Industrial Azo Dye Research Articles

Genome-Scale Investigation of the Regulation of azoR Expression in Escherichia coli Using Computational Analysis and Transposon Mutagenesis

Bacterial azoreductases are enzymes that catalyze the reduction of ingested or industrial azo dyes. Although azoreductase genes have been well identified and characterized, the regulation of their expression has not been systematically investigated. To determine how different factors affect the expression of azoR, we extracted and analyzed transcriptional data from the Gene Expression Omnibus (GEO) resource, then confirmed computational predictions by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Results showed that azoR expression was lower with higher glucose concentration, agitation speed, and incubation temperature, but higher at higher culture densities. Co-expression and clustering analysis indicated ten genes with similar expression patterns to azoR: melA, tpx, yhbW, yciK, fdnG, fpr, nfsA, nfsB, rutF, and chrR (yieF). In parallel, constructing a random transposon library in E. coli K-12 and screening 4320 of its colonies for altered methyl red (MR)-decolorizing activity identified another set of seven genes potentially involved in azoR regulation. Among these genes, arsC, relA, plsY, and trmM were confirmed as potential azoR regulators based on the phenotypic decolorization activity of their transposon mutants, and the expression of arsC and relA was confirmed, by qRT-PCR, to significantly increase in E. coli K-12 in response to different MR concentrations. Finally, the significant decrease in azoR transcription upon transposon insertion in arsC and relA (as compared to its expression in wild-type E. coli) suggests their probable involvement in azoR regulation. In conclusion, combining in silico analysis and random transposon mutagenesis suggested a set of potential regulators of azoR in E. coli.

Feasibility and sludge analysis of electrocoagulation process for Direct Violet-35 dye remediation

The present study investigates Direct Violet-35 (DV-35) remediation using electrocoagulation process. DV-35 which is an industrial azo dye, after release significantly affects the visual appearance of water bodies and hinders the process of photosynthesis affecting plant growth. Perturbing the food chain, it promotes toxicity, mutagenicity, and carcinogenicity. Therefore, dye remediation is essential before discharge into water streams. To determine the effectiveness of the electrocoagulation process for DV-35 dye remediation, and understand the influence of parameters like current density, inter-electrode spacing, concentration of electrolyte, pH, agitation speed, and initial dye concentration, a detailed study was carried out. Maximum removal efficiency (>98 %) was achieved in 16 min at 263.15 A/m2 current density and pH 7.2 for DV-35 concentration of 50 to 500 mg/L. Further, optimized parameters were applied to real textile effluent achieving 99.8 % efficiency. EC mechanism was corroborated by Sips isotherm matching adequately with experimental results. The findings also demonstrated a heterogeneous surface of the produced EC flocs. Pseudo-second-order was obtained with a low operating cost of 0.0018 US $/m3. The DV-35 removal and functional groups were confirmed by UV/VIS and Fourier transforms infrared spectroscopy analysis. The sludge was examined by X-ray Diffraction and Scanning Electron Microscope revealing Crystalline aluminum oxides i.e. bayerite (Al(OH)3) and diaspore (AlO(OH)). The conclusion of the results revealed EC to be an effective and economical technique for DV-35 remediation from textile wastewater.

Enhanced photocatalytic degradation and antimicrobial activities of biogenic Co3O4 nanoparticles mediated by fenugreek: sustainable strategies

The present study introduces Trigonella foenum-graecum (TFG, fenugreek)-mediated Co3O4 nanoparticles (NPs) as an innovative solution for eliminating industrial azo dyes from contaminated water.

A study on redox reactions of the azo dye Sudan I and its hydroxylated metabolites on pyrolytic graphite and boron doped diamond electrodes to support electrochemical studies of metabolic transformations

Sudan I (1-(Phenyldiazenyl)naphthalen-2-ol) is an orange industrial azo dye. It is utilized as a marker substrate in studies of metabolic transformation of xenobiotics through processes involving cytochrome P450 hydroxylase. In this complex study, redox and subsequent chemical/electrochemical reactions of Sudan I and its three major metabolites (4′‑hydroxy, 6‑hydroxy, and 4′,6-dihydroxy derivatives of Sudan I) were investigated using boron doped diamond and basal plane pyrolytic graphite electrodes. Cyclic voltammetry (CV) in Britton – Robinson buffer pH 7 showed distinct differences in the number and potential of signals, depending on the number and positions of the hydroxy groups. While in CV scans initiated in anodic direction, primary oxidations of paired or unpaired hydroxy groups are dominating, cathodic scans lead primarily to reduction of the azo group and to cleavage of the parent compounds and formation of 1-aminonaphthalen-2-ol and aniline or their corresponding hydroxylated derivatives. These are oxidizable in reverse anodic scans. Combinations of CV scans can be used to distinguish among all tested compounds. Basal plane pyrolytic graphite electrode provides better sensitivity than boron doped diamond electrode due to enhanced adsorption of the aromatic analytes/intermediates. The possibility of detecting Sudan I and its metabolites in the presence of excess amounts of NADPH as an essential component of enzymatic hydroxylation systems, was tested. Although the oxidation signal of NADPH partially interferes with signals of primary oxidation of hydroxy groups (particularly for Sudan I), our results suggest that electrochemical assays could be applicable in monitoring transformation of Sudan I in biochemical studies.

Physiological and transcriptome profiling of Chlorella sorokiniana: A study on azo dye wastewater decolorization

Over decades, synthetic dyes have become increasingly dominated by azo dyes posing a significant environmental risk due to their toxicity. Microalgae-based systems may offer an alternative for treatment of azo dye effluents to conventional physical-chemical methods. Here, microalgae were tested to decolorize industrial azo dye wastewater (ADW). Chlorella sorokiniana showed the highest decolorization efficiency in a preliminary screening test. Subsequently, the optimization of the experimental design resulted in 70% decolorization in a photobioreactor. Tolerance of this strain was evidenced using multiple approaches (growth and chlorophyll content assays, scanning electron microscopy (SEM), and antioxidant level measurements). Raman microspectroscopy was employed for the quantification of ADW-specific compounds accumulated by the microalgal biomass. Finally, RNA-seq revealed the transcriptome profile of C. sorokiniana exposed to ADW for 72 h. Activated DNA repair and primary metabolism provided sufficient energy for microalgal growth to overcome the adverse toxic conditions. Furthermore, several transporter genes, oxidoreductases-, and glycosyltransferases-encoding genes were upregulated to effectively sequestrate and detoxify the ADW. This work demonstrates the potential utilization of C. sorokiniana as a tolerant strain for industrial wastewater treatment, emphasizing the regulation of its molecular mechanisms to cope with unfavorable growth conditions.

Adsorption and Photodegradation of Lanasol Yellow 4G in Aqueous Solution by Natural Zeolite Treated by CO2-Laser Radiation.

Natural zeolite is a widely used material with excellent environmental cleaning performance, especially in water and wastewater treatment. Natural zeolite (Zini) calcined by CO2-laser radiation (ZL) was tested as a catalyst for the photodegradation and the adsorption of industrial azo dye Lanasol Yellow 4G (LY4G) in water. Morphology, chemical structure, and surface composition of Zini and ZL were analyzed by XRD, SEM, EDS, and XPS. UV/Visible spectrophotometry was used to evaluate the photocatalytic activity of Zini and ZL. The photocatalytic activity of the studied zeolites was associated with the presence of Fe oxides in their composition. Laser-treated natural zeolite showed higher efficiency as a photocatalyst compared to untreated natural zeolite.

Enzymatic degradation of azo dyes methylene blue and congo red with peroxidase purified from cauliflower using affinity chromatography technique: Kinetic study, optimization and metal binding activity

The effective results of the enzymatic decolorization of industrial azo dyes found in wastewater, which cause serious health and environmental problems, with peroxidases have recently increased the interest in these enzyme sources. Redox-mediated decolorization of Methylene Blue and Congo Red azo dyes with cauliflower (Brassica oleracea var. botrytis L.) peroxidase (CPOD) purified in one step using 4-amino 3-bromo 2-methyl benzohydrazide molecule was investigated for the first time. The inhibition effect of this molecule, which is used as a ligand in affinity chromatography, on the CPOD enzyme was investigated. The Ki and IC50 values for this enzyme were calculated as 0.113 ± 0.012mM and 0.196 ± 0.011mM, respectively. With the affinity gel obtained by binding to the Sepharose-4B-l-tyrosine matrix of this molecule, which shows a reversible inhibition effect, the purification values of CPOD enzyme were determined as 562-fold with a specific activity of 50,250 Umg-1. The purity of the enzyme was checked by the SDS-PAGE technique and its molecular weight was determined. A single band at 44kDa was observed for the CPOD enzyme. In dye decolorization studies, the effects of dye, enzyme, and hydrogen peroxide concentrations as well as time, pH, and temperature were investigated. The profiles of the optimum conditions for both dyes were similar, and the percentages of decolorization of Methylene Blue and Congo Red under these conditions were 89% and 83%, respectively, at the end of the 40min reaction time. Again, when examining the effect of metal ions on enzyme activity, it was found that there was no significant negative change in CPOD.

Performance evaluation of in situ Fenton-mediated photocatalysis of industrial dye effluent with enhanced TiO2 nanoparticle

Abstract Effluents resulting from the frequent use of industrial azo dyes in textile operations have posed great toxicological impacts on man and the environment. The limitations of conventional treatment infrastructure necessitate the use of rapid Fenton-mediated catalytic systematic process to tackle the attendant treatment limitations. The study applied in situ Fenton-mediation process with constructed low power UV-LED reactor for rapid catalytic treatment of dye-laden effluent using enhanced acid and alkali TiO2-nanoparticles (Nps) (1–5%, i.e. 1–5 M) at definite experimental conditions, respectively. A comprehensive instrumental study was done to access the morphological, functional and elemental constituents of these nanocatalysts. The performance of the respective catalyst was evaluated using methylene blue (MB) dye at definite experimental conditions of pH, dosage, concentration and irradiation time. The results revealed a mesoporous structural nanocatalyst with increasing surface area after enhanced modification. The optimal experimental conditions of pH and concentration were recorded as 5 and 10 mg/L, respectively; while the most efficient nanocatalyst was 3 wt% alkali-modified TiO2 (3% Ak-TiO2) having a degradation efficiency of 89.15% at 90 min of irradiation using 50 mg dosage in contrast to higher irradiation time and catalyst dosage for other catalysts.

Synthesis, Characterization and Performance Evaluation of Burmese Grape (Baccaurea ramiflora) Seed Biochar for Sustainable Wastewater Treatment

Biochar prepared from different bio-sources serves as a feasible solution for the decontamination of dye-contaminated wastewater. In this study, biochar was synthesized from a sustainable source, i.e., local fruit waste, Burmese grape seeds (BGSs). The seeds were collected from a local market, washed, pre-teated and finally converted into biochar by pyrolysis in a N2 furnace. The removal efficiency of the synthesized biochar was evaluated towards a cationic industrial azo dye, methylene blue (MB). The phosphoric acid (H3PO4) and potassium hydroxide (KOH) pretreated BGS were pyrolized at 500 °C for 3 h in a N2 furnace at a heating rate of 10 °C/min. The spectroscopic analysis confirmed the presence of multiple surface functional groups, e.g., R-OH, OH, -C=O, -COOH, etc. The surface of the biochar was randomized with porous tunnel-like structures. The specific surface area and pore volume obtained from BET analysis were 19.90 ± 1.20 m2/g and 5.85 cm3/g. The MB concentration (mg/L), contact duration (min) and pH were varied to assess the MB sorption phenomena. The optimum pH was found to be 8. During the first 20 min of contact time, adsorption was rapid and equilibrium was reached after 75 min. The adsorption was best described by pseudo-first-order kinetics with a good fit (R2 = 0.99). The maximum removal percentage was ~85%, and per gram of BGS can adsorb 166.30 mg of MB, which supports the Langmuir adsorption isotherm model. The obtained results were compared with the reported literature, and BGS showed its excellent candidacy to be industrially utilized in the tertiary stage of wastewater treatment plants.

Optimized synthesis of mono and bimetallic nanoparticles mediated by unicellular algal (diatom) and its efficiency to degrade azo dyes for wastewater treatment.

The silver/palladium nanoparticles (Ag/Pd NPs) were efficiently absorb UV-Visible light and reveal greater photocatalytic activity as compared to monometallic NPs. The aim of this study is photodegradation of the industrial azo dye using bimetallic Ag/Pd NPs and monometallic Ag NPs in presence of UV light for wastewater treatment. Bacillariophyceae (diatom) algae extract was utilized for the green synthesized Ag and Ag/Pd NPs. Biosynthesized nanoparticles were characterized by various useful characterization techniques viz. UV-Vis, FT-IR, SEM, TEM, and XRD. The crystallite size is found to be ∼23nm and ∼56nm for Ag NPs and Ag/Pd NPs, respectively, which is same as results obtained from TEM analysis, as the particle size and shape were analyzed as ∼27 and ∼56nm, with a spherical geometry. The NPs was used to develop the optimization parameters for dye degradation such as time, temperature, and NP concentrations. A total 15 runs were considered for the study and procured by statistical software. Response surface methodology technique was implied and Box-Behnken design (BBD) design was built into the workflow. The results of the present study manifested a good connection between experimental and predicted values (R2=0.9838). Therefore, present study promises that the prepared NPs possess excellent photocatalytic activity against harmful dyes.

Removal of the industrial azo dye crystal violet using a natural clay: Characterization, kinetic modeling, and RSM optimization

Natural clay (NC) was employed as a natural adsorbent for the elimination of an azo dye Crystal Violet (CV) from aqueous media. The characterization of the clay was performed by X-ray diffractometry (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) equipped with an X-ray energy dispersion spectrometer (EDS) and Brunauer–Emmett–Teller (BET) specific surface area analysis. The Box–Behnken design (BBD) was used as a powerful tool to determine the stationary points of the main independent factors: initial CV concentration, initial pH, temperature, and adsorbent dose on the adsorption efficiency. The significance and adequacy of the model were investigated using analysis of variance (ANOVA). The obtained results indicated an optimal dye removal of 99.1% at pH = 3, initial CV concentration of 11.767 mg/L, adsorbent load of 3.075 g/L, and T = 298.0 K. The kinetic study was evaluated using three models: a pseudo-first-order (PFO), a pseudo-second-order (PSO), and an intraparticle diffusion model. The observed kinetics is in excellent agreement with the PSO kinetic model. Therefore, both isotherms Langmuir and Freundlich fitted well the adsorption equilibrium data. The thermodynamic study revealed that the main parameters including (ΔG°, ΔH°, and ΔS°) indicated that the adsorption of CV onto NC was an endothermic and spontaneous process.

High impact of thiol capped ZnS nanocrystals on the degradation of single and binary aqueous solutions of industrial azo dyes under sunlight

Sulfur zinc (ZnS) nanocrystals were prepared using an aqueous colloidal route with thioglycolic acid (TGA) as a stabilizer. These ZnS-TGA nanocrystals were used as a low-cost and environmental friendly alternative for the photodegradation of methylene blue (MB) and methyl orange (MO) from aqueous solutions using sunlight irradiation. Structural and optical properties of nanocrystals were determined via X-ray diffraction, Fourier transform infrared spectroscopy, Transmission electron microscopic, UV–Visible and photoluminescence spectroscopy. Results showed a blue shift of absorbance band and higher energy band gap values than bulk ZnS materials, which was in agreement with the quantum confinement effect. X-ray diffraction confirmed the formation of cubic phase of ZnS-TGA containing also a slight wurtzite phase. Calculated average size of ZnS nanocrystals by the Debye Scherrer relation was 3.5 nm. Characterization results showed the fixation of TGA on ZnS-NCs via sulphur and carboxylic functionalities on catalyst surface. Photoluminescence spectra obtained under excitation wavelength at 325 nm showed three emission bands (416, 441 and 484 nm), which were mainly related to band edge and defect-activated emissions. The photocatalytic activity of ZnS-TGA nanocrystals under sunlight irradiation to degrade tested MB and MO dyes and their mixture in aqueous solutions was evaluated. High dye degradation efficiency was achieved at a very short time (27 min) and this performance was attributed to the negative surface charge, surface area, surface defects and high dispersion of ZnS-TGA nanocrystals on the aquatic medium. Overall, this study demonstrates that these nanocrystals could be employed as low-cost nanocatalyst for the degradation of organic dyes in wastewater treatment.

Environmentally benign hybrid nanocomposite beads for azo dye remediation via synchronized dual degradation mechanisms.

Practically, 12% of used dyes are excluded as waste in the mobile aqueous environment. Methyl orange (MO), an industrial azo dye, is known to be carcinogenic. Accordingly, this work was engaged to fabrication of a high-efficiency visible light photocatalysts based on Ag-Alginate/Chitosan-coated MgO nanocomposite beads. MgO and Ag were prepared via precipitation and γ-radiation reduction technique as a green physical one, respectively. The degradation mechanisms depended on catalytic reduction by means of sodium borohydride/Ag and photooxidative degradation. XRD proved the periclase crystalline form of MgO of size 20 nm and the formation of face-centered cubic silver crystals of size 15 nm. The degradation yield varied directly with time, MgO, and dye concentration until certain limit. Five and twenty minutes were enough to get clear solution of MO (30 and 15 ppm, respectively) while 60 min was required to achieve the same target for 60 ppm MO solution. The catalysts showed high efficiency for MO of high concentration. The incorporation of Ag into catalytic beads could support both mechanisms as it could elevate the degradation efficiency up to 50% and save the time to a great extent. Thus, this carrier fruitfully converted wastewater into an effluent that can be repaid to the water cycle with minimal strike on the ecosystem.

Photocatalytic efficiency of Na4Co(MoO4)3 for the degradation of industrial azo dye under solar irradiation

Cobalt and sodium molybdate Na4Co(MoO4)3 was synthesized using the solid state method. X-ray diffraction (XRD), IR and Raman spectroscopy confirmed a monoclinic structure of the prepared sample. The morphology of the obtained nanoparticles was analyzed using scanning electron microscopy (SEM). The Surface area was determined using the Brunauer Emmett Teller (BET) method. The photoluminescence (PL) spectrum exhibits an emission band located at 2.45 eV and a weak green emission associated with deep-level defects. The UV–vis spectroscopy shows that band gap energy (Eg) of the sample is about 3.12 eV. The photocatalytic performance evaluates by means of the degradation of Navy Blue 5R (C.I. Acid Blue 113) azo dye under solar irradiation. Na4Co(MoO4)3 shows good photocatalytic removal efficiency of azo dye. The removal of Navy Blue 5R solution reaches 90% after 210 min of reaction under solar light irradiation. The experiments reveal that the deterioration rate of this dye usually follows pseudo-first-order kinetics for photodegradation mechanisms and the mean kinetic constant values of the Navy Blue 5 R solution is equal to 7.60 × 10−3 min−1. These results indicate that the prepared Na4Co(MoO4)3 compound may be of interest to degrade other organic pollutants.

Photocatalytic Degradation of Industrial Dye in Semi-Pilot Scale Prototype Solar Photoreactor: Optimization and Modeling Using ANN and RSM Based on Box–Wilson Approach

Photodegradation of an industrial Azo dye C.I Basic Red 46, was examined in a semi-pilot scale prototype solar photoreactor under solar radiation. In our study, photodegradation of the dye was optimized using Response Surface Methodology (RSM) based on Box-Wilson approach. The Artificial Neural Network (ANN) was used to establish suitable modeling and optimal conditions for the Solar UV/Immobilized-TiO2 process in order to evaluate the individual effects of three factors that independently affect the effectiveness of the photodegradation process: (1) initial concentration of the dye, (2) pH, and (3) flow rate. The RSM was in good agreement with the prediction model (R2Dec = 0.95); meanwhile, the ANN approach revealed that the predicated model fit perfectly with the experimental data to yield the highest value of R2 = 0.999. The effects of these three factors could be estimated from a second-order polynomial equation, and the optimal parameters of photodegradation consisted of three main parameters: (1) initial concentration of colorant 10.65 mg.L−1, (2) pH 10.82, and (3) rate of fluid flow of 852 L h−1. The decolorization removal efficiency under these optimal conditions was 99%.

Combinatıon of a Box-Behnken design technique with response surface methodology for optimization of the photocatalytic mineralization of C.I. Basic Red 46 dye from aqueous solution

The photodegradation of an industrial azo dye C.I Basic Red 46 was examined in a fixed-bed photoreactor using UV-lamps simulated to the solar irradiation. In our photodecolorization study, the UV/TiO2 process was optimized using the Box-Behnken approach to evaluate the synergistic effects of three independent parameters (initial concentration of the dye, flow rate, and UV intensity) on mineralization effectiveness. The response surface methodology was in good promise with the prediction model (coefficients of determination of decolorization and mineralization were R2Dec = 0.997 and R2TOC = 0.994, respectively). The effects of the factors could be estimated from a second–order polynomial equation and student’s t-test. The optimal parameters of decolorization and mineralization were as follows: initial concentration of colorant 25 mg L−1, rate of fluid flow 0.3 L min−1, and ultraviolet light intensity 38.1 W m−2. The decolorization and mineralization removal efficiency under these optimal conditions were 100% and 57.63% respectively. These results indicate that optimization using response surface methodology, based on the Box-Behnken approach, is an excellent tool for determining the optimal conditions, and the process can be easily extrapolated for a specific treatment of real waste water containing the azo dye C.I Basic Red 46. Also, the intermediates that were produced during photodegradation process of Basic Red 46 were determined by GC/MS.

Adsorption Studies of Textile Dye (Chrysoidine) from Aqueous Solutions Using Activated Sawdust

Chrysoidine is a type of industrial azo dye and a well-known toxicant. Due to its good dyeing characteristics, it is widely used for dyeing leather, paper, feather, grass, wood, bamboo, etc. Hence, it is very important to remove or reduce its concentration below the contamination level in the waste line by using low-cost technologies. Sawdust is a plentiful material available very cheaply from sawmills and woodworks. Therefore, the present work was conducted to study sorption ability of both raw sawdust and chemically activated sawdust carbon on the removal of chrysoidine from the aqueous solutions. Adsorption isotherms of the dye on sawdust were determined and correlated with usual isotherm equations like Freundlich and Langmuir. Experimental results have shown that sawdust has a high adsorption efficiency, and the adsorption of chrysoidine followed Freundlich’s isotherm. Although raw sawdust proved to be slightly less efficient in comparison to chemically treated sawdust but in economic terms, raw sawdust is more cost-effective as the difference in the percent dye removal is less than the difference in the manufacturing costs. The influence of several parameters such as effect of temperature, adsorbent dose, adsorption time, etc., on the adsorption process was studied along with thermodynamic parameters such as enthalpy (ΔH°) and entropy (ΔS°).

Biodegradation of Azure-B dye by Serratia liquefaciens and its validation by phytotoxicity, genotoxicity and cytotoxicity studies

The azo dyes in textile industry are a major source of environmental pollution and cause serious threat to aquatic flora and fauna. The present study aims to evaluate the potential of previously isolated lignin peroxidase (LiP) enzyme producing Serratia liquefaciens in degradation of Azure-B (AB) dye. S. liquefaciens showed rapid decolourisation of AB dye (100 mg L−1) in mineral salt medium (MSM) supplemented with 0.2% glucose and yeast extract, and more than 90% dye decolourisation was observed at 48 h when incubated at 30 °C. Decolourisation conditions were optimized by Response Surface Methodology (RSM) using Box-Behnken Designs (BBD). The dye degradation was further confirmed by ATR-FTIR and GC-MS analysis. Toxicological studies of untreated (UT) and bacterial treated (BT) AB dye solutions were studied by using phytotoxicity, genotoxicity and cytotoxicity endpoints. Phytotoxicity assay using Vigna radiata indicated that bacterial treatment led to detoxification of AB dye. Genotoxicity assay with Allium cepa showed that pure AB dye solutions significantly reduced mitotic index (MI) and induced various chromosomal abnormalities (CAs) like c-mitosis, stickiness, chromosome break, anaphase bridges, vagrant chromosomes and binucleated and micronucleated cell in the root tip cells, whereas, bacterial treated solutions induced relatively less genotoxicity in nature. Improved cell survivability (%) was also noted in kidney cell line (NRK-52E) after S. liquefaciens treated dye solutions than the pure dye solutions. The findings suggest that S. liquefaciens could be a potential bacterium for azo dye degradation, as it is effective in lowering of toxic effects of AB dye.

Decolourization and COD reduction of textile wastewater by ozonation in combination with biological treatment

In this study, the characteristics of colour and chemical oxygen demand (COD) removal of azo dye by ozonation and biological treatment were evaluated for applying in industrial azo dye effluent treatment. Reactive Red 120 has been selected from among azo dyes due to its high solubility in an aquatic environment. The experimentation was arranged in two stages: during the first, only ozonation was performed, while, during the second stage, ozonation was integrated with biological treatment of completely mixed activated sludge (CMAS). COD removal was contributed simultaneously by the ozonation and biological treatment mechanism at lower ozone doses. However, it was significantly the result of direct oxidation at higher ozone doses. Ozonation of dyes usually leads to small organic molecular fragments that lead to a residual COD. The biological treatment is more efficient at mineralizing the by-products of the ozonation, but less efficient at colour reduction than the ozonation process itself. Thus, COD resulting from these small newly formed molecules can be further degraded by biological treatment. Therefore, ozonation should be applied at a medium ozone dose as a pre-treatment for a combined ozonation– biological treatment for azo dye removal.

Implementation of a venturi photocatalytic reactor: Optimization of photodecolorization of an industrial azo dye

The photocatalytic decolorization of the textile azo dye C.I. Basic Red 46 was studied in a semi-pilot photocatalytic reactor combined with an emulsion venturi. The venturi has two principal roles, bring dissolved oxygen necessary for the photocatalytic reaction, and ensure a good homogenization, within its divergent, of the mixture dye solution-air-TiO2 particles. This study shows that this proposed photoreactor can be easily applied and extrapolated in photocatalysis reactions with a significant performance.The optimization of UV/TiO2 process in the photoreactor was carried out using the response surface methodology (RSM), based on the central composite design (CCD), to assess individual and interactive effects of the four main independent parameters (initial dye concentration, concentration of TiO2, flow rate (QL) and initial (pH) on the decolorization Efficiency Y (%) of (BR46)). Experimental results found from RSM was in good agreement with the model prediction (R2=0.96 and Adj-R2=0.92) and the presence of venturi has increased the discoloration rate of 20%. The optimization results showed that maximum decolorization efficiency was achieved at the optimum conditions: pH 8.68, TiO2=0.97g/L, QL 1324Lh−1, [RB46] 5mgL−1.