Removal of anilinic compounds using the NF-97 membrane: Application of the solution-diffusion and SKK models

Prediction of Flux and Rejection Coefficients in the Removal of Emerging Pollutants Using a Nanofiltration Membrane

The removal of three emerging pollutants: carbamazepine, ketoprofen, and bisphenol A, has been studied using the nanofiltration flat sheet membrane NF99HF. The removal efficiencies of the membrane have been evaluated by two system characteristic parameters: permeate flux and rejection coefficient. The influence of two operating variables has been analysed: operating pressure and feed concentration. Before and after the tests with emerging pollutants, the membrane has been characterized by determining its water permeability coefficient and its magnesium chloride rejection coefficient to find out if the removal of emerging pollutants causes membrane fouling. The results show that operating pressure has significant separation effects, obtaining the highest efficiencies at a pressure of 20 bar for pollutant concentrations between 5 and 25 mg/L. Moreover, rejection of ketoprofen was found to be dependent on electrostatic repulsion, while rejection of bisphenol A was significantly affected by adsorption onto the membrane. Finally, the experimental data have been fitted to the solution diffusion model and to the simplified model of Spiegler-Kedem-Katchalsky to predict the behaviour of the nanofiltration membrane in the removal of the tested pollutants. Good agreement between the experimental and predicted carbamazepine and bisphenol A data has been obtained with each model, respectively.

Ultrafiltration and Nanofiltration for the Removal of Pharmaceutically Active Compounds from Water: The Effect of Operating Pressure on Electrostatic Solute-Membrane Interactions

The present work investigates nanofiltration (NF) and ultrafiltration (UF) for the removal of three widely used pharmaceutically active compounds (PhACs), namely atenolol, sulfamethoxazole, and rosuvastatin. Four membranes, two polyamide NF membranes (NF90 and NF270) and two polyethersulfone UF membranes (XT and ST), were evaluated in terms of productivity (permeate flux) and selectivity (rejection of PhACs) at pressures from 2 to 8 bar. Although the UF membranes have a much higher molecular weight cut-off (1000 and 10,000 Da), when compared to the molecular weight of the PhACs (253-482 Da), moderate rejections were observed. For UF, rejections were dependent on the molecular weight and charge of the PhACs, membrane molecular weight cut-off (MWCO), and operating pressure, demonstrating that electrostatic interactions play an important role in the removal of PhACs, especially at low operating pressures. On the other hand, both NF membranes displayed high rejections for all PhACs studied (75-98%). Hence, considering the optimal operating conditions, the NF270 membrane (MWCO = 400 Da) presented the best performance, achieving permeate fluxes of about 100 kg h-1 m-2 and rejections above 80% at a pressure of 8 bar, that is, a productivity of about twice that of the NF90 membrane (MWCO = 200 Da). Therefore, NF270 was the most suitable membrane for this application, although the tight UF membranes under low operating pressures displayed satisfactory results.

Ultrafiltration Membranes Modified with Reduced Graphene Oxide: Effect on Methyl Green Removal from Aqueous Solution

In this work, three types of ultrafiltration membranes with different characteristics (GR60PP, RC70PP and GR80PP) have been tested for the removal of the dye methyl green. The tests were first carried out with the three membranes without any modification and then with the membranes' surfaces modified with reduced graphene oxide (rGO). The modification was achieved through physical treatment. The CR70PP membrane did not support the modification treatment and was discarded. The other membranes were initially characterized with distilled water tests to study the permeability to the solvent, and later, the permeate fluxes and the values of rejection coefficients were obtained at different working pressures with a fixed dye initial concentration. In addition, SEM images and SEM-EDX spectra of the native and modified membranes were obtained before and after the dye tests. The GR60PP membrane has shown the best results in relation to the modification because it has increased its rejection levels. On the opposite, the GR80PP membrane performs better without surface modification, achieving the highest rejection values and the highest permeate fluxes in its native form.

Application of polyamide thin-film composite layered on polysulfone-GO/TiO2 mixed matrix membranes for removal of nitrotoluene derivatives from petrochemical wastewaters

Release of harmful organic intermediates or byproducts during the manufacture of petrochemical compounds is a serious problem in petrochemical plants. In this work, polysulfone membranes blended with GO/TiO₂ nanocomposite were synthesized by phase inversion method and coated with a polyamide layer formed by interfacial polymerization to prepare a thin-film composite (TFC) sample. Analysis and characterization of the sample were carried out by XRD, FE-SEM, BET, FTIR/ATR, AFM, TGA, and zeta potential. Results indicated that incorporation of GO/TiO₂ into the membrane structure enhanced porosity, surface roughness, and macrovoid formation along the cross-section of the sublayer and permeability of the membrane. The TFC membranes were applied to remove mononitrotoluene (MNT) and dinitrotoluene (DNT) as the basic intermediates of toluene diisocyanate (TDI). The membranes demonstrated high efficiency (> 90%) for the removal of MNT and DNT according to the charge exclusion mechanism and Donnan effect. Application of the TFC membrane for treatment of wastewater in the TDI plant showed that the removal of pollutants is variable in the range of 45-65% and 53-69% for the membrane with the highest flux and highest rejection in different transmembrane pressure, respectively.

Screening ultrafiltration membranes to separate lactose and protein from sheep whey: application of simplified model

Several studies demonstrated that protein from whey milk could be a new strategy to reduce energy intake and increase satiety. Sheep whey has high protein content, but it is also rich in lactose. The aim of this study was to screening different ultrafiltration membranes to separate protein and lactose from sheep whey in one step. Protein was recovered in the concentrate feed, and lactose passed through three membranes and was recovered in the permeate feed. Membranes with different chemical composition and molecular weight cut-offs were assayed, and the influence of operating pressure and lactose concentration feed in the permeate flux and lactose rejection coefficients were studied. Lactose separation was not affected by pressure in GR60PP or GR90PP, and 85% and 80%, respectively of the lactose was separated into permeate feed. When the feed concentration increased, lactose separation remained stable in all three membranes, being GR60PP the most efficient, as 90% of the disaccharides were separated. In all cases 100% of the protein was recovered. Finally, the Spiegler-Kedem-Katchalsky model perfectly fitted the results obtained about lactose rejection coefficients.

Removal of glyphosate and aminomethylphosphonic acid from synthetic water by nanofiltration

The removal of glyphosate and aminomethylphosphonic acid (AMPA) with synthetic water was carried out on a lab-scale nanofiltration unit using two membranes, NFX and NFW. The presence of humic acid and some inorganic matters (CaCl2 and NaCl) was tested in the experiment. The results demonstrate that NFX exhibits better separation performance than NFW. The herbicide filtration is found to have little effect on the permeate flux as compared to transmembrane pressure. Intermediate concentrations of NaCl act positively on foulant separation, and an increment of 3.3-5.4 percentage points in foulant rejection is obtained with the addition of 100 mg/L of NaCl. In Contrast, CaCl2 has negative effect on foulant separation during nanofiltration. Humic acid alone shows little influence on the rejection performance, whereas it is slightly improved in the coexistence of humic acid and CaCl2. The nanofiltration technology proves to be a good approach to treat the problem of pesticide micropollution in a one-step process. This work clearly shows that the composition of the water matrices may influence the efficiency of the nanofiltration process in terms of the separation of the micropollutants.