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The enormous demand for water and the creation of effluent that is dye-rich make the textile industry a hazard to water resources. Electrocoagulation (EC) is considered an appealing approach for treatment, which offers effective color removal in a quick, dependable, and affordable manner. Using 33full factorial design trials, the performance of EC in the treatment of synthetic wastewater including textile coloring, such as methyl orange, was examined using the response surface methodology (RSM). In the presence of iron electrodes, wastewater was electrolyzed at room temperature with a pH of 7 under various working parameters, including initial dye concentration, applied voltage, and electrolysis time. The findings suggested that utilizing EC has been a successful strategy for removing color from textile dyeing effluent. At an applied voltage of 15 V, an electrolysis period of 30 min, and an initial dye concentration of 50 mg/L, the maximum color removal efficiency was 96.6%. The comparable Electrical Energy Consumption (EEC) for these circumstances was 23.7 kWh/m3. It was noticed that 87.5%–91.0% of the color was eliminated during the first 20 min of the process.

The preparation of modified membranes utilizing the UiO-66 framework for wastewater filtration is regarded as one of the most promising approaches to wastewater treatment, owing to its high efficiency and cost-effectiveness. In this study, a post-modified MOF, UiO-66-RSA, was synthesized via the condensation reaction of UiO-66-NH2and 2,4-dihydroxybenzaldehyde. PVDF mixed matrix membranes (MMMs) were fabricated for the first time by mixing UiO-66-RSA into PVDF using the non-solvent induced phase separation (NIPS) method. Compared to pure PVDF membranes, the newly developed membrane, M4, demonstrated enhanced compatibility and superior mechanical strength. In dyeing wastewater treatment applications, M4 showed excellent separation efficiency for dye and heavy metal mixed wastewater, achieving rejection rates exceeding 90 %. Additionally, it maintained a high flux recovery rate (FRR > 90 %) and rejection rate (Rejection > 90 %) after six filtration cycles of dye-containing wastewater, indicating strong recyclability. These findings suggest that MMMs embedded with UiO-66-RSA hold significant promise for dyeing wastewater treatment.

In this paper, the inorganic–organic composite flocculant (PAC/PMAPTAC) was prepared with polyaluminum chloride (PAC) and the self-made PMAPTAC. Then, the flocculation sedimentation experiment was used to evaluate the flocculation performance of single flocculant PAC, PMAPTAC and the composite flocculant PAC/PMAPTAC in dyeing wastewater. At the same time, the flocculation effect of PAC/PDMDAAC was compared with that of PAC/ PMAPTAC under the same condition. Finally, the flocculation mechanism was analyzed by zeta potential and floc morphology. The results showed that compared with PAC, the flocculation performance of composite flocculant PAC/PMAPTAC could be markedly improved, resulting in the higher decolorization rate and CODMnremoval rate. Besides, the increase of (η) or content of PMAPTAC in PAC/PMAPTAC could enhance the decolorization rate and CODMnremoval rate simultaneously. Furthermore, the lower dosage was required to achieve the best removal effect, which meant that the cost of the flocculant was reduced. Moreover, the comparison of flocculation performance turned out that the decolorization rate and CODMnremoval rate of PAC/PMAPTAC were higher than those of PAC/PDMDAAC under the same condition. Finally, the zeta potential and floc morphology analysis showed that the flocculation mechanism of the reactive dye simulated wastewater was mainly charge neutralization and adsorption bridging. The above results not only fill the gaps in the research of PAC/PMAPTAC during the treatment of dyeing wastewater, but also provide an experimental basis for its application in dyeing wastewater and expand the application fields of PMAPTAC.

The low solubility of ozone in water limits its oxidation reaction rate, while microbubbles can enhance the gas–liquid mass transfer process and effectively improve the mass transfer rate of ozone. In this study, we set up an ozone microbubble generation system, with an internal recycle, a self-made releasing device using 3D printing and other designs to keep the system running steadily, with constant pressure, high ozone concentrations, and slow microbubble dissipation rate. This study investigated the ozone feed rate and optimization of mixing conditions through the test. With the increase of ozone feed rate, the average concentration of ozone in the solution tends to increase linearly, then decreases slightly after reaching the maximum 13.75 mg/L. On a stable running of the system, the ozone concentration of the solution could reach 13.29 mg/L. The ozone microbubble was then investigated by calculation and measurement of bubble disappearance time, particle size and mass transfer capacity. This study found the particle size of bubbles was about 42.66 μm and KLa(20) was 10.712 min–1. The system’s applications were then studied to demonstrate the effect of ozone microbubbles. Under strong alkaline conditions and without acid adjustment, COD of printing and dyeing wastewater could reach Chinese first-class A discharge standards after treatment with ozone microbubbles. Another experiment proved that ozone microbubble solution of 8 mg/L had more than 99% killing effect on Escherichia coli.

In the textile industry, the process of washing off dyes requires a substantial amount of water, leading to the generation of heavily polluted wastewater. This study assessed the viability of electrocoagulation (EC) treatment for degradation of reactive orange 84 dye in wash-off liquor and its repetitive utilization in the same process by using a laboratory-scale experimental setup. Optimal operational factors, including electrolysis time, pH and applied current were determined through experimentation, resulting in a maximum color removal efficiency of 99 %. This efficiency was achieved at reaction time of 10 min, pH 7.5 and a current 1.0 A. Evaluation of fabric quality, considering color difference and wash fastness properties, indicated that the color difference values for dyed fabric samples over five repetitive reuses fell within an industrially acceptable range (ΔEcmc <1). Wash fastness properties remained comparable to conventionally washed fabric samples, with negligible differences in color strength (K/S) values. Despite an escalation in pH, COD, TDS, and turbidity level after each reuse, the overall quality of dyeing was not compromised. This work pioneers the integration of iron and aluminum electrocoagulation in practical conditions, demonstrating enhanced contaminant removal efficiency, promoting water reuse in the textile industry, and enhancing environmental sustainability.

Polyamide (PA)/polydopamine (PDA)/poly(vinylidene fluoride) (PVDF) nanocomposite membranes were prepared by the method of dopamine (DA)/polyethyleneimine (PEI) co-deposition integrating with interfacial polymerization (IP) with trimesoyl chloride. Fourier transform infrared spectrometer, scanning electron microscopy, atomic force microscopy and water contact angle were used to characterize the PA/PDA/PVDF nanocomposite membranes. Effects of the co-deposition time, the mass ratio of DA to PEI, the molecular weight of PEI and the content of DA + PEI on the morphologies and roughness of the membrane surface, the cross-section of the selective layer and the performance of the PA/PDA/PVDF nanocomposite membranes were investigated. Results showed that the co-deposition time has significant effect on the rejection of PA/PDA/PVDF nano-composite membranes, the other three factors have few effects on the rejection. All the four factors have remarkable effects on the permeation of the PA/PDA/PVDF nanocomposite membranes. When the rejection of PEG1000 and RB5 was 99%, the permeation of water and reactive black five (RB5) dyeing wastewater was 16.67 and 8.2 L m–2h–1bar–1, respectively. The water flux and the RB5 dyeing wastewater permeation of the PA/PDA/PVDF nanocomposite membranes were 31.14 and 15.03 L m–2h–1bar–1, respectively, when the PEG1000 and RB5 rejections were above 90%. Results above showed that the PA/PDA/PVDF nanocomposite membranes developed in this paper possess the potential application value in the dyeing wastewater treatment and reclamation

The advanced treatment of printing and dyeing wastewater by adsorption using activated coke was studied. Specifically, the effects of adsorption conditions on wastewater treatment were examined by adsorption experiments. Meanwhile, the adsorption behaviors of organic pollutants by activated coke were investigated by the adsorption kinetics and isotherms. The chemical oxygen demand (COD) removal met the printing and dyeing wastewater discharge requirement under the conditions of initial COD concentration 158 mg/L, adsorption time 360 min, activated coke concentration 30 g/L and adsorption temperature 308 K. After adsorption, 53.86% of COD was removed. The adsorption kinetics of COD by activated coke followed the pseudo-second-order model and the adsorption isotherms could be expressed by the Freundlich model. Moreover, thermal regeneration of spent activated coke was studied. Specifically, the effects of regeneration conditions on the thermal regeneration efficiency of spent activated coke were examined by thermal regeneration experiments. Meanwhile, the reusability of activated coke for organic pollutants removal was evaluated by the successive adsorption-regeneration cycles. 98.13% of thermal regeneration efficiency could be achieved under the conditions of regeneration temperature 1,073 K, regeneration time 30 min and CO2flow rate 150 mL/min, and activated coke still maintained 92.54% of regeneration efficiency after ten adsorption-regeneration cycles.

A simple process for the preparation of mesoporous silica microsphere (MSM) as adsorbent was synthesized via sol–gel method between tetraethyl orthosilicate and polyethylene oxide-polypropylene oxide-polyethylene oxide (F127). The influencing factors of MSM on methyl orange simulated dyeing wastewater were investigated in detail. Five adsorption isotherm models, kinetics, thermodynamics, and mechanism were studied. Under the optimum conditions, the adsorption rate was up to 86.44% (only at 21 min). The adsorption process of methyl orange by MSM was indicated as a non-spontaneous monolayer chemical adsorption process, which obeyed the pseudo- second-order kinetic model. The above showed that the MSM as-prepared in this paper was a simple, efficient and promising adsorbent for wastewater treatment, which provided a theoretical basis and technical support for the dyeing wastewater treatment.

After the advanced treatment of textile and dyeing wastewater, the concentration of total nitrogen (mainly nitrate) was still high while it lacked a biodegradable organic carbon source for further biological denitrification. Biological denitrification reactor with iron-based materials (both Fe and Fe/Cu) resulted in higher nitrogen removal efficiency (30% and 20%) compared to control (12%). However, the microbial mechanism was unknown. 16S rRNA genes sequencing and metagenomic sequencing were used to analyze the microbial community structure and functional genes in the process of iron-based materials enhanced biological denitrification of textile and dyeing wastewater. Microbial communities obtained from the two sequencing methods were quite different. The results of 16s rRNA genes sequencing indicated that both Fe and Fe/Cu influenced the microbial communities. Fe/Cu had a more profound effect on the microbial community and the diversity of the microbial community in the Fe/Cu reactor was relatively low. Metagenomic analysis showed that Proteobacteria was dominant in all samples (47%–80%). The biofilm formed on the surface of Fe and Fe/Cu enriched more functional microorganisms, which promoted denitrification of nitrate. The abundance of genes relating to nitrogen metabolism was higher in the samples on the surface of Fe and Fe/Cu, and therefore they had a stronger ability of nitrogen metabolism.

In this study, advanced oxidation processes were applied to the treatment of a textile dyeing wastewater. The effluent presents a dark blue color, with a maximum absorbance peak at 594 nm, alkaline pH (pH = 12.4), high organic contents (COD = 1,400 mg L–1). Experiments were conducted on a lab-scale prototype using UV lamp as light source and pillared natural clay with Fe and Al as catalyst. All the processes examined lead to an effective decolorization and mineralization, but the most efficient process was the photo-Fenton, contributing to 93% decolorization and 88.8% mineralization after 3 h of reaction under UV irradiation. Characteristics of wastewater after treatment were COD below 250 mg L–1, pH 8.5 and uncolored. Thus the resultant water has conditions that are suitable for releasing in public sewage systems.

Chitosan-gelatin composite copper polymer (CG for short) was prepared as an adsorption catalyst. The CG was combined with sodium persulfate to construct a heterogeneous Fenton-like system, which was applied to the decolorization of C.I. Reactive Blue 78 dyeing wastewater. The effects of sodium persulfate, CG, temperature, initial dyeing wastewater pH value and additives (sodium chloride, sodium carbonate) on the decolorization were investigated. The results show that the decolorization percentage of 0.1 g/L C.I. Reactive Blue 78 dyeing wastewater can reach 93.84 % under the conditions of sodium persulfate dosage of 0.3 g/L, CG dosage of 0.8 g/L, decolorization at 40 °C for 30 min. At the same time, the catalytic system has the characteristic of good decolorization effect on C.I. Reactive Blue 78 dyeing wastewater within a wide pH values range of 3–9. Even for dyeing wastewater containing 0.4 g/L high concentration C.I. Reactive Blue 78, the decolorization percentage can reach over 90 % after decolorization at 40 °C for 2 h. Moreover, CG can be reused. After repeated use of CG four times, the decolorization percentage of C.I. Reactive Blue 78 dyeing waste remains above 90 %. In addition, the weight loss rate of CG after each decolorization is less than 12 %. However, the presence of sodium chloride and sodium carbonate in the dyeing wastewater is not conducive to the decolorization of C.I. Reactive Blue 78 by the system.

Improved anaerobic baffled reactor-anoxic/oxic (ABR–A/O) coupling process was used for printing and dyeing wastewater treatment in our full-scale study, which was able to reach the effluent standard stably, especial for the characteristic pollutants and aromatics removal. According to our results of microbial community analysis by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), the divisions of ABR enabled the functional microorganisms to distribute in different compartments and contributed to each compartment of performing its own functions with more efficiency. The first, second, and third compartments are major in macromolecular organics hydrolysis and sulfate reduction, while the main responsibilities of the fourth, fifth, and sixth compartments are aromatic compounds degradation and denitrification. Many kinds of aromatic anaerobic degradation microorganisms were found in our ABR, such as Pseudomonas stutzeri, Dechloromonas aromatic, Pseudomonas putida, and Aromatoleum aromaticum. Initially, abundances of bcrA genes climbed up and then dropped along with the sequential six compartments of ABR and it indicated that the highest aromatics degradation efficiency were obtained at the fifth compartment, rather than other compartments, which was probably caused by its moderate substrate concentration and biodegradability.

The processing of gemstones, mainly the dyeing step, generates a high volume of wastewater containing a high concentration of Rhodamine B. This wastewater is potentially toxic and contains non-biodegradable substances. For this reason, it is necessary to develop methodologies to treat this type of wastewater. Therefore, in this work, a sequential process of electro-Fenton conjugated with adsorption were developed to treat this type of wastewater. The gemstones dyeing wastewater presented between 735.5 and 1,943.0 mg L–1of Rhodamine B. Firstly, the electro-Fenton process was applied, and removal superior to 65% of the RhB concentration were observed. Subsequently, adsorption was applied using a strong cationic resin at a pH of 2.0. In this condition, the adsorption capacity predicted by the Langmuir model was 247.3 mg g–1. The breakthrough curves were inclined with a suitable mass transfer zone. The sequential process of electro-Fenton and fixed-bed adsorption were able to remove 100% of the RhB from the gemstones’ wastewater, being an effective alternative to treat this type of effluent.

Membrane biofouling is an unevadable problem that occurr during the reverse osmosis (RO) desalination of dyeing wastewater; therefore, it is necessary to minutely understand biofouling characteristics of RO membranes to effectively hinder the fouling. In this study, two sets of laboratory-scale desalination systems of biologically treated dyeing wastewater were operated, respectively, for 10 and 30 d, and the performance and biofouling of RO membrane were investigated. The obvious decrease of permeate flux after 10 d of operation reflected a more serious membrane fouling. The analysis on surface morphology, foulant characteristics, and active biomass of membrane fouling layer exemplified that biofouling was perhaps responsible for the permeate flux decline, and the fouling was more serious after operation of 30 d than that of 10 d. Further, bacterial community of biofilm showed that Proteobacteria was the most predominant, followed by Firmicutes and Bacteroidete. The relative abundance of γ-Proteobacteria significantly decreased and that of α-Proteobacteria, Clostridia, and Sphingobacteria increased with operation time, which seemed to facilitate the more developed/mature biofilm formation. The results would provide fundamental information for effective strategy on prevention and control of membrane biofouling during RO desalination of dyeing wastewater.

Textile industry wastewater includes organic dyes and decomposition products which could have toxic and mutagenic effects on life. The majority of industries in this sector use nonbiodegradable, heat-resistant, light, oxidizing agents and therefore synthetic dyes that are difficult to remove color. In this study, Dianix Yellow Brown CC (0.22%), Dianix Rubine CC (0.79%) and Setapers Blue CE3R (0.015%) containing disperse dye have been used in the production of wastewater from the dyehouse. In this study, textile wastewater has been treated which has applied adsorption and photocatalytic methods by using nano-titanium dioxide (nTiO2). Optimum chemical oxygen demand (COD) and color removal efficiencies have been determined for these two methods. Moreover, under the optimum conditions in the adsorption method, the COD removal efficiency has been obtained as 58.07% and also color removal efficiencies have been obtained as 95.24%, 95.15%, 96.83% for 436, 525 and 620 nm, respectively (pH 2, nTiO2dose 2.5 g L–1and 30 min reaction time). Therefore, under the optimum conditions in the photocatalytic method the COD removal efficiency has been obtained as 57.59% and also color removal efficiencies have been obtained as 95.24%, 96.31%, 94.71% for 436, 525 and 620 nm, respectively (pH 2, nTiO2dose 1.5 g L–1and 60 min reaction time). Four different kinetic, that is, first-order kinetic, second-order kinetic, pseudo-first-order, pseudo-second-order, models have been used for the processes adsorption and photocatalytic. The pseudo-second-order kinetic model has been found to be the most suitable model for both processes. As a result, regression coefficients (R2) has been obtained for adsorption as 1 and for photocatalytic as 0.9999 and reaction rate constants (k) have been obtained for adsorption as 6.9 × 10–4L mg–1min–1and for photocatalytic as 2.2 × 10–3L mg–1min–1.

The present study investigates the electrochemical oxidation (EO) of real leather dyeing wastewater coming from a local modern tannery in Fez (Morocco). Experiments were performed in an electro-chemical reactor using Ti/Pt anode. Response surface methodology and full factorial central composite design were used to investigate the combined effect of three independent operating parameters considered for the optimization of the EO process: electrolysis time (t), current density (j) and temperature (T). Chemical oxygen demand (COD) removal (Y1) and specific energy consumption (SEC) in kWh/kg of COD removed (Y2) were used as responses to examine the degradation of wastewater. The obtained quadratic model was statistically tested using analysis of variance. The correlation coefficients for the model (R2) were 0.9986 and 0.9830 for COD removal and SEC, respectively. The best conditions for maximum COD removal and minimum specific energy consumption in the present study were t = 2.11 h, j = 18.70 mA/cm2and T = 286.18 K. Under these optimum conditions, 81.2% of COD removal was observed with energy consumption of 93.85 kWh/kg of COD removal. Fourier transformed infrared spectroscopy analysis was used for the characterization of effluent. Evolution of inorganic ions concentration and changes of turbidity, pH and conductivity of wastewater during the EO process were also followed.

An iron-activated carbon catalyst was prepared by calcination of an activated carbon derived from banana spike previously impregnated with iron sulphate, and then characterized by N2and CO2adsorption–desorption experiments and scanning electron microscopy coupled to energy dispersive spectroscopy. The presence of iron-based nanoparticles highly dispersed in the porosity was demonstrated and the nanoparticles were identified as wüstite (FeO) by X-ray photoelectron spectroscopy. The performances of this catalyst were investigated for the treatment of actual textile wastewater from Bamako handicraft loincloths dyeing by the heterogeneous Fenton process. The response surface methodology was used to optimize the effects of three independent parameters (catalyst dose, H2O2concentration, and initial total organic carbon (TOC) concentration) on the efficiency of wastewater treatment assessed by the rate of TOC reduction. The optimal conditions are found for 2 g/L catalyst, 16.73 mmol/L H2O2and 99.83 mg/L initial TOC corresponding to a prediction of 90.2% reduction of TOC. In these experimental conditions, the measured rate of degradation of 90.4% is in agreement with the proposed model. This high level of mineralization demonstrates that the Fenton process using the prepared catalyst is a viable treatment for the waste water from Bamako handicraft textile dyeing.

AbstractIn this work, the occurrence and removal of polycyclic aromatic hydrocarbons (PAHs) were investigated in a combination process of anoxic baffled reactor (ABR)-hybrid coagulation/membrane bioreactor (HCMBR) for real textile dyeing wastewater treatment. It was found that the target compounds except for the chrysene, benzo(b)fluoranthene, dibenzo(a,h)anthracene, and benzo(g,hi)perylene occurred widely in raw textile dyeing wastewater, treated effluent and sludge samples. In the raw wastewater, two-ring naphthalene was the dominant compound, while three-ring PAHs predominated in the final effluent. The dominant compounds in the raw sludge samples were phenanthrene, while they were pyrene and indeno(1,2,3-cd)pyrene for final discharge sludge. The combination process achieved over 88% removal for all the PAHs. Low molecular weight (LMW) PAHs might be mainly removed by volatilization, adsorption, and sedimentation in the ABR treatment unit. High molecular weight (HMW) PAHs might be mainly removed by adsorption and sedimentation processes after coagulation and solid–liquid separation in the HCMBR treatment unit. The final discharge of treated textile dyeing wastewater and sludge was biologically safe based on the toxicity evaluation test.

AbstractMost natural and synthetic textile dyes, especially vat dyes, are resistant to degradation and decolorization by conventional treatment methods. In this study, the purification of synthetic textile wastewater containing commercial indigo dye by a green technological treatment system was investigated. A vertical-flow constructed wetland model comprising three different bedding materials, sand, gravel, and zeolite, was used to treat synthetic indigo dyeing wastewater. Treatment efficiency was evaluated by measuring color and pollution parameters such as chemical oxygen demand (COD), pH, oxidation–reduction potential, and electrical conductivity. According to the results, the constructed wetland system reduced color by up to 97% and lowered the COD by up to 62%. This study demonstrated that the constructed wetland system is a promising technique for purification of indigo dyeing textile effluents of COD and color as compared to conventional methods.

AbstractThe printing and dyeing wastewater was treated by a pilot-scale hybrid anaerobic baffled reactor (HABR) which was modified from general anaerobic baffled reactor by adding combined packing in the upper part of each compartment and inert carrier at the bottom of the reactor. The start-up of the reactor, the performance of HABR in treating printing and dyeing wastewater, and the transformation of sulfate and removal of bivalent sulfur in the treatment were investigated. The results showed that less time was taken during the start-up in comparison with the general one, and higher COD removal efficiency and sufficient color removal rate were also obtained in the HABR. When the hydraulic retention time was 12–13 h and the sludge return ratio was 0.3, the average COD and color removal rates were 47% and 56%, respectively. The anaerobic bacteria community in each compartment developed well because of available substrates and specific environmental conditions. The results also showed that high reduction rate of was reached in the HABR, and the S2−transformed from could be removed by adding Fe2+into the wastewater in order to reduce the inhibitory effect on the anaerobic bacteria and the odor.

AbstractPhysicochemical and dyeing properties using reactive dyes of curaua and banana fibers were studied by means of color strength (K/S), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy analyses. SEM analysis of alkali-treated fibers showed an increase in roughness due to surface lignin and hemicellulose defibrillation. DSC analysis showed for all the samples an endothermic and an exothermic peak at 70–80 and 340–360°C due to the loss of adsorbed/absorbed water and to decomposition of α-cellulose, respectively. Alkali-treated fibers displayed a second peak around 290°C attributed to the degradation of hemicellulose. FTIR spectra of the studied fibers show similar bands with different intensities attributed to the main components of cellulose-based materials. Alkali-pretreated fibers demonstrated excellent dyeing ability for all the tested dyes. Dye absorption depends on the chemical fiber, dye structure, and concentration. The results of washing fastness are very good for all the tested fibers. The dyeing effluent treated with an advanced microfiltration method using an improved alumina ceramic membrane shows an average efficiency of 98% in turbidity and color reduction. Low-cost ceramic alumina microfiltration membranes are a very promising advanced treatment for textile industrial effluents allowing water reuse.

To study the effect of salt on decolorization in reactive dyeing wastewater, a chitosan-gelatin composite copper polymer (CG) was prepared as a catalyst, and its structure was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy. With the help of CG and H2O2, a heterogeneous Fenton catalytic system was created, and it was then used to decolorize simulated reactive dyeing effluent. The decolorization effect of C.I. Reactive Blue 19 (RB19) in the CG/H2O2catalytic system was studied with and without NaCl. The effects of the initial pH of the decolorization solution, NaCl, and temperature on the decolorization rate and decolorization kinetic properties of RB19 were investigated. The results show that the catalytic decolorization system containing NaCl has a good decolorization effect in a wide range of neutral and alkaline pH values, and the decolorization rate of the CG/H2O2catalytic system on the simulated RB19 dyeing wastewater increases with increasing pH value in the pH range of 5~10 and with increasing NaCl concentration. At 50°C for 30 min under neutral and alkaline conditions, the decolorization rate of simulated RB19 dyeing wastewater by CG/H2O2catalytic system reaches more than 90%. In the CG/H2O2catalytic system, the kinetic models of the catalytic decolorization system with and without NaCl accord with the pseudo-second-order kinetic model. The decolorization rate constant and the initial decolorization rate with NaCl in the dyeing wastewater are more than 3.9 times higher than those recorded without NaCl. The half decolorization time of dyeing wastewater containing NaCl is at least 74% shorter than that of dyeing wastewater without NaCl at the same decolorization temperature.

The fractionation of dye and salt effectively is crucial in the nanofiltration of dyeing wastewater. However, the present commercial nanofiltration membrane often rejected dye and salt simultaneously due to the dense selective layer of the membrane. To obtain nanofiltration membranes with a loose selective layer, β-cyclodextrin (β-CD) was added to the co-deposition of dopamine/polyethyleneimine in the PA/PDA-β-CD/PVDF composite loose nanofiltration membrane by the method of combination of co-deposition and interfacial polymerization. The effect of β-CD content on the structure and morphologies of PA/PDA-β-CD/PVDF composite loose nanofiltration membrane was investigated. The chemical structure, microstructure, surface roughness, and hydrophilicity of the membrane surface were characterized by an infrared spectrometer (attenuated total reflection-Fourier-transform infrared spectroscopy), scanning electron microscope, atomic force microscope, and dynamic water contact angle meter. The filtration performance of the PA/PDA-β-CD/PVDF composite loose nanofiltration membrane was tested by filtration experiments. The results showed that with the increase of β-CD concentration, the hydrophilicity, water flux, and salt permeability of the selective layer were significantly increased, indicating that β-CD had improved the porosity and hydrophilicity of the selective layer. When the β-CD concentration was 2 g/L, the flux of water and dyeing wastewater was the maximum, but the dye rejection was lower than 90%. The performance of the composite nanofiltration membrane with the β-CD concentration of 1 g/L was the best.

The reuse of the printing and dyeing wastewater is limited by its large chromaticity, high alkalinity, high chemical oxygen demand (CODCr), high salinity. In this study, electrodialysis, as a promising technology, was applied for the advanced treatment for printing and dyeing wastewater. With the Design-Expert software and Box–Behnken central composite design method, the optimal operating condition was: operating voltage 85 V, inlet flow rate 1,000 L/h, temperature 25°C, in which the energy consumption was 3.52 kW h/m3and the desalination processing cost was 0.33 $/m3. The characteristics of the desalination process and membrane pollution were further revealed and discussed. The maximum concentration was obtained at 15,000 mg/L during the concentrated water circulation. And the cation exchange membrane pollution was mainly calcium carbonate, while the anion exchange membrane pollution was organic. In addition, the reversal time fixed at 2 h could effectively reduce membrane fouling. The present work is expected to provide reference technical support for practical industrial applications.

A series of simple and low-cost Ca-doped g-C3N4(Ca/CN-X) photocatalysts were fabricated through a two-step calcination method for photodegradation of methylene blue (MB) simulated dyeing wastewater. The results showed that the photodegradation efficiency of Ca/CN-15% on MB removal under visible light was 97.7%, and the degradation rate constant was 4 times that of CN, showing the best photocatalytic performance. This was attributed to the fact that the doping of Ca expanded the absorption band edge, reduced the band gap, and suppressed the photogenerated electron-hole recombination, thereby increasing its corresponding photocatalytic activity. A possible photodegradation mechanism was explored, and it was found that h+was the main active species during the process. The above indicated that Ca/CN-X can be regarded as a promising catalyst for dyeing wastewater treatment.

The preparation of nanofiltration membranes with good separation performance and stability for dye wastewater treatment is imperative. The composite nanofiltration membrane prepared by the method of interfacial polymerization usually have the drawback of the instability. The selective layer inclined to peel off the substrate due to the weak adhesion between the selective layer and the substrate. In this work, inspired by polyphenol chemistry, polyethylenimine (PEI) was co-de-posited with the mixture of tannic acid (TA) and gallic acid (GA), on the surface of polyvinylidene fluoride ultrafiltration membrane, then a nanometers thickness polyamide selective layer was formed by the interfacial polymerization of PEI and homophthaloyl chloride. The chemical structure, surface roughness, microstructure and hydrophilicity of the surface of the selective layer of the composite nanofiltration membrane were characterized by Fourier-transform infrared spectroscopy, atomic force microscopy, scanning electron microscopy, and water contact angle meter, respectively. The present work focused on the effects of the ratio of TA to GA on the performance and structure of the selective layer. Lastly, the performance and stability of the prepared nano-composite membranes in the simulating Reactive black 5 (RB5) dyeing wastewater treatment were investigated. The results showed that: the surface roughness, the thickness and the water contact angle of the selective layer and the water flux all tended to decline and the polyethylene glycol (PEG1000) rejections kept being above 97% with the ratio of TA to GA decrease; the change of the dye effluent flux, the RB5 and the salt rejection were similar to that of the water flux and PEG1000, the RB5 rejection had being kept above 91%, the separation factor of dye and salt was up to 12.97, the prepared nanocomposite membranes displayed good operational stability within operating time.

As an effective and in situ purification strategy, adsorption technology has drawn much attention and recently the utilization of biomass substrate has been regarded as a promising way to enhance the adsorption performance and reduce cost. In this study, chitosan was applied as matrix and the magnetic Fe-crosslinked chitosan (CS-Fe@Fe3O4) composite was obtained through a chelation procedure with cheap and environmentally friendly chitosan and iron salts. Then, the resultant CS-Fe@Fe3O4composites were characterized by scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and thermogravimetric analysis. The sorption and desorption of methyl orange (MO), a common type of azo dye, on CS-Fe@Fe3O4composite was systematically studied to understand its availability for dyeing wastewater. The results revealed that CS-Fe@Fe3O4composites could efficiently remove MO in a wide pH range. The mixed Fe3O4particles were physically mixed andalmost had no negative effect on its adsorption. Moreover, the dye adsorption process was found to be controlled by the pseudo-second-order rate model and the adsorption isotherm behavior could be described by the Langmuir model. The repeatability test showed that the CS-Fe@Fe3O4composites could retain its high efficiency after desorption and regeneration. In summary, the results presented herein indicated that the resultant CS-Fe@Fe3O4nanocomposite with high adsorption efficiency and strong magnetic property could serve as a potential adsorbent for remediating industrial dyeing wastewater.

The membrane technology has become one of the promising techniques to promote cleaner production and emission reduction in the printing and dyeing industry. It is important to understand the current situation and prospect of membrane technology applications to treat wastewater from the dyeing industry, which provides comprehensive overview of wastewater treatment by the technology in the industry. The research history of the membrane technology applications in the dyeing industry was investigated by literature metrology with National Knowledge Infrastructure (CNKI) and Web of Science™ (SCI). A national survey was conducted to collect information of current applications and prospect, complemented by literature investigations. Results showed that: (1) the membrane technology was initially applied in recycling dyes and gradually was spread to treat and reuse wastewater. Three development stages of the research history are identified: pre-1998 (slow development), 1998–2008 (rapid growth), and 2009 to present (steady development). (2) China is leading in publishing SCI papers in related filed. The top domestic institutes include Donghua University, South China University of Technology, Dalian University of Technology, Zhejiang University, Zhejiang University of Technology, and Tianjin University. (3) By 2015, the total capacity of the membrane technology in dyeing wastewater treatment in China was about 662,000 m3·d–1and the number of applications was 128 (with capacity ≥500 m3·d–1). Geographical distribution is also analyzed and most applications are located in Zhejiang, Jiangsu, Guangdong, Fujian, and Shandong. (4) “Ultrafiltration (UF) + ‘reverse osmosis’ (RO)” was the most widely applied process of membrane technologies in dyeing wastewater treatment, the “membrane bioreactor (MBR) + RO” and “Continuous Membrane Filtration (CMF) + RO” were closely behind. The operational cost of membrane technology applications is relatively higher than that of conventional technology applications in the dyeing industry. However, the membrane technology treats wastewater more effectively and efficiently, and thus could provide reclaimed water for reuse. It is a promising and important technology in dyeing wastewater treatment and reuse in near future because of environmental stress, strict water management, increasing water price, decreasing membrane cost, and increasing life span of membranes.

Dicyandiamide-formaldehyde condensation product shows excellent decolorization performance for dyeing wastewater. The cross-linking agent plays an important role in the decolorization performance. In this work, a three-dimensional modified dicyandiamide-formaldehyde decolorizing decolorant (defined as DF1) was synthesized using hexamethylenetetramine as the three-dimensional cross-linking agent. The influences of dosage of DF1, settling time, settling temperature, pH value and inorganic salt on the flocculation ability of DF1were investigated. The existence of inorganic salt has a slight effect on the color removal of DF1. The maximum color removal of 98.8% was achieved with the DF1dosage of 35 mg/L. The infrared spectra of samples demonstrate that chemical reactions occurred between DF1and Reactive Brilliant Red X-3B.