Azo Dye Wastewater Treatment Research Articles

Azo dye wastewater treatment in a novel three-dimensional electrode reactor

Azo dye wastewater treatment in a novel three-dimensional electrode reactor

Activated carbon modified with nano manganese dioxide triggered electron transport pathway changes for boosted anaerobic treatment of dyeing wastewater

Herein, an expanded granular sludge bed (EGSB) reactor with activated carbon (AC)-nano manganese dioxide (MnO2) added was employed for azo dye wastewater treatment to investigate its effectiveness at decolorizing of azo dyes and removing COD. The results showed that the treatment of azo dye wastewater with the AC-MnO2 modified EGSB reactor gave an 83% average decolorization efficiency, which was more efficient than the pure AC modified EGSB reactor. Moreover, the COD removal and changes in the intermediate products were controlled by AC-MnO2. Additionally, there was a sharp increase in the sludge conductivity, while there was a significant decrease in the coenzyme F420 concentration with long-term operation. Moreover, electrochemical analysis showed that the addition of AC-MnO2 can enhance electron transfer in anaerobic system. The AC-MnO2 can act as redox mediator; in the presence of the Mn4+/Mn2+ cycle, accelerating the electron transfer between the microbial cells and dyes, thereby promoting the decolorization of azo dyes. This caused a decrease in the methanogenic activity. Furthermore, high-throughput sequencing showed that the relative abundances of Pseudomonas and Desulfovibrio were significantly high among the acidogenic bacteria community, while Methanobacterium and Methanosaeta had very low abundances from among the methanogenic archaea community.

Detoxification of azo dye Direct Black G by thermophilic Anoxybacillus sp. PDR2 and its application potential in bioremediation

Direct Black G (DBG) is a highly toxic synthetic azo dye which is difficult to degrade. Biological treatment seems to be a promising option for the treatment of azo dye containing effluent. A thermophilic bacterial strain (Anoxybacillus sp. PDR2) previously isolated from the soil can effectively remove DBG. However, the molecular underpinnings of DBG degradation and the microbial detoxification ability remains unknown. In the present study, the genetic background of PDR2 for the efficient degradation of DBG and its adaptation to azo dye-contaminated environments was revealed by bioinformatics. Moreover, the possible biodegradation pathways were speculated based on the UV–vis spectral analysis, FTIR, and intermediates identified by LC-MS. Additionally, phytotoxicity and the comet experiment studies clearly indicated that PDR2 converts toxic azo dye (DBG) into low toxicity metabolites. The combination of biodegradation pathways and detoxification analysis were utilized to explore the molecular degradation mechanism and bioremediation of azo dye for future applications. These findings will provide a valuable theoretical basis for the practical treatment of azo dye wastewater.

Simulating the synergy of electron donors and different redox mediators on the anaerobic decolorization of azo dyes: Can AQDS-chitosan globules replace the traditional redox mediators?

During anaerobic treatment of azo dye wastewater, the decolorization efficiency is low and dissolved redox mediators (RMs) added to the system are easy lost. In order to solve these issues, immobilized RMs have been a hot area of research. In this study a novel immobilized RM material, disodium anthraquinone-2,6-disulfonate (AQDS)-chitosan globules, which is natural, highly efficient and environmentally friendly, was prepared. Compared with natural immobilized RMs (activated carbon) and dissolved RMs (AQDS), it can be considered that it has a significant strengthening effect on the anaerobic biological degradation and decolorization of azo dye wastewater. An electron donor (ED, glucose) or RM (AQDS solution) was dosed into an anaerobic reactor to determine the enhancing effect and appropriate concentration for the decolorization treatment. The results indicate that a certain concentration of ED or RM [300 mg/L (1.667 mmol/L) glucose or 200 μmol/L AQDS solution] can improve effectively the anaerobic biological degradation and decolorization effect of azo dye wastewater. While by adding both 300 mg/L (1.667 mmol/L) glucose and 300 μmol/L AQDS (the concentrations were the initial reactive concentrations) together the decolorization efficiency was improved further. At the same time, the synergy of ED (glucose) and RM (AQDS solution) on the anaerobic decolorization of azo dye was simulated by the central combination design. A mathematical model for the decolorization efficiency has been established. According to this model, the hydraulic retention time of the best decolorization speed and efficiency has been obtained.

Photocatalytic Activity of Magnetic Nano-β-FeOOH/Fe3O4/Biochar Composites for the Enhanced Degradation of Methyl Orange Under Visible Light.

A novel nano-β-FeOOH/Fe3O4/biochar composite with enhanced photocatalytic performance and superparamagnetism was successfully fabricated via an environmentally friendly one-step method. The structural properties of the prepared composite were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and a vibrating sample magnetometer. The XPS spectrum of the as-prepared composites confirmed the presence of Fe-O-C bonds between β-FeOOH and biochar, which could be conducive to transfer photo-generated electrons. UV-vis spectroscopy confirmed the existence of an electron–hole connection between β-FeOOH and biochar, which promoted the rapid interface transfer of photogenerated electrons from β-FeOOH to biochar. These novel structures could enhance the response of biochar to accelerate the photoelectrons under visible light for more free radicals. Electron spin resonance analysis and free radical quenching experiments showed that •OH was the primary active species in the photodegradation process of methyl orange by nano-β-FeOOH/Fe3O4/biochar. In the synergistic photocatalytic system, β-FeOOH/Fe3O4/biochar exhibited excellent catalytic activity for the degradation of azo dye (methyl orange), which is 2.03 times higher than that of the original biochar, while the surface area decreased from 1424.82 to 790.66 m2·g−1. Furthermore, β-FeOOH/Fe3O4/biochar maintained a stable structure and at least 98% catalytic activity after reuse, and it was easy to separate due to its superparamagnetism. This work highlights the enhanced photocatalytic performance of β-FeOOH/Fe3O4/biochar material, which can be used in azo dye wastewater treatment.

Degradation of azo dye wastewater by the combination process of 3D BER and CW-MFC

The treatment of azo dye wastewater has become a hot issue in the area of water pollution control. In this paper, a novel combined process of constructed wetland-microbial fuel cell (CW-MFC) and three dimensional biofilm electrode reactor (3D BER) was carried out for treatment of reactive brilliant red X-3B dye wastewater. Decolorization rate, COD removal and electricity generation in the combination process were studied, and the main factors affecting the system’s performance were also investigated. The results showed that the decolorization rate of combination process (3D BER-CW-MFC) was over 96%, and closed-circuit CW-MFC had better decolorization effect than open-circuit CW-MFC. COD removal rate of the combination process was far higher than the 3D BER and CW-MFC operated alone (78.9%∼90.8% and 50.6%∼66.2%, respectively). With the increase of influent dye concentration in the 3D BER, Cell voltages of the CW-MFCs all increased firstly and then decreased. The cell voltage reached the maximum at influent dye concentration of 600 mg L-1, and then decreased by 6.42%∼14.34% after the dye concentration increased to 1000 mg L-1. In addition, cell voltage could be enhanced by increasing the cathode area of CW-MFCs, due to improved cathode potential and reduced total internal resistance of the system.

Enhanced anaerobic treatment of azo dye wastewater via direct interspecies electron transfer with Fe3O4/sludge carbon

In this study, enhancement of anaerobic treatment of azo dye wastewater with Fe3O4/SC is investigated. Fe3O4/sludge carbon (SC) is prepared from waste activated sludge using a simple impregnation method. Two identical laboratory-scale upflow anaerobic sludge blanket reactors with a working volume of 1.5 L are filled with 2 g/L of SC (reactor 1) and 2 g/L of Fe3O4/SC (reactor 2). Another reactor (reactor 0) is operated as a control. FTIR, XPS, SEM, and BET results indicate that Fe3O4 is successfully loaded on the SC. Addition of Fe3O4/SC to the reactor results in high chemical oxygen demand (78.13%) and color (97.60%) removal rates. Furthermore, Fe3O4/SC effectively decreases the amount of aniline generated and increases CH4 production. The Fe3O4/SC anaerobic system is stable with fast recovery in terms of both organic matter removal and aniline control with high toxic substance concentrations and fluctuating organic loads. Moreover, Fe3O4/SC greatly enhances enzymatic activity and sludge granulation, which could greatly improve anaerobic reactor stability. High electron transport system and conductivity values and the enrichment of Geobacter and Methanosaeta species confirm that direct interspecies electron transfer occurs with Fe3O4/SC in the reactor. These results provide a scientific basis for further applications to azo dye wastewater treatment and promote resource utilization of waste sewage sludge.

Genome and transcriptome analysis of a newly isolated azo dye degrading thermophilic strain Anoxybacillus sp.

Understanding azo dye degrading enzymes and the encoding of their functional genes is crucial for the elucidation of their molecular mechanisms. In this study, a thermophilic strain capable of degrading azo dye was isolated from the soil near a textile dye manufacturing factory. Based on its morphological, physiological and biochemical properties, as well as 16S rRNA gene sequence analysis, the strain was identified as Anoxybacillus sp. PDR2. The decolorization ratios of 100–600 mg/L Direct Black G (DBG) by strain PDR2 reached 82.12–98.39% within 48 h of dyes. Genome analysis revealed that strain PDR2 contains a circular chromosome of 3791144 bp with a G + C content of 42.48%. The genetic basis of azo dye degradation by strain PDR2 and its capacity to adapt to harsh environments, were further elucidated through bioinformatics analysis. RNA-Seq and qRT-PCR technology confirmed that NAD(P)H-flavin reductase, 2Fe-2S ferredoxin and NAD(P)-dependent ethanol dehydrogenase genes expressed by strain PDR2, were the key genes involved in DBG degradation. The combination of genome and transcriptome analysis was utilized to explore the key genes of strain PDR2 involved in azo dye biodegradation, with these findings providing a valuable theoretical basis for the practical treatment of azo dye wastewater.

Enhanced mineralization of Reactive Black 5 by waste iron oxide via photo-Fenton process

Advanced oxidation process is a promising technology for the treatment of azo dye wastewater, owing to its high degradation performance and less secondary contamination. Herein, the mineralization of azo dye Reactive Black 5 (RB5) by the heterogeneous photo-Fenton process was investigated in a three-phase fluidized bed reactor. The waste iron oxide (denoted as BT) obtained from tannery wastewater process with Fenton’s reagent was selected as a heterogeneous catalyst. The introduction of BT to the UV/H2O2 process (UV/H2O2/BT) shows obviously higher mineralization efficiency because ferric complexes of carboxylic acid, the degradation intermediates of RB5, could be readily decomposed by UV irradiation. The decolorization was achieved by homogenous photo-Fenton reaction induced by leached iron, while the mineralization was contributed to heterogeneous oxidation. Under the conditions of 254 nm UV irradiation, 19.00 mM H2O2, 2.0 g L–1 catalyst loading and natural pH0 of 5.0, 90.2% TOC removal of RB5 could be achieved. The catalyst indicated an acceptable stability and reusability after four cycles. The proposed heterogeneous photo-Fenton process with stable performance is environmental-friendly for the mineralization of RB5.

Electrochemical oxidative degradation of X-6G dye by boron-doped diamond anodes: Effect of operating parameters

Boron-doped diamond (BDD) is an excellent electrode material. As the anode in an electrochemical degradation tank, BDD has been receiving widespread attention for the treatment of azo dye wastewater. In this study, electrochemical oxidation (EO) was applied to electrolyze reactive brilliant yellow X-6G (X-6G) using BDD as the anode and Pt as the cathode. To balance the degradative effects and power consumption in the electrolysis process, the effects of a series of operating parameters, including current density, supporting electrolyte, initial pH, reaction temperature and initial dye concentration, were systematically studied. The oxidative process was analyzed by color removal rate, and the degree of mineralization was evaluated by TOC. The optimal experimental parameters were finally determined: 100 mA cm−2, 0.05 M Na2SO4 electrolyte, pH 3.03, 60 °C, and an initial X-6G concentration of 100 mg L−1. As a result, color completely disappeared after 0.75 h of electrolysis, and TOC was removed by 72.8% after 2 h of electrolysis. In conclusion, the EO of a BDD electrode as an anode can be a potent treatment method for X-6G synthetic wastewater.

Heterologous expression of azoreductase-encoding gene azrS of Bacillus sp. MR-1/2 for enhanced azo dye decolorization and wastewater treatment.

In Pakistan, 55% of textile exports are contributed by textile-units of Faisalabad. The effluents of these textile units, being discharged without any treatment, contain the contamination of a huge amount of synthetic azo dyes. The objective of the current research was to evaluate the contribution of an azoreductase-encoding gene (azrS) from a pre-characterized azo dye decolorizing bacterial strain Bacillus sp. MR-1/2 in a high copy number host system (pUC19-T7-Top-T) of Escherichia colistrain DH5α followed by in-silico prediction of azoreductase enzyme (AzrS) function. The recombinant cells that contained azrS had a significantly higher rate of color removal in congo red and reactive black-5 dyes when compared to wild-type MR-1/2 and E. coli DH5α after 72h of incubation. Moreover, we were able to show that the recombinant strain significantly reduced the values of all tested parameters (pH, EC, turbidity, TSS, and COD) in actual wastewater. In support of our results, it was also predicted through bioinformatics analysis that the deduced azoreductase protein of strain MR-1/2 is linked with the dye decolorization ability of the strain through NAD(P)H-ubiquinone: oxidoreductase activity. Furthermore, we also found that the deduced protein resembled closely related proteins of protein databank in many features, yet some unique features were predicted in the enzyme activity of strain MR-1/2. It was concluded that the recombinant strain could be examined in pilot-scale experiments for textile wastewater treatment.

Treatment of azo dye wastewater by the self-flocculating marine bacterium Aliiglaciecola lipolytica

Microorganisms with capacity to degrade and separate azo dyes from water are potential in developing eco-friendly and cost-effective method for azo wastewatertreatment, challenged for large volume, toxicity and high salinity. Marine bacterium Aliiglaciecola lipolytica (A. lipolytica) was examined to decolorize Congo Red (CR), a typical azo dye in sythesized water. The results showed that the bacterium could achieve aerobic decolorization (more than 90%) and self-flocculation under wide conditions (temperature 25–35°C, initial CR concentration 25–100 mg L−1, salinity 0–20 g L−1, pH 5–6, glucose concentration 4–8 g L−1, and (NH4)2SO4 concentration 1–2 g L−1). It was proved that the dyes were firstly adsorbed onto cells by extracellular polymeric substances (EPS), and about 46% of them were then degraded. This degradation process was through co-metabolism with the glucose and also mediated by azoreductase and intracellular laccase. The azo linkage (-N=N-), the chromophore groups (C-N) and sulfonate groups (−SO3) were cleaved; then the naphthalene rings were decomposed, which made CR into smaller molecules. The bacterium secreted many EPS, especially protein-like and humic acid substances in tightly bound EPS (TB-EPS), which could decrease electrostatic force and increase hydrophobicity of cell surface contributed to dye adsorption and cell self-flocculation. It was stressed that self-flocculation marine bacterium A. lipolytica could provide a promising technique for azo dye wastewater treatment.

Evaluation of integrated UFCW-MFC reactor for azo dye wastewater treatment and simultaneous bioelectricity generation

Evaluation of integrated UFCW-MFC reactor for azo dye wastewater treatment and simultaneous bioelectricity generation

Acceleration of Persulfate Activation by MIL-101(Fe) with Vacuum Thermal Activation: Effect of FeII/FeIII Mixed-Valence Center

In this work, the activation effect of vacuum thermal treatment on MIL-101(Fe) (MIL: Materials of Institute Lavoisier) was investigated for the first time. It demonstrated that vacuum thermal activation could accelerate the activation of persulfate (PS) by MIL-101(Fe), and the enhancement of the catalytic capacity of MIL-101(Fe) was mainly attributed to the change in the FeII/FeIII mixed-valence center. The results of the SEM and XRD showed that vacuum thermal activation had a negligible effect on the crystal structure and particle morphology of MIL-101(Fe). Meanwhile, the higher temperature of vacuum thermal activation caused a higher relative content ratio of FeII/FeIII. A widely used azo dye, X-3B, was chosen as the probe molecule to investigate the catalytic performance of all samples. The results showed that the activated samples could remove X-3B more effectively, and the sample activated at 150 °C without regeneration could effectively activate PS to remove X-3B for at least 5 runs and approximately 900 min. This work highlights the often-overlooked activation effect of vacuum thermal treatment and provides a simple way to improve the catalytic capacity and reusability of MIL-101(Fe) which is beneficial for the application of MIL-101(Fe)/PS systems in azo dye wastewater treatment.

Efficient azo dye wastewater treatment in a hybrid anaerobic reactor with a built-in integrated bioelectrochemical system and an aerobic biofilm reactor: Evaluation of the combined forms and reflux ratio

A combined process that consisted of a hybrid anaerobic reactor (HAR) with an integral bioelectrochemical system and aerobic biofilm reactor (ABFR) was established for simulated azo dye wastewater treatment (domestic wastewater containing dye acid orange 7). The split combination form that separated HAR and ABFR into two individual reactors recorded a decolorization efficiency of 81.23 ± 0.12%, which was about 8% higher than that HAR and ABFR were stacked together into a single up-flow reactor. Implementation of reflux improved the decolorization and chemical oxygen demand (COD) removal in both the processes. Decolorization efficiency achieved 97.52 ± 0.66% in split process at a reflux ratio of 1 and the COD was 89 ± 2 mg/L in the final effluent. Further increasing the reflux ratio to 3 did not have any significance in treatment performance of the reactors. This study comprehensively revealed the influence of combination forms and reflux ratio on the performance of combined process.

Study on the treatment of simulated azo dye wastewater by a novel micro-electrolysis filler

A new type of iron-copper-carbon (Fe-Cu-C) ternary micro-electrolysis filler was prepared with a certain proportion of iron powder, activated carbon, bentonite, copper powder, etc. The effect of the new type of micro-electrolysis filler on the simulated methyl orange dye wastewater was studied. The effects of various operational parameters, such as reaction time, initial pH value, aeration rate, filler dose and reaction temperature, on the degradation rate of methyl orange were studied to determine the optimum treatment conditions, and the micro-electrolysis filler was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The experimental results show that the degradation rate of 220 mL of simulated dye wastewater with a concentration of 100 mg/L reached 93.41% ± 2.94% after 60 mL/min of aeration, with an initial pH = 2, a dose of 45 g and 125 minutes of reaction at room temperature. The new micro-electrolysis filler has a high degradation rate for methyl orange solution, which is attributed to the iron and activated carbon particles sintered into an integrated structure, which makes the iron and carbon difficult to separate and affects the galvanic cell reaction. The addition of copper also greatly increases the transmission efficiency of electrons, which promotes the reaction. In addition, the surface iron is consumed, the adjacent carbon is stripped layer by layer, and the new micro-electrolytic filler does not easily passivate and agglomerate during its use.

Meso-microporous carbon nanofibers with in-situ embedded Co nanoparticles for catalytic oxidization of azo dyes

To meet the current challenges in the treatment of azo dye wastewater by advanced oxidation processes (AOPs), meso-microporous carbon nanofiber with in-situ embedded Co nanoparticles (Co/P-CNF) is developed by electrospinning Co salt/polyvinylpyrrolidone (PVP)/polyacrylonitrile (PAN) solution followed by carbonization process. The use of PVP as pore-forming agent in PAN solution promotes the formation of meso-microporous structure of P-CNF in carbonization phase, achieving micropore surface area of 98 m2 g−1 and mesopore surface area of 214 m2 g−1 by BET analysis. The heterogeneous catalytic performance of synthesized Co/P-CNF is evaluated by the degradation of Acid Red 1 (AR1) with peroxymonosulfate (PMS). Complete removal of AR1 of 50 × 10−6 M is achieved within 6 min by Co/P-CNF and PMS system. The superior catalytic performance of Co/P-CNF is attributed to both the nanofibrous morphology and meso-microporous structure due to using the pore-forming agent (PVP), which endow the uniform distribution of Co nanoparticles, favor the exposure of active sites and promote electron and mass transfer. Co/P-CNF not only possesses excellent magnetic property but also has good stability and recyclability, which is desirable for the practical application of the treatment of azo dye wastewater. Co/P-CNF is validated to activate PMS using Co0/Co2+/Co3+ for generating sulfate radicals, hydroxyl radical and singlet oxygen and then degrade AR1. Therefore, the combination of electrospun nanofibrous structure and the use of pore-forming agents is a promising strategy for the preparation of high-performance carbon nanofiber supported catalysts.

Core-shell magnetic nano-powders with an excellent decolorization effect on dye wastewater.

In recent years, zero-valent nano-iron (nZVI) has received extensive attention due to its excellent decolorization effect on dye wastewater. In this paper, zero-valent nano-iron-nickel (nZVIN) powders were prepared by a simple, efficient and non-polluting method. The powder has a unique core–shell structure and excellent oxidation resistance. Hence the problem that nZVI powders are easily oxidized and difficult to store is solved. Due to the addition of Ni, the magnetic properties of the nZVIN powders are enhanced, which facilitates the recycling of the powders using a magnetic field after sewage treatment. In the decolorization treatment of dye wastewater simulated with Congo red (CR) dye, nZVIN powders can maintain a removal rate of more than 90% for CR solutions with different pH values (7.0–11.5) and an initial dye concentration (50–200 mg L−1). The research results show that nZVIN powders have broad application prospects in the treatment of azo dye wastewater.

Azo dye wastewater treatment in a bioelectrochemical-aerobic integrated system: effect of initial azo dye concentration and aerobic sludge concentration

Azo dye wastewater treatment in a bioelectrochemical-aerobic integrated system: effect of initial azo dye concentration and aerobic sludge concentration

Fe-Based Powders Prepared by Ball-Milling with Considerable Degradation Efficiency to Methyl Orange Compared with Fe-Based Metallic Glasses

In this study, the degradation efficiencies of zero-valent iron (ZVI) powders with different structures and components were evaluated for methyl orange (MO). The results show that the structure is an essential factor that affects degradation, and added non-metallic elements help optimize the structure. The amorphous and balled-milled crystalline Fe70Si10B20 has comparative degradation efficiencies to MO with t1/2 values of 6.9 and 7.0 min, respectively. Increasing the boron content can create a favorable structure and promote degradation. The ball-milled crystalline Fe70B30 and Fe43.64B56.36 powders have relatively short t1/2 values of 5.2 and 3.3 min, respectively. The excellent properties are mainly attributed to their heterogeneous structure with boron-doped active sites in ZVI. Composition segregation in the nanoscale range in an amorphous FeSiB alloy and small boron particles in the microscale range embedded in large iron particles prepared by ball-milling, both constitute effective galvanic cells that promote iron electron loss and therefore decompose organic chemicals. These findings may provide a new, highly efficient, low-cost commercial method for azo dye wastewater treatment using ZVI.