Characterization and Performance of LbL-Coated Multibore Membranes: Zeta Potential, MWCO, Permeability and Sulfate Rejection

The characterization of membranes is suitable to investigate changes in the membrane properties caused by Layer-by-Layer (LbL) modification. Besides permeability, rejection, and molecular-weight cut-off (MWCO), which give information about the modification of the separation behaviour of the membrane, the zeta potential is capable of describing the surface charge of the membrane and its variation impacted by the properties of the polyelectrolyte multilayers (PEM). In this study, a new method for zeta potential measurement of hollow fibre membranes with several capillaries was developed and further investigations on the LbL modification of such membranes were performed. The results showed that an LbL coating with 8 DL PDADMAC/PSS led to a significant increase in the membrane charge of more than 20 mV. The coating with a different number of polyelectrolyte (PE) layers showed a zig-zag behaviour, comparable to data from flat sheet studies. However, in contrast to most flat sheet membranes, the charge curve assumes a totally negative trajectory at neutral pH. Further experiments on the MWCO of the LbL-modified membrane showed a reduction in the pore diameter from approx. 20 nm to less than 2 nm, reaching the range of nanofiltration membranes. With information on both the zeta potential and the MWCO, it was found that the rejection mechanism in LbL-modified multibore membranes is a complex interplay between the sieving effect due to reduction in the pore diameter and the repulsion effect of the charged membrane.

Vita käppen – redskapet som hjälper och stjälper

The White Cane – A tool that both helps and hinders Bodies, shame, normality and the agency of objects Maria Bäckman The article discusses the attempts of visually impaired individuals tosometimes pass as seeing. The background is the resistance that many blind or visually impaired people testify they feel, during their ongoingrehabilitation, about a white cane. Often, on these occasions they provid descriptions of dramatic narratives in which the user explains what it was like when they first realized that it was now really time to start using a cane (for example: When I fell in the water from the quay, or stepped out in front of a bus, etc.). However, many also relate the way a cane, even in more mundane contexts, makes the individual’s visual inability obvious to others and thereby makes the person particularly vulnerable. The tool that connects the visually impaired with the outside world is thus also a material expression which makes both the visual damage and the cane usersmore noticeable as less than a fully functional individual.By holding on to the materiality of the cane and its nature of being a physical object, our understanding can be increased of the ambivalent relationship that many visually impaired people develop with a white cane. On the basis of social materiality studies and the concept of ableism, taken from critical handicap research, the article shows how the use of a white cane takes place in a public space; a space where the user variously inhabits an “imaginary” full-sighted body and another, existing body, which on the contrary is characterized by its weakened vision. However, it is important to realize that the persistent rejection mechanism that many visually impaired people have for a cane is intimately linked to ableism and existing norms of bodily functions. A desire to repel an object that reduces one to something else, and consequently to a somewhat lower standing, is a perfectly reasonable reaction to a deeply rooted social conflict. For many people with visual impairment, the resistance to a white cane must therefore be understood as a refusal to embody a functional normative failure.

Graph Dilated Network with Rejection Mechanism

Recently, graph neural networks (GNNs) have achieved great success in dealing with graph-based data. The basic idea of GNNs is iteratively aggregating the information from neighbors, which is a special form of Laplacian smoothing. However, most of GNNs fall into the over-smoothing problem, i.e., when the model goes deeper, the learned representations become indistinguishable. This reflects the inability of the current GNNs to explore the global graph structure. In this paper, we propose a novel graph neural network to address this problem. A rejection mechanism is designed to address the over-smoothing problem, and a dilated graph convolution kernel is presented to capture the high-level graph structure. A number of experimental results demonstrate that the proposed model outperforms the state-of-the-art GNNs, and can effectively overcome the over-smoothing problem.

Investigation of polar mobile organic compounds (PMOC) removal by reverse osmosis and nanofiltration: rejection mechanism modelling using decision tree

Polar mobile organic compounds (PMOC) are highly polar chemicals and tend to accumulate in short water cycles. Due to their properties, PMOC might be partially eliminated by advanced water treatment technologies. The goal of this study is to investigate the rejection of 22 PMOC (highly mobile and persistent) by reverse osmosis (RO) and nanofiltration (NF) membranes. The impact of transmembrane pressure was evaluated through laboratory-scale cross-flow constant pressure filtration tests. Among the investigated experimental conditions, PMOC rejection with NF at eight bars is comparable to values obtained on RO at 15 bars. Negatively charged PMOC are highly rejected by both RO and NF membranes while guanidine-like compounds exhibit higher passage values and are strongly impacted by transmembrane pressure. In order to model the rejection mechanism, decision tree methodology was employed to link PMOC physicochemical properties to rejection values. Based on laboratory-scale results, decision trees were computed and emphasized that the NF rejection mechanism is governed by electrostatic interaction and sieving effects. In contrast, PMOC rejection on the RO membrane strongly depends on the topological polar surface area (TPSA) of the PMOC. This study suggests that micropollutant TPSA should be more investigated in order to describe RO removal efficiency. Moreover, it is shown that the decision tree is a powerful numerical tool in order to reveal the specific sequence leading to micropollutant removal by RO and NF membranes.

The role of interaction between low molecular weight neutral organic compounds and a polyamide RO membrane in the rejection mechanism

Reverse osmosis (RO) is a membrane technology that separates dissolved species from water.