Treatment Of Azo Dye-containing Wastewater Research Articles

Treatment of azo dye-containing wastewater in a combined UASB-EMBR system: Performance evaluation and membrane fouling study

This work investigated the treatment of azo dye-containing wastewater in an upflow anaerobic sludge blanket (UASB) reactor combined with an electro-membrane bioreactor (EMBR). Current densities of 20 A m−2 and electric current exposure mode of 6′ON/30′OFF were applied to compare the performance of the EMBR to a conventional membrane bioreactor (MBR). The results showed that dye (Drimaren Red CL-7B) removal occurred predominantly in the UASB reactor, which accounted for 57% of the total dye removal achieved by the combined system. When the MBR was assisted by electrocoagulation, the overall azo dye removal efficiency increased from 60.5 to 67.1%. Electrocoagulation batch tests revealed that higher decolorization rates could be obtained with a current density of 50 A m−2. Over the entire experimental period, the combined UASB-EMBR system exhibited excellent performance in terms of chemical oxygen demand (COD) and NH4+-N removal, with average efficiencies above 97%, while PO43--P was only consistently removed when the electrocoagulation was used. Likewise, a consistent reduction in the absorption spectrum of aromatic amines was observed when the MBR was electrochemically assisted. In addition to improving the pollutants removal, the use of electrocoagulation reduced the membrane fouling rate by 68% (0.25–0.08 kPa d−1), while requiring additional energy consumption and operational costs of 1.12 kWh m−3 and 0.32 USD m−3, respectively. Based on the results, it can be concluded that the combined UASB-EMBR system emerges as a promising technological approach for textile wastewater treatment.

Recovery of titanium dioxide from catalyst effluents of polyethylene production plants and its application in the photocatalytic treatment of azo dye-containing wastewater

Recovery of titanium dioxide from catalyst effluents of polyethylene production plants and its application in the photocatalytic treatment of azo dye-containing wastewater

Construction of integrated system for the treatment of Acid orange 7 dye from wastewater: Optimization and growth kinetic study

In this work, an effort has been made to develop an integrated system (ozonation followed by biodegradation) for the treatment of Acid orange 7 (AO 7) dye. The process parameters such as pH (3.0–11) and ozone dosage (5–25 mg/L) were optimized and obtained as 3.0 and 25 mg/L, respectively to treat the AO 7 by ozonation. Similarly, the process parameters, namely pH (5.0–9.0) and temperature (25–45 °C) were optimized and found to be 7.0 and 35 °C, respectively by biological treatment. Bacillus sp. was found to be the most effective bacteria to remove the AO 7. An integrated system obtained an overall 98.7% removal of AO 7 under optimum conditions. Andrews-Haldane model was best to predict the experimental data and the bio-kinetic constants; µmax: 0.1875 day−1; Ks: 49.53 mg/L; Ki: 133.32 mg/L were obtained. The developed integrated system can be a promising option for the treatment of azo dye containing-wastewaters.

Ozonation of the dye Reactive Red 239 and biodegradation of ozonation products in a moving-bed biofilm reactor: Revealing reaction products and degradation pathways

The ozonation of the azo dye Reactive Red 239 (RR 239) was investigated in a bench-scale reactor. Decolorization and organic matter removal were monitored in batch assays. The toxicity of the dye and its ozonation products to the test-organism Aliivibrio fischeri was also assessed. Identification of ozonation products was performed using analytical techniques (GC-MSD and high resolution mass spectrometry). Ozonated and non-ozonated dye solutions were supplemented with organic matter (glucose) and nutrients sources and subjected to biological treatment in a moving-bed biofilm reactor (MBBR). Five experimental runs were conducted, varying the influent characteristics and monitoring organic matter removal and nitrification performance. Identification of residual compounds in the effluent was also performed. Color was very rapidly removed by ozonation, but the degree of mineralization achieved was rather low. Moreover, toxicity was completely removed after 4 min of ozone reaction. Based on the ozonation products, a two-way mechanism was proposed for the degradation of RR 239 by ozone. Further biological treatment in the MBBR revealed that the removal of organic matter (evaluated as COD) was not affected by the ozonation products. However, nitrification efficiency dropped significantly when the dye or the ozonated dye was fed to the bioreactor. Furthermore, inhibition of nitrite oxidizers resulted in partial nitrification and consequent accumulation of nitrite, which consisted of the main oxidized nitrogen specie in the reactor effluent. The identification of compounds resulting from the ozonation and biological treatment steps suggests that the partial inhibition of nitrifying organisms was possibly caused by triazine- and benzofuran-related organic compounds. Nevertheless, their adverse effect on nitrification was found to be reversible and practically ceased once these compounds were removed from the influent. Overall, the results revealed that the combination of ozonation and MBBR for the treatment of azo dye containing-wastewaters is promising but the ozone-based process should be optimized in order to enable the degradation of compounds inhibiting nitrification.

Decolourisations and biodegradations of model azo dye solutions using a sequence batch reactor, followed by ultrafiltration

The main objective of this study was to investigate the efficiency of biological treatment of azo dye-containing wastewater with a sequencing batch reactor system, followed by ultrafiltration. The performance of the system was quantified by measuring the chemical oxygen demand and azo dye concentration. The biodegradation was carried out under combined alternating anaerobic and aerobic conditions with Nylosan Yellow E2RL SGR as a model azo dye contaminant. The bioprocess revealed a maximal reduction in chemical oxygen demand and dye removal efficiency of 91 and 85%, respectively. After ultrafiltration of effluent from the biological treatment, the efficiency increased to 94% for chemical oxygen demand and to 97% for the azo dye decolourisation. Samples of activated sludge from the bioprocess were collected for microbial characterisation. Bacteria and fungi were isolated and identified by 16S rRNA gene and ITS1-5.8S rDNA-ITS2 sequence analysis, respectively. Serratia marcescens and Klebsiella oxytoca were the most common bacteria with the highest number present during the aerobic and anaerobic phases of the bioprocess. In addition, a high number of Elizabethkingia miricola, Morganella morganii, Comamonas testosteroni, Trichosporon sp. and Galactomyces sp. were detected. Taken together, our results demonstrated that the sequencing batch reactor system combined with ultrafiltration is an efficient technique for treatment of wastewater containing azo dye. Moreover, the ultrafiltration effectively removes the microbiota from the final effluent resulting in stable product water.

Removal of azo dye in an up-flow membrane-less bioelectrochemical system integrated with bio-contact oxidation reactor

An up-flow membrane-less bioelectrochemical system integrated with bio-contact oxidation (BES-BCO) was developed for degradation and/or mineralization of the Acid Orange 7 (AO7) in wastewater. The performance of BES-BCO was evaluated based on decolorization removal efficiency, chemical oxygen demand (COD) removal efficiency and the concentration of decolorized byproducts in effluent. The study found that the BES-BCO system can degrade AO7 and COD effectively. Further, the toxic decolorized byproducts of azo dye, which are not generally degrade in the traditional BES system, can be further mineralized by the BES-BCO system. In addition, the COD removal efficiency increased with the increase of aeration at BCO. However, higher DO concentration at anode can hinder the electrons transfer between anode and exoelectrogen, resulting in a significant decrease of decolorization removal efficiency. This study provided a novel compact technology for advanced treatment of azo dyes wastewater for engineering applications, and concluded that the integrated BES-BCO system is effective for advanced treatment of azo dye-containing wastewater.

A novel quinone/reduced graphene oxide composite as a solid-phase redox mediator for chemical and biological Acid Yellow 36 reduction

A novel quinone-modified graphene material was developed to enhance the catalytic performance of graphene for the transformation of environmental pollutants. Graphene oxide (GO) was first reduced with diethylenetriamine and the obtained NH2-RGO was further covalently modified with anthraquinone-2-sulfonic acid (AQS). The prepared AQS-modified RGO (AQS-RGO) was characterized by XPS, IR and SEM, respectively. The catalytic performance of AQS-RGO was investigated during azo dye Acid Yellow 36 (AY 36) decolorization. It was shown that pH and temperature had significant effects on AY 36 chemical decolorization by Na2S. At the pH of 6.0, AQS-RGO exhibited better catalytic performance compared with NH2-RGO due to the lower activation energy of the AQS-RGO amended system. AY 36 bio-decolorization could be enhanced in a dose-dependent manner with AQS-RGO. In the presence of 25 mg L−1 AQS-RGO, the AY 36 bio-decolorization rate was 6.7-fold higher than that mediated by NH2-RGO, indicating that AQS-RGO is a better electron-transfer mediator. Based on the above results, the electron transfer pathways of AQS-RGO-mediated AY 36 decolorization were proposed. These findings indicate that the application of AQS-RGO is a feasible method to enhance the treatment of azo dye-containing wastewater.

Catalytic performance of functionalized polyurethane foam on the reductive decolorization of Reactive Red K-2G in up-flow anaerobic reactor under saline conditions.

Soluble anthraquinone compounds including anthraquinone-2-sulfonate (AQS) and anthraquinone-2,6-disulfonate can accelerate anaerobic decolorization of azo dyes. To realize the application of these compounds, the catalytic performance and stability of AQS-modified polyurethane foam (AQS-PUF) for Reactive Red K-2G decolorization were investigated in an up-flow anaerobic bioreactor under saline conditions. The results showed that the optimal influent pH value and hydraulic retention time were 7 and 10 h, respectively, in a continuous-flow bioreactor amended with AQS-PUF (R1). Under the above conditions, R1 (93.8 % color removal) displayed better decolorization performance than the bioreactor amended with PUF (R2, 64 % color removal) in 10 days, when influent K-2G concentration was 50 mg/L. Moreover, compared with R2, R1 could more effectively cope with 50-400 mg/L K-2G and exhibited better stability with over 85 % color removal efficiency within 75 days. Further bacterial community analysis using polymerase chain reaction-denaturing gradient gel electrophoresis showed that AQS-reducing bacteria played an important role in accelerating K-2G decolorization in R1. Extracellular polymeric substances analysis found that biofilm formed on AQS-PUF had very limited negative effects on K-2G decolorization. The catalytic performance of used AQS-PUF only decreased less than 9 % in batch experiments. These findings indicate that AQS-PUF has potential application for the treatment of azo dye-containing wastewater.

Treatment of azo dye-containing wastewater by a Fenton-like process in a continuous packed-bed reactor filled with activated carbon

In this work, oxidation with a Fenton-like process of a dye solution was carried out in a packed-bed reactor. Activated carbon Norit RX 3 Extra was impregnated with ferrous sulfate and used as catalyst (7wt.% of iron). The effect of the main operating conditions in the Chicago Sky Blue (CSB) degradation was analyzed. It was found that the increase in temperature leads to a higher removal of the dye and an increased mineralization. However, it also increases the iron leaching, but the values observed were below 0.4ppm (thus, far below European Union limits). It was possible to reach, at steady-state, a dye conversion of 88%, with a total organic carbon (TOC) removal of ca. 47%, being the reactor operated at 50°C, pH 3, Wcat/Q=4.1gminmL−1 (Wcat is the mass of catalyst and Q the total feed flow rate) and a H2O2 feed concentration of 2.25mM (for a CSB feed concentration of 0.012mM). The same performance was reached in three consecutive cycles.

Simultaneous removal of color, organic compounds and nutrients in azo dye-containing wastewater using up-flow constructed wetland

Combination of aerobic and anaerobic processes in constructed wetlands can enhance the treatment performance in textile wastewater. This study assessed the treatment of azo dye Acid Orange 7 (AO7) and nutrients using five laboratory-scale up-flow constructed wetlands (UFCW) with and without supplementary aeration, and with different emergent plants. Supplementary aeration controlled the size of aerobic and anaerobic zones in the UFCW reactors as evidenced by the oxidation–reduction potential (ORP) and dissolved oxygen (DO) profile of the UFCW. The AO7 removal efficiency was above 95% in all UFCW reactors and most of the color was extensively removed in the anaerobic region of the UFCW beds. The intermediates produced through the breakage of azo bond were significantly reduced in the UFCW reactors with supplementary aeration. The results indicated the applicability of the UFCW reactors to the treatment of azo dye-containing wastewater. The removals of T-N and T-P were in the range of 60–67% and 26–37%, respectively, among the UFCW reactors. The COD and NH 4-N removals in the aerated reactors were about 86 and 96%, respectively. On the other hand, the COD and NH 4-N removals were in the range of 78–82% and 41–48%, respectively, in the non-aerated reactors. The supplementary aeration enhanced the removal efficiencies in organic matter, NH 4-N and aromatic amines in the UFCW reactors.

Combined chemical and biological treatment of azo dye-containing wastewaters

Wastewaters produced in textile industrial processes contain organic dyes, such as azo dyes, which are not amenable to direct biological treatment. This work examines the possibility of combining ozonation with biological treatment for the effective treatment of wastewaters containing the azo dye Orange II. Oxalate, formate, and benzene-sulfonate are found to be the final products of ozonation. Sulfonated aromatics such as benzene-sulfonate cause organic pollution and are not readily degradable because of their xenobiotic character. For the biological treatment of the ozonation products, activated sludge acclimated to the main product (benzene-sulfonate) was used, and batch experiments under aerobic conditions were performed. On the basis of experimental data, mathematical models describing both processes were developed. An overall mathematical model describing the integrated chemical and biological treatment of the dye was used to estimate the cost of the whole process. The implications of this study for the design of effective dye-containing wastewater treatment plants are discussed.

Molecular Cloning and Characterization of the Gene Coding for Azoreductase from Bacillus sp. OY1-2 Isolated from Soil

Azo dyes are regarded as pollutants because they are not readily reduced under aerobic conditions. Bacillus sp. OY1-2 transforms azo dyes into colorless compounds, and this reduction is mediated by a reductase activity for the azo group in the presence of NADPH. A 1.2-kbp EcoRI fragment containing the gene that encodes azoreductase was cloned by screening the genomic library of Bacillus sp. OY1-2 with digoxigenin-labeled probe designed from the N-terminal amino acid sequence of the purified enzyme. An open reading frame encoding the azoreductase, consisting of 178 amino acids, was predicted from the nucleotide sequence. In addition, because only a Bacillus subtillis hypothetical protein was discovered in the public databases (with an amino acid identity of 52.8%), the gene encoding the azoreductase cloned in this study was predicted to be a member of a novel family of reductases. Southern blot analysis revealed that the azoreductase gene exists as a single copy gene on a chromosome. Escherichia coli-expressing recombinant azoreductase gave a ten times greater reducing activity toward azo dyes than the original Bacillus sp. OY1-2. In addition, the expressed azoreductase purified from the recombinant E. coli lysate by Red-Sepharose affinity chromatography showed a similar activity and specificity as the native enzyme. This is the first report describing the sequencing and characterization of a gene encoding the azo dye-reducing enzyme, azoreductase, from aerobic bacteria and its expression in E. coli.