Use Of Nanofiltration Research Articles

Treatment of sulfides in tannery baths by nanofiltration

The periodic disappearance of fish from the marshes of Reghaïa (Algiers) caused by industrial waste alarmed responsible personnel at the Department of the Environment to pollution that threatens one of the most significant wet sites of Algeria. An anti-pollution plan was developed and put in action. This plan aims to provide an overall basis for evaluating the pollution generated by the various units in the industrial park of Rouïba – Reghaïa, in order to reduce or to stop pollution affecting the marshes of Reghaïa. Our work presents a complementary study on the effluent of a leather processing unit at Rouïba [1–4]. Our study was based on the effluent of liming baths which contain a great quantity of sulfides. To reduce the pollution generated by sulfides in the effluent, we were interested in the use of nanofiltration in order to refine post-processing such as precipitation.

Use of nanofiltration for partial softening of very hard water

Nanofiltration, a recent membrane technique, was used for the softening of very hard water. Our study was based on the elimination of one part of the temporary hardness of Hamma water which provides Constantine City with drinking water. Two techniques were used in order to obtain a partial softening. The first is related to weak pressures (0.5, 1, 2 bar) whereas the second is based on relatively high pressures (4–16 bar) and which is applied on feed water. However, we should mention that at the end of this experience, 50% of filtered water was mixed with 50% of hard water. The results show that this membrane technique is of great interest in the process of eliminating temporary hardness of water, which depends mainly on the applied pressure and the tangential flow rate.

Studies on nanofiltration membrane fouling in the treatment of water solutions containing humic acids

A major factor limiting the use of nanofiltration (NF) in the water treatment process is membrane fouling by natural organic matter. Two NF membranes, Desal 5 DK and DL, which have different hydraulic permeabilities, were compared. Solution chemistries selected for this investigation were concentrated on the common salts found in a variety of wastewaters, including monovalent ions (Na +, Cl −), divalent hardness cations (Ca 2+, Mg 2+) and divalent anions (SO 2− 4). Results of fouling experiments with humic acids demonstrated that the condition of hydrodynamics and the chemical compositions of the feed solutions could significantly influence the fouling tendency. Higher crossflow velocity and lower initial flux mitigated accumulation of humic acid (HA) on the membrane to some extent. The adsorption of humic substances onto the membrane surface was markedly enhanced in the presence of divalent cations due to the formation of HA-complexed divalent cations. The experiment also indicated that the membrane surfaces preferred to adsorb divalent cations rather than divalent anions because the membrane had a negative charge in the higher pH range investigated. In addition, choosing a proper divalent cation chelating agent as a cleaning reagent, especially at basic conditions, can improve the membrane process by dissolving and removing the HA fouling substance.

Fouling of nanofiltration and ultrafiltration membranes applied for wastewater regeneration in the textile industry

Textile effluents usually contain high concentrations of inorganics as well as organics, and the therefore difficult to treat. Membrane processes can be used for many of these wastewaters in the textile industry. Two typical examples are discussed: (1) the use of nanofiltration for the treatment of exhausted dye baths, in view of water recycling, and (2) the use of ultrafiltration for the removal of spin finish from waste water resulting from rinsing of textile fibres. Both applications are in principle feasible, but in practice the process is negatively influenced by membrane fouling. In the first application, fouling is assumed to be caused by (ad)sorption of organic compounds, which has a large influence because of the high concentrations used in textile dyeing. Furthermore, the high salt concentrations result in a decrease of the effective driving force because of the high osmotic pressures obtained for typical dye baths. Experimental results are discussed, and the applicability of nanofiltration is related to the characteristics of the dye baths for different dyeing methods. In the second application, the concentration of organic compounds is relatively low, but because of the hydrophobic nature of the spin finish compounds, a significant effect of membrane fouling is expected. An improvement is suggested by using nanofiltration membranes instead of ultrafiltration membranes.

Separation of glutathione and its related amino acids by nanofiltration

Nanofiltration experiments of glutathione and its related amino acids ( l-glutamate, l-cysteine, glycine, and l-glutamine) were carried out using NTR-7450 nanofiltration membrane in order to determine the potential use of nanofiltration in the enzymatic glutathione synthesis, in which the reaction equilibria are need to be driven to production by separating glutathione from starting substrates. In the experiments with a single component system, the rejection of NTR-7450 membrane for the electrolytes corresponded well to the ratio of their anionic species varying with pH. Difference in the rejection between glutathione and some amino acids was maximal in the neutral pH region: at pH 7.4, the rejection for glutathione and l-glutamate was almost 100%, whereas that for l-cysteine, glycine, and l-glutamine was below 30%. In the presence of divalent metal ions, the rejection for glutathione and l-glutamate decreased with increasing the metal concentration, probably due to partial neutralization of negative charges of the electrolytes forming complexes with the metal ions. In the experiments with a multi-component system, glutathione was completely blocked again by the membrane in a range of glutathione concentration from 0.1 to 5.0 mM in the presence of 1.0, 2.0, or 5.0 mM each of l-glutamine, glycine, and l-cysteine. The amino acid rejection decreased with increasing the amino acid concentrations. These results suggest that nanofiltration would be applicable to the separation of glutathione from substrates, l-cysteine, glycine, and l-glutamine, in the enzymatic glutathione synthesis.

Nanofiltration membrane fouling by conventionally treated surface water

Nanofiltration is a very effective technique for improving the removal of trace organics after a conventional chemical water treatment train. However, the fouling of the membranes decreases the applicability of the process, and thus, an understanding and control of membrane fouling are crucial for a more widespread use of nanofiltration in water treatment. The fouling of different nanofiltration membranes by pre-treated surface waters was investigated in a laboratory-scale filtration unit in this study. The results indicate that the traditional chemical treatment does not remove membrane foulants from the surface water. No correlation was found between the feed water constituents and nanofiltration performance, but most feed water components are expected to interact in membrane fouling. Actually, the performance of the nanofiltration process was more related to membrane than to feed water characteristics.

Selective Concentration of Uranium from Seawater by Nanofiltration

A new procedure for the concentration of uranium, dissolved in seawater with extremely low concentration, was studied. Plate module membrane filtration equipment was operated to evaluate the performance and selectivity of four different nanofiltration flat sheet membranes. Experiments were first carried out using different model waters. The membranes were discriminating by the rejection of uranium, calcium, and sodium. Then, a uranium concentration test using a nanofiltration membrane showing the highest selectivity for uranium toward alkaline and alkaline-earth ions has been performed on natural seawater. A nanofiltration membrane shows a high selectivity for U(VI), illustrating the advantageous use of nanofiltration for the concentration of uranium from seawater.

By-product recovery from cottage cheese production by nanofiltration

Cottage cheese whey has been a problem waste as it is dilute, salty and acidic. The use of nanofiltration has been applied to cottage cheese whey to concentrate its solids content four fold, while removing about three-quarters of the sodium and potassium salts and some acid. This desalted nanoconcentrated whey was found to be quite stable under refrigeration for up to 6 weeks. It could then be considered as a recovered by-product for use as an ingredient in dairy and other food products. A preliminary process economics case study was carried out for a plant producing 30,000 l/day of cottage cheese whey. The capital cost required was estimated as $700,000. The payback period was calculated to be less than 10 months.

Novel Block Copolymers as Nanofiltration Materials

The overarching goal of this research was to forge a link between materials science and engineering that may eventually lead to development of new membranes with decreased fouling tendency. Polymer structure influences water transport rates, solute partitioning, and fouling resistance. This article presents the results of testing the first generation of a novel class of nonporous block copolymers for use in nanofiltration (NF) membranes. The block copolymers comprised low surface energy fluoropolymers and highly hydrophilic hydrocarbon-based polymers. The very low surface energy of the fluoropolymer block was intended to resist adhesion of natural organic matter (NOM), a common foulant in drinking water applications of nanofiltration technology. The hydrophilic block was intended to provide channels for water permeation. Thin-film composite membrane tests with a coagulated, settled, and cartridge-filtered drinking water sample showed that the experimental membrane produced comparable water flux to a comme...

Homogeneous phase transfer catalyst recovery and re-use using solvent resistant membranes

This paper explores the use of nanofiltration (NF) membranes in phase transfer catalysis for separating the catalyst and product present in the post-reaction mixture and recycling the catalyst. The conversion of bromoheptane into iodoheptane with toluene as solvent, using an aqueous solution of potassium iodide, and catalysed by tetraoctylammonium bromide as the phase transfer catalyst, was employed as a model reaction. A range of NF membranes from commercial manufacturers were evaluated in terms of membrane stability, solvent and product permeation rates, and catalyst rejection. The best performance resulted in a catalyst rejection of >99% and a solvent flux of >10 l m −2 h −1, with negligible product rejection. The catalyst was 100% recycled and re-used in subsequent reactions. No loss in catalyst activity was observed over a cycle of three consecutive reactions.

Flux decline during nanofiltration of organic components in aqueous solution.

Flux decline due to interaction of the membrane with the feed solution is a major drawback for the use of nanofiltration in environmental applications. This paper studies different mechanisms of flux decline for the nanofiltration of aqueous solutions containing organic compounds. The resistance model for flux decline is used: different mechanisms contribute through an increase of the resistance of the membrane against mass transport. The focus in this research is on pore blocking and adsorption inside the membrane pores. Osmotic pressure is also taken into account as it decreases the driving force. The nanofiltration membranes used were NF70 (Dow), UTC-20 and UTC-60 (Toray Ind.), and NTR 7450 (Nitto-Denko). Experiments with different organic components in aqueous solution showed that adsorption resulted in a strong decrease of the water flux. The results of the flux decline as a function of the concentration could well be fitted with the Freundlich equation for adsorption. The components that showed the largest effect had the highest polarity (permanent dipole moment or polarizability), which indicates that adsorption is favored by the polarity of the components in solution. Moreover, the molecules with a size similar to the pore size had a stronger effect on the water flux than other molecules. This can be explained by blocking of the pores by adsorbed compounds.

The use of nanofiltration for the removal of pesticides from groundwater: an evaluation

This study explores the combined removal of four pesticides (atrazine, simazine, diuron, isoproturon) and hardness from groundwater with nanofiltration (NF). Four NF membranes were used: NF45 and NF70 (Dow/FilmTec), and UTC-20 and UTC-60 (Toray Ind. Inc.). Each pesticide was added to groundwater samples in a concentration of 1 μg/l, representative for contaminated sources. For the determination of pesticides in such low concentrations, an analytical method using solid-phase extraction and high performance liquid chromatography was elaborated. The retentions with NF were compared and explained by means of molecular size and dipole moment. Molecular size, expressed as an effective diameter representing the projection of the molecule on the membrane surface, was calculated by determining the energetically most favourable molecular configuration. The largest molecules had the highest retentions, when all other properties are comparable. A high dipole moment decreases retentions because of charge interactions with the membrane. The hardness retentions were high. For drinking water production, it might be necessary to add hardness after filtration. The groundwater flux was approximately 5% lower compared to the distilled water flux. This relatively small flux decline indicates pore blocking due to adsorption in the membrane pores. The flux decline was proved reversible; no membrane fouling occurred.

Phase-transfer catalyst separation and re-use by solvent resistant nanofiltration membranes

This communication describes the use of nanofiltration (NF) membranes for efficient separation and recycling of phase-transfer catalysts, using the conversion of bromoheptane into iodoheptane with tetraoctylammonium bromide as the PT catalyst, as an example; a solvent flux of >10 L m−2 h−1 was achieved with >99% catalyst recycle and no loss in PT catalyst activity over a cycle of three consecutive reactions.

Application of ultra low pressure reverse osmosis (ULPRO) membrane to water and wastewater

There is a worldwide grave concern about water pollution control. To mitigate the water scarcity, in arid zones and in the areas with no other sources but brackish water, reverse osmosis technology has played an important role. In an effort to reduce the cost of energy requirement for RO operation, nanofiltration has been developed. Until recently the nanofiltration has been used in water softening and removal of disinfection byproduct (DBO). Use of nanofiltration to desalinate brackish water has been ruled out due to low rejection of salts. The introduction of ultra-low pressure reverse osmosis membrane, categorically a nanofiltration, has widened the horizon of using the nanofiltration in desalinating brackish water as well as surfacewater and wastewater. This development ensures the increase in flux due to improvement in active surface layer formation with the application of very small pressure. The surface charge and hydrophilicity on the surface material of the membrane have shown better flux stability in the high fouling conditions. With the addition of higher flux and higher rejection based on the same chemistry, ULPRO has made another step forward. This introduction will certainly reduce the operation cost and, more importantly, improve the overall reliability of the RO system. Application of nanofiltration is broadened to surface water treatment, wastewaters for nutrient removal and heavy metal rejection from wastewater.

Microbiological quality before and after nanofiltration

A long‐term study identifies the benefits accrued when a distribution system fed with biologically treated water switches to a nanofiltered supply.The authors investigated microbiological behavior of a distribution system supplied initially with biologically treated water and then with nanofiltered water. Their purpose was to identify and evaluate the changes in microbiological water quality attributable to modifications in water treatment at the plant. During the course of the study, all data from various indicators of microbiological quality (i.e., heterotrophic plate counts, coliform enumeration, total direct counts, and fixed bacterial biomass) showed similar trends. Results indicated that the use of nanofiltration allows utilities to reduce chlorination of treated water and at least maintain or increase the microbiological quality of distributed water for areas with high residence times.

Preparation, characterization, and performance of poly(acrylamidocaproic acid) partially neutralized with calcium for use in nanofiltration

The preparation, characterization, and application to nanofiltration of a membrane made of poly(acrylamidocaproic acid) partially neutralized with calcium using the thin-film composite membrane technique are reported in this study. The long hydrophobic side substituent prevents excessive swelling with water and binds the chain. The neutralized ionic group is designed to enhance the affinity of the membrane to water. By controlling the degree of neutralization, the performance of the membrane could be adjusted. The amount of water molecules participating in the hydration shell surrounding an ionic group was increased with increasing ionic concentration in the membrane. The exponential increase of flux with increasing degree of neutralization is due to the increase of the number and size of the hydration shell. The effect of the pressure and molecular weight of the solute on performance was also investigated. The surface interaction between the solute and the membrane seemed to mainly affect the characteristics of performance.

Use of nanofiltration for concentration and demineralization in the dairy industry: Model for mass transport

For whey products intended for human or animal consumption, demineralization enhances the nutritional value of the product. In industrial processes, whey is concentrated by evaporation (EV) and subsequently demineralized by electrodialysis (ED) and/or ion-exchange. Nanofiltration (NF) is an alternative for partial demineralization of whey. NF-membranes which are suitable for dairy applications have a high permeability for (monovalent) salts (NaCl, KCl) and a very low permeability for organic compounds (lactose, proteins, urea). The use of NF instead of EV followed by ED has the advantage of simultaneous concentration and demineralization of whey. This eventually reduces processing costs. Models were developed, based on the extended Nernst-Planck equation, which describe the salt rejection as a function of the flux for binary and ternary salt solutions. Effects of concentration polarization, composition of feed and concentration are incorporated in the model. In laboratory-scale experiments, rejection-flux curves of four different commercial membranes were established for three different model solutions (NaCl, CaCl 2 and (NaCl+CaCl 2)) and for ultrafiltration (UF) whey-permeate (pH 4.6, 5.8 and 6.6). The results indicated that the salt transport through all the NF membranes investigated depends on the flux. At low flux, when the contribution of diffusive transport is the most important, permeation of (especially monovalent) cations is high. At high flux, when transport by convection is the most important, rejection reaches a maximum (constant) value. From this it follows that the salt transport can be controlled by the flux. For binary salt solutions (NaCl or CaCl 2), rejection data could be described by the (two-parameter) model for binary systems. For ternary systems (NaCl and CaCl 2) the model was simplified from a model with four transport parameters to a model with three transport parameters. Rejection data for a ternary system could also be described adequately. Decoupling of transport parameters allowed that the model for the ternary system could be reduced from a four-parameter model to a three-parameter model without losing accuracy. For ultrafiltration (UF)-whey-permeate, a multicomponent mixture, it is shown that an approach in which monovalent cations, divalent cations and anions were grouped separately and lumped into one concentration can be used to describe the rejection-flux data adequately. The experimental data for the (cumulative) anion equivalent charges were predicted accurately only at pH 4.6 and 5.8. At pH 6.6, the rejection calculated for the anions based on equivalent charges was somewhat lower than the rejection actually measured. About halve of the difference could be ascribed to lactate and carbonate. which were not determined separately. As a result there was also a non-matching charge balance. The transport parameters derived from the results with UF-whey-permeate can be used to predict the salt rejection for similar multi-component systems like whey and UF-permeate in indutrial systems.

Rejection of mineral salts on a gamma alumina nanofiltration membrane Application to environmental process

Nanofiltration of salt solutions through an alumina membrane prepared by a sol gel process was investigated: rejections depend on the charge of the ions and decrease in the order: (divalent cation, monoanion) > (monocation, monoanion) or (dication, dianion) > (monocation, dianion). The surface charge of the membrane in the investigated solutions was shown to be positive over a very large pH range. The rejection of ionic species can be rationalised by taking into account the low pore diameters of the membrane and its surface charge: as in the case of organic nanofiltration membranes, the rejection mechanism depends on the relative ratio of the coulombic, dielectric and hydration interactions between the membrane material and the ionic species. The use of nanofiltration through the alumina nanofiltration membrane for denitration of water is also presented.

Modelling of nanofiltration applied to the recovery of salt from waste brine at a sugar decolourisation plant

The implementation of a computer model to simulate reverse osmosis in systems with several components is described. The model was based on the Spiegler-Kedem theory of reverse osmosis. The results of a pilot-scale investigation of the use of nanofiltration to recover sodium chloride from waste brine from the regeneration of anion exchange resin were used in this study. This effluent contains around 50 g/l of sodium chloride and 5 g/l (as total carbon) of organic colourants, many of which are negatively charged. When using the SelRO TM MPT-30 or MPT-31 membrane at an operating pressure of 3 MPa, temperatures between 45°C and 60°C, and linear feed flow rates around 1.6 m/s, the retention of sodium chloride was found to be between 0% and 20%, while the organic compounds had an overall retention of 80% to 97%. The experimental results were used to obtain a set of parameters relating to the system, which were then used to generate design data for a full-scale plant. Suitable module arrangements were proposed and the system performance for each case was predicted.

Trace element removal from ash dam waters by nanofiltration and diffusion dialysis

Liquid waste streams in coal-fired power plants contain a wide spectrum of trace elements, most of which originate in the coal and remain in the fly ash or bottom ash when the coal is burned. Electric power authorities seek methods for removing toxic elements from such streams. The use of nanofiltration and diffusion dialysis for removing boron and fluoride from ash dam water is described in this article. Negatively charged Nitto Denko NTR-7410 and Filmtec NF40 nanofiltration membranes gave better results than amphoteric Toray UTC-20HF and UTC-60 membranes. Membrane performance depended on pH, the best results being obtained when the pH of the ash dam water was in the 3–4.5 range. Diffusion dialysis membranes with negatively charged functional groups gave better results than membranes with positively charged functional groups.