50 research outputs found
A tale of two charges: zwitterionic polyelectrolyte multilayer membranes
No full textIn this thesis, the development of selective membranes for water treatment facilities to cope with the aforementioned issues is covered. By using hollow fiber membranes, the water purification process can be simplified compared to using spiral wound membranes, a significant advantage for decentralized water treatment plants. The selectivity of ultrafiltration membranes is improved by coating a dense separation layer on the membrane. For this, the simple and versatile “layer-bylayer” (LbL) technique is used. By exposing a negative substrate to a polycation in an aqueous solution, a thin layer of that polycation is adsorbed on the surface. With the modified substrate, now positively charged, the same process can be done with an aqueous solution of a polyanion. This process can be repeated over and over again, steadily building a polyelectrolyte multilayer on top of the substrate. If the chosen substrate is a porous support (e.g., an ultrafiltration membrane), the formed polyelectrolyte multilayers can be used as a selective layer in water purification. The versatility of the LbL technique allows for an easy control over layer properties, such as thickness, density and charge, by varying the coating conditions, the type of polyelectrolytes and the amount of layers. This versatility makes the LbL system well suited for the design of dense filtration layers. A key property of all membranes for water treatment purposes is the life time of the membrane. In this thesis we show that an adequate membrane life time can indeed be obtained for polyelectrolyte multilayers modified membranes, if certain criteria are met (Chapter 2). First of all, the presence of ionic groups on the membrane support significantly enhances the adherence of the multilayer on the membrane when high shear forces and reversed flow are applied. Second, the capability to withstand chemical degradation by hypochlorite is superior when quaternary ammonium polycations are used in the layer. We show that when both criteria are met, backwashable hollow fiber nanofiltration membranes can be made with a life time that is comparable to commercial ultrafiltration membranes
Membrane set to make water purification more efficient and cheaper
No full textResearch work done at the University of Twente, in The Netherlands, which aimed to understand how different polyelectrolyte multilayers can be used to make hollow-fibre membranes, has resulted in the development of a "straw membrane" that removes micro-pollutants, such as pharmaceuticals residues, from drinking water. Furthermore, by making it possible to purify water in a single process step, it permits cheaper and more efficient water purification
Method for the Production of Positively Charged Membranes
No full textThe present invention relates to a method for the production of a positively charged membrane. Furthermore the present invention relates to a positively charged membrane obtainable by the methods of present invention and the use of these positively charged membranes.</p
Effects of Concentration Polarization and Membrane Orientation on the Treatment of Naproxen by Sulfate Radical-Based Advanced Oxidation Processes within Nanofiltration Membranes with a Catalytic Support
No full textThe structure with a selective nanofiltration (NF) layer on top of a catalytic ultrafiltration (UF) membrane provides the possibility of treating micropollutants (MPs) by both rejection and degradation. However, such a dense selective layer unavoidably induces a formation of a highly concentrated retentate and a low utilization of the oxidant due to its rejection. A different membrane orientation is expected to solve the problems mentioned above since the concentrated MPs can be degraded within the catalytic support, and the rejection of the oxidants can be avoided when the pressure is applied from the porous support side. However, the resulting complex concentration polymerization (CP) effects are not well understood, and the effects of the following concentration changes of the MPs and the oxidants around the catalyst within the porous support membrane are unclear as well. In this work, three polyelectrolyte multilayers with different selectivity were fabricated on PES@CoFe2O4 catalytic UF membranes by sequential dip-coating. Concentration polarization models are utilized to predict the concentrations of naproxen and peroxymonosulfate (PMS) within the porous catalytic support under different membrane orientations. The results of naproxen removal after adding PMS show that a higher naproxen removal can be obtained with a higher concentration ratio of PMS to naproxen (cPMS/cNPX). Moreover, it is shown that the MPs in the feed solution can be degraded in a catalysis-separation sequence, exhibiting the potential of rejecting and simultaneously degrading MPs. However, the coating of a selective polyelectrolyte multilayer on the catalytic UF membranes also causes lower accessibility of PMS and naproxen to the catalysts embedded within the polymeric membranes, resulting in the decline of degradation efficiency. By coating only one side of the membranes, this negative effect caused by the polyelectrolyte coating can be mitigated. Overall, a 97% removal of naproxen on the permeate side and a 12% degradation of naproxen on the feed side were observed with the one-side-coated membranes under a catalysis-separation sequence. This work highlights the key role that concentration polarization can play in the degradation efficiency of naproxen in catalytic NF membranes, providing valuable guidance for the design of further improved catalytic membranes.</p
Five journeys from nanotechnology research to successful products in the water industry
No full textNanotechnology-based semipermeable membranes have been actively studied for their potential application in the production of clean water. Fundamental nanotechnology research has been turned into award-winning water industry products.</p
Removal of BPA by enzyme polymerization using NF membranes
No full textThe application of laccase and peroxidase from horseradish (HRP) to facilitate the removal of bisphenol A (BPA) from aqueous solutions was investigated. Effect of pH and the enzyme dose was evaluated in order to determine the optimum conditions for the enzyme performance. The results indicate that BPA was quickly removed from aqueous solution since a BPA conversion over 95% was obtained in 180 min for both enzymes in optimal conditions; the higher the enzyme dose, the higher the removal percentage of BPA. It was also found that the optimum pH for the removal efficiency of BPA was around 7 for both enzymes. The use of a membrane-reactor integrated system with recycling of enzyme for BPA degradation is also presented. These results demonstrate the potential and limitations of using enzymatic BPA degradation, operated in a recycling mode coupled to a nanofiltration membrane. BPA removal efficiencies for several NF membranes were related to the BPA molecular weight, membrane pore sizes and membrane hydrophobicity. NF270 showed the best performance in membrane-assisted enzyme treatment: 89% removal of BPA for the two enzyme treatments and less than 35% flux decay were observed
Polyelectrolyte multilayer (PEM) membranes and their use
No full textThe present invention relates to a polyelectrolyte multilayer (PEM) membrane comprised of at least one bilayer, wherein the bilayer is comprised of a layer of a polymeric polycation and a layer of a polymeric polyanion. Furthermore, present invention relates to methods for the production of these PEM membranes by layer-by-layer deposition and the use of these PEM membranes for the decontamination of liquids, preferably water.</p
Stable Polyelectrolyte Multilayer-Based Hollow Fiber Nanofiltration Membranes for Produced Water Treatment
No full textProduced water (PW) constitutes a massive environmental issue due to its huge global production as well as its complexity and toxicity. Membrane technology could, however, convert this complex waste stream into an important source of water for reuse, but new and more efficient membranes are required. In particular, in the last few years, polyelectrolyte multilayers (PEMs) established themselves as a very powerful method to prepare hollow fiber-based nanofiltration (NF) membranes, and this membrane type and geometry would be ideal for PW treatment. Unfortunately, the presence of surfactants in PW can affect the stability of polyelectrolyte multilayers. In this work, we investigate the stability of polyelectrolyte multilayers toward different types of surfactant, initially on model surfaces. We find that chemically stable multilayers such as poly(diallyldimethylammonium chloride) (PDADMAC)/poly(sodium 4-styrenesulfonate) (PSS), based only on electrostatic interactions, are substantially desorbed by charged surfactants. For poly(allylamine hydrochloride) (PAH)/PSS multilayers, however, we demonstrate that chemical cross-linking by glutaraldehyde leads to surfactant stable layers. These stable PEM coatings can also be applied on hollow fiber support membranes to create hollow fiber NF membranes dedicated for PW treatment. Increased cross-linking time leads to more stable and more selective separation performance. These newly developed membranes were subsequently studied for the treatment of synthetic PW, consisting of freshly prepared oil-in-water emulsions stabilized by hexade-cyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) in the presence of a mixture of ions. For both types of produced water, the membranes show excellent oil removal (∼100%) and organics removal (TOC reduced up to ∼97%) as well as good divalent ion retentions (∼75% for Ca2+ and up to ∼80% for SO42–). Moreover, we observe a high flux recovery for both emulsions (100% for CTAB and 80% for SDS) and especially for the CTAB emulsion a very low degree of fouling. These stable PEM-based hollow fiber membranes thus allow simultaneous deoiling and removal of small organic molecules, particles, and divalent ions in a single step process while also demonstrating excellent membrane cleanability
Evaluation of Membrane Integrity Monitoring Methods for Hollow Fiber Nanofiltration Membranes: Applicability in Gray Water Reclamation Systems
No full textSource-separated gray water reclamation using nanofiltration as an advanced post-treatment option has received substantial interest in meeting the growing water demand. During reclamation, membrane integrity is crucial to ensure the water’s safety. This study evaluated several chemical and novel microbial indicators as indirect membrane integrity-monitoring methods for hollow fiber nanofiltration membranes in reclamation schemes. Under normal conditions, high retention of divalent ions and organic matter and near-complete removal of Escherichia coli (E. coli) were observed. Limited removal of the antibiotic gene (ARG) tetO was observed due to low feed concentrations and a higher detection limit (LOD). While 16S rRNA and ARG sul1 were not limited by their LODs, lower removals were observed, most likely due to free-floating DNA passing through the membranes. A broken fiber in a pilot-scale module reduced organic matter and microorganism removal substantially, while flux and ion rejection remained similar. Predictions made using the observed results and a previously proposed model allowed for the evaluation of the selected methods in upscaled reclamation systems. Based on these results, it was concluded that microorganisms could be employed as indicators in indirect membrane integrity-monitoring methods in large-scale reclamation schemes, while UV254nm absorbance (used in organic matter determination) could be a viable solution in pilot-scale systems.BT/Environmental Biotechnolog
Multifunctional polyelectrolyte multilayers as nanofiltration membranes and as sacrificial layers for easy membrane cleaning
No full textThis manuscript investigates the modification of an ultra-filtration (UF) membrane support with polyelectrolyte multilayers (PEMs) consisting of the weak polyelectrolytes poly(allyl amine) hydrochloride (PAH) and poly(acrylic acid) (PAA). These prepared polyelectrolyte multilayer membranes have a dual function: They act as nanofiltration (NF) membranes and as sacrificial layers to allow easy cleaning of the membranes. In order to optimize the conditions for PEM coating and removal, adsorption and desorption of these layers on a model surface (silica) was first studied via optical reflectometry. Subsequently, a charged UF membrane support was coated with a PEM and after each deposited layer, a clear increase in membrane resistance against pure water permeation and a switch of the zeta potential were observed. Moreover these polyelectrolyte multilayer membranes, exhibited rejection of solutes in a range typical for NF membranes. Monovalent ions (NaCl) were hardly rejected (60% were observed for a neutral organic molecule sulfamethoxazole (SMX) and for the divalent ion SO32−. The rejection mechanism of these membranes seems to be dominated by size-exclusion. To investigate the role of these PEMs as sacrificial layers for the cleaning of fouled membranes, the prepared polyelectrolyte multilayers were fouled with silica nano particles. Subsequent removal of the coating using a rinse and a low pressure backwash with pH 3, 3 M NaNO3 allowed for a drop in membrane resistance from 1.7 ⋅ 1014 m−1 (fouled membrane) to 9.9 ⋅ 1012 m−1 (clean membrane), which is nearly equal to that of the pristine membrane (9.7 ⋅ 1012 m−1). Recoating of the support membrane with the same PEMs resulted in a resistance equal to the resistance of the original polyelectrolyte multilayer membrane. Interestingly, less layers were needed to obtain complete foulant removal from the membrane surface, than was the case for the model surface. The possibility for backwashing allows for an even more successful use of the sacrificial layer approach in membrane technology than on model surfaces. Moreover, these PEMs can be used to provide a dual function, as NF membranes and as a Sacrificial coating to allow easy membrane cleaning
