Decomposition pathways and reaction intermediate formation of the purified, hydrolyzed azo reactive dye C.I. Reactive Red 120 during ozonation

In this study, an aqueous solution of purified, hydrolyzed C.I. Reactive Red 120 (RR 120, Color Index), was selected as a model to investigate the degradation pathways and to obtain additional information on the reaction intermediate formation. The dye was purified to avoid the influence of the impurities on the ozonation process and on the formation of oxidation by-products. To simulate the dye-bath effluents from dyeing processes with azo reactive dyes, a hydrolyzed form of the dye was chosen as a representative compound. High performance liquid chromatography/mass spectrometry and its tandem mass spectrometry was chosen to identify the decomposition pathways and reaction intermediate formation during the ozonation process. In addition total organic carbon and high performance ion chromatography analysis were employed to obtain further information on the reaction processes during ozonation. Purified, hydrolyzed RR 120 was decomposed under the direct nucleophilic attack by ozone resulting in oxidation and cleavage of azo group and aromatic ring, while the triazine group still remained in the solution even after prolonged oxidation time (120 min) due to its high resistance to ozonation. Phenol, 1,2-dihydroxysulfobezene, 1-hydroxysulfonbezene were detected as the degradation intermediates, which were further oxidized by O(3) and *OH to other open-ring products and then eventually led to simple oxalic and formic acid identified by HPIC.     

Decolorization of azo dye reactive black B by Bacillus cereus strain HJ-1

Reactive black B (RBB) is a group of azo dyes that are widely used in the textile industry. In this study, a new microbial strain was isolated from azo dye contaminated river sediment which is capable of degrading RBB. The strain was identified as Bacillus cereus strain HJ-1 by 16S rRNA gene sequences analysis. The optimal conditions for RBB decolorization by B. cereus strain HJ-1 are: 25 °C, pH 8, 1 CMC of triton X-100, 0.15 g L^?1 of added yeast extract, 0.125 g L^?1 of added glucose and static culture. Then the toxicity of RBB on the green algae Chlorella vulgaris was determined. The results showed that the median effective concentration (EC₅₀) of RBB for C. vulgaris is 48 mg L^?1 and toxicity will really decrease after decolorization. In the end, B. cereus strain HJ-1 was amended into the origin river sediment and analyzed the whole microbial community structure of river sediment samples by PCR-DGGE technique. The result showed that B. cereus strain HJ-1 could survive in the river sediment after 12 d of incubation. Based on this work, we hope that these findings could provide some useful information for applying the decolorization of RBB in our environment.     

Ozonation of azo dye in a semi-batch reactor: a determination of the molecular and radical contributions

Azo dye ozonation was carried in a semi-batch reactor to evaluate both the molecular and radical contributions of ozone on the dye decay. From two mass balance equations, the simultaneous determination of mass transfer, self-decomposition and solubility parameters of ozone were determinated; thus establishing the steady state conditions in the experimental system. The results of kinetic studies showed that the decay of azo dye was a pseudo-first-order reaction with respect to dye concentration and the overall rate constant increased with an increase in the pH, however declined with an increase in the dye concentration. Furthermore, from the overall rate constants obtained at various pH values a mathematical analysis of dye decay was performed, which provides a practical new method to quantify the radical and molecular contributions in the ozonation of azo dyes.     

Ozonation of azo dye Acid Red 14 in a microporous tube-in-tube microchannel reactor: decolorization and mechanism

Despite the great success of time-weighted average passive sampling of hydrophobic contaminants, such as PCBs and PAHs, the sampling of polar organic compounds still presents a challenge because the equilibrium between water and most sampling phases is attained in a relatively short time. In this study, we proposed a new time-integrative sampler using in situ solvent extraction (TISIS) for polar organic chemicals. The sampler was composed of a 15 cm poly(dimethylsiloxane) (PDMS) tubing, with an internal diameter of 0.5 mm and wall thickness of 0.5 mm, through which an extraction solvent (acetonitrile) was passed. Four polar organic contaminants, caffeine, atrazine, diuron and 17α-ethynylestradiol, were chosen for the evaluation of the performance of the sampler. Without the use of in situ solvent extraction, the PDMS tubing when exposed to a constant aqueous concentration of the four model compounds was able to linearly accumulate those compounds for less than 12 h and equilibrium between the PDMS tubing and water was attained in 2 d under our laboratory conditions. However, TISIS when exposed to a constant aqueous concentration was able to linearly accumulate all the model compounds without any exposure time limitation. The measured sampling rates at three different extraction flow rates (0.2, 0.5, 1.5 mL min⁻¹) were similar, regardless of the chemicals, indicating that the overall mass transfer from aqueous solution to the extraction solvent was most likely dominated by partitioning to the PDMS tubing and the internal diffusion within PDMS. In addition, a pulsed exposure experiment confirmed that TISIS operated in a time-integrative mode when the environmental concentration was highly fluctuated.     

Predictive modeling of sorption and desorption of a reactive azo dye by pumpkin husk

The use of effective disposal of redundant pumpkin husk (PH) to remove pollutants is an important issue for environmental protection and utilization of resource. The aim of this study was to remove a potentially toxic reactive azo dye, Reactive Red (RR) 120, by widespread PH as a low-cost adsorbent. Particle size, adsorbent dose, pH, temperature, initial dye concentration, and contact time affected the sorption process. Amine, amide, hydroxyl, and carboxyl groups of PH played significant roles on the sorption process. Rapid sorption occurred within the first 2 min and equilibrium was reached within 60 min. Sorption kinetic was well represented by logistic equation. Generated secondary logistic model can be used to describe effects of initial dye concentration, contact time, and temperature by a single equation with high R ² value. Monolayer sorption capacity was found as 98.61 mg g^-1. Activation energy, thermodynamic, and desorption studies showed that this process was physical, endothermic, and spontaneous. This study indicated that redundant PH as a low-cost adsorbent had a great potential for the removal of RR 120 as an alternative eco-friendly process.     

粉煤灰负载铁离子催化氧化活性黄染料废水

以粉煤灰为载体,制备铁/粉煤灰负载型催化剂,并利用该催化剂催化H2O2氧化降解活性黄染料废水,探讨了H2O2投加量、催化剂投加量、染料初始浓度和初始pH值等因素对染料废水COD去除率和脱色率的影响。结果表明,当染料废水COD初始浓度为200 mg/L,初始pH值为1.7,投加0.5 g/100 mL催化剂及加入1.0 mL浓度为1.13 mol/L的H2O2溶液时,处理效果最好,此时染料废水的COD去除率和脱色率分别达到63%和99%,并且废水的可生化性得到很大的提高。利用该负载催化剂能够有效地减少活性黄染料废水中Fe3+的残留量。     

Sorption and desorption studies of a reactive azo dye on effective disposal of redundant material

The effective disposal of redundant elephant dung (ED) is important for environmental protection and utilization of resource. The aim of this study was to remove a toxic-azo dye, Reactive Red (RR) 120, using this relatively cheap material as a new adsorbent. The FTIR–ATR spectra of ED powders before and after the sorption of RR 120 and zero point charge (pH_zpc) of ED were determined. The sorption capacity of ED for removing of RR 120 were carried out as functions of particle size, adsorbent dose, pH, temperature, ionic strength, initial dye concentration, and contact time. Sorption isotherm, kinetic, activation energy, thermodynamic, and desorption parameters of RR 120 on ED were studied. The sorption process was found to be dependent on particle size, adsorbent dose, pH, temperature, ionic strength, initial dye concentration, and contact time. FTIR–ATR spectroscopy indicated that amine and amide groups have significant role on the sorption of RR 120 on ED. The pH_zpc of ED was found to be 7.3. Sorption kinetic of RR 120 on ED was well described by sigmoidal Logistic model. The Langmuir isotherm was well fitted to the equilibrium data. The maximum sorption capacity was 95.71 mg?g^?1. The sorption of RR 120 on ED was mainly physical and exothermic according to results of D–R isotherm, Arrhenius equation, thermodynamic, and desorption studies. The thermodynamic parameters showed that this process was feasible and spontaneous. This study showed that ED as a low-cost adsorbent had a great potential for the removal of RR 120 as an alternative eco-friendly process.     

Ozonation of an azo dye C.I. Remazol Black 5 and toxicological assessment of its oxidation products

The effect of ozonation (20.5 mgl(-1)) on the degradation processes of an azo dye, Remazol Black 5 (RB5; CI) was studied. Conventional parameters such as chemical oxygen demand (COD), total organic carbon (TOC), pH, conductivity, colour removal, biodegradability (BOD(5/28)), and toxic potential of the dye and its degradation products were monitored during the process. The results obtained indicated that ozonation is a highly effective way to remove the colour of a corresponding dye solution. However, a considerable organic load still remained as indicated by high COD and TOC residues. The COD, TOC reductions were about 40% and 25% for 6 h ozonation of 2 gl(-1) RB5 aqueous solution. During the ozonation process the rapid decrease of pH and the sharp increase of conductivity indicated the formation of acidic by-products and small fragments and ions which were identified by high performance ion chromatography. The BOD28 data revealed that first by-products after partial ozonation (10-150 min) of RB5 were more biodegradable than the parent compound and ozonation can enhance the biodegradability of azo dyes. During the first 150 min of total 360 min of oxidation, the formation of first by-products with high toxic potential took place as it could be confirmed by two acute toxicity-screening tests, the bioluminescence test (Vibrio fischerii) and the neutral red cytotoxicity assay (rat hepatoma cells). The significant enhancement of microbial biodegradability after long-term ozonation could also be seen as a decrease of toxic intermediates in correlation with the ozonation time as indicated in BOD28 biological degradation test results.     

Characterization of tannery sludge activated carbon and its utilization in the removal of azo reactive dye

Introduction  

The removal of azo Reactive Red 31(RR31) from synthetic dye solution using tannery sludge-developed activated carbon (TSC) was investigated.     

Functional group influences on the reactive azo dye decolorization performance by electrochemical oxidation and electro-Fenton technologies

Electrochemical water treatment technologies are highly promising to achieve complete decolorization of dyebath effluents, as demonstrated by several studies reported in the literature. However, these works are focused on the treatment of one model pollutant and generalize the performances of the processes which are not transposable since they depend on the pollutant treated. Thus, in the present study, we evaluate, for the first time, the influence of different functional groups that modify the dye structure on the electrochemical process decolorization performance. The textile azo dyes Reactive Orange 16, Reactive Violet 4, Reactive Red 228, and Reactive Black 5 have been selected because they present the same molecular basis structure with different functional groups. The results demonstrate that the functional groups that reduce the nucleophilicity of the pollutant hinder the electrophilic attack of electrogenerated hydroxyl radical. Thereby, the overall decolorization efficiency is consequently reduced as well as the decolorization rate. Moreover, the presence of an additional chromophore azo bond in the molecule enhances the recalcitrant character of the azo dyes as pollutants. The formation of a larger and more stable conjugated π system increases the activation energy required for the electrophyilic attack of ^?OH, affecting the performance of electrochemical technologies on effluent decolorization.     

Performance of oxalic acid-chitosan/alumina ceramic biocomposite for the adsorption of a reactive anionic azo dye

Environmental Science and Pollution Research - A biocomposite system was developed and tested for the removal of the azo dye Reactive Red (RR195) from wastewater. The biocomposite was synthesized...     

Photodegradation of an azo dye of the textile industry

An advanced oxidation treatment, UV/H2O2, was applied to an azo dye, Hispamin Black CA, widely used in the Peruvian textile industry. Rates of color removal and degradation of the dye have been evaluated. A strongly absorbing solution was completely decolorized after 35 min of treatment, and after 60 min an 82% reduction of the total organic carbon (TOC) was obtained. It has been found that the degradation rate increased until an optimum value, beyond which the reagent exerted an inhibitory effect. The degradation rate was also function of pH.     

电-生物耦合技术对偶氮染料的去除研究

酸性大红GR是一种较难生物降解的偶氮染料,采用一种电场和生物耦合的新型技术处理酸性大红GR模拟废水,并与单纯电化学法和好氧生物法进行试验对照。结果表明：反应6 h后,电化学法、好氧生物法、电-生物耦合技术对酸性大红GR的去除率分别达到15.7%、25.8%和71.2%,电-生物耦合技术能明显提高酸性大红GR的去除效果,起到强化生物处理的作用。在15 mA微电流条件下电-生物技术能克服50 mg/L酸性大红GR对好氧生物处理的抑制作用,为高浓度难降解染料废水的生物强化处理提供了可能。     

Degradation mechanism of azo dye C. I. reactive red 2 by iron powder reduction and photooxidation in aqueous solutions

We have made a comparison of the UV-VIS spectra of three azo dyes, C. I. reactive red 2, orange II and C. I. reactive black 8, in aqueous solutions during treatment with iron powder reduction and photooxidation. From this, we propose their mechanisms for reduction photooxidation. GC/MS analyses of the degradation products of the dye C. I. reactive red 2 demonstrated some important steps producing hydrogenated azo structure, substituted benzene and substituted naphthalene.     

亚铁羟基络合物还原转化水溶性偶氮染料

偶氮染料是印染工艺中应用最广泛的一类染料,目前染料废水脱色是污水处理难题。亚铁混凝处理染料废水过程中可能存在亚铁的还原作用,本实验制备了比溶解态亚铁更具还原反应活性的亚铁羟基络合物(ferrous hydroxycomplex,FHC),以5种不同类型的水溶性偶氮染料为目标污染物,研究FHC还原水溶性偶氮染料的脱色性能。实验结果表明,FHC对活性艳红X-3B、酸性大红GR和阳离子红X-GRL有较好的还原脱色效果,仅投加含铁89.6 mg/L的FHC,染料脱色率达到90%以上,继续增大FHC投加量可以完全脱色;中性枣红GRL的FHC还原脱色效果较差,需加入313.6 mg/L的FHC才能达到90%以上脱色率;134.4 mg/L的FHC能够将直接耐酸大红4BS完全脱色,但其脱色主要以混凝沉淀为主;溶液pH对FHC的还原性能产生重要影响,FHC还原染料脱色的适宜的pH值范围为4～10。该研究为亲水性染料脱色提供了一种新的技术,也为FHC运用于印染废水脱色提供了理论基础。     

Degradability of selected azo dye metabolites in activated sludge systems

The stability of eight environmentally relevant azo dye metabolites [o-aminotoluene (2), 4,4'-thiodianiline (4), 4,4'-diaminodiphenylmethane (6), p-chloroaniline (7), 2,4-toluylenediamine (9), p-kresidine (14), 2,4-diaminoanisole (15), and 2-naphthylamine (18)] was investigated in activated sludge systems and compared to their hydrolysis stability. For both studies, test systems of the EC and EPA were used. The results show that degradation under aerobic conditions proceeds via oxidation of the substituents located on the aromatic ring or on the side chain. Under anaerobic conditions, the azo bond is reductively cleaved, which leads to the substituted amines. These are toxic and potentially hazardous to the environment.     

Decolourization of azo dye methyl red by Saccharomyces cerevisiae MTCC 463

Saccharomyces cerevisiae MTCC 463 decolourizes toxic azo dye, methyl red by degradation process. Methyl red (100mgl(-1)) is degraded completely within 16min in plain distilled water under static anoxic condition, at the room temperature. Effect of physicochemical parameters (pH of medium, composition of medium, concentration of cells, concentration of dye, temperature and agitation) on methyl red decolourization focused the optimal condition required for decolourization. Biodegradation (fate of metabolism) of methyl red in plain distilled water was found to be pH dependent. Cells of Saccharomyces cerevisiae could degrade methyl red efficiently up to 10 cycles in plain distilled water. Analysis of samples extracted with ethyl acetate from decolourized culture flasks in plain distilled water (pH 6.5) and at pH 9 using UV-VIS, TLC, HPLC and FTIR confirm biodegradation of methyl red into several different metabolites. A study of the enzymes responsible for the biodegradation of methyl red in the control and cells obtained after decolourization in plain distilled water (pH 6.5) and at pH 9 showed different levels of the activities of laccase, lignin peroxidase, NADH-DCIP reductase, azoreductase, tyrosinase and aminopyrine N-demethylase. A significant increase in the activities of lignin peroxidase and NADH-DCIP reductase was observed in the cells obtained after decolourization in plain distilled water (pH 6.5), however cells obtained at pH 9 shows increased activities of azoreductase, tyrosinase, lignin peroxidase and NADH-DCIP reductase. High efficiency to decolourize methyl red in plain distilled water and low requirement of environmental conditions enables this yeast to be used in biological treatment of industrial effluent containing azo dye, methyl red.     

Reducing degradation of azo dye by zero-valent iron in aqueous solution

The reducing degradation kinetics of five azo dyes, Acid orange II, Acid orange IV, Acid orange GG, Acid red 3B and Orange I, by zero-valent iron powder in aqueous solution were studied. It showed that the degradation is a two-step reaction, with the first step being reversible. Solution acidity and iron surface area are the factors greatly influencing the degradation rates, and with increasing of acidity and iron surface area, the degradation rates increase.     

Removal of azo dye from water by magnetite adsorption-Fenton oxidation.

The aim of this study is to highlight the possibility of using powder magnetite adsorption-Fenton oxidation as a method for removal of azo dye acid red B (ARB) from water. The adsorption properties of magnetite powder towards ARB were studied. The oxidation of adsorbed ARB and regeneration of magnetite adsorbent at the same time by Fenton reagent (hydrogen peroxide [H2O2] + iron (II) [Fe2+]) in another treatment unit with a smaller volume was also investigated. The efficiency of Fenton oxidation of ARB was compared for the reaction carried out in solution and on magnetite. The magnetic separation method was used to recover magnetite after adsorption or regeneration. The results indicated that the adsorption rate was fast. The capacity was strongly dependent on pH and inorganic anions, and pH 3.8 was optimal for the adsorption of ARB. The adsorption can be described well using the Langmuir model. The oxidation was more efficient for ARB adsorbed on magnetite than in solution. The adsorption capacity of magnetite increased significantly after regeneration, which was the result of an increase in surface area of the adsorbent and change of elemental ratio (oxygen:iron [O:Fe]) on the surface. The maximum adsorption capacity for ARB was 32.4 mg/g adsorbent.     

高压电弧放电处理偶氮染料废水

用高压电弧放电产生的低温等离子体对含偶氮染料的废水进行了处理,以甲基橙为例研究了电压幅值、处理时间、溶液初始浓度、溶液初始pH值、投加Fe^2＋和Fe^3＋对染料脱色的影响。实验结果表明,甲基橙浓度为50mg／L时其降解率随时间和电压幅值的增加而增加。溶液初始浓度对染料去除效果影响较为明显,同等条件下初始浓度越低降解率越高。酸性条件下有利于低温等离子体处理甲基橙。Fe^2＋和Fe^3＋对低温等离子体降解甲基橙有一定的催化作用。电压8kV处理3min,Fe^2＋为20mg／L时去除率由89．64％增至99．72％。Fe2（SO4）,的最佳投加量为5mg／L（以Fe^3＋计）,而FeCl,的最佳投加量为80mg／L（以Fe^3＋计）。