A rapid preparation technique for studying highly water-swollen membranes with a scanning electron microscope (SEM) supplied with a cryo-unit

In this study the cryo-unit is introduced as a new and useful instrument to investigate water-containing specimens with the SEM. Often water-containing biological specimens are studied, but in our case we used water-swollen polymer membranes. The results show that application of a cryo-unit permits the study of this material at low temperatures up to magnifications of about 10 000 times, while other techniques failed to give reproducible results

Characterization of new membrane materials by means of fouling experiments Adsorption of bsa on polyetherimide-polyvinylpyrrolidone membranes

The hydrophilicity of polyetherimide-polyvinylpyrrolidone (PEI-PVP) microfiltration membranes can be adjusted by means of a suitable post-treatment. The influence of the nature of the membrane surface on fouling properties was studied using permeation experiments before and after exposure to a protein (BSA) solution and adsorption experiments with 14C labelled BSA. A correlation between the permeation experiments and the radiolabelled BSA adsorption experiments was found. The PVP in the membrane matrix prevents BSA adsorption taking place to a large extent and it appeared that heat-treated PEI-PVP membranes showed the same nonfouling behaviour as, for example, cellulose acetate membranes

Surface chemistry-dependent antiviral activity of silver nanoparticles

Environmental Biolog

Single-step synthesis of a polyelectrolyte complex hollow-fiber membrane for forward osmosis

We present the simultaneous synthesis of a hollow fiber membrane with a selective layer created by means of polyelectrolyte complexation (PEC), to be used as a membrane in forward osmosis. The aim of this single-step approach was to create a defect-free robust selective layer and circumvent the challenges associated with coating via interfacial polymerization. The nascent hollow fiber membrane with a PEC layer was characterized by SEM imaging as well by determining the streaming potential and pure water permeance. We also evaluated several electrolytes as potential draw solutes in combination with the developed membrane and selected trisodium citrate (TSC) as it showed a very high rejection of 97 ± 2%. Using 1 M TSC as draw solution showed promising osmotic performance in selective layer facing feed solution (FO) mode, having a water flux of 7.8 ± 0.2 (L·m−2⋅h−1) and a reverse salt flux of 2.1 ± 0.7 (g·m−2⋅h−1). A significantly higher reverse salt flux of was gained in PRO mode which was attributed to the high ionic strength of the charged draw solute near the PEC layer. It is highlighted that the choice of draw solute as well as process orientation (FO or PRO mode) are crucial for charged selective layers such as our PEC selective layer. We conclude that our approach shows substantial promise for use in FO processes using TSC as the draw solution. In addition, the taken approach successfully eliminates the time-consuming and challenging extra step of coating hollow fibers through interfacial polymerization, opening up opportunities for the cost-effective synthesis of FO hollow-fiber membranes

Retention of micropollutants by polyelectrolyte multilayer based hollow fiber nanofiltration membranes under fouled conditions

To meet the increasing global water demand, local solutions, such as the reuse of greywater, are becoming of greater importance. While greywater reclamation has been implemented, full-scale adaptation has been limited by the occurrence of micropollutants in treated greywater effluent. To reduce the risks posed by micropollutants, advanced post-treatment is required. One promising technology is the implementation of hollow fiber nanofiltration, which has proven to effectively remove micropollutants. However, the effect of fouling on the overall membrane performance has received limited attention. In this research, the effect of fouling on the performance of polyelectrolyte multilayer nanofiltration membranes was evaluated. Filtration experiments were performed using hollow fiber nanofiltration membranes using model solutions and greywater effluent. Synthetic greywater effluent with different model foulants was implemented to simulate bio- and colloidal fouling. Afterwards, the fouling propensity of greywater effluent from a source-separated treatment plant was evaluated. The performed experiments demonstrated that the studied hollow fiber nanofiltration membranes are mainly sensitive to biofouling. Permeability loss was observed in all foulant experiments, and overall, sodium alginate most severely reduced the flux. Regardless of the loss in permeability, micropollutant retention remained relatively constant, demonstrating the potential suitability of hollow fiber nanofiltration membranes in greywater reclamation schemes

Annealing of Polyelectrolyte Multilayers for Control over Ion Permeation

Polyelectrolyte multilayer based membranes are highly promising systems to create stable and versatile nanofiltration membranes. One very popular and well-studied polyelectrolyte pair, is the polycation poly(diallyldimethylammonium chloride) (PDADMAC) and polyanion poly(sodium 4-styrenesulfonate) (PSS), due to its excellent separation properties and high chemical and physical stability. Membrane charge can be easily controlled by simply terminating the multilayer by either PDADMAC or PSS. Unfortunately, a phenomenon that occurs during multilayer coating, is overcompensation by PDADMAC. In this study, it is shown that overcompensation of PDADMAC results in a positive surface charge even when the multilayer is PSS-terminated. In addition, it is shown that this leads to poorer membrane separation properties with sulfate retention decreasing from 94 to 39%. At the same time, it is demonstrated that a so-called annealing cycle with a high salt concentration leads to recovery of the negative surface charge, increasing the sulfate retention from 39 to 95%. Even for multilayers at which no irreversible positive surface charge is measured, separation properties improved substantially (increasing sulfate retention from 94 to 97%, at a higher membrane permeability) after salt-annealing. It is concluded that post-treatment by salt-annealing results in an improved membrane performance and allows an additional degree of control over the membrane separation properties

Virus reduction through microfiltration membranes modified with a cationic polymer for drinking water applications

Virus penetration is a significant problem in water treatment membrane filtration. To effectively remove waterborne viruses nano-filtration, reverse osmosis or ultrafiltration must be used, all of which are high energy filtration schemes. Novel approaches and technologies for the production of virus-free drinking water are therefore warranted. In this study, we modified model surfaces and commercial polyether sulfone, (PES) microfiltration (MF) membranes to achieve a substantial virus reduction under gravity based filtration membranes. The successful modification using the cationic polymer polyethyleneimine (PEI) was confirmed by Fourier transform infrared spectroscopy (FTIR) and zeta potential measurements. MS2 bacteriophages, a surrogate for human pathogenic waterborne viruses like norovirus were used to challenge the modified surfaces. The membrane modification resulted in ∼22% loss of the membrane permeability while an increase of ≥3 log10-units (≥99.9%) in MS2 reduction was observed. These reductions were comparable to the reduction of PEI-coated model surfaces tested for contact reduction. This simple modification of a commercially available MF membrane led to substantial viral reductions with a significant flux of 5000 L/m2 in approximately 2.5 h. This work therefore, highlights the potential modified MF membranes for gravity-based filtrations to produce safe drinking water. Further studies should be done to show similarly enhanced reductions of human pathogenic viruses