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ABSTRACT: Selectivity for monovalent ions is a very important feature of ion exchange membranes in view of a further expansion of the scope of electrodialysis (ED). An efficient one‐step chemical process to graft a thin polyaniline (PANI) layer on the surface and pores of an ultrafiltration (UF) membrane is reported. The existence of a PANI layer on such modified UF membrane was confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy images. These membranes were extensively characterized by studying their properties such as water uptake, ion‐exchange capacity, contact angle, and performance in diffusion dialysis. ED experiments were conducted by comparing desalting of sodium chloride and magnesium chloride solutions. During the desalting procedure, the driving force has two contributions, the electrical field and the salinity‐gradient. Initially, transport of ions by the electrical field is dominant, while at the end of the experiment, diffusion dialysis by the salinity gradient plays a larger role in ion transport. The presence of PANI can hinder Mg2+ transport from the concentrate to the diluate compartment because of the electrostatic effect, while there is no obvious effect on Na+ ions. The ability of such a surface modification layer to improve the membrane selectivity for Na+/Mg2+ was confirmed by means of ED in a mixed solution. The flux of Na+ was slightly increased to 13.21 × 10−8 mol/L/min while the flux of Mg2+ was reduced to 3.32 × 10−8 mol/L/min, so that the permselectivity is almost doubled. The protonation reaction of the PANI layer creates positive charges, thus leading to an electrical repulsion barrier, which may reduce the penetration of divalent cations with respect to monovalent ions. Polyacrylonitrile‐based UF membranes with different molecular cutoff was used to determine the influence of the permselectivity. Results showed that the membrane permselectivity of smaller molecular cutoff UF membranes is higher. It can be concluded that this method is suitable for preparing membranes based on UF membranes for efficient separation of monovalent ions by electro‐driven separation techniques. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45692. [ABSTRACT FROM AUTHOR]

Nanofiltration (NF) membranes have been used previously for the recovery of dyes, salts, and water from textile wastewaters with high salinity. However, commercially available NF membranes have a high rejection for divalent salts (i.e., Na 2 SO 4 ), substantially reducing the salt recovery and membrane flux when treating textile wastewater containing Na 2 SO 4 . In this study, a tight ultrafiltration membrane (UH004, Microdyn-Nadir) was proposed to fractionate the dye and Na 2 SO 4 in the textile wastewater. The UH004 membrane with a molecular weight cutoff of 4700 Da provided complete passage of monovalent salts, with little rejection of Na 2 SO 4 . This significantly increases the filtrate flux that can be achieved with high-salinity wastewater since osmotic pressure and concentration polarization effects are minimized. Furthermore, the retention behavior of four different dyes was evaluated to determine the efficiency of this membrane process. This tight ultrafiltration membrane offered the high retention for direct dyes (i.e., direct red 80, direct red 23, and Congo red) and reactive blue 2. For instance, the UH004 membrane yielded >98.9% rejection for all of the dyes at a pressure of 4 bar even in the presence of 60 g L −1 Na 2 SO 4 . Subsequently, an ultrafiltration-diafiltration process was designed to separate a dye/Na 2 SO 4 aqueous mixture with 98% desalination efficiency and greater than 97% dye recovery after 5 diavolumes. These results clearly demonstrate that tight ultrafiltration membranes can be a stand-alone alternative to NF membranes for the effective fractionation of dye and Na 2 SO 4 in the direct treatment of high-salinity textile wastewater. [ABSTRACT FROM AUTHOR]

High-salinity textile wastewater is a pressing environmental concern, urgently requiring the appropriate treatment. Sustainable management of high-salinity textile wastewater via fractionation of the existing dyes and inorganic salts (NaCl) using selective separation membranes is a key approach to address this detrimental concern. Herein, tight composite ultrafiltration membranes with impressive antibacterial function were constructed using one-step co-deposition of dopamine and tobramycin on the porous substrate to fractionate the dyes and NaCl. Triggered by ammonia persulfate, the polydopamine/tobramycin coating layer imparts the fabricated composite ultrafiltration membranes with tight surface structure and narrow pore size distribution, enabling effective dyes/salts fractionation. Specifically, the tight composite ultrafiltration membrane with a molecular weight cutoff of 3692 Da experienced a > 98.0 % rejection against various reactive dyes (molecular weight: <1000 Da) with nearly complete salt transmission (<0.8 % NaCl rejection), demonstrating an effective fractionation of dyes and salts. Additionally, the incorporated tobramycin as a broad-spectrum antibiotic endowed the tight composite ultrafiltration membrane with a sufficient inhibition efficiency (i.e., 100 %) against E. coli bacteria in a short-time contact (i.e., 3 min). Thereby, the tight composite ultrafiltration membrane constructed by fast co-deposition of dopamine and tobramycin established an unparalleled platform technology for sustainable resource recovery (dyes or salts) from high-salinity textile wastewater. [Display omitted] • Tight ultrafiltration (UF) membrane with 3692 Da MWCO was designed by rapid co-deposition of dopamine and tobramycin. • Tight UF membrane had an impressive rejection of >98.0 % for various reactive dyes with >99.2 % NaCl transmission. • Tight UF membrane showed a robust stability in fractionation of dyes and salts. • Tight UF membrane yielded a 100 % inhibition efficiency against E. coli for mitigating the biofouling. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Precipitation process of gypsum in the presence of FA and Mg2+ was investigated. • The pH had significant effect on gypsum precipitation in the presence of FA and Mg2+. • The optimal temperature and pH were found to be 70 °C and around 2.5. • H-bonds and hydrophobic effect were predominant interactions at around pH 2.5. • Gypsum formation in the presence of FA and Mg2+ corresponded with 1st-order kinetics. Abstract The present work focused on the reduction of the calcium and sulfate ions in a membrane permeate generated from a newly developed two-stage of tight ultrafiltration (TUF) for recovering humic substance from leachate nanofiltration (NF) concentrate by a precipitation process of calcium sulfate dihydrate (gypsum). The operating parameters (temperature and pH), mechanism of precipitating behaviors, and kinetics of this process in the presence of fulvic acid (FA) and magnesium ion simultaneously were investigated. It was found that Ca2+ removal increased with increasing temperature. The decline in pH, especially towards low pH range of 2–3 around the point of zero charge of gypsum, showed a significant effect on gypsum precipitation. Adsorption of FA onto gypsum surface had an important effect on the precipitating behavior of gypsum whose mechanism might be mainly weak interactions of hydrogen bonding and hydrophobic effect at low pH, while electrostatic interactions became dominant at neutral pH. In contrast, retardation effect of Mg2+ ion on gypsum precipitation was negligible at pH 2.5. The soluble calcium removal during precipitation process corresponded with first order rate equation. The results indicated that the optimal operating parameters were found at 70 °C and around pH 2.5, which can be applied to the scale-up and industrial design of the precipitation process of gypsum for removing the calcium and sulfate ions in the presence of FA and magnesium ion. [ABSTRACT FROM AUTHOR]

Membrane bioreactor (MBR) and nanofiltration (NF) hybrid process has dominated in the treatment of leachate, however, NF concentrate generated from the process remains a challenge to be addressed. Given the high content of humic substances (HS) in NF concentrate, a promising approach by using a two-stage tight ultrafiltration (TUF) process for recovering HS as a water-soluble fertilizer was proposed. The effect of operating factors on membrane flux and rejection of organic matters, and the concentration and desalination performance of this TUF process were investigated on pilot scale. The pressure and temperature posed significant influence on the flux, while slight impact on the rejection of organics, and pH had negligible effect on the flux and the retention of organics. During the concentration and desalting process, the chemical oxygen demand (COD) retention increased slightly from 91% to 94%, and the rejections of divalent and monovalent ions had the respective range of 21–62% and 10–26%, except chloride ion with a negative rejection. The results demonstrated that HS dominated in organics could be effectively separated and refined from inorganic salts. The end concentrate achieved with the two-stage TUF process can meet the requirements of Chinese nation professional standards for water-soluble fertilizers containing HS. This study illustrates the feasibility of recycling HS from NF concentrate. [ABSTRACT FROM AUTHOR]

A novel polyvinyl chloride (PVC) membrane was modified with graphene oxide (GO) via phase inversion method to improve its hydrophilicity and mechanical properties. The GO presented a large amount of hydrophilic groups after the modification through the modified Hummers method. It was observed that with the addition of low fraction of GO powder, the GO/PVC hybrid membranes exhibited a significant enhancement in hydrophilicity, water flux, and mechanical properties. With optimal dosage (0.1 wt%), the pure water flux of GO/PVC membrane increased from 232.6 L/(m 2 h bar) to 430.0 L/(m 2 h bar) and the tensile strength increased from 231.3 cN to 305.3 cN. The improved properties of the PVC/GO hybrid membranes are mainly attributed to the strong hydrophilicity of functional groups on the GO surface, indicating that GO has a promising candidate for modification of PVC ultrafiltration membranes in wastewater treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Superhydrophilic g-C 3 N 4 /SiO 2 composite membrane is prepared by vacuum filtration. • The g-C 3 N 4 /SiO 2 composite membrane has effective oil/water separation performance. • Incorporation of g-C 3 N 4 endows the composite membrane with photocatalytic self-cleaning property. • g-C 3 N 4 /SiO 2 composite membrane effectively retains and inactivates the bacteria. Conventional membrane processes, e.g., microfiltration and ultrafiltration, suffer from severe permeation flux decline and fouling during the oily wastewater treatment. The superhydrophilic surface decoration provides an important and effective strategy to address this challenge. Herein, a surperhydrophilic/underwater superoleophobic nanocomposite surface with the photocatalytic properties was constructed via one-step facile vacuum-assisted filtration of a g-C 3 N 4 nanosheet/SiO 2 nanoparticle dispersion onto a microfiltration membrane substrate. Specifically, with the intercalation of 20 mg∙L−1 SiO 2 nanoparticles into the g-C 3 N 4 nanosheets, the g-C 3 N 4 /SiO 2 composite membrane showed the superhydrophilic/underwater superoleophobic properties with an underwater oil contact angle of 170.0 ± 0.3°. Such a g-C 3 N 4 /SiO 2 composite membrane yielded a permeation flux of >1290 LMH·bar−1 with an oil rejection of >99.91% during the vacuum filtration of oil-in-water emulsions. The g-C 3 N 4 /SiO 2 composite membrane significantly outperformed the pristine microfiltration substrate that had severe fouling caused by oil blockage. Additionally, the g-C 3 N 4 /SiO 2 composite membrane not only effectively retained the E. coli bacteria through size exclusion effect, but also promoted the inactivation of bacteria via visible-light photocatalysis. Therefore, our membrane has a great promise in practical oily wastewater treatment due to its excellent separation performance and biofouling resistance. [ABSTRACT FROM AUTHOR]

• Tight UF membrane with 1700 Da MWCO was designed by rapid co-deposition of PDA/PEI triggered by APS. • Tight UF membrane had an impressive rejection of >98.2% for 6 reactive dyes with >97.0% salt permeation. • Integrated UF-diafiltration enriched reactive blue 4 from 2.04 to 50.70 g·L−1 with 0.9% dye loss. • 99.95% salt removal was obtained by integrated UF-diafiltration with 8 diavolumes. • Tight UF membrane yielded a 90.6% flux recovery by water rinsing, showing a low fouling propensity. Mussel-inspired polydopamine (PDA) coating has received increasing interest in membrane modification for versatile liquid filtration applications, due to its intrinsic adhesion nature. Nevertheless, the bio-inspired PDA deposition initiated by air-oxidation is time-consuming process and generally results in an uneven and unstable coating, which compromises the membrane filtration performance. In this study, the PDA/polyethylenimine (PEI) co-deposition triggered by ammonium persulfate (APS) was conducted to fabricate the tight ultrafiltration (t-UF) membranes with 1000–5000 Da molecular weight cut-offs (MWCOs) for sustainable treatment of highly-saline textile wastewater. APS with strong oxidation capacity can rapidly induce the co-deposition of PDA/PEI layer onto hydrolyzed polyacrylonitrile (HPAN) substrate through the Michael addition or Schiff base reactions, simultaneously minimizing the covalent polymerization of dopamine for PDA aggregation. With 1.5-h coating, a smooth, compact and defect-free PDA/PEI layer with 1700 Da MWCO was evolved on the HPAN substrate, evincing a >98.2% retention for various reactive dyes (610–1000 Da molecular weights) with >97.0% permeation of inorganic salts. In addition, an integrated UF-diafiltration procedure was applied to fractionate the reactive blue 4 (RB4)/NaCl and RB4/Na 2 SO 4 mixtures, enriching the RB4 dye from ca. 2.04 to 50.70 g·L−1 with ca. 99.95% desalination efficiency and ca. 99.2% dye recovery. These results demonstrate that the bio-inspired t-UF membrane through fast PDA/PEI co-deposition is of great promise to sufficiently fractionate the dyes and salts for dye desalination and recovery, realizing the sustainable management of highly-saline textile wastewater. [ABSTRACT FROM AUTHOR]