Degradation of Polyamide Nanofiltration Membranes by Bromine: Changes of Physiochemical Properties and Filtration Performance.

The potential coexistence and interaction of bromine and polyamide membranes during membrane-based water treatment prompts us to investigate the effect of bromine on membrane performance. For fully aromatic polyamide membrane NF90 exposed under a mild bromination condition (10 mg/L), bromine incorporation resulted in more negatively charged (-13 vs -25 mV) and hydrophobic (55.2 vs 58.9°) surfaces and narrower pore channels (0.3 vs 0.29 nm). The permeabilities of water and neutral solutes were reduced by 64 and 69-87%, respectively, which was attributed to the decreased effective pore radius and hydrophilicity. NaCl permeability was reduced by 90% as a synergistic result of enhanced size exclusion and charge repulsion. The further exposure (100 and 500 mg/L bromine) resulted in a more hydrophobic surface (61.7 and 65.5°) and the minor further reduction for water and solute permeabilities (1-9%). Compared with chlorine, the different incorporation efficiency and properties (e.g., atomic size, hydrophilicity) of bromine resulted in opposite trends and/or different degrees for the variation of physicochemical properties and filtration performance of membranes. The bromine incorporation, the shift and disappearance of three characteristic bands, and the increased O/N ratio and calcium content indicated the degradation pathways of N-bromination and bromination-promoted hydrolysis under mild bromination conditions (480 mg/L·h). The further ring-bromination occurred after severe bromine exposure (4800-24,000 mg/L·h). The semi-aromatic polyamide membrane NF270 underwent a similar but less significant deteriorated filtration performance compared with NF90, which requires a different explanation.

A comprehensive analysis of evolution and underlying connections of water research themes in the 21st century.

This work aimed to reflect the advancements in water-related science, technology, and policy and shed light on future research opportunities related to water through a systematic overview of Water Research articles published in the first 21.5 years of the 21st century. Specific bibliometric analyses were performed to i) reveal the temporal and spatial trends of water-related research themes and ii) identify the underlying connections between research topics. The results showed that while top topics including wastewater (treatment), drinking water, adsorption, model, biofilm, and bioremediation remained constantly researched, there were clear shifts in topics over the years, leading to the identification of trending-up and emerging research topics. Compared to the first decade of the 21st century, the second decade not only experienced significant uptrends of disinfection by-products, anaerobic digestion, membrane bioreactor, advanced oxidation processes, and pharmaceuticals but also witnessed the emerging popularity of PFAS, anammox, micropollutants, emerging contaminants, desalination, waste activated sludge, microbial community, forward osmosis, antibiotic resistance genes, resource recovery, and transformation products. On top of the temporal evolution, distinct spatial evolution existed in water-related research topics. Microplastics and Covid-19 causing global concerns were hot topics detected, while metagenomics and machine learning were two technical approaches emerging in recent years. These consistently popular, trending-up and emerging research topics would most likely attract continuous/increasing research input and therefore constitute a major part of the prospective water-related research publications.

The structural and functional properties of polysaccharide foulants in membrane fouling.

Polysaccharide foulant is known to play a crucial role in membrane fouling, however the detailed influential mechanisms and the pertinence to specific structure of polysaccharides, as well as intermolecular interactions among them with and without divalent cation are still indistinct. In this study, seven polysaccharides including agarose, sodium alginate, carrageenan, pectin, starch, sodium carboxymethylcellulose (CMC) and xanthan gum, with different chain and molecular structures, were used as model foulants to investigate the role of structural and functional features of polysaccharides in membrane fouling. Two Hermia's models (classical and mass-transfer models) as well as the resistance-in-series model were used to analyze the fouling mechanism. Results show that the spatial configuration of foulant molecule is significant in membrane fouling which actually controls the resistance of gel layer formed on membrane. Polysaccharides with different properties show distinct fouling mechanisms which are in accordance with the four models described by Hermia respectively. Cations may change the interaction of polysaccharide foulant which further leads to the structural change of the gel layer. It turns out that mass-transfer model is more suitable for interpreting of crossflow filtration data. So far, little has been known about the effects of molecule structure of polysaccharides on membrane fouling. In this paper, we provide a basic database for polysaccharide fouling which will work as a theoretical basis for finding more effective measures to prevent and control membrane fouling.

Photocatalyzed surface modification of poly(dimethylsiloxane) with polysaccharides and assay of their protein adsorption and cytocompatibility.

An improved approach for the surface modification of poly(dimethylsiloxane) (PDMS) using carboxymethyl cellulose (CMC), carboxymethyl beta-1,3-dextran (CMD), and alginic acid (AA) was investigated. The PDMS substrates were first oxidized in a H(2)SO(4)/H(2)O(2) solution to transform the Si-CH(3) groups on their surfaces into Si-OH groups. Then methacrylate groups were grafted onto the substrates through a silanization reaction using 3-(trimethoxysilyl)propyl methacrylate. Sequentially, cysteamine was conjugated onto the silanized surfaces by the reaction between the thiol and methacrylate groups under 254 nm UV exposure. Afterward, the amino-terminated PDMS substrates were sequentially reacted with CMC, CMD, and AA in the presence of N-hydroxysuccinimide and 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide, resulting in the grafting of polysaccharides onto PDMS surfaces. The composition and chemical state of the modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS). In addition, the stability and dynamic characteristics of the polysaccharide-grafted PDMS substrates were investigated by XPS and temporal contact angle experiments. A protein adsorption assay using bovine serum albumin (BSA), chicken egg albumin, lysozyme, and RNase-A showed that the introduction of CMD and AA can reduce the adsorption of negatively charged BSA and chicken egg albumin, but increase the adsorption of the positively charged lysozyme and RNase-A. However, CMC-modified PDMS surfaces showed protein-repelling properties, regardless of whether the protein was positively or negatively charged. A cell culture and migration study of glioma C6, MKN-45, MCF-7, and HepG-2 cells revealed that the polysaccharide-modified PDMS greatly improved the cytocompatibility of native PDMS.

Role of calcium ions on the removal of haloacetic acids from swimming pool water by nanofiltration: mechanisms and implications.

We investigated the removal of haloacetic acids (HAAs) from swimming pool waters (SPWs) by two nanofiltration membranes NF270 and NF90. The strong matrix effect (particularly by Ca2+) on membrane rejection prompts us to systematically investigate the mechanistic role of Ca2+ in HAA rejection. At typical SPW pH of 7.5, NF90 maintained consistently high rejection of HAAs (>95%) with little influence by Ca2+, thanks to the dominance of size exclusion effect for this tight membrane (pore radius âˆ¼ 0.31 nm). In contrast, the rejections of both inorganic ions (e.g., Na+ and Cl-) and HAA anions were decreased at higher Ca2+ concentration for NF270 (pore radius âˆ¼ 0.40 nm). Further tests show that the rejection of neutral hydrophilic molecular probes and the membrane pore size were not affected by Ca2+. Although Ca2+ is unable to form strong complex with HAAs, we observed the binding of Ca2+ to NF270 together with a reduction in its surface charge. Therefore, the formation of membrane-Ca2+ complex, which weakens charge interaction effect, was responsible for the reduced HAA rejection. The current study reveals important mechanistic insights of the matrix effect on trace contaminant rejection, which is critical for a better understanding of their fate and removal in membrane-based treatment.

Removal of haloacetic acids from swimming pool water by reverse osmosis and nanofiltration.

Recent studies report high concentrations of haloacetic acids (HAAs), a prevalent class of toxic disinfection by-products, in swimming pool water (SPW). We investigated the removal of 9 HAAs by four commercial reverse osmosis (RO) and nanofiltration (NF) membranes. Under typical SPW conditions (pH 7.5 and 50 mM ionic strength), HAA rejections were >60% for NF270 with molecular weight cut-off (MWCO) equal to 266 Da and equal or higher than 90% for XLE, NF90 and SB50 with MWCOs of 96, 118 and 152 Da, respectively, as a result of the combined effects of size exclusion and charge repulsion. We further included 7 neutral hydrophilic surrogates as molecular probes to resolve the rejection mechanisms. In the absence of strong electrostatic interaction (e.g., pH 3.5), the rejection data of HAAs and surrogates by various membranes fall onto an identical size-exclusion (SE) curve when plotted against the relative-size parameter, i.e., the ratio of molecular radius over membrane pore radius. The independence of this SE curve on molecular structures and membrane properties reveals that the relative-size parameter is a more fundamental SE descriptor compared to molecular weight. An effective molecular size with the Stokes radius accounting for size exclusion and the Debye length accounting for electrostatic interaction was further used to evaluate the rejection. The current study provides valuable insights on the rejection of trace contaminants by RO/NF membranes.