Search

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]

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]

[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]