Decolorization of textile dyes by laccases from a newly isolated strain of Trametes modesta

Four ligninolytic fungi, Trametes modesta, Trametes hirsuta, Trametes versicolor and Sclerotium rolfsii, were compared for their ability to produce laccases. The fungal laccases were screened for their ability to decolorize eight synthetic dyes (anthraquinone, azo, indigo and triarylmethane). The decolorization rate depended both on the source of the enzyme preparation and on the structure of the dye. Based on laccase production and dye decolorizing ability, T. modesta was selected for further studies. All the tested dyes were decolorized by the T. modesta laccase most efficiently under acid conditions (pH 3-6) but the optimum pH for decolorization of the individual dye varied. The decolorization rate of this laccase increased with the rise in temperature to 50-60 degrees C. The decolorization efficiency of T. modesta laccase was improved remarkably in the presence of mediators like 1-hydroxybenzotriazole and 2-methoxyphenothiazine.     

Application of the laccase,produced on coconut flesh by Pleurotus florida for dye decolorization

We investigated the ability of Pleurotus florida to produce laccase on coconut flesh as a solid substrate fermentation. The decolorization of two structurally different dyes such as azo (Reactive Blue 198) and triphenylmethane dye (Malachite Green) were analysed. The decolorization of Reactive blue 198 and Malachite Green at 8 hrs was 93% and 63% respectiely. The untreated and treated dye was characterized by UV-Vis spectral and fourier transform infrared (FTIR) Spectroscopy scan. FTIR analysis pointed out the involvement of alkene (C=C) and carboxylic (C-O) groups in the decolorization process. The toxicity with respect to Allium cepa root inhibition was measured to demonstrate the potential of laccase in the detoxication and bioremediation process.     

Enzymatic biodegradation and detoxification of azo and anthraquinone dyes by indigenously isolated bacterial monocultures and their synergistic behaviour in developed consortia

Wastewater generated by textile industry needs to be treated to reduce its toxicity before final disposal and/or for recycling purposes. In the current study, several bacterial strains were screened for dye decolorization potential. UV–visible spectroscopy was used to determine maximum absorption wavelength of disperse dyes. HPLC and MTS assay were used to confirm the degradation and detoxification of disperse dyes, respectively. Results revealed that indigenously isolated Bacillus licheniformis, Glutamicibacter uratoxydans and Pseudomonas aeruginosa showed strong decolorization of red, blue and violet, respectively in 6–9 h. MTS assay revealed 100% viability of NIH/3T3 cell lines in presence of treated dyes. Enzyme screening assay confirmed the production of intracellular and membrane bound oxidoreductases in presence of specific dye as substrate. To resolve this issue, bacterial consortia were prepared, and better decolorization of all dyes was achieved in synergistic behaviour of Consortia 1 and 4 with 85% and 88% decolorization potential, respectively.     

Bioaccumulation of Cu-complex reactive dye by growing pellets of Penicillium oxalicum and its mechanism

In this paper bioaccumulation of Cu-complex reactive dye by growing pellets of Penicillium oxalicum and its mechanism was investigated. Shaking flasks experiment showed that 99.7% of dye removal at 400 mg/l was attained after 48 h contact. Column reactor experiment showed that air lift ferment tower was a suitable reactor for both pellets formation and dye bioaccumulation. Repeated inoculation of the dye-loaded pellets accelerated dye bioaccumulation, leading to complete dye removal within 12 h. Dye initially was adsorbed on surface of cell, followed by penetration into cytoplasm. During bioaccumulation, mycelium expanded unevenly and thickened locally in diameter, generating a chain of spindles along the mycelium. In addition, the cell walls grew loose and thickened remarkably, being 4-5 folds as thick as the control one. The loose cell wall may offer both dye accumulation space and route way for dye to enter cytoplasm. There were certain unknown active matters in cytoplasm, which played an important role in dye accumulation. Desorption experiments suggested that electrostatic attraction was mainly attributed to the dye bioaccumulation.     

Novel heterocyclic chitosan‐based Schiff base: evaluation as adsorbent for removal of methyl orange from aqueous solution

A Schiff base has been made by reacting chitosan with 2‐hydroxy quinoline‐3‐carbaldehyde in the presence of acetic acid. The synthesized compound was characterized by FTIR, TGA, XRD and SEM techniques. The Schiff base was evaluated for removal of anionic dye from aqueous solution using methyl orange as model dye. Influences of initial dye concentration, pH and contact time on the extent of adsorption were investigated. The adsorption data fits best with Freundlich isotherm model and the maximum adsorption capacity was found to be 55.55 mg/g. The kinetic study indicated second‐order adsorption. The thermodynamic parameters showed the adsorption to be endothermic and non‐spontaneous. Desorption studies indicated the reusability of the compound as adsorbent material.     

Mechanism of textile metal dye biotransformation by Trametes versicolor

The biodegradation of Grey Lanaset G, which consists of a mixture of metal complexed dye, was studied. Experiments were carried out in a bioreactor with retained pellets of the fungus Trametes versicolor that was operated under conditions of laccase production. Although decolorization was highly efficient (90%), no direct relationship to extracellular enzyme was apparent. Moreover, the extracellular enzyme was found to be unable to degrade the dye in vitro. The process involves several steps. Thus, the initial adsorption of the dye and its transfer into cells is followed by breaking of the metal complex bond in the cells release of the components. The metal (Cr and Co) contents of the biomass and treated solutions, and their closer relationship to intracellular enzyme and degradation of the dye, confirm the initial hypothesis.     

Laccase-catalyzed removal of bisphenol-A from water: protective effect of PEG on enzyme activity

The feasibility of using the enzyme laccase to treat synthetic wastewater containing bisphenol-A (BPA) was examined. Optimization of pH, laccase concentration, polyethylene glycol (PEG) as an additive for >95% conversion and precipitation of BPA over 3 h of reaction period was determined through colorimetric assay and HPLC. PEG reduced enzyme inactivation, allowing a 5.2-fold reduction in the amount of laccase required for >95% removal of BPA in the range of 0.1-1 mM over 3 h. The fate of PEG after the reaction was also monitored. Linear relationships were found between the concentration of BPA (0.1-1 mM) and the optimum concentrations of laccase and PEG. Little PEG remained in the solution when up to 75 mg/L of PEG was used to treat 0.5 mM BPA. Beyond this level, PEG concentration increased linearly in the supernatant. It is inferred that an interaction between PEG and the polymeric products resulted in the protection of laccase.     

Bioremediation of crystal violet using air bubble bioreactor packed with Pseudomonas aeruginosa

Seven water and sediment samples were collected and tested for decolorizing crystal violet. Pseudomonas aeruginosa was the most effective isolate for dye decolorization. The LC₅₀ of the crystal violet (115 mg/l) was measured using Artemia salina as a biomarker. The effect of different heavy metals on crystal violet decolorization was investigated. Cd²⁺ and Fe³⁺ ions showed marginal enhancement of the decolorization process, the rate was 1.35 mg/l/h compared to 1.25 mg/l/h for the control. Phenol and m-cresol showed no effect on crystal violet decolorization, meanwhile p-cresol and p-nitrophenol reduced the decolorization rate to 1.07 and 0.01 mg/l/h, respectively. P. aeruginosa cells were immobilized by entrapment in agar–alginate beads. The beads were cultivated and reused in Erlenmeyer flask and in an air bubble column bioreactor and they enhanced the crystal violet decolorization rate to 3.33 and 7.5 mg/l/h, respectively.     

Further treatment of decolorization liquid of azo dye coupled with increased power production using microbial fuel cell equipped with an aerobic biocathode

A microbial fuel cell (MFC) incorporating a recently developed aerobic biocathode is designed and demonstrated. The aerobic biocathode MFC is able to further treat the liquid containing decolorization products of active brilliant red X-3B (ABRX3), a respective azo dye, and also provides increased power production. Batch test results showed that 24.8% of COD was removed from the decolorization liquid of ABRX3 (DL) by the biocathode within 12 h. Metabolism-dependent biodegradation of aniline-like compound might be mainly responsible for the decrease of overall COD. Glucose is not necessary in this process and contributes little to the COD removal of the DL. The similar COD removal rate observed under closed circuit condition (500 Ω) and opened circuit condition indicated that the current had an insignificant effect on the degradation of the DL. Addition of the DL to the biocathode resulted in an almost 150% increase in open cycle potential (OCP) of the cathode accompanied by a 73% increase in stable voltage output from 0.33 V to 0.57 V and a 300% increase in maximum power density from 50.74 mW/m² to 213.93 mW/m². Cyclic voltammetry indicated that the decolorization products of the ABRX3 contained in the DL play a role as redox mediator for facilitating electron transfer from the cathode to the oxygen. This study demonstrated for the first time that MFC equipped with an aerobic biocathode can be successfully applied to further treatment of effluent from an anaerobic system used to decolorize azo dye, providing both cost savings and high power output.     

Effect of anaerobic reactor process configuration on useful energy production

The effect of reactor process configuration on anaerobic production of useful energy (hydrogen and methane) from a complex substrate was investigated for the following reactor systems: suspended growth, two-phase mixed, two-stage mixed, upflow anaerobic sludge blanket (UASB) reactor, and two-phase UASB. The mixed two-phase and two-stage configurations yielded the highest specific energy productions of 13.3 and 13.4 kJ/g COD fed, respectively. Reactor process configuration influenced microbial pathways in acidogenic reactors in that butyrate was the predominant volatile acid in phased configurations, whereas acetate was predominant in the staged configuration. The UASB reactor achieved the highest average daily energy production per reactor volume of 101 kJ/L reactor-d. All reactor configurations achieved high COD removals on the order of 99%. However, hydrogen represented only 3% of the total energy produced by the two-phase mixed and two-phase UASB configurations. Theoretical analysis revealed that the maximum specific energy production by the two-phase suspended-growth configuration is only 9% higher than that for a single-stage mixed reactor. Consequently, the production of hydrogen from complex substrates in these process configurations does not seem to be justifiable solely from an energy point of view. Instead, it is suggested that phased anaerobic systems should be considered primarily for improved process stability whereas resultant hydrogen production is of secondary benefit.     

Magnetic binary oxide particles (MBOP): a promising adsorbent for removal of As (III) in water

Magnetic binary oxide particles (MBOP) synthesized using chitosan template has been investigated for uptake capacity of arsenic (III). Batch experiments were performed to determine the rate of adsorption and equilibrium isotherm and also effect of various rate limiting factors including adsorbent dose, pH, optimum contact time, initial adsorbate concentration and influence of presence cations and anions. It was observed that uptake of arsenic (III) was independent of pH of the solution. Maximum adsorption of arsenic (III) was ∼99% at pH 7.0 with dose of adsorbent 1 g/L and initial As (III) concentration of 1.0 mg/L at optimal contact time of 14 h. The adsorption equilibrium data fitted well to Langmuir and Freundlich isotherm. The maximum adsorption capacity of adsorbent was 16.94 mg/g. With increase in concentration of Ca²⁺, Mg²⁺ from 50 mg/L to 600 mg/L, adsorption of As (III) was significantly reduced while for Fe³⁺ the adsorption of arsenic (III) was increased with increase in concentration. Temperature study was carried out at 293 K, 303 K and 313 K reveals that the adsorption process is exothermic nature. A distinct advantage of this adsorbent is that adsorbent can readily be isolated from sample solutions by application of an external magnetic field. Saturation magnetization is a key factor for successful magnetic separation was observed to be 18.78 emu/g which is sufficient for separation by conventional magnate.     

Preparation of free‐standing chitosan membranes for Chlorella vulgaris harvest and examination on suppression of algae‐fouling properties

Free‐standing chitosan membranes were prepared using genipin as crosslinker, using several molecular weights of polyethylene glycol (PEG) as a void‐forming agent. The membrane surface formation and chitosan polymer chain crosslinking were confirmed through SEM and FTIR, respectively. The water flux was remarkably increased with increasing molecular weight of PEG employed in preparation of composite chitosan membrane (J∝[PEG(MW)]0.85), it appeared over 6000 Da of PEG. During Chlorella vulgaris harvest using chitosan membranes, focus was made on algae‐fouling caused by the deposition of cells and extracellular organic matter, and it was found that membranes employing lower molecular weight of PEG (under 10000 Da) had been maintaining the high flux recovery after alternating filtration cycles, in addition to PEG20000 containing membrane. The chitosan membrane prepared with lower molecular weight of PEG exhibited better suppression of algae‐fouling properties. The Chlorella vulgaris harvesting results indicated that cell rejection rate reached above 98%.     

The photocatalytic degradation of reactive black 5 using TiO2/UV in an annular photoreactor

The textile effluent is a major industrial polluter because it is highly colored, containing about 15% unfixed dyes as well as high levels of salts that can potentially be discharged into the environment. Photocatalytic oxidation using an thin gap annular UV reactor with TiO2 was used to break down the colour of a synthetic effluent ranging up to 400 ppm in dye concentration of Reactive Black 5 and up to 80 g/L in NaCl. Results show that the reaction kinetics was dominated by the TiO2 loading, the initial dye concentration, and the dissolved oxygen concentration; with the other parameters showing less significant effects. High rates of decolorization were found, with a linear fit to the Langmuir-Hinshelwood equation yielding a reaction rate constant (k) of 2.45 ppm/min, and an adsorption equilibrium constant (K) of 0.048 ppm(-1) based on color removal. The presence of the combination of high dissolved oxygen (15 ppm) and sodium chloride (up to 80 g/L) was found to enhance the decolorization and mineralization rates of the reactive dye. However, pH was found to not significantly affect the degradation rate. Since textile effluent is strongly alkaline, this result is significant, as no solution neutralisation is required and direct treatment of the effluent is possible.     

Removing 17β-estradiol from drinking water in a biologically active carbon (BAC) reactor modified from a granular activated carbon (GAC) reactor

Estrogenic compounds in drinking water sources pose potential threats to human health. Treatment technologies are needed to effectively remove these compounds for the production of safe drinking water. In this study, GAC adsorption was first tested for its ability to remove a model estrogenic compound, 17β-estradiol (E2). Although GAC showed a relatively high adsorption capacity for E2 in isotherm experiments, it appeared to have a long mass transfer zone in a GAC column reactor, causing an early leakage of E2 in the effluent. With an influent E2 concentration of 20 μg/L, the GAC reactor was able to bring down effluent E2 to ∼200 ng/L. To further enhance E2 removal, the GAC reactor was converted to a biologically active carbon (BAC) reactor by promoting biofilm growth in the reactor. Under optimal operating conditions, the BAC reactor had an effluent E2 concentration of ∼50 ng/L. With the empty bed contact times tested, the reactor exhibited more robust E2 removal performance under the BAC operation than under the GAC operation. It is noted that estrone (E1), an E2 biodegradation intermediate, was frequently detected in reactor effluent during the BAC operation. Results from this study suggested that BAC could be an effective drinking water treatment process for E2 removal and in the meantime E1 accumulation needs to be addressed.     

Investigation of isolation and immobilization of a microbial consortium for decoloring of azo dye 4BS

Eight high-effective decolorization strains were isolated by enrichment using Direct Fast Scarlet 4BS as sole source of carbon and energy. The optimal microbial consortium consisting of fungus 8-4(*) and bacterium 1-10 was selected by optimizing combination decolorization experiments with these eight freely suspended strains, whose decolorization activity was higher than individual strains due to synergistic reaction with each other. The optimal microbial consortium was also immobilized using polyvinyl alcohol (PVA) as the carrier. This paper optimized the immobilization and operational conditions, investigated the effect of the environmental factors (temperature, pH and dissolved oxygen (DO)) and initial dye concentration on the rate of decolorization by immobilized microbial consortium. The results showed that the optimal decolorization activity was observed in pH range (5-8), temperature range (25-40 degrees C) under shaking culture of high DO level. Decolorization with the optimal microbial consortium gave a relatively high maximum decolorization activity (ca. 81.25 mgl(-1)h(-1)), which occurred at a dye concentration of 1000 mgl(-1), suggesting the applicability of the strains in remediation of wastewater containing high azo dye concentrations. The immobilized beads could be reused for more than 30 cycles, without losing any degradation capacity. The changes of UV-visible spectra and the change curve of COD of 4BS solution before and after decolorization cultivation and the proliferation and distribution of microbial consortium in gel beads were also microscopically observed, which could be used for conferring the decolorization mechanisms of dye 4BS.     

Bioremediation of crystal violet using air bubble bioreactor packed with Pseudomonas aeruginosa

Seven water and sediment samples were collected and tested for decolorizing crystal violet. Pseudomonas aeruginosa was the most effective isolate for dye decolorization. The LC₅₀ of the crystal violet (115 mg/l) was measured using Artemia salina as a biomarker. The effect of different heavy metals on crystal violet decolorization was investigated. Cd²⁺ and Fe³⁺ ions showed marginal enhancement of the decolorization process, the rate was 1.35 mg/l/h compared to (1.25 mg/l/h) for the control. Phenol and m-cresol showed no effect on crystal violet decolorization, meanwhile p-cresol and p-nitrophenol reduced the decolorization rate to 1.07 and 0.01 mg/l/h, respectively. P. aeruginosa cells were immobilized by entrapment in agar-alginate beads. The beads were cultivated and reused in Erlenmeyer flask and in an air bubble column bioreactor and they enhanced the crystal violet decolorization rate to 3.33 and 7.5 mg/l/h, respectively.     

Continuous water treatment by adsorption and electrochemical regeneration

This study describes a process for water treatment by continuous adsorption and electrochemical regeneration using an air-lift reactor. The process is based on the adsorption of dissolved organic pollutants onto an adsorbent material (a graphite intercalation compound, Nyex^®1000) and subsequent electrochemical regeneration of the adsorbent leading to oxidation of the adsorbed pollutant. Batch experiments were carried out to determine the adsorption kinetics and equilibrium isotherm for adsorption of a sample contaminant, the organic dye Acid Violet 17. The adsorbent circulation rate, the residence time distribution (RTD) of the reactor, and treatment by continuous adsorption and electrochemical regeneration were studied to investigate the process performance. The RTD behaviour could be approximated as a continuously stirred tank. It was found that greater than 98% removal could be achieved for continuous treatment by adsorption and electrochemical regeneration for feed concentrations of up to 300 mg L⁻¹. A steady state model has been developed for the process performance, assuming full regeneration of the adsorbent in the electrochemical cell. Experimental data and modelled predictions (using parameters for the adsorbent circulation rate, adsorption kinetics and isotherm obtained experimentally) of the dye removal achieved were found to be in good agreement.     

Multifunctional biomagnetic capsules for easy removal of phenol and bisphenol A

This paper reports fabrication, optimization and characterization of multifunctional biocapsules with immobilized enzyme using a layer-by-layer configuration and their application for removal of phenol and bisphenol A (BPA). The method is based on the combined use of enzymatic oxidation of the BPA and subsequent binding of the reaction product onto a chitosan core biopolymer. This platform has multiple functions including: (1) enzymatic degradation of BPA, (2) adsorption of the degraded compound within the core material, (3) colorimetric quantification and (4) magnetic capabilities. We examined various configurations of core/shell structures of alginate and chitosan and determined the stability and the optimum conditions in which these structures provide the most effective removal capacity. The amount of BPA that can be removed per capsule is 5.6 ppm while phenol can be removed up to 10 ppm per capsule within 15 h.     

Electro-peroxone treatment of Orange II dye wastewater

Degradation of a synthetic azo dye, Orange II, by electro-peroxone (E-peroxone) treatment was investigated. During the E-peroxone process, ozone generator effluent (O₂ and O₃ gas mixture) was continuously sparged into an electrolysis reactor, which was equipped with a carbon-polytetrafluorethylene (carbon-PTFE) cathode to electrochemically convert the sparged O₂ to H₂O₂. The in-situ generated H₂O₂ then reacted with the sparged O₃ to produce •OH, which can oxidize ozone-refractory organic pollutants effectively. Thus, by simply combining conventional ozonation and electrolysis processes, and using a cathode that can effectively convert O₂ to H₂O₂, the E-peroxone process degraded Orange II much more effectively than the two processes individually. Complete decolorization and 95.7% total organic carbon (TOC) mineralization were obtained after 4 and 45 min of the E-peroxone treatment, respectively. In comparison, only 55.6 and 15.3% TOC were mineralized after 90 min of the individual ozonation and electrolysis treatments, respectively. In addition to its high efficiency, the E-peroxone process was effective over a wide range of pH (3–10) and did not produce any secondary pollutants. The E-peroxone process can thus provide an effective and environmentally-friendly alternative for wastewater treatment.     

Repeated phosphate removal from recirculating aquaculture system using cyanobacterium remediation and chitosan flocculation

Unicellular cyanobacterium Synechocystis sp. was used for phosphate removal in a recirculating aquaculture system. The cell harvesting was performed using chitosan solution in this study. The parameters (i.e. cell density, pH of cell suspension and chitosan concentration) affecting the flocculation efficiency of chitosan were investigated. With the optimal condition, the repeated flocculation for phosphate removal in a photobioreactor was demonstrated. The results show that the flocculation efficiency of chitosan depends on cell density, pH of cell suspension and chitosan concentration. The optimal flocculation process could be accomplished by adjusting the pH to 7.2 before adding 20 mg/L chitosan followed by pH adjustment to 7.5. With single inoculation, the sequential process of phosphate removal using cyanobacterial uptake followed by cell flocculation using chitosan with the optimal condition in the photobioreactor was successfully achieved for 12 cycles with water from a recirculating fish tank.