Mechanism and kinetic model for the decolorization of the azo dye Reactive Black 5 by hydrogen peroxide and UV radiation

A kinetic model for the decolorization of C.I. Reactive Black 5 by the combination of hydrogen peroxide and UV radiation was developed based on experimental results and known chemical and photochemical reactions. The observed kinetic reaction coefficient was determined and correlated as a function of hydrogen peroxide concentration and UV intensity. The validity of the rate expression was tested experimentally in a parameterization study. The decolorization rate follows pseudo-first order kinetics with respect to dye concentration. The rate increases linearly with UV intensity and nonlinearly with increasing hydrogen peroxide concentration, going from a linear relationship at low H(2)O(2) concentrations to a maximum as hydrogen peroxide concentration continues to increase. The decolorization rate expression derived from the proposed reaction mechanism was reconciled with that used for correlating the experimental data.     

Photocatalytic and combined anaerobic-photocatalytic treatment of textile dyes

A photocatalytic process based on immobilized titanium dioxide was used to treat crude solutions of azo, anthraquinone and phthalocyanine textile dyes. In addition, the process was applied to the treat autoxidized chemically reduced azo dyes, i.e. representatives of recalcitrant dye residues after biological sequential anaerobic-aerobic treatment. Photocatalysis was able to remove more than 90% color from crude as well as autoxidized chemically reduced dye solutions. UV-absorbance and COD were also removed but to a lower extent (50% in average). The end products of photocatalytic treatment were not toxic toward methanogenic bacteria. The results demonstrate that photocatalysis can be used as a pre- or post-treatment method to biological anaerobic treatment of dye-containing textile wastewater.     

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。     

Enhanced biodegradation of azo dyes using an integrated elemental iron-activated sludge system: I. Evaluation of system performance.

The objective of this research is to evaluate an integrated system coupling zero-valent iron (Fe(0)) and aerobic biological oxidation for the treatment of azo dye wastewater. Zero-valent (elemental) iron can reduce the azo bond, cleaving dye molecules into products that are more amenable to aerobic biological treatment processes. Azo dye reduction products, including aniline and sulfanilic acid, were shown to be readily biodegradable at concentrations up to approximately 25 mg/L. Batch reduction and biodegradation data support the proposed integrated iron pretreatment and activated sludge process for the degradation of the azo dyes orange G and orange I. The integrated system was able to decolorize dye solutions and yield effluents with lower total organic carbon concentrations than control systems without iron pretreatment. The success of the bench-scale integrated system suggests that iron pretreatment may be a feasible approach to treat azo dye containing wastewaters.     

The effect of pre-ozonation on the biocompatibility of reactive dye hydrolysates

Pre-ozonation of 14 different reactive dyestuff hydrolysates at alkaline pH was investigated to assess possible relationships between ozone transfer efficiency, first order decolourization kinetics, release of initially complexed heavy metals and relative changes in the biodegradability of the partially oxidized dye waste samples. Biocompatibility of the raw (untreated) and ozonated dye hydrolysates was comparatively tracked through specific oxygen uptake rate measurements from which the respirometric inhibition of biological activated sludge imparted by raw and ozonated reactive dye wastewater with respect to synthetic domestic wastewater was determined. It could be demonstrated that preliminary ozonation of reactive azo dyes increases their biological compatibility more significantly than formazan copper complex, copper complex azo and phythalocyanine dyes as a consequence of heavy metal release associated with the cleavage of associated chromophoric groupings right at the initial stages of pre-ozonation.     

A batch kinetic study on decolorization and inhibition of Reactive Black 5 and Direct Brown 2 in an anaerobic mixed culture

Decolorization and inhibition kinetic characteristics of two azo dyes namely Reactive Black 5 (RB 5) and Direct Brown 2 (DB 2) were investigated with partially granulated anaerobic mixed culture using glucose (3000 mg l(-1) COD) as carbon source and electron donor during batch incubation. Monod, zero-, first-, and second-order reaction kinetic models were tested in order to determine the most suitable rate model of substrate and color removal kinetic. The course of the decolorization and substrate removal process approximates to first-order kinetic model under batch conditions. Decolorization, and substrate removal were achieved effectively under test conditions but ultimate removal of azo dyes and substrate were not observed at high dye concentrations. Aromatic amine and volatile fatty acid accumulation were observed proportionally at a higher azo dye concentration. A competitive kinetic model that describes the anaerobic co-metabolism of increasing RB 5 and DB 2 dye concentrations with glucose as co-substrate has been developed based on the experimental data.     

Solar light induced and TiO2 assisted degradation of textile dye reactive blue 4

Aqueous solutions of reactive blue 4 textile dye are totally mineralised when irradiated with TiO2 photocatalyst. A solution containing 4 x 10(-4) M dye was completely degraded in 24 h irradiation time. The intensity of the solar light was measured using Lux meter. The results showed that the dye molecules were completely degraded to CO2, SO4(2-), NO3-, NH4+ and H2O under solar irradiation. The addition of hydrogen peroxide and potassium persulphate influenced the photodegradation efficiency. The rapidity of photodegradation of dye intermediates were observed in the presence of hydrogen peroxide than in its absence. The auxiliary chemicals such as sodium carbonate and sodium chloride substantially affected the photodegradation efficiency. High performance liquid chromatography and chemical oxygen demand were used to study the mineralisation and degradation of the dye respectively. It is concluded that solar light induced degradation of textile dye in wastewater is a viable technique for wastewater treatment.     

臭氧氧化降解含染料废水的研究

探讨了臭氧氧化技术处理染料 (酸性、直接、活性、分散和还原颜料 )模拟废水的影响因素———pH值、初始浓度和臭氧含量等对其的影响 ;臭氧氧化能提高染料废水的可生化性 ,可用来作为高浓度染料废水的预处理手段     

Biological decolourisation of simulated azo dye in aqueous phase by algae Spirogyra species

Biological decolourisation of two azo dye effluents (direct and reactive dye) were investigated using a commonly available green algae Spirogyra sp. in viable form. Batch studies revealed the potential of algal species in removing the dye colour and dye removal was dependant on initial algal inoculum, concentration and application class of the dye. Maximum dye uptake was noticed on the third day for both the dyes. Higher dye uptake was observed in the case of direct red 28 compared to reactive red 2. Dye colour removal by the algal species may be attributed to biosorption of the dye molecules onto the surface of algal cell and subsequent diffusion and participation in metabolism (bioconversion). The remaining dye molecules could be further removed from the aqueous phase by adsorption and/or chelation reaction of the exopolymers released by the algae (biocoagulation). The results of the present study reveal the potential nature of algae in treating azo dyes which in turn can be extended to oxidation pond system of wastewater treatment.     

树脂固载纳米铁对偶氮染料直接湖蓝5B的脱色性能研究

以FeSO4和NaBH4水溶液为前驱溶剂,以聚苯乙烯型阳离子交换树脂为载体,制备了树脂固载的纳米铁,室温下用于对偶氮染料直接湖蓝5B水溶液进行脱色研究。研究结果发现,脱色反应遵循准一级反应动力学,在初始pH为3~10的范围内,反应进行14 m in时,50 mg/L的染料溶液脱色率均能达到83%以上。固载的纳米铁材料可多次重复利用,溶液中释放的铁离子浓度不超过0.1 mg/L。     

Novel imazethapyr detoxification applying advanced oxidation processes

Different degradation methods have been applied to assess the suitability of advanced oxidation process (AOPs) to promote mineralization of imazethapyr [(RS)-5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid], a widely used imidazolinone class herbicide, the persistence of which has been demonstrated in surface and ground waters destined to human uses. Independent of the oxidation process assessed, the decomposition of imazethapyr always followed a pseudo-first order kinetic. The direct UV-irradiation (UV) of the herbicide as well as its oxidation with ozone (O?), and hydrogen peroxide tied to UV-irradiation (H?O?/UV) were sufficiently slow to permit the identification of intermediate products, the formation pathway of which has been proposed. Ozonation joined to UV-irradiation (O?/UV), ozonation joined to titanium dioxide photo-catalysis (TiO?/UV+O?), sole photo-catalysis (TiO?/UV), and photo-catalysis reinforced with hydrogen peroxide-oxidation (TiO?/UV+H?O?) were characterized by a faster degradation and rapid formation of a lot of small molecules, which were quickly degraded to complete mineralization. The most effective oxidation methods were those using titanium dioxide photo-catalysis enhanced either by ozonation or hydrogen peroxide. Most of all, these last processes were useful to avoid the development of dangerous by-products.     

Decolorization of structurally different synthetic dyes using cobalt(II)/ascorbic acid/hydrogen peroxide system

The cobalt(II)/ascorbic acid/hydrogen peroxide system was used for decolorization of azo, acridine, anthraquinone, thiazine and triphenylmethane dyes. More than 90% decolorization was obtained with all dyes except Remazol Brilliant Blue R (75%). With other transition metals the system was less efficient. With copper, higher concentration and prolonged incubation time was necessary to obtain the same extent of decolorization. The rate of decolorizaton was not affected by pH in the range of 3-9. The reaction is very fast, with more than 90% decolorization being attained within 15 min. The system produces hydroxyl radicals which are responsible for the decolorization.     

UV/Fenton技术处理某工厂高浓度乳化油废水

研究了UV/Fenton技术对高浓度金属清洗乳化油废水的处理效果,考察了亚铁与双氧水浓度、pH、反应时间和搅拌对COD去除效果的影响。实验结果表明,UV/Fenton技术对高浓度乳化油废水(COD平均浓度为35 000 mg/L)具有较高的去除效果,最佳工艺条件为:亚铁与双氧水浓度分别为2 400 mg/L和6 000 mg/L,pH为3,经过2 h反应,COD可降低至1 050 mg/L,去除率为97%。搅拌会降低COD的去除率。研究表明,UV/Fenton技术对高浓度乳化油废水具有很好的降解效果,且药品消耗较低,为目前此类高浓度有机废水的处理提供了技术参考。     

Degradation of acid orange 7 in an aerobic biofilm.

A stable microbial biofilm community capable of completely mineralizing the azo dye acid orange 7 (AO7) was established in a laboratory scale rotating drum bioreactor (RDBR) using waste liquor from a sewage treatment plant. A broad range of environmental conditions including pH (5.8-8.2), nitrification (0.0-4.0 mM nitrite), and aeration (0.2-6.2 mg O2 l(-1)) were evaluated for their effects on the biodegradation of AO7. Furthermore the biofilm maintained its biodegradative ability for over a year while the effects of these environmental conditions were evaluated. Reduction of the azo bond followed by degradation of the resulting aromatic amine appears to be the mechanism by which this dye is biodegraded. Complete loss of color, sulfanilic acid, and chemical oxygen demand (COD) indicate that AO7 is mineralized. To our knowledge this is the first reported occurrence of a sulfonated phenylazonaphthol dye being completely mineralized under aerobic conditions. Two bacterial strains (ICX and SAD4i) originally isolated from the RDBR were able to mineralize, in co-culture, up to 90% of added AO7. During mineralization of AO7, strain ICX reduces the azo bond under aerobic conditions and consumes the resulting cleavage product 1-amino-2-naphthol. Strain SAD4i consumes the other cleavage product, sulfanilic acid. The ability of the RDBR biofilm to aerobically mineralize an azo dye without exogenous carbon and nitrogen sources suggests that this approach could be used to remediate industrial wastewater contaminated with spent dye.     

Fixed bed adsorption of acid dyes onto activated carbon

The context of the study here is the adsorption of acid dyes from wastewater arising from a nylon carpet printing plant which currently receives no treatment. Since nylon is a particularly difficult fibre to dye, acid dyes are required for successful coloration. However, their presence, in high concentrations, in aqueous effluent arising from the plant can create major problems with respect to disposal. A treatment method based on adsorption onto granular activated carbon (GAC F400) in a fixed column configuration is described and breakthrough data of the dyes determined. The breakthrough data were correlated using a model based on liquid and pore diffusion with a good fit of experimental results obtained. Trends in the effective diffusivity used in the model correlated with other authors. A slight decrease in effective diffusivity was found with decrease in particle size and was attributed to interactions between the relatively large molecular sized dye and the microspore structure found in granular activated carbon.     

New catalyst comprising Silicotungstic acid and MCM-22 for degradation of some organic dyes

A heterogeneous catalyst comprising Keggin type polyoxometalate, silicotungstic acid (SiW₁₂), and MCM-22 was synthesized using wet impregnation method and characterized by acidity measurement, BET, FT-IR, XRD, and SEM. Their catalytic activity was evaluated for the degradation of cationic organic dyes like methylene blue (MB), crystal violet (CV), and an azo dye Chryosidine Y (CY) in an aqueous solution. The experimental parameters such as catalyst amount, initial dye concentration, and contact time were studied for the degradation of dyes, and it was found that the cationic dyes like methylene blue and crystal violet show better activity as compared to azo dye Chryosidine Y. This may be attributed to better electrostatic interaction of these cationic dyes with the residual negative surface charge of the catalyst, due to presence of SiW₁₂ ion as it is rich in surface oxygens and surface hydroxyl groups. The control experimental results showed that the presence of SiW₁₂ at the surface of MCM-22 promoted the degradation reactions, and presence of multiple W–O bonds in polyoxometalate also played a key role in this reaction. The catalyst exhibits recycling ability without any significant loss in activity up to four cycles.

     

Degradation of azo dyes using low iron concentration of Fenton and Fenton-like system

This study investigated Fenton and Fenton-like reactions at low iron concentration (相似文献   

The influence of FeCl3 on the photocatalytic degradation of dissolved azo dyes in aqueous TiO2 suspensions

The study concerned decolouration of solutions of azo, anionic (Acid Orange 7, Reactive Red 45, Acid Yellow 23) and cationic (Basic Blue 41 and Basic Orange 66) dyes during illumination with UV (lambdamax 366 nm) irradiation in the presence of TiO2 and FeCl3. The process of decolouration during illumination of the solutions studied containing FeCl3 underwent significant intensification in the case of anionic dyes and unfavourable inhibition in case of cationic dyes. It was also observed that FeCl3 had a diverse influence on the adsorption of the dyes studied on TiO2. The adsorption of anionic dyes and decolouration of solutions before the illumination was observed only in the presence of FeCl3. In case of cationic dyes the addition of FeCl3 caused elimination of these phenomena. An additional cause of decolouration of anionic dyes solutions before illumination was the precipitation of their poorly soluble compounds from Fe3+. The processes of degradation and mineralization of the dye that accompanied decolouration of Acid Orange 7 solutions were also observed. It was stated that similarly to the case of Acid Orange 7, the decolouration of the studied anionic dyes' solutions can depend on the concentration of FeCl3, the amount of TiO2 and the initial concentration of the dye in its solution.     

Solar photocatalytic decolorization of methylene blue in water

In this study, a photocatalytic decolorization system equipped with immobilized TiO2 and illuminated by solar light was used to remove the color of wastewater. To examine the decoloring efficiency of this system, photocatalytic decolorization of an organic dye such as methylene blue was studied as an example. The effects of light source, pH, as well as the initial concentration of dye were also investigated. It was observed that the solution of methylene blue could be almost completely decolorized by the solar light/TiO2 film process while there was about 50% color remaining with solar irradiation only. In addition, it was found that the decoloring efficiency of solution was higher with solar light irradiation than with artificial UV light irradiation, even though the artificial UV light source supplied higher UV intensity at 254 nm. The color removal rate of methylene blue with solar light irradiation was almost twice that of artificial UV light irradiation. This phenomena was mainly attributed to that some visible light range of solar light was useful for exciting the methylene blue molecules adsorbed on TiO2 film, leading to a photosensitization process undergoing and decoloring efficiency promoted. This solar-assisted photocatalytic device showed potential application for decoloring organic dyes in wastewater.     

Oxidation of polyvinylpyrrolidone and an ethoxylate surfactant in phase-inversion wastewater.

In this paper, components of an industrial wastewater that cause operational problems during biological treatment were oxidized by UV light and hydrogen peroxide (UV/H202). Preoxidation of wastewater was shown to remove polyvinylpyrrolidone (PVP) and ethoxylate surfactant and increase overall biodegradability. Several UV intensities and hydrogen peroxide concentrations were tested to find optimal conditions for the complete depolymerization of PVP in a synthetic wastewater composed of high concentrations of hydroxyl radical scavengers. To compare treatment options, absorption isotherms for PVP on granular activated carbon (GAC) in water and in the synthetic phase-inversion wastewater matrix were determined. The data were extrapolated to estimate the cost of using UV/H2O2, GAC, or off-site treatment. It was found that UV/H2O2 pretreatment was economically viable. Incomplete oxidation of an ethoxylate surfactant increased foaming tendency and foam stability; however, extended oxidation (> 90 minutes) destroyed the foam.