Maximum Decolorization Rate Research Articles

Synthesis of flower-like manganese wad and its decolorization performance for azo dye Congo red

Flower-like manganese wad(MW) with high activity was synthesized via ultrasonic-assisted redox reaction of sole manganese salt MnO4−. MW was characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS). The experimental results indicate that the maximum decolorization rate of Congo red(CR) reached above 95% within 15 min in a wide pH range from 2.0 to 6.0. Results also show that MW has excellent decolorization performance for azo dye CR which implies potential application for removing dye pollutants from industrial effluents.

Facile decolorization of methylene blue with flower-like manganese wads

Flower-like manganese wads (MWs) were synthesized via a simple and inexpensive ultrasonic irradiation method for the first time. MWs were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray and transmission electronic microscopy. The decolorization efficiency of MWs for methylene blue (MB) azo dye was examined as a function of pH, stirring time, MW dosage and initial concentration of the MB solution. Results show that MWs have excellent decolorization performance for MB with a higher efficiency (and without using H2O2 or other devises such as UV light and ultrasonic irradiation) compared to other catalysts, such as the mixture of Mn3O4 and H2O2 (with a maximum decolorization rate of 99.7% in 3 h), ZnS and CdS under light irradiation (with a maximum decolorization rate of 73% in 6 h), and sulfate modified titania under solar radiation (with a maximum decolorization rate of nearly 100% in 4 h).

Dye Congo Red adsorptive decolorization by adsorbents obtained from Trametes pubescens pellets

A design of various dyes decolorization was conducted with the adsorbents obtained from Trametes pubescens pellets in submerged cultures. The results demonstrated that the adsorbents prepared by moist heat sterilization exhibited preferable decolorization capacity on azo dye Congo Red. A maximum decolorization rate of Congo Red of 72.31% was observed, which was all around 2.25 times higher than that of anthraquinone dye Disperse Blue B at the same level. Moreover, the decolorization rate-dependent influencing factors, i.e. salinity, Tween80, temperature, pH, and dye concentration, were optimized by Box–Behnken full factorial design. When they were 1.06% (m/V), 3.50% (V/V), 41.0°C, 6.15, and 114.34 mg/L respectively, the decolorization rate was up to 100% after a 7-day incubation period. Adsorptive decolorization was caused by the electrostatic forces between dye molecules and adsorbents obtained from T. pubescens pellets, amido group played a major role during the biosorption process, and this course did not alter any functional groups at all, as evidenced by fourier transform infrared spectroscopy, chemical modifications, and scanning electron microscope data. All the results indicated that the adsorbents performed well at lowering the possible limitations arising out of the poor stability and enhancing convenient operability.

Flocculation Performance of Trimethyl Quaternary Ammonium Salt of Lignin-Sodium Alginate Polyampholyte

In order to improve the molecular weight and application of a lignin byproduct, the trimethyl quaternary ammonium salt of lignin-sodium alginate polyampholyte (QL-SA) was prepared with trimethyl quaternary ammonium salt of lignin (QL) and sodium alginate (SA), using the cross-linker glutaraldehyde. Its structure was analyzed by FTIR, SEM, and analysis of nitrogen and carboxylic contents. Results showed that QL and SA were grafted successfully. The nitrogen content was diminished from 4.21% to 3.69% and its carboxyl content increased from 2.66 mmol/g to 6.47 mmol/g. The product behaved as flocculant by electrostatic interactions and bridging actions. The effects of QL-SA on the flocculation performance of dyes were investigated with methylene blue and acid black ATT water as the representative dyes. The maximum decolorization rate of acid black ATT was 94.91% and methylene blue was 97.11% under the corresponding optimal conditions (5 g/L of the flocculant at pH 3, 30 °C, and 8 g/L at pH 8, 30 °C). The effect of QL-SA was found to be markedly superior to SA and QL on the whole. The QL-SA showed promise for practical applications.

Decolorization of Orange II using an anaerobic sequencing batch reactor with and without co-substrates

AbstractWe investigated the decolorization of Orange II with and without the addition of co-substrates and nutrients under an anaerobic sequencing batch reactor (ASBR). The increase in COD concentrations from 900 to 1750 to 3730 mg/L in the system treating 100 mg/L of Orange II-containing wastewater enhanced color removal from 27% to 81% to 89%, respectively. In the absence of co-substrates and nutrients, more than 95% of decolorization was achieved by the acclimatized anaerobic microbes in the bioreactor treating 600 mg/L of Orange II. The decrease in mixed liquor suspended solids concentration by endogenous lysis of biomass preserved a high reducing environment in the ASBR, which was important for the reduction of the Orange II azo bond that caused decolorization. The maximum decolorization rate in the ASBR was approximately 0.17 g/hr in the absence of co-substrates and nutrients.

Photodegradation of Hazardous Dye Naphthol Yellow S Over Titanium Dioxide

The present study involves the photocatalytic degradation of a hazardous dye Naphthol Yellow S, employing heterogeneous photocatalytic process. Photocatalytic activity of semiconductor such as anatase titanium dioxide (TiO2) has been investigated. An attempt has been made to study the effect of process parameters viz., amount of catalyst, concentration of dye, temperature, electron acceptor hydrogen peroxide (H2O2) and pH on photocatalytic degradation of Naphthol Yellow S. The experiments were carried out by irradiating the aqueous solutions of dyes containing photocatalysts with ultraviolet (UV) light. The rate of decolorization was estimated from residual concentration spectrophotometrically. The degradation rate of Naphthol Yellow S was high when the photolysis was carried out in the absence of TiO2 and it was negligible in the absence of UV light. The results obtained from the experiments after adding H2O2/TiO2 show that maximum decolorization rate is achieved by the combination of (UV + TiO2 + H2O2). The decolorization efficiencies are 2.6%, 34.8%, 70.2%, and 95.3% in the runs UV, UV + H2O2, UV + TiO2, and (UV + TiO2 + H2O2) after approximately 40 minutes illumination periods, respectively. The optimum experimental conditions for the degradation of the dye are dye concentration 8 × 10−5 M, pH 5.4, and 12 mg catalyst dose. At the used experimental conditions the substrate photooxidation rate follows pseudo-first order kinetics. The adsorption trends of Naphthol Yellow S at various initial concentrations followed the Langmuir isotherm trend. Measuring chemical oxygen demand (COD) also monitors the toxicity of the degraded dye solution and a significant decrease is observed, which implies the photodegradation through TiO2 a safer technique. Results show that the employment of efficient photocatalysts and the selection of optimal operational parameters may lead to complete decolorization and to substantial decrease of the chemical oxygen demand (COD) of the dye solutions.

Decolorization and Biotransformation of Triphenylmethane Dye, Methyl Violet, by Aspergillus sp. Isolated from Ladakh, India

Methyl violet, used extensively in the commercial textile industry and as a biological stain, is a hazardous recalcitrant. Aspergillus sp. strain CB-TKL-1 isolated from a water sample from Tsumoriri Lake, Karzok, Ladakh, India, was found to completely decolorize methyl violet within 24 h when cultured under aerobic conditions at 25 degrees C. The rate of decolorization was determined by monitoring the decrease in the absorbance maxima of the dye by UV-visible spectroscopy. The decolorization of methyl violet was optimal at pH 5.5 and 30 degrees C when agitated at 200 rpm. Addition of glucose or arabinose (2%) as a carbon source and sodium nitrate or soyapeptone (0.2%) as a nitrogen source enhanced the decolorization ability of the culture. Furthermore, the culture exhibited a maximum decolorization rate of methyl violet after 24 h when the C:N ratio was 10. Nine N-demethylated decolorized products of methyl violet were identified based on UV-visible spectroscopy, Fourier transform infrared (FTIR), and LC-MS analyses. The decolorization of methyl violet at the end of 24 h generated mono-, di-, tri-, tetra-, penta-, and hexa-Ndemethylated intermediates of pararosaniline. The variation of the relative absorption peaks in the decolorized sample indicated a linear decrease of hexa-N-demethylated compounds to non-N-demethylated pararosaniline, indicating a stepwise N-demethylation in the decolorization process.

Interaction in anaerobic biodecolorization of mixed azo dyes of Acid Red 1 and Reactive Black 5 under batch and continuous conditions

Anaerobic biodecolorization of mixed azo dyes of Acid Red 1 (AR1) and Reactive Black 5 (RB5) was investigated by both batch assays and a continuous process consisting of a photo-rotating biological contactor (PRBC) and an aerobic moving bed biofilm reactor (MBBR). Batch assays showed that the decolorization of RB5 in the mixed dye systems is in preference to AR1, and decolorization products of RB5 had acted as redox mediators to stimulate the decolorization of AR1. The addition of a final concentration of 720 mg/L RB5 increased the maximum decolorization rate of 420 mg/L of AR1 by 1.5-fold than RB5-free control. During the continuous treatment of AR1 with abundant cosubstrate, the addition of RB5 increased the biodecolorization efficiency of AR1 from 62.9% to 91.0%. The analysis using cyclic voltammetry (CV) and high performance liquid chromatography/mass spectrometry (HPLC–MS) indicates the mediating properties of the decolorization products from RB5.

Kinetics of zero-valent iron reductive transformation of the anthraquinone dye Reactive Blue 4

The effect of operational conditions and initial dye concentration on the reductive transformation (decolorization) of the textile dye Reactive Blue 4 (RB4) using zero-valent iron (ZVI) filings was evaluated in batch assays. The decolorization rate increased with decreasing pH and increasing temperature, mixing intensity, and addition of salt (100 g L −1 NaCl) and base (3 g L −1 Na 2CO 3 and 1 g L −1 NaOH), conditions typical of textile reactive dyebaths. ZVI RB4 decolorization kinetics at a single initial dye concentration were evaluated using a pseudo first-order model. Under dyebath conditions and at an initial RB4 concentration of 1000 mg L −1, the pseudo first-order rate constant ( k obs) was 0.029 ± 0.006 h −1, corresponding to a half-life of 24.2 h and a ZVI surface area-normalized rate constant ( k SA) of 2.9 × 10 −4 L m −2 h −1. However, as the initial dye concentration increased, the k obs decreased, suggesting saturation of ZVI surface reactive sites. Non-linear regression of initial decolorization rate values as a function of initial dye concentration, based on a reactive sites saturation model, resulted in a maximum decolorization rate ( V m) of 720 ± 88 mg L −1 h −1 and a half-saturation constant ( K) of 1299 ± 273 mg L −1. Decolorization of RB4 via a reductive transformation, which was essentially irreversible (2–5% re-oxidation), is believed to be the dominant decolorization mechanism. However, some degree of RB4 irreversible sorption cannot be completely discounted. The results of this study show that ZVI treatment is a promising technology for the decolorization of commercial, anthraquinone-bearing, spent reactive dyebaths.

Adsorption and photocatalytic decolorization of a synthetic dye erythrosine on anatase TiO 2 and ZnO surfaces

The UV radiation assisted photocatalytic decolorization/degradation kinetics of an anionic dye erythrosine (ER), has been studied over TiO 2 and ZnO surfaces. Since adsorption is the prerequisite condition for decolorization/degradation of dye molecules in presence of heterogeneous catalysis, the Langmuir and Freundlich isotherms were examined to verify the adsorption intensity. Standard adsorption free energy measurement implies that the adsorption of ER on both TiO 2 and ZnO surfaces is spontaneous endothermic process. The effect of catalyst loading (TiO 2/ZnO) revealed the fact that the maximum decolorization rate is obtained under an optimized catalyst loading condition. The decolorization efficiency was also investigated over the pH range of 5.0–10.0 indicating that increasing pH enhances decolorization efficiency. The influence of H 2O 2 on decolorization efficiency was found noticeable since it is a hydroxyl radical provider. The kinetic study of this degradation indicates that under the experimental condition, the decolorization mechanism follows zero order kinetics on the basis of Langmuir–Hinshelwood (L–H) heterogeneous reaction mechanism.

Exploring bioaugmentation strategies for azo-dye decolorization using a mixed consortium of Pseudomonas luteola and Escherichia coli

In this study, replacement-series method and contour analysis were applied to investigate optimal bioaugmentation strategies for the treatment of a dye-contaminated aquatic system using a constructed mixed-community for biodecolorization of a model azo dye Reactive Red 22. The novelty emphasizes that a species without essential target functions in a mixed culture could still play a crucial role in influencing the treatment performance. That is, although non-decolorizers (i.e., Escherichia coli DH5α) were considered metabolically “dormant” in this model binary-biosystem, their presence still significantly enhanced decolorization performance of the decolorizers (i.e., Pseudomonas luteola). In aerobic growth conditions, E. coli DH5α possessed a growth advantage to out-compete P. luteola due to preferential growth rate of DH5α. However, in static decolorization conditions, DH5α seemed to produce decolorization-stimulating extracellular metabolites to help the major decolorizer ( P. luteola) decompose the toxic pollutant (i.e., the azo dye) in a short term for the benefit of total survival in the environment. The experimental results show that the presence of E. coli DH5α increased the decolorization efficiency of P. luteola even though DH5α was an inefficient decolorizer in this microbial community. Thus, addition of DH5α into a mixed culture containing P. luteoa as a major decolorizer may lead to a bioaugmentation effect on decolorization activity. The optimal population ratio for bioaugmentation was determined by the contour analysis. The results indicate that the optimal community species ecology for maximum overall decolorization rate almost maintained at a ratio of one viable P. luteola (0.78 × 10 9 cells/mL) to one DH5α cell (0.70 × 10 9 cells/mL), representing a maximal diversity (i.e., H max ≅ 1.0).

Biological Decolorization of Reactive Anthraquinone and Phthalocyanine Dyes Under Various Oxidation–Reduction Conditions

The decolorization of two anthraquinone dyes (Reactive Blue 4 [RB4] and Reactive Blue 19 [RB19]) and two phthalocyanine dyes (Reactive Blue 7 [RB7] and Reactive Blue 21 [RB21]) was investigated at an initial dye concentration of 300 mg/L using an unacclimated, enrichment culture. The culture was fed a mixture of organic compounds and maintained initially under aerobic conditions, and then progressively developed anoxic/ anaerobic conditions. Biotransformation-related decolorization of the dyes did not take place under aerobic conditions, but use of the feed organic mixture and biomass production by the enrichment culture were not affected. Complete ammonia removal occurred in the control and all dye-amended cultures. The development and extent of nitrification were much lower in the latter cultures, in which ammonia removal via air stripping was the dominant mechanism. Prolonged incubation of the culture under anoxic/anaerobic conditions with multiple carbon source additions resulted in a high decolorization extent of anthraquinone dyes (over 84%) and only partial decolorization of phthalocyanine dyes (49 to 66%). Development of significant methanogenic activity took place in the control and, to a lesser extent, in the two phthalocyanine dye-amended cultures, but the anthraquinone dyes severely inhibited the development of methanogenic activity. The RB4 and RB19 decolorization was attributed to nonreversible, microbially mediated dye transformation(s), demonstrated by the accumulation of decolorization products with absorbance maxima in the 420- to 460-nm region. The decolorization of RB4 and RB19 followed Michaelis-Menten kinetics. At an initial dye concentration of 300 mg/L, the observed maximum decolorization rate per unit biomass was 9.1 and 37.5 mg dye/mg volatile suspended solids x day for the RB4 and RB19, respectively. Thus, partial decolorization of reactive phthalocyanine dyes and extensive biological decolorization of reactive anthraquinone dyes is feasible only under anoxic/anaerobic conditions.

Decolorization kinetics of the azo dye Reactive Red 2 under methanogenic conditions: effect of long-term culture acclimation

The biological decolorization of the textile azo dye Reactive Red 2 was investigated using a mixed, mesophilic methanogenic culture, which was developed with mixed liquor obtained from a mesophilic, municipal anaerobic digester and enriched by feeding a mixture of dextrin/peptone as well as media containing salts, trace metals and vitamins. Batch decolorization assays were conducted with the unacclimated methanogenic culture and dye decolorization kinetics were determined as a function of initial dye, biomass, and carbon source concentrations. Dye decolorization was inhibited at initial dye concentrations higher than 100 mg l(-1) and decolorization kinetics were described based on the Haldane model. The effect of long-term culture exposure to the reactive dye on decolorization kinetics, culture acclimation, as well as possible dye mineralization was tested using two reactors fed weekly for two years with an initial dye concentration of 300 mg l(-1) and a mixture of dextrin/peptone. The maximum dye decolorization rate after a 2-year acclimation at an initial dye concentration of 300 mg l(-1) was more than 10-fold higher as compared to that obtained with the unacclimated culture. Aniline and the o-aminohydroxynaphthalene derivative resulting from the reductive azo bond cleavage of the dye were detected, but further transformation(s) leading to dye mineralization were not observed. Reactive Red 2 did not serve as the carbon and energy source for the mixed culture, and dye decolorization was sustained by the continuous addition of dextrin and peptone. Thus, biological decolorization of reactive azo dyes is feasible under conditions of low redox potential created and maintained in overall methanogenic systems, but supply of a biodegradable carbon source is necessary.

Biological Decolorization of the Azo Dye Reactive Red 2 Under Various Oxidation–Reduction Conditions

The decolorization of the azo dye reactive red 2 (RR2) was investigated under aerobic, anoxic, and methanogenic conditions. The dye was not decolorized by an aerobic culture kept under aerobic conditions for 7 days. However, incubation of the same culture under anoxic conditions resulted in RR2 decolorization with an initial rate of 40 mg/L·d and to an extent of 91.7% after the culture oxidation–reduction potential (ORP) dropped to less than ‐50 mV. A second addition of RR2 to the same culture kept under anoxic conditions resulted in a greater initial RR2 decolorization rate (86 mg/L·d) at an ORP value of –250 mV. Decolorization of RR2 at an initial dye concentration of 300 mg/L was achieved by an unacclimated methanogenic culture at an initial rate of 83 mg/L·d and without any inhibition. However, as a result of acclimation, initial RR2 decolorization rates of 523 and 1050 mg/L·d were achieved by the same methanogenic culture after 5 months and 2 years of weekly additions of 300 mg/L RR2, respectively. Dye decolorization followed Michaelis–Menten kinetics. Under methanogenic conditions and at an initial dye concentration of 300 mg/L, the maximum RR2 decolorization rate per unit biomass was 0.12 and 0.70 mg RR2/mg volatile suspended solids d without acclimation and after a 2‐year acclimation, respectively. Lack of significant RR2 decolorization was observed in autoclaved methanogenic culture controls. Therefore, the reductive cleavage of the dye azo bond resulting in the decolorization of RR2 and formation of aromatic amines was biologically mediated and is attributed to the reduced conditions created and maintained by the anoxic and anaerobic cultures. Thus, biological decolorization of reactive azo dyes is feasible under anoxic–anaerobic conditions and should be further explored for textile wastewater management.