The photoelectrocatalytic oxidative treatment of textile wastewater containing disperse dyes

This paper presents a study of a prospective photoeletrocatalytic oxidation treatment system for disperse dyes obtained from a textile industry. The process utilizes titanium dioxide thin-film electrodes prepared by the sol-gel method as a photo-oxidative anode. Using UV irradiation and an applied potential of + 1.0 V on the nanoporous photoanode of Ti/TiO₂ it is possible to reach a reduction of color removal of 90%, 94% and 100% and 63%, 45% and 61% for TOC removal of DOD, DRD and DRR dyes. The method has been successfully applied to treat textile industry effluent collected at different steps in the industrial process namely before and after conventional wastewater treatment. The results were satisfactory for both effluent samples, leading to a reduction from 52.6% to 69.0% of COD, a diminishing of 80-89% of discoloration and a removal of TOC in the range of 47 to 50%.     

Treatment of wastewater containing dyes used in the Syrian textile industry

Three types of wastewater, from commercial dyeings containing reactive, disperse and direct dyes were treated using an organic coagulant at pH 5.5 as a first step, with stirring for 5 min. The second step was oxidation by Fenton's reagent (hydrogen peroxide and iron(II) sulfate) at pH 2.5–3 for 30 min. The pH of the solution was then raised to 7.5–8 where coagulation by iron hydroxide took place over 20 min. Finally, sand filtration was performed. The percentage of color removal from treated wastewater was more than 99.00% and the percentage decrease in COD was more than 96.00%. © 2002 Society of Chemical Industry     

Electrocoagulation process applied to wastewater containing dyes from textile industry

In the present work, electrocoagulation was applied for the colour removal of solutions containing Direct red 81. Experiments were performed for synthetic solutions in batch mode.     

Reuse of decolourised wastewater of azo dyes containing dichlorotriazinyl reactive groups using an advanced oxidation method

The possibility of reusing textile wastewater in dyeing processes is investigated in this study. Wastewater was first decolourised by an advanced oxidation method and was then reused in the dyeing of cotton fabric. It was found that decomposition products of the azo dyes used in this study released hydrogen peroxide and sodium sulphate, which were found to be present in the initial wastewater following decolourisation. Removal of this hydrogen peroxide from the wastewater prior to subsequent dyeings produced a dyeing colour strength of 98.4% as compared to that of the standard dyeing. A second reuse of this wastewater resulted in a slightly lower colour strength of 94.4% as compared to standard dyeing.     

Biological treatment of effluent containing textile dyes

Colour removal of textile dyes from effluent was evaluated using a laboratory 'upflow anaerobic sludge blanket' reactor. Several commercial dyes were selected to study the effect of dye structure on colour removal. The anaerobic reactor was fed with glucose, an easily biodegradable organic matter and selected individual dyes. Results show that some of the dyes are readily reduced under anaerobic conditions even at a high concentration of 700 mg/l. The average removal efficiency for acid dyes using this method was between 80 and 90% and that observed for the direct dye used was 81%. Laboratory experiments using the anaerobic reactor with disperse dyes, such as an anthraquinonebased dye, were unsuccessful even at low concentrations of 35 mg/l. Additional experiments were conducted to evaluate the toxicity of a selected disperse dye to an anaerobic environment. Results indicate that the purified dye is more toxic to the biomass than the commercial one.     

Combination of biological and chemical processes for the treatment of textile wastewater containing reactive dyes

The treatment of a segregated textile wastewater containing reactive dyes was investigated in two continuous‐flow process trains using ozonation and biological processes. The degree of decolorization and dissolved organic carbon (DOC) removal achieved by ozonation followed by aerobic treatment (two‐stage) was compared with that found when an anaerobic and aerobic pretreatment was added (four‐stage). Although the biological pretreatment reduced color by ～70%, similar amounts of ozone were required in both trains to achieve high degrees of overall removal of color and DOC. In both trains, ozonation increased biodegradability in the following aerobic reactor, however, in order to reach ～80% overall DOC removal, a specific ozone absorption (A*) of ～6 gO₃ gDOC_o^?1 was required and >50% of the DOC was mineralized in the ozone reactor. A comparison of cost estimates based on investment and operating costs for the process alternatives showed that a four‐stage train would reduce costs only if it enabled a decrease in A* to less than 2 gO₃ gDOC_o^?1. Difficulties in comparing treatment processes for segregated vs full‐stream wastewaters are discussed. Copyright © 2003 Society of Chemical Industry     

Removal of chemical oxygen demand from textile wastewater using a natural coagulant

A biomaterial was successfully synthesized from Plantago ovata by using an FeCl₃-induced crude extract (FCE). The potential of FCE to act as a natural coagulant was tested for the pretreatment of real textile wastewater. Tests were performed to evaluate the effects of FCE quantity, salt concentration, and wastewater pH on chemical oxygen demand (COD) reduction during a coagulation/flocculation process. Experimental results indicated that the wastewater could be effectively treated by using a coagulation/flocculation process, where the BOD₅/COD ratio of the effluent was improved to 0.48. A low coagulant dose, 1.5mg/L, achieved a high COD removal percentage, 89%, at operational conditions of neutral pH and room temperature. The experimental data revealed that the maximum COD removal occurred at water pH<8. Increasing the salt promoted the COD removal. The settling and filterability characteristics of the sludge were also studied. Scanning electron microscopy and energy dispersive spectroscopy studies were conducted to determine the sludge structure and composition, respectively. Overall, FCE as an eco-friendly biomaterial was revealed to be a very efficient coagulant and a promising option for the removal of COD from wastewaters.     

Emerging bioremediation technologies for the treatment of textile wastewater containing synthetic dyes: a comprehensive review

The tremendous increase in human population and industrialization has exacerbated the existing problem of water pollution to a great extent. The textile industry is the major cause of this problem due to its significant use of organic synthetic dyes as coloring materials during the dyeing process. The presence of color in wastewater is a major environmental concern, as these dyes are resistant to degradation by physio-chemical treatments. Bioremediation is an attractive method that can completely degrade these dyes while also being cost-effective. This comprehensive review aims to provide a brief insight into bioremediation based on some of the latest emerging wastewater treatment technologies for the removal of synthetic dyes. Starting with the importance of decolorization of synthetic dyes and their environmental impacts, different physio-chemical treatment technologies are analyzed with a special emphasis on their limitations. The bioremediation of textile wastewater with detailed biodegradation mechanisms using different bacterial species (bacteria, fungal, algae, enzyme, and mixed culture) under aerobic and anaerobic conditions is thoroughly discussed. In this article, the major factors affecting the implementation of biological treatment are explained. In addition, the latest emerging treatment technologies, such as nano-bio materials, genetic engineering, phytoremediation, electro-bioremediation (microbial electrochemistry technology, MET), and integrated/hybrid technologies (such as biological processes with physio-chemical processes, electro-coagulation, adsorption, ultra-filtration, membrane, and advanced oxidation) are critically reviewed; their challenges and the future perspectives in textile wastewater treatment are also highlighted. © 2021 Society of Chemical Industry (SCI).     

Removal of reactive dyes from wastewater using Fe(III) coagulant

The coagulation-flocculation process was employed for the treatment of reactive dye wastewaters, with ferric chloride hexahydrate employed as the coagulant. The process was found to be very effective with a more than 99.5% colour removal. Typical representatives of monochlorotriazine reactive dyes, with azo and anthraquinone chromophores, were CI Reactive Red 45 and CI Reactive Green 8, which were chosen as the model dyes. In order to determine the optimum pH range and coagulant concentration, a series of jar tests was done. Further experiments were conducted using a square flocculation tank with turbine impeller applying rapid and slow mix operations. The optimisation of initial rapid mixing, which has an important role in the overall coagulation process efficiency, was carried out. The optimum combination of velocity gradient and time of rapid mix was suggested for reactive dye wastewater treatment. Sedimentation curves for both model dyes were also obtained.     

Direct dyes containing two urea groups

J-acid and γ-acid were condensed with tolueneisocyanate to prepare new coupling components , containing two urea groups, with similar properties to those of the known J-acid urea. The diurea dyes obtained from the new intermediates show similar properties to those of conventional phosgenated direct dyes.     

Removal of methylene blue dyes from wastewater using cellulose‐based superadsorbent hydrogels

Superadsorbent cellulose‐graft‐acrylic acid (C‐g‐AA) hydrogels were successfully prepared via free radical polymerization in phosphoric acid solution. Phosphoric acid solution provides a homogeneous reaction system. The C‐g‐AA hydrogels have a porous network inner structure with cellulose as the backbone. The introduced carboxyl groups enable the C‐g‐AA hydrogels with good swelling property (swelling ratio 7327%) and excellent MB adsorption capacity (equilibrium adsorption amount 2197 mg g^?1). The dynamic swelling behaviors of the hydrogels were tested, water intake of hydrogels followed a non‐Fickian type diffusion. The effects of mole ratio of AA to cellulose, the pH of adsorption medium and the initial MB concentration on dye adsorption capacity of hydrogels were investigated. The adsorption isotherm and kinetics fit the Langmuir model and the Pseudo‐second‐order model well, respectively. Desorption was carried out in weak acid solution and 70% MB could be removed, suggesting the C‐g‐AA hydrogels had the potential for reuse. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Cathodic decolourisation of textile waste water containing reactive dyes using a multi‐cathode electrolyser

The reductive decolourisation of textile dyestuffs containing an azo group was investigated by direct cathodic electron transfer CI Acid Red 27 and CI Acid Yellow 9 were used as model compounds for azo dyes. Reactive dyes, eg CI Reactive Red 4, CI Reactive Orange 4, and CI Reactive Black 5, which are in technical use for cellulose dyeing were investigated as representatives of practical importance. A basic characterisation of the reduction–decolourisation behaviour of the dyes was achieved by redox titration with Fe(II)–triethanolamine as reducing agent and parallel spectrophotometric observation of changes in the chromogenic system. From the redox titration experiments basic data describing the experimental conditions for successful cathodic electron transfer can be derived. The electrochemical dyestuff reduction experiments were performed in batch trials using a multi‐cathode electrolyser with high cathode area. According to the typical composition of such dyebaths 0.12 mol dm^?3 NaOH was used as ground electrolyte. The absorbance of the investigated dyestuff solutions could be decreased to below 20% of the initial value. For a 50% decrease in absorbance, electrical energy of about 6 kWh m^?3 is consumed. The process is of particular interest for the treatment of concentrated dyestuff solutions as they are used in continuous dyeing processes. © 2001 Society of Chemical Industry     

Use of microemulsions for removal of color and dyes from textile wastewater

One of the major environmental problems in the textile dyeing industry is the removal of color from effluents. The present study deals with color removal from effluents using microemulsions. The wastewater used in this study was the reactive exhausted dye liquor from a dyeing house containing Procion Yellow H‐E4R (CI Reactive Yellow 84), Procion Blue H‐ERD (CI Reactive Blue 160) and Procion Red H‐E3B (CI Reactive Red 120). Color removal was determined by CIE L*a*b* (CIELAB) color space, CIE L*a*b* color difference, ΔE*_ab, and absorbance. Color removal greater than 95% was achieved, attaining values lower than the consent requirements established by the Environmental Agency. It was observed that pH is an important parameter in color removal and effluent pH correction from 10.44 to 9 before extraction improved results. The results obtained were modeled using the Scheffé net method and evaluated through the construction of isoresponse diagrams by correlation graphics between experimental values and those obtained through use of model equations, providing an experimental error of less than 2%. The optimized method very efficiently removed all dyes contained in the effluent. The same microemulsion phase recovered after the extraction process can be used at least a further 14 times and all the extractions gave good color removal. Copyright © 2004 Society of Chemical Industry     

白腐真菌对不同种类直接染料废水的脱色性能研究

试验考察了白腐真菌对直接耐晒大红、直接耐晒黄、直接耐晒果绿3种染料的脱色情况.试验结果表明,白腐真菌对不同种类的染料,色度的去除有不同的效果,对绿色染料的去除效果最好,其脱色率为83.8%:其次是黄色染料,脱色率为78.7%;而最难脱色的是红色染料,仅为35.8%.混合染料更难脱色,黄绿染料的脱色效果较好,脱色率为71...     

Removal of reactive dyes from wastewater by acrylate polymer beads bearing amino groups: isotherm and kinetic studies

The aim of this study was to prepare a novel resin for the removal of reactive dyes from aqueous media. To prepare the resin, poly(2‐hydroxyethyl methacrylate/ethylene glycol dimethacrylate) beads were grafted with poly(glycidyl methacrylate) by surface‐initiated atom transfer radical polymerisation. Epoxy groups of the grafted polymer were modified with tris(2‐aminoethyl)amine ligand. The modified resin was characterised by swelling studies, FT‐IR and SEM. Three different reactive dyes were selected (CI Reactive Brown 10, CI Reactive Red 120 and CI Reactive Green 5) and used in the removal studies. The effects of pH, temperature, ionic strength and initial dye concentration on the adsorption capacity of the resin were investigated. The adsorption capacity of the resin for Reactive Brown 10, Reactive Red 120 and Reactive Green 5 was 0.029 ± 0.010, 0.032 ± 0.0019 and 0.042 ± 0.0013 mmol/g resin (34.1 ± 1.2, 47.6 ± 2.3 and 69.3 ± 1.7 mg/g resin) respectively. The equilibrium adsorption data were analysed by Langmuir, Dubinin–Radushkevich, Freundlich and Temkin isotherm models. A good fit was found between the Langmuir isotherm and data for the three dyes on resin. The adsorption kinetic data were modelled using pseudo‐first‐order, pseudo‐second‐order and intraparticle diffusion kinetic equations. It was found that the pseudo‐second‐order equation could describe the adsorption kinetics. The results indicated that the modified resin is an attractive alternative for removing reactive dyes from wastewater.     

Packed bed column studies for the removal of synthetic dyes from textile wastewater using immobilised dead C. tropicalis

An efficient dye biosorbent was developed for the treatment of textile wastewater by entrapping dead cells of C. tropicalis, within sodium alginate matrix. The biosorbent performance was evaluated in packed bed column with different pH (3 to 6), wastewater strength (25%, 50% 75%), bed height (5 cm–15 cm) and flow rate (0.5 mL min^?1 to 1 mL min^?1). pH 5, undiluted wastewater, bed height 15 cm and flow rate 0.5 mL min^-1 were found to be optimum for dye biosorption. The linearized form of the modified Thomas model equation fitted well with the experimental data and described the dynamic adsorption of synthetic dyes from textile wastewater. The Bed depth service time model was used to express the effect of bed height on breakthrough curves. Dye laden immobilised dead C. tropicalis was regenerated using 0.01 mol L^?1 NaOH at an elutant flow rate of 1 mL min^?1. The reusability of the immobilised biomass was tested in consecutive adsorption–desorption cycles. The FT-IR spectral analysis showed the involvement of amine, hydroxyl, carbonyl, amide and phosphoryl groups in biosorption of dyes from wastewater. The analysis of treated samples showed almost zero colour and a significant decrease in Total Dissolved Solids (TDS).     

Removal of dyes from wastewater by growing fungal pellets in a semi-continuous mode

To increase the efficiency of dye removal from wastewater using mycelial pellets, a bubble column reactor with a simple structure was designed and efficiently used to remove dyes from solution containing dyes. The mycelial pellets were prepared by marine fungus Aspergillus niger ZJUBE-1. Eight dyes were tested as dye targets for the adsorption capacity of mycelial pellets and good removal results were obtained. Eriochrome black T was selected as a model dye for characterizing the adsorption processes in detail. The measurement results of Zeta potential and FT-IR analysis indicate that the electrostatic attraction may play a key role in the biosorption process. The bubble column reactor was utilized to study the batch dye-removal efficiency of mycelial pellets. A re-culture process between every two batches, which was under non-sterile condition, successfully enhanced the utilization of mycelium biomass. The dye removal rate is 96.4% after 12 h in the first batch and then decreases slowly in the following batches. This semi-continuous mode, which consists of commutative processes of dye-removal and re-culture, has some outstanding advantages, such as low power consumption, easy operation, high dye removal rate, and efficient biomass utilization.

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Removal of reactive dyes using organofunctionalized mesoporous silicas

Mesoporous inorganic–organic hybrids with mono- or bifunctional pendant chains anchored onto the silica backbones were investigated for reactive dye removal. The organofunctionalized silicas obtained from silylating agents contain the functional groups: 3-aminopropyl, octadecyldimethyl(silylpropyl)ammonium and 3-mercaptopropyl. The pendant electrophilic chains attached on the new porous silicas interact with the negative charge of industrial textile reactive dyes: yellow GR, red RB and blue RN. The best maximum sorption results were obtained for both mercapto and amino groups, to give 351, 388 and 203 mg g^?1 for GR, RN and RB dyes. These silicas also have the advantage of undergoing sorption without initial pH adjustment and surface saturation in short times. The high sorption capacity is due to the combination of properties associated with higher pore volume, surface area, smaller particle and the presence of two different functional groups, also emphasizing the presence of one mercapto group in the hybrid. These silicas, mainly the structurally bifunctional arrangement, with available disposition of pendant chains, are promising for textile effluent removal.