decolouration potential of T. meyenii, T. pubescens, and T. multicolor. Supplementing with Mn(II) increased assayable manganese peroxidase activity, but not long-term decolouration, indicating that laccase is the main decolourizing enzyme in these Trametes species. This appears to be because of inadequate Mn(3+) chelation required by manganese peroxidase because adding relatively low amounts of malonate enhanced decolouration rates. The ability of Trametes meyenii to simultaneously decolour dye over prolonged periods of time while growing in relatively nutrient-rich medium appears to be unique amongst white-rot fungi, indicating its potential in wastewater bioremediation.

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Biological process is an important approach to treat the dye wastewater. The azo dyes decolouration by special azoreductase of different aerobic bacteria and fungi was summarized. Under anaerobic condition, reductive decolourization of azo dyes was carried in the presence of redox mediators which act as electron shuttle. It was also pointed out that azo dye reduction occurred mainly under anaerobic condition. Different electron donor resulted in different decolourization rate. Problems of current biotechnology were analyzed and corresponding measures were discussed.