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Membrane fouling is one of the main drawbacks of ultrafiltration technology during the treatment of dye-containing effluents. Therefore, the optimization of the membrane cleaning procedure is essential to improve the overall efficiency. In this work, a study of the factors affecting the ultrasound-assisted cleaning of an ultrafiltration ceramic membrane fouled by dye particles was carried out. The effect of transmembrane pressure (0.5, 1.5, 2.5 bar), cross-flow velocity (1, 2, 3 m s−1), ultrasound power level (40%, 70%, 100%) and ultrasound frequency mode (37, 80 kHz and mixed wave) on the cleaning efficiency was evaluated. The lowest frequency showed better results, although the best cleaning performance was obtained using the mixed wave mode. A Box Behnken Design was used to find the optimal conditions for the cleaning procedure through a response surface study. The optimal operating conditions leading to the maximum cleaning efficiency predicted (32.19%) were found to be 1.1 bar, 3 m s−1 and 100% of power level. Finally, the optimized response was compared to the efficiency of a chemical cleaning with NaOH solution, with and without the use of ultrasound. By using NaOH, cleaning efficiency nearly triples, and it improves up to 25% by adding ultrasound., This research has been financially supported by the Spanish Ministerio de Ciencia e Innovacion (MICINN) through the Project Ref. CTM2009-13048. The authors of this work also acknowledge the assistance of the Spanish Ministerio de Educacion for the award of a F.P.U. Grant (Ref. AP2009-3509).

An ultrafiltration (UF) ceramic membrane was used to decolorize Reactive Black 5 (RB5) solutions at different dye concentrations (50 and 500 mg/L). Transmembrane pressure (TMP) and cross-flow velocity (CFV) were modified to study their influence on initial and steady-state permeate flux (J(p)) and dye rejection (R). Generally, J(p) increased with higher TMP and CFV and lower feed concentration, up to a maximum steady-state J(p) of 266.81 L/(m(2)h), obtained at 3 bar, 3m/s and 50mg/L. However, there was a TMP value (which changed depending on operating CFV and concentration) beyond which slight or no further increase in steady-state J(p) was observed. Similarly, the higher the CFV was, the more slightly the steady-state J(p) increased. Furthermore, the effectiveness of ultrafiltration treatment was evaluated through dye rejection coefficient. The results showed significant dye removals, regardless of the tested conditions, with steady-state R higher than 79.8% for the 50mg/L runs and around 73.2% for the 500 mg/L runs. Finally response surface methodology (RSM) was used to optimize membrane performance. At 50mg/L, a TMP of 4 bar and a CFV of 2.53 m/s were found to be the conditions giving the highest steady-state J(p), 255.86 L/(m(2)h), and the highest R, 95.2% simultaneously.

Textile industries are rated as the most polluting among all industrial sectors taking into account both wastewater volume and composition. In order to be able to reuse these effluents, membrane technologies have been proven as a viable alternative. However, these technologies show some drawbacks, such as the retentate stream management and the worsening of their performance due to membrane fouling. Therefore, effluents must be pre-treated in order to prevent fouling. Membrane technologies also provide some alternatives for these pre-treatments by means of the application of ceramic ultrafiltration among others. This work studies the performance of ceramic membranes by carrying out experiments with three commercial ceramic membranes with molecular weight cut-offs (MWCO) of 30, 50 and 150 kDa, respectively. Moreover, the effect of cross-flow velocity (CFV) was studied by performing the essays at different flow velocities of 3, 4 and 5 m/s. According to the obtained results, ceramic UF membranes proved to be a feasible pre-treatment alternative. Permeate flux increased as flow velocity was increased for most of the cases, owing to the fact that the cake layer formation was limited. Furthermore, flux decline along operating time was negligible for the higher flow velocities, whereas it was noticeable for the lowest flow velocity tested. For the lowest MWCO analyzed, lower cross-flow velocities were needed in order to limit the cake layer formation and reach the steady-state. This implies that, although fouling was significant for all the three molecular weight cut-off studied, it was much more noticeable when MWCO was increased. Slightly better results in terms of permeate quality were achieved as MWCO was lower. In addition, higher chemical oxygen demand (COD) and conductivity retention coefficients were obtained for the lowest cross-flow velocity. Turbidity and color removals seemed to be more influenced by water composition than CFV, with rejections higher than 99% and between 84 and 98%, respectively.

Water scarcity makes industrial wastewater reuse necessary, especially in those industries characterized by both high water consumptions and extremely polluted effluents as textile industries. Membrane technologies are very efficient to treat industrial effluents for water reuse successfully, since their application entails important reductions in pollutant concentration. In the present work, a direct treatment of a textile industry effluent by means of a combination of ultrafiltration (UF) followed by a final nanofiltration (NF) stage is presented. Two different NF membranes were tested in order to compare their behaviors. For that, the influence of the feed water pH and transmembrane pressure (TMP) of the NF process were investigated. The UF results showed that the highest permeate fluxes were achieved at pH 11. Related to NF experiments, NF270 reached for the same operational conditions higher fluxes and salts rejection values than the Duraslick NF. No influence of pH was found for the permeate flux. However, the pH effect was manifest for the salts rejection. Although COD, color, and turbidity removals were high in all tests, Duraslick NF showed an average slightly better removal of COD and color. The results obtained confirm the viability of this treatment for water reuse in most of the different processes carried out in these kinds of industries.

Textile industry processes (dyeing, bleaching, printing and finishing) require a high-water consumption generating high amounts of wastewater. According to the literature, typically 200 and 500 L of water are needed to produce 1 kg of finished product [1]. This fact in combination with the current water scarcity makes necessary textile wastewater reuse. In this work, nanofiltration of biologically treated textile wastewater has been evaluated testing three nanofiltration membranes. It was studied that the influence of different volume concentration factors (VCF) on the permeate flux and salts and COD rejections. Nanofiltration experiments were carried out in a laboratory plant equipped with a pressure vessel containing one spiral wounded membrane element. The membranes tested were Ds-5 DK and DURASLICK from General Electric and Fluid System® TFC® SR®2 from KMS. For all membranes, the COD values in the permeate were negligible and flux reduction was not severe even for the maximum operating VCF (3). According to the permeate characteristics the main use of the treated water is for machinery washing processes and print implements.

Physical-chemical and biological processes are the most common methods for the textile effluents treatment. However, in many occasions the pollutants removal efficiency can be increased through the combination of these conventional methods with advanced ones. In this paper, initially the ozonation influence on the coagulation-flocculation process has been studied in textile wastewater from a dyeing, printing and finishing industry. Thus, several jar-tests were carried out using wastewater before and after an ozonation process, with reaction times of 30 and 60 min. It can be highlighted that a short time preozonation enhanced the coagulation process, achieving after sedimentation COD and turbidity reductions of 57% and 95%, respectively. After that, two different NF membranes were tested using as feeding stream the wastewater after the ozone and physical-chemical stages in order to reduce the water conductivity and COD. NF experiments were carried out in a laboratory plant containing a plane module with an effective area of 120 cm2. The membranes tested were Desal DK-5 from Osmonics and NF-90 from Dow Chemical. The results showed that the COD and conductivity of the nanofiltration permeates were around 100 mg/L and 0.5 mS/cm, respectively with NF-90 membrane.

This work was supported by the "Ministerio de Ciencia e Innovación" through the project ref. CTM2009-13048 and the "Ministerio de Educación" through the FPU grant ref. AP2009-3509.

Ultrafiltration membrane processes have become an established technology in the treatment and reuse of secondary effluents. Nevertheless, membrane fouling arises as a major obstacle in the efficient operation of these systems. In the current study, the performance of tubular ultrafiltration ceramic membranes was evaluated according to the roles exerted by membrane pore size, transmembrane pressure and feed concentration on a binary foulant system simulating textile wastewater. For that purpose, carboxymethyl cellulose sodium salt (CMC) and an azo dye were used as colloidal and organic foulants, respectively. Results showed that a larger pore size enabled more solutes to get adsorbed into the pores, producing a sharp permeate flux decline attributed to the rapid pore blockage. Besides, an increase in CMC concentration enhanced severe fouling in the case of the tighter membrane. Concerning separation efficiency, organic matter was almost completely removed with removal efficiency above 98.5%. Regarding the dye, 93% of rejection was achieved. Comparable removal efficiencies were attributed to the dynamic membrane formed by the cake layer, which governed process performance in terms of rejection and selectivity. As a result, none of the evaluated parameters showed significant influence on separation efficiency, supporting the significant role of cake layer on filtration process., This research has been financially supported by the Spanish Ministerio de Ciencia e Innovacion (MICINN) through the project ref. CTM2009-13048. The authors of this work also acknowledge the assistance of the Spanish Ministerio de Educacion for the award of a F.P.U. grant (Ref. AP2009-3509).

The present study reports the results of the ultrafiltration with a ceramic membrane of model solutions containing NaCl and a reactive dye, which simulate textile wastewaters. The effect of salt concentration (1, 2.5 and 4 g/L NaCl) and transmembrane pressure (1, 2, and 3 bar) on the evolution over time of both permeate flux and solutes rejection was tested. Membrane fouling was also investigated in terms of analysis of resistances-in-series, determining the contribution of both reversible and irreversible fouling under any condition tested. More severe flux decline and a slight reduction in color rejection were observed under higher pressure. Furthermore, it was demonstrated that the membrane performance was significantly worsened in the presence of salt, according to permeate flux, dye rejection and the values of the different resistances. Higher flux decline and total resistance together with lower color removal were observed when adding NaCl to the solution. These results were attributed to membrane charge and repulsion-attraction phenomena. It was then suggested that electrostatic interactions between the solutes and the membrane materials have an important role in the ultrafiltration performance, as well as influencing the kind of fouling affecting the membrane., This research was financially supported by the Spanish Ministerio de Ciencia e Innovacion (MICINN) through the Project ref. CTM2009-13048. The authors of this work would also thank the Spanish Ministerio de Educacion for the award of a F.P.U. grant (Ref. AP2009-3509).

[EN] This work studies the performance of three commercial ceramic ultrafiltration membranes (ZrO 2-TiO 2) treating raw effluent from a textile industry. The effect of crossflow velocity at 3, 4 and 5 m s -1 as well as membrane characteristics, such as molecular weight cut-off (30, 50 and 150 kDa), on process performance were studied. Experiments were carried out in concentration mode in order to observe the effect of volume reduction factor simultaneously. Results showed a combined influence of both crossflow velocity and molecular weight cut-off on flux performance. TOC and COD removals up to 70% and 84% respectively were reached. On the other hand, almost complete color (>97%) and turbidity (>99%) removals were achieved for all the membranes and operating conditions. © IWA Publishing 2011., This work was supported by the Spanish Ministry of Science and Education through the project CTM2009-13048.

This work was supported by the Spanish Ministerio de Educación y Ciencia (CTM2004-03130/TECNO).