Immobilized laccase for decolourization of Reactive Black 5 dyeing effluent

Reactive Black 5 industrial dyeing effluent was decolourized by free and immobilized laccase. The stability of the enzyme (194 h free and 79 h immobilized) depended on the dyeing liquor composition and the chemical structure of the dye. In the decolourization experiments with immobilized laccase, two phenomenons were observed – decolourization due to adsorption on the support (79%) and dye degradation due to the enzyme action (4%). Dyeing in the enzymatically recycled effluent provided consistency of the colour with both bright and dark dyes.     

De-colourization of textile effluent using immobilized Geotrichum candidum: an insight into mycoremediation

Textile effluent is generally complicated to manage because of its extremely noxious and recalcitrant coloured compositions. Mycoremediation is an extensively used strategy for the competent degradation of hazardous pollutants present in textile effluent. Fungus could be immobilized in synthetic or natural matrices. The current study shows the decolourization of the textile effluent by 85·5 and 98·5% within 6 h using suspended and immobilized fungus, Geotrichum candidum with optimized parameters like inoculum size (5%), pH (4·5), and temperature (30°C). To maintain a high biomass of fungal population and enhance the retention of fungal strain in the contaminated sites, the fungi need to be immobilized. Hence, the fungus was immobilized naturally onto the selected inert support that is, coconut fibres by the means of adsorption, where they grew as active films on the fibres after being grown in the culture broth. The optimized process parameters of inoculum size, fibre quantity and agitation speed for immobilized G. candidum were 5%, 2·2 g l⁻¹ of effluent and 100 rev min⁻¹ respectively. High level of laccase (22 and 25 U l⁻¹ in suspended and immobilized fungal cells treatment respectively) was observed during the process of decolourization and it was found that decolourization was directly proportional to the laccase activity. The UV–vis, FTIR, ¹H NMR and GC-MS analyses of treated textile industrial wastewater revealed the degradation of toxic pollutants in the textile effluent and formation of lower molecular weight intermediates. The study revealed a higher efficacy of immobilized G. candidum in comparison to suspended fungal culture, employing ligninolytic enzyme laccase, which catalyzes the degradation/transformation of aromatic dyes in the textile effluent thus decolourizing it.     

Decolourization of textile dye Reactive Violet 5 by a newly isolated bacterial consortium RVM 11.1

Summary Soil samples collected from contaminated sites of Vatva, Gujarat, India were studied for screening and isolation of organisms capable of decolourizing textile dyes. A bacterial consortium RVM 11.1 was selected on the basis of rapid dye decolourization. Reactive Violet 5 (RV 5) was used as model dye. The consortium exhibited 94% decolourization ability within 37 h under a wide pH range from 6.5 to 8.5 and temperature ranging from 25 to 40 °C. The bacterial consortium was able to grow and decolourize RV5 under static conditions in the presence of glucose and yeast extract and also showed an ability to decolourize in the presence of starch in place of glucose. Maximum decolourization efficiency was observed at 200 ppm (mg/l) concentration of RV 5. Bacterial consortium RVM11.1 had the ability to decolourize 10 different dyes tested. The transformation and degradation products after decolourization were examined by HPTLC.     

Optimisation for enhanced decolourization and degradation of Reactive Red BS C.I. 111 by Pseudomonas aeruginosa NGKCTS

Soil samples collected from dye contaminated sites of Vatva, Gujarat, India were studied for the screening and isolation of organisms capable of decolourizing textile dyes. The most efficient isolate, which showed decolourization zone of 48 mm on 300 ppm Reactive Red BS (C.I.111) containing plate, was identified as Pseudomonas aeruginosa. Reactive Red BS (C.I.111) was used as a model dye for the study. The isolated culture exhibited 91% decolourization of 300 ppm dye within 5.5 h over a wide pH range from 5.0 to 10.5 and temperature ranging from 30 to 40°C. The culture was able to decolourize more than 91% of Reactive Red BS under static conditions in presence of either glucose, peptone or yeast extract. Addition of 300 ppm of Reactive Red BS, in each step, in ongoing dye decolourization flask, gave more than 90% decolourization within 2 h corresponding to 136 mg l⁻¹ h⁻¹ dye removal rate. The isolate had the ability to decolourize six different reactive dyes tested as well as the actual dye manufacturing industry’s effluent. The degradation of the dye was confirmed by HPTLC.     

Biological treatment of textile dye acid violet-17 by bacterial consortium in an up-flow immobilized cell bioreactor

AIMS: To develop a cost effective and efficient biological treatment process for small scale textile processing industries (TPI) releasing untreated effluents containing intense coloured Acid violet-17 (AV-17), a triphenyl methane (TPM) group textile dye. METHODS AND RESULTS: The samples collected from effluent disposal sites of TPI were used for selective enrichment of microbial populations capable of degrading/decolourizing AV-17. A consortium of five bacterial isolates was used to develop an up-flow immobilized cell bioreactor for treatment of feed containing AV-17. The bioreactor, operating at a flow rate of 6 ml x h(-1), resulted in 91% decolourization of 30 mg AV-17/l with 94.3 and 95.7% removal of biochemical oxygen demand and chemical oxygen demand of the feed. Comparison of the input and output of the bioreactor by UV-visible, thin layer chromatography and (1)H-nuclear magnetic resonance spectroscopy indicates conversion of the parent dye into unrelated metabolic intermediates. SIGNIFICANCE: These results will form a basis for developing 'on-site' treatment system for TPI effluents to achieve decolourization and degradation of residual dyes.     

Decolourization of Amaranth dye by bacterial biofilm in batch and continuous packed bed bioreactor

The aim of this study was to exploit the bacterial biofilms to remove dyes from industrial effluents. Biofilms of strains AK1, AK2, VKY1 and a consortium on sheep bone chips were examined in batch, repeated batch and continuous packed bed bioreactor. Biofilms are more efficient for decolourization of Amaranth dye at three different dye concentrations (200, 400, and 600 mg l⁻¹). 100% decolourization of Amaranth dye was observed even at higher concentrations (400 and 600 mg l⁻¹) by all the tested biofilms in 24 h than that of corresponding free cells. The biofilms were superior over those of free cells and could be reused for more than 18 repeated cycles. In a packed bed bioreactor, biofilms could be operated with much higher dilution rates and at lower hydraulic retention time. Further, the decolourization of dye was confirmed by UV–visible spectrophotometer, TLC and HPLC analysis of Amaranth dye degradation products from packed bed bioreactor effluent.     

Decolourization and Detoxification of Methyl Red by Aerobic Bacteria from A Wastewater Treatment Plant

Bacterial cultures from a wastewater treatment plant degraded a toxic azo dye (methyl red) by decolourization. Complete decolourization using a mixed-culture was achieved at pH 6, 30 °C within 6 h at 5 mg/l methyl red concentration, and 16 h at 20—30 mg/l. Four bacterial species were isolated that were capable of growth on methyl red as the sole carbon source, and two were identified, namely Vibrio logei and Pseudomonas nitroreducens. The Vibrio species showed the highest methyl red degradation activity at the optimum conditions of pH 6--7, and 30—35 °C. Analysis by NMR showed that previously reported degradation products 2-aminobenzoic acid and N,N-dimethyl-1,4-phenylenediamine were not observed. The decolourized dye was not toxic to a monkey kidney cell line (COS-7) at a concentration of 250 μM. This revised version was published online in July 2006 with corrections to the Cover Date.     

Utilization of short chain monocarboxylic acids in an effluent of a petrochemical industry by Acinetobacter calcoaceticus

The aqueous effluent generated by the Fischer--Tropsch process, containing a total of 13 g/L C(2)-C(5) monocarboxylic acids, was investigated as a potential substrate for the production of single-cell protein (SCP). A bacterial isolate, Acinetobacter calcoaceticus, could utilize all the acids in the effluent simultaneously in chemostat cultures, and no residual acids were detected in the culture below a dilution rate of 0.78 h(-1). The critical dilution rate was 1.04 h(-1). The maintenance energy requirement of the cells growing on the monocarboxylic acid mixture was considerably lower than that of cells growing on acetate as the sole carbon source. Enrichment of the effluent with ethanol to increase the biomass concentration was successful and still allowed the simultaneous and efficient utilization of all the carbon sources, but resulted in a decrease of the critical dilution rate by ca. 20%.     

Influence of culture parameters on paper mill effluent decolourization by a white rot fungus Ganoderma lucidum

Efficacy of a white rot fungus G. lucidum for reduction of colour of paper mill effluent under various growth conditions was evaluated. G. lucidum cultured in IBME medium supported maximum colour reduction on 18th day of fungal growth. The optimization of growth parameters further improved colour reduction. The 18 day old culture at 4 g/l inoculum concentration resulted in maximum decolourization (89%) of the effluent with pH adjusted to 6.5 at 35 degrees C along with maximum reduction in biological oxygen demand and chemical oxygen demand. Relative contribution of lignin peroxidase and laccase to the decolourization of paper mill effluent by G. lucidum was also observed.     

Bifidobacterium longum ATCC 15707 cell production during free- and immobilized-cell cultures in MRS-whey permeate medium

Bifidobacterium longum ATCC 15707 cell production was studied in MRS medium supplemented with whey permeate (MRS-WP) during free-cell batch fermentations and continuous immobilized-cell cultures. Very high populations were measured after 12 h batch cultures in MRS-WP medium controlled at pH 5.5 (1.7+/-0.5x10(10) cfu/ml), approximately 2-fold higher than in non-supplemented MRS. Our study showed that WP is a low-cost source of lactose and other components that can be used to increase bifidobacteria cell production in MRS medium. Continuous fermentation in MRS-WP of B. longum immobilized in gellan gum gel beads produced the highest cell concentrations in the effluent (4.9+/-0.9x10(9) cfu/ml) at a dilution rate (D) of 0.5 h(-1). However, maximal volumetric productivity (6.9+/-0.4x10(9) cfu ml(-1)h(-1)) during continuous cultures was obtained at D =2.0 h(-1), and was approximately 9.5-fold higher than during free-cell batch cultures at an optimal pH of 5.5 (7.2x10(8) cfu ml(-1)h(-1)).     

Cerebral endothelial cells release TNF-alpha after stimulation with cell walls of Streptococcus pneumoniae and regulate inducible nitric oxide synthase and ICAM-1 expression via autocrine loops.

TNF-alpha, inducible NO synthase (iNOS), and ICAM-1 are considered to be key proteins in the inflammatory response of most tissues. We tested the hypothesis that cell walls of Streptococcus pneumoniae (PCW), the most common cause of adult bacterial meningitis, induce TNF-alpha, iNOS, and ICAM-1 expression in rat primary brain microvascular endothelial cell cultures. We detected TNF-alpha mRNA by RT-PCR already 1 h after stimulation with PCW, while TNF-alpha protein peaked at 4 h (9.4 +/- 3.6 vs 0.1 +/- 0.1 pg/microgram protein). PCW induced iNOS mRNA 2 h after stimulation, followed by an increase of the NO degradation product nitrite (18.1 +/- 4 vs 5.8 +/- 1.8 at 12 h; 18.1 +/- 4 vs 5.8 +/- 1.8 pmol/microgram protein at 72 h). The addition of TNF-alpha Ab significantly reduced nitrite production to 62.2 +/- 14.4% compared with PCW-stimulated brain microvascular endothelial cells (100%). PCW induced the expression of ICAM-1 (measured by FACS), which was completely blocked by TNF-alpha Ab (142 +/- 18.6 vs 97.5 +/- 12.4%; 100% unstimulated brain microvascular endothelial cells). Cerebral endothelial cells express TNF-alpha mRNA as well as iNOS mRNA and release the bioactive proteins in response to PCW. PCW-induced NO production is mediated in part by an autocrine pathway involving TNF-alpha, whereas ICAM-1 expression is completely mediated by this autocrine loop. By these mechanisms, cerebral endothelial cells may regulate critical steps in inflammatory blood-brain-barrier disruption of bacterial meningitis.     

The use of a radial basis neural network and genetic algorithm for improving the efficiency of laccase-mediated dye decolourization

A radial basis function neural network (RBF) and genetic algorithm (GA) were applied to improve the efficiency of the oxidative decolourization of the recalcitrant dye Reactive Black 5 (RB 5) by a technical laccase (Trametes spp.) and the natural mediator acetosyringone (ACS). The decolourization of RB 5 in aqueous solution was studied with a 3(4) factorial design including different levels of laccase (2, 100, 200UL(-1)), acetosyringone (5, 50, 100μM), pH value (3, 4.5, 6) and incubation time (10, 20, 30min). The generated RBF network was mathematically evaluated by several statistical indices and revealed better results than a classical quadratic response surface (RS) model. The experimental data showed that within 10min of incubation time a complete decolourization (>90%) was achieved by using the highest amount of laccase (200UL(-1)) and acetosyringone (100μM) at pH 6. By applying the RBF-GA methodology, the efficiency of the laccase-mediated decolourization was improved by minimising the required amount of laccase and acetosyringone by 25% and 21.7% respectively. Complete decolourization (>90%) was obtained within 10min at the GA-optimised process conditions of laccase (150UL(-1)) and acetosyringone (78.3μM) at pH 5.67. These results illustrate that the RBF-GA methodology could be a powerful technique during scale-up studies.     

Biodegradation of disperse textile dye Brown 3REL by newly isolated Bacillus sp. VUS

Aims:  To isolate the potential micro-organism for the degradation of textile disperse dye Brown 3 REL and to find out the reaction mechanism.
Methods and Results:  16S rDNA analysis revealed an isolate from textile effluent contaminated soil as Bacillus sp. VUS and was able to degrade (100%) dye Brown 3REL within 8 h at static anoxic condition. A significant increase in the activities of lignin peroxidase, laccase and NADH-DCIP reductase was observed up to complete decolourization of Brown 3REL. The optimum temperature required for degradation was 40°C and pH 6·5–12·0. Phyto-toxicity and chemical oxygen demand revealed nontoxic products of dye degradation. The biodegradation was monitored by UV–VIS, FTIR spectroscopy and HPLC. The final products 6,8-dichloro-quinazoline-4-ol and cyclopentanone were characterized by gas chromatography-mass spectrometry. This Bacillus sp. VUS also decolourized (80%) textile dye effluent within 12 h.
Conclusions:  This study suggests that Bacillus sp. VUS could be a useful tool for textile effluent treatment.
Significance and Impact of the Study:  The newly isolated Bacillus sp. VUS decolourized 16 textile dyes and textile dye effluent also. It achieved complete biodegradation of Brown 3REL. Phytotoxicity study demonstrated no toxicity of the biodegraded products for plants with respect to Triticum aestivum and Sorghum bicolor .     

Modulation of gonadotropin-releasing hormone receptor concentration in cultured female rat pituitary cells by estradiol treatment

Short-term (0.5-4 h) treatment of rat pituitary cells in culture with estradiol (E2) results in a significant decrease of Gonadotropin-Releasing Hormone (GnRH) induced LH-release. We studied whether changes in the concentrations of GnRH-receptors (GnRH-R) might account for this phenomenon: pituitary cells from adult female rats were incubated for 4 or 24 h in the presence or absence of 10(-9) M E2. Then saturation curves of D-Ala6-des-Gly10-GnRH ethylamide binding were obtained. In addition, binding studies were carried out in cultures incubated for 0.5, 1, 2 or 4 h with or without 10(-9) M E2 using a near saturating concentration of GnRH-analog. No changes of GnRH-R affinity occurred (4 h experiments: Ka in vehicle treated cells: 0.94 +/- 0.2 x 10(9) M-1, Ka in E2 treated cells: 1.06 +/- 0.3 x 10(9) M-1; 24 h experiments: Ka vehicle: 0.95 +/- 0.2 x 10(9) M-1, Ka E2: 0.82 +/- 0.3 x 10(9) M-1). The GnRH-R concentrations, however, were significantly reduced (44 +/- 3%; P less than 0.001) by 4 h E2 treatment and increased (by 68 +/- 8%; P less than 0.01) by 24 h of E2 treatment. The GnRH induced LH-release in aliquots of the same cell preparations was significantly reduced after 4 h and markedly increased after 24 h of E2 treatment. The experiments on the time-course of the reduction of D-Ala6-GnRH-binding by E2 treatment showed that the number of GnRH-R was significantly decreased (24 +/- 1%; P less than 0.05) already after 0.5 h of exposure to the estrogen. This is also the time period after which the negative E2-effect on GnRH-induced LH-release becomes significant. These data provide first evidence that the short-term negative E2-effect on GnRH induced LH-release by rat pituitary cells in culture could be mediated via a reduction of available GnRH-R.     

Opioid modulation of LH secretion by pig pituitary cells in vitro

The effects of naloxone and beta-endorphin on LH secretion by pig pituitary cells were studied in primary cultures. On Day 4 of culture, cells (10(5) seeded/well) were challenged with 10(-9), 10(-8) or 10(-7) M gonadotrophin-releasing hormone (GnRH), 10(-10), 10(-9), 10(-8) or 10(-7) M-beta-endorphin or 10(-6) M-naloxone individually or in combinations. Secreted LH was measured at 4 h and 24 h after treatment and cellular content of LH was measured after 24 h. Basal LH secretion (control) was 23.5 +/- 7.6 and 36.9 +/- 10.3 ng/well at 4 h and 24 h, respectively. Relative to control at 4 h, 10(-9), 10(-8) or 10(-7) M-GnRH stimulated (P less than 0.05) LH secretion 140%, 210% and 250%, respectively. At 24 h, LH secretion was increased (P less than 0.05) by GnRH compared to control, but the dose-response to GnRH was absent. Naloxone increased (P less than 0.01) LH secretion 166 +/- 13% at 4 h and 141 +/- 13% (P less than 0.06) at 24 h. Secretion of LH after simultaneous addition of 10(-8) M-GnRH plus naloxone was greater (P less than 0.01) than after GnRH alone at 4 h but not at 24 h. beta-Endorphin at 10(-10), 10(-9), 10(-8) or 10(-7) M failed to alter basal LH secretion at 4 h but decreased secretion at 24 h, while cellular LH content was similar to control at 24 h.(ABSTRACT TRUNCATED AT 250 WORDS)     

Decolourization of olive mill waste-waters by the white-rot fungus Phanerochaete chrysosporium: involvement of the lignin-degrading system

Summary The decolourization of olive mill waste-waters (OMW) by Phanerochaete chrysosporium was investigated. OMW decolourization occurred during the primary phase of growth when glycerol was used as the carbon source, and during secondary metabolism in nitrogen-limited cultures. The decolourization was found to be extensive (74% of colour removal, 80% of chemical oxygen demand removal) when the cultures were supplement d with veratryl alcohol and flushed with O₂. The biodegradation system was repressed with glutamate as a nitrogen source. These results suggest that all or part of the lignin-degrading system of P. chrysosporium played a role in biodegradation of OMW. The decolourization of OMW corresponds to depolymerization of high-molecular-mass aromatics combined with mineralization of a wide range of monoaromatic compounds. Correspondence to: S. Sayadi     

Role and mechanism of PKC in ischemic preconditioning of pig skeletal muscle against infarction

Protein kinase C (PKC) inhibitors, chelerythrine (Chel, 0.6 mg) and polymyxin B (Poly B, 1.0 mg), and PKC activators, phorbol 12-myristate 13-acetate (PMA, 0.05 mg) and 1-oleoyl-2-acetyl glycerol (OAG, 0.1 mg), were used as probes to investigate the role of PKC in mediation of ischemic preconditioning (IPC) of noncontracting pig latissimus dorsi (LD) muscles against infarction in vivo. These drugs were delivered to each LD muscle flap (8 x 12 cm) by 10 min of local intra-arterial infusion. It was observed that LD muscle flaps sustained 43 +/- 5% infarction when subjected to 4 h of global ischemia and 24 h of reperfusion. IPC with three cycles of 10 min ischemia-reperfusion reduced muscle infarction to 25 +/- 3% (P < 0.05). This anti-infarction effect of IPC was blocked by Chel (42 +/- 7%) and Poly B (37 +/- 2%) and mimicked by PMA (19 +/- 10%) and OAG (14 +/- 5%) treatments (P < 0.05), given 10 min before 4 h of ischemia. In addition, the ATP-sensitive K(+) (K(ATP)) channel antagonist sodium 5-hydroxydecanoate attenuated (P < 0.05) the anti-infarction effect of IPC (37 +/- 2%), PMA (44 +/- 17%), and OAG (46 +/- 9%). IPC, OAG, and Chel treatment alone did not affect mean arterial blood pressure or muscle blood flow assessed by 15-microm radioactive microspheres. Western blot analysis of muscle biopsies obtained before (baseline) and after IPC demonstrated seven cytosol-associated isoforms, with nPKCepsilon alone demonstrating progressive cytosol-to-membrane translocation within 10 min after the final ischemia period of IPC. Using differential fractionation, it was observed that nPKCepsilon translocated to a membrane compartment other than the sarcolemma and/or sarcoplasmic reticulum. Furthermore, IPC and preischemic OAG but not postischemic OAG treatment reduced (P < 0.05) muscle myeloperoxidase activity compared with time-matched ischemic controls during 16 h of reperfusion after 4 h of ischemia. Taken together, these observations indicate that PKC plays a central role in the anti-infarction effect of IPC in pig LD muscles, most likely through a PKC-K(ATP) channel-linked signal-transduction pathway.     

Nutrition and fetal brain maturation : II. Impact of maternal starvation on changing levels of acetylcholinesterase and enolase in vitro

The impact of maternal starvation during Days 17-20 of gestation was examined in 20-day fetal rat brain tissue cultured for 6 days in MEM and 10% adult rat serum. Acetylcholinesterase (AChE) activities were consistently greater in fetal brain cell cultures from starved mothers. When fetal tissues from starved mothers were continuously exposed to 72-h fasted serum, AChE activities increased from 1.03 +/- 0.14 to 1.59 +/- 0.21 mumol/h/mg protein (P less than 0.001). In fetal tissues from fed mothers, lower AChE activities were increased from 0.78 +/- 0.09 to 1.04 +/- 0.07 mumol/h/mg protein (P less than 0.05) when 72-h fasted serum was used to replace the fed serum during incubation. When fetal brain cell cultures from fed mothers were exposed for 6 days to graded concentrations of fed serum (2.5-15%), the activities of AChE fell reciprocally from 1.34 +/- 0.10 to 0.82 +/- 0.12 mumol/h/mg protein (P less than 0.05). The levels of AChE activity in tissues exposed to fasted serum were consistently greater, but fell similarly from 1.62 +/- 0.10 to 0.97 +/- 14 mumol/h/mg protein (P less than 0.01), when serum concentrations were increased from 2.5 to 15%. AChE activities were 30% higher in tissues incubated with cycloheximide 10(-3) M (P less than 0.02). Unlike AChE, fetal brain enolase activities were unaffected by maternal starvation. In fetal brain cell cultures from fed mothers, enolase fell from 1.85 +/- 0.10 to 1.37 +/- 0.12 mumol/min/mg protein following exposure to fasted instead of fed serum (P less than 0.02). In fetal cultures from starved mothers, enolase activities were depressed similarly from 1.76 +/- 0.08 to 1.41 +/- 0.09 mumol/min/mg protein when fasted replaced fed serum (P less than 0.02). Thus, the fetal brain cell cultures appear to maintain enzymatic realignments imposed by maternal starvation for at least 6 days. In addition, serum from fasted animals has significant growth inhibiting properties manifested by heightened activities of AChE and lower activities of enolase.     

Inhibition of microbial adhesion to silicone rubber treated with biosurfactant from Streptococcus thermophilus A

Microbial adhesion of four bacterial and two yeast strains isolated from explanted voice prostheses to silicone rubber before and after conditioning with a biosurfactant obtained from the probiotic bacterium Streptococcus thermophilus A was investigated in a parallel plate flow chamber. The silicone rubber with and without an adsorbed biosurfactant layer was characterized using contact angle measurements. Water contact angles indicated that the silicone rubber surface with adsorbed biosurfactant was more hydrophilic (58 degrees) than bare silicone rubber (109 degrees). The results obtained showed that the biosurfactant was effective in decreasing the initial deposition rates, and the number of bacterial cells adhering after 4 h, for all microorganisms tested. A decrease in the initial deposition rate was observed for Rothia dentocariosa GBJ 52/2B and Staphylococcus aureus GB 2/1 from 1937+/-194 to 179+/-21 microorganisms cm(-2) s(-1) and from 1255+/-54 to 233+/-26 microorganisms cm(-2) s(-1), respectively, accounting for an 86% reduction of the initial deposition rate for both strains. The number of bacterial cells adhering to the silicone rubber with preadsorbed biosurfactant after 4 h was further reduced by 89% and 97% by the two strains, respectively. The two yeast strains tested showed less reduction in adhesion after 4 h, to values between 67% and 70%. Such a pretreatment with surface-active compounds may constitute a promising strategy to reduce the microbial colonization rate of silicone rubber voice prostheses.     

Detoxification and mineralization of Acid Blue 74: study of an alternative secondary treatment to improve the enzymatic decolourization

Many reports describe the decolourization of dyes by fungal enzymes. However, these enzymes do not contribute to dye mineralization but only to its biotransformation into less coloured or colourless molecules persisting in solution. Therefore, it is essential to analyse the identity of the metabolites produced during enzymatic treatments and its biodegradation into an appropriate system. The present work examines the decolourization/detoxification of a simulated effluent (containing Acid Blue 74) by fungal enzymes and proposes a secondary treatment using an anaerobic system to improve the enzymatic decolourization through the complete mineralization of the dye. Ligninolytic enzymes were produced by solid culture using the thermo-tolerant fungus Fomes sp. EUM1. The enzymes produced showed a high rate of decolourization (>95 % in 5 h) and were stable at elevated temperature (40 °C) and ionic strength (NaCl, 50 mM). Isatin-5-sulphonic acid was identified via ¹H-NMR as oxidation product; tests using Daphnia magna revealed the non-toxic nature of this compound. To improve the enzymatic degradation and avoid coupling reactions between the oxidation products, the effluent was subjected to an anaerobic (methanogenic) treatment, which achieved high mineralization efficiencies (>85 %). To confirm the mineralization of isatin-5-sulphonic acid, a specific degradation study, which has not been reported before, with this single compound was conducted under the same conditions; the results showed high removal efficiencies (86 %) with methane production as evidence of mineralization. These results showed the applicability of an anaerobic methanogenic system to improve the enzymatic decolourization/detoxification of Acid Blue 74 and achieve its complete mineralization.