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Abstract: The concept “critical flux” allows for a relatively new operation optimization of ultrafiltration (UF) in fouling control strategies. The present studies mostly pay attention to colloids, organic solution and surface fresh water, which are of a less complex chemistry than that of seawater. In this work, “critical flux” was applied into the field of seawater desalination to investigate the utility of this concept for dealing with UF membrane fouling. Firstly, the nature flux mode, a new measurement for the critical flux, was proposed for UF in treating seawater and compared favorably with other measurements such as constant flux mode and constant pressure mode. Secondly, the definition (strong form J cs and weak form J cw) of critical flux for UF of seawater was evaluated to make sure whether or not the perfect operating condition (without UF fouling) is in existence. Thirdly, the effects of sub- and super-critical flux operations using different operating modes on the extent of membrane fouling were investigated by measuring hydraulic resistance. Moreover, a brief analysis of the economic feasibility of sub-/super-critical flux operations was covered. The results showed that the highest E p was yielded when operating in constant pressure mode with higher TMP under super-critical flux conditions, while the lowest E p in constant/nature flux mode with higher permeate flux under sub-critical flux conditions. When operating in constant/nature flux modes, lower E p was achieved under sub-critical flux conditions than under super-critical flux conditions. [Copyright &y& Elsevier]

A series of self-supporting and substrate-supporting polysulfone (PSf) ultrafiltration (UF) membranes was fabricated using various substrates including glass plates, polypropylene random plates (PPR) and three kinds of non-woven fabrics (NWFs) via a typical phase inversion technique. Effects of the substrate hydrophilicity and structure on the membrane characteristics, morphology, separation and anti-fouling performance were systematically investigated. For self-supporting membranes, compared to glass plates, PPR facilitated more porous membranes and higher pure water permeability ( L p ), permeation flux as well as anti-fouling property. NWFs density played an important role in the separation performance of the NWFs-supporting membranes. The resulting membrane with loosest NWFs exhibited an ultrahigh L p of approximate 13,572 L/m 2 h per MPa without any sacrifice of rejection, which significantly outperformed almost all the PSf membranes with L p of 1000–7000 L/m 2 h per MPa in literature. In addition, fouling filtration tests were performed in dead-end mode using humic acids solution followed by physical washing. More reversible rather than irreversible fouling was found in the NWFs-supporting membranes, especially for the membrane with loosest NWFs, indicating an improved anti-fouling property. This work endows the conventional PSf membranes with the outstanding properties such as ultrafast water transport and high flux recovery in an efficient and facile way. [ABSTRACT FROM AUTHOR]

[Display omitted] • A gradient polyelectrolyte hydrogel is synthesized with aid of electric field. • Interfacial and build-in potentials verified by microanalysis and numerical calculation. • Removal efficiencies of anionic heavy metals boosted by the self-induced potentials. With the aggravation of pollutants damage to the environment, it is crucial yet rather challenging to design powerful matrixes for nanomaterials with high ions permeability and migration, as well as multiple exposed active sites. However, most of the current nanomaterial matrixes just act as carrier supporters with introduced invalid mass. Here, a gradient natural polycation electrolyte (chitosan) hydrogel was engineered as nanomaterials matrix to boost anionic heavy metals removal such as antimonate (Sb(V)) and arsenate (As(V)) for the first time, based on the generated interfacial and build-in electric potentials due to the diffusion of counterions. The resulting dual electric potentials allow for rapid diffusion and removal efficiency of heavy metal ions. Exemplified by Sb(V) removal, the chitosan gradient hydrogel matrixes with embedded UiO-66 MOFs exhibited a 3-fold higher removal velocity than the homogeneous hydrogel matrix, and their removal efficiencies were also promoted by gathering on the high charge density side of hydrogels. In contrast to the other reported matrix materials without driving force, the gradient polyelectrolyte hydrogel can greatly boost the removal efficiency and shorten the treatment times. This study offers inspirations on eliminating heavy metal contaminations based on self-driving forces stemming from the heterogeneous structure of materials. [ABSTRACT FROM AUTHOR]

Tubular porous silicate cement compacts with hierarchical porosity were successfully fabricated via a tert-butyl alcohol (TBA)-based freeze-casting technique in one single step. These samples were characterized by unidirectional aligned pore channels and completely open porosity. Various experimental parameters affecting the macropore size, mesopore size, porosity, and compression strength were investigated, including the initial solids loading, freezing temperature and curing period. Both the research findings of microstructure observations and property tests show that the pore size decreased significantly with decreasing freezing temperature and increasing solids loading. The porosity increased significantly with decreasing solids loading, while the compressive strength decreased remarkably. In addition to their tunable physical characteristics, these brand-new inorganic porous materials with oriented aligned pore channels and dense layer surface showed high permeation performance and desirable separation ability. These results endow the silicate cement, a kind of low-cost and high-performance architecture material, with great potential as a novel ordered porous inorganic material for numerous applications, especially in separation process. [ABSTRACT FROM AUTHOR]

Highlights: [•] PVC-Li1.6Mn1.6O4 precursor membranes were prepared by the solvent exchange method. [•] The lithium ion-sieve membrane has high selectivity for Li+ with coexisting ions. [•] It exhibits high stability after eight repeated adsorption–desorption cycles. [•] The thickness of membrane effects on adsorption capacity and mechanical strength. [Copyright &y& Elsevier]

Abstract: In this study, several anti-fouling approaches including coagulation conditions (FeCl3 dosage and feed pH), air-enhanced backwash (AEB) conditions (backwash interval and AEB duration) and chemical cleaning conditions (reagents, soak time and temperature) were evaluated to enhance the feasibility of a commercial ultrafiltration (UF) membrane as a pretreatment of RO seawater desalination. A tubular commercial ceramic UF membrane with a surface layer of zirconium dioxide (ZrO2) and a supporting layer of α-alumina oxide (α-Al2O3) was employed in this study. The results showed that ferric coagulation was functional to enhance the performance of ceramic UF for seawater treatment, especially on COD removal. The trial of cleaning demonstrated that the performance of NaClO was much better than that of HNO3 under various evaluated pH values. The relevant additional experiments showed that the cleaning efficiency increased with NaClO concentration, soak time and soak temperature but decreases when soak temperature was up to 60°C. An important finding of this study is that the fouled membrane from coagulation-filtration trial can be easily and quickly recovered by acid cleaning regents followed by NaClO solution. Furthermore, short backwash interval performed more efficiently. However, it is certain that both backwash interval and AEB duration enhanced less than other approaches on the permeate quality. This study finally summarized the operating condition of each anti-fouling approach for the further potential application of UF ceramic membrane as a pretreatment of RO seawater desalination. [Copyright &y& Elsevier]

Highlights: [•] Melanoidins could be effectively removed from wastewater through SNF. [•] The treatment efficiency of SNF is mainly affected by the TMP and VCF. [•] Steady flux of 3.9L/m2 h could be obtained at TMP of 0.8bar and VCF of 4.0. [•] Color removal of 99.5% and COD reduction of 93.8% could be achieved. [•] SNF is more anti-fouling and easily to be physically cleaned than PNF. [Copyright &y& Elsevier]

• Smooth (R a less than 2 nm) surface of the GQDs-interlayered membrane was achieved. • The 25 nm-thick skin layers of the GQDs-interlayered membranes. • The GQDs-PEI interlayer covalent bonded between substrate and skin layer. • The prepared membrane maintained stable performance in DMF for 45 days at 80 °C. Novel thin film nanocomposite (TFN) organic solvent nanofiltration (OSN) membranes with sandwich-like structure were developed via interfacial polymerization (IP) using both low concentration m-phenylenediamine (MPD) and trimesoyl chloride (TMC), on graphene quantum dots (GQDs)-polyethyleneimine (PEI) modified polyimide substrate surface, and followed by post-IP crosslinking and solvent activation. Such GQDs-interlayered OSN membranes have exhibited a remarkable reduced thickness (about 25 nm) and an ultra-low average surface roughness (less than 2 nm) of their IP skin layers, respectively. Both material features are rarely reported in literature. Meanwhile, our GQDs-interlayered OSN membranes have shown an increased Rhodamine B (479 Da) rejection (from 87.4% to 98.7%) and an increased ethanol permeance (from 33.5 to 40.3 L m−2 h−1 MPa−1) compared with the pristine OSN membrane. Superior solvent resistance was demonstrated after long immersion in pure N , N -dimethylformamide (DMF) at room temperature for 81 days, and at 80 °C for 45 days, and after a long-term consecutively filtration with Rose Bengal (1017 Da) DMF solution at 25 °C for 5 days, without scarifying solute rejection. Antifouling properties during the long-term filtration were also indicated. This paper presents a novel GQDs-interlayered strategy in developing high-performance TFN membranes for OSN application. [ABSTRACT FROM AUTHOR]