Search

The hybrid membrane bioreactor - nanofiltration treatment process can be an effective approach for treating the landfill leachate, but the residual leachate concentrate highly loaded with the humic substance and salts remains an environmental concern. Herein, a loose nanofiltration membrane (molecular weight cut-off of 860 Da) was used to recover the humic substance, which can act as a key component of organic fertilizer, from the leachate concentrate. The loose nanofiltration membrane showed the high permeation fluxes and high transmissions (>94.7%) for most inorganic ions (i.e., Na+, K+, Cl−, and NO 3 −), while retaining 95.7 ± 0.3% of the humic substance, demonstrating its great potential in effective fractionation of humic substance from inorganic salts in the leachate concentrate. The operation conditions, i.e., cross-flow rates and temperatures, had more pronounced impacts on the filtration performance of the loose nanofiltration membrane. Increasing cross-flow rates from 60 to 260 L h−1 resulted in an improvement of ca. 7.3% in the humic substance rejection, mainly due to the reduced concentration polarization effect. In contrast, the solute rejection of the nanofiltration membrane was negatively dependent on the temperature. The rejection of humic substance decreased from 96.3 ± 0.3% to 92.0 ± 0.4% with increasing the temperature from 23 to 35 °C, likely due to the enlargement of the membrane pore size and enhancement in solute diffusivity. The humic substance was enriched from 1735 to 15,287 mg L−1, yielding a 91.2% recovery ratio with 85.7% desalination efficiency at a concentration factor of 9.6. The recovered HS had significantly stimulated the seed germination and growth of the green mungbean plants with no obvious phytotoxicity. These results demonstrate that loose nanofiltration can be an effective promising technology to recover the humic substance as a valuable fertilizer component towards sustainable management of the landfill leachate concentrate. Image 1 • Loose nanofiltration (NF) membrane was used for sustainable treatment of leachate concentrate. • Loose NF can effectively separate humic substance (HS) and salts in leachate concentrate. • NF concentration process can significantly enrich and harvest HS with 85.7% salt removal. • The recovered HS stimulated the plant growth, presenting a potential as water-soluble fertilizer. [ABSTRACT FROM AUTHOR]

Abstract Developing a highly efficient, cost-effective, easily scalable and sustainable cathode for oxygen reduction reaction (ORR) is a crucial challenge in terms of future "green" energy conversion technologies, e.g., microbial fuel cells (MFCs). In this study, a natural and widely available lotus leaf with intrinsically hierarchical structure was employed to serve as the single precursor to prepare the catalyst applied as the MFC cathode. The hierarchically particle-coated bio‑carbon was self-constructed from the lotus leaf, which yielded a large specific surface area, highly porous structure and superhydrophobicity via facile pyrolysis coupling hydrothermal activation by ZnCl 2 /(NH 4) 2 SO 4. Electrochemical evaluation demonstrated that these natural leaf-derived carbons have an efficient ORR activity. Specifically, the HC-900 catalyst with hydrothermal activation achieved an onset potential of −0.015 V vs. Ag/AgCl, which was comparable to the commercial Pt/C catalyst (−0.010 V vs. Ag/AgCl) and was more efficient than the DC-900 catalyst through direct pyrolysis. Furthermore, the HC-900 catalyst achieved an outstanding ORR activity via a one-step and four-electron pathway, exhibiting a potential alternative to Pt/C as electrocatalyst in ORR, due to its better long-term durability and methanol resistance. Additionally, the HC-900 catalyst was applied as an effective electrocatalytic cathode in an MFC system with a maximum power density of 511.5 ± 25.6 mW⋅m−2, exhibiting a superior energy harvesting capacity to the Pt/C cathode. Graphical abstract Unlabelled Image Highlights • Lotus leaf-based carbon (HC-900) with hierarchical micro/nanostructure was obtained. • HC-900 has a highly porous structure and super-hydrophobic property. • HC-900 has an efficient and stable ORR activity, outperforming 20 wt% Pt/C catalyst. • HC-900 can be used as effective cathode catalyst for microbial energy harvesting. [ABSTRACT FROM AUTHOR]

[Display omitted] • Downstream waste-to-hydrogen process can be realised with 2D material-based membrane. • Mechanism and fabrication methods of 2D material-based gas separation membrane are outlined. • 2D COFs, MOFs and carbon-based materials are reviewed for H 2 /CO 2 gas separation membranes. • Challenges and future prospect of 2D material-based membrane in waste-to-hydrogen are discussed. Waste management has become an ever-increasing global issue due to population growth and rapid globalisation. For similar reasons, the greenhouse effect caused by fossil fuel combustion, is leading to chronic climate change issues. A novel approach, the waste-to-hydrogen process, is introduced to address the concern of waste generation and climate change with an additional merit of production of a renewable, higher energy density than fossil fuels and sustainable transportation fuel, hydrogen (H 2) gas. In the downstream H 2 purifying process, membrane separation is one of the appealing options for the waste-to-hydrogen process given its low energy consumption and low operational cost. However, commercial polymeric membranes have hindered membrane separation process due to their low separation performance. By introducing novel two-dimensional materials as substitutes, the limitation of purifying using conventional membranes can potentially be solved. Herein, this article provides a comprehensive review of two-dimensional materials as alternatives to membrane technology for the gas separation of H 2 in waste-to-hydrogen downstream process. Moreover, this review article elaborates and provides some perspectives on the challenges and future potential of the waste-to-hydrogen process and the use of two-dimensional materials in membrane technology. [ABSTRACT FROM AUTHOR]

In the textile industry, high salinity waste streams are a challenge urging for the recovery and purification of dyes and salts (e.g., NaCl), requiring a treatment going beyond the classical filtration by e.g., reverse osmosis to produce pure water. In this work, two commercial loose nanofiltration (NF) membranes (Sepro NF 6 and NF 2A, Ultura) are proposed to fractionate dye/salt aqueous mixtures. It was observed that both NF membranes have a salt rejection <33.3% in solutions with 0.1–40.0 g L −1 of NaCl at 6 bar. Furthermore, both membranes have >99.6% retention of direct dyes (direct red 80, direct red 23, and congo red), even though 40.0 g L −1 NaCl is present, indicating salt addition has no obvious impact on the dye retention. The combination of a low salt rejection and a high dye rejection indicates the feasibility for the reuse of salt from fractionation in forward osmosis and bipolar membrane electrodialysis. Application of diafiltration for an aqueous mixture containing direct red 80 (1000 ppm) and NaCl (~20 g L −1 ) by both membranes demonstrates that above 95% of NaCl is removed from aqueous mixture, and <0.9 g L −1 NaCl remains after the addition of pure water with a volume factor of 4.0 in the feed solution. At the premise of excellent diafiltration performance, concentration as the post-treatment for dye recovery expectedly indicates direct red 80 is concentrated by a factor of 4.0 for both membranes while keeping the salt concentration with a very slight increase. Over 99.9% dye retention in both diafiltration and concentration procedures yields a very high recovery since <0.045% of dye is permeated. These results indicate that loose nanofiltration membranes have potential for dye/salt fractionation. [ABSTRACT FROM AUTHOR]

Effective fractionation of dyes and salts (NaCl) potentially paves a new path to sustainable treatment of textile wastewater. Herein, a loose nanofiltration (NF) membrane was innovatively used as the anion conductive membrane in electrodialysis (ED) for dye and salt separation. The NF membrane with a molecular weight cut-off of 678 Da showed a sufficient retention for reactive dyes with small molecular weights (<627 Da) predominantly based on synergistic effect of steric repulsion and Donnan repulsion. Simultaneously, the NF membrane had a considerably fast transport for anions (i.e., Cl−), as its loose surface structure created extra nano-channels for ion transfer. The anion conductive loose NF membrane based ED process yielded excellent separation performance in a one-step dye/NaCl fractionation. Specifically, a 98.9% desalination efficiency was obtained by the loose NF-based ED process along with 99.4% dye recovery. Additionally, an extremely low fouling propensity was observed during a 5-cycle ED operation, as the negative surface charge of the loose NF membrane served as an intrinsic barrier to prevent the dye species from entering the membrane pores through electrostatic repulsion. This study demonstrated a desirable potential of loose NF membranes as anion conductive membranes in ED for resource recovery from highly-saline wastewater. Image 1 1. Loose nanofiltration (NF)-based electrodialysis (ED) was used for dye/salt separation 2. Loose NF membrane shows an excellent ion transport as anion conductive membrane 3. Loose NF-based ED yields 98.9% desalination efficiency and 99.4% dye recovery 4. Low fouling propensity is observed for loose NF membrane as anion conductive membrane [ABSTRACT FROM AUTHOR]

Limited information is available on the bioaccessible fraction of trace metals in the resuspended fraction of settled bus dust in order to estimate bus drivers ' occupational exposure. In this study, 45 resuspended fraction of settled dust samples were collected from gasoline and compressed natural gas (CNG) powered buses and analyzed for trace metals and their fraction concentrations using a three-step sequential extraction procedure. Experimental results showed that zinc (Zn) had the greatest bioaccessible fraction, recorded as an average of 608.53 mg/kg, followed in order of decreasing concentration by 129.80 mg/kg lead (Pb), 56.77 mg/kg copper (Cu), 34.03 mg/kg chromium (Cr), 22.05 mg/kg nickel (Ni), 13.17 mg/kg arsenic (As) and 2.77 mg/kg cadmium (Cd). Among the three settled bus dust exposure pathways, ingestion was the main route. Total exposure hazard index (HIt) for non-carcinogenic effect trace metals was lower than the safety level of 1. The incremental lifetime cancer risk (ILCR) for drivers was estimated for trace metal exposure. Pb and Ni presented relatively high potential risks in the non-carcinogenic and potentially carcinogenic health assessment for all drivers. ILCR was in the range of 1.84E − 05 to 7.37E − 05 and 1.74E − 05 to 6.95E − 05 for gasoline and CNG buses, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A promising and sustainable renewable source of phosphate was obtained through crystallization of calcium phosphate from wastewater. The aim of the present study was to evaluate the feasibility of an integrated selectrodialysis/crystallization process to recover phosphate, in which selectrodialysis was first used to pre-concentrate the phosphate before crystallization in a pellet reactor. The results of selectrodialysis show that an increase in current density, initial pH of the product, and initial feed concentration of phosphate led to an increase in phosphate concentration in the product. The desalination efficiency from wastewater was 87%, the phosphate concentration in the product can reach 16 mM with a purity of 44%, the current efficiency to transport phosphate and chloride was 26.6% for standard anion exchange membrane and 63% for monovalent selective anion exchange membrane. The optimal operational conditions for phosphate recovery with a pellet reactor were examined by changing the initial concentration, the pH and the superficial velocity. A precipitation efficiency of 82.7% of phosphate was achieved at pH 11, an inlet concentration of phosphates of 2.5 mM, a Ca/P molar ratio of 1.5 and a superficial velocity of 61 m/h. From the results, it can be concluded that the pellet reactor combined with selectrodialysis is an appropriate method to recover phosphate from wastewater as calcium phosphate, which is not only technically but also environmentally feasible, reducing water pollution, preventing eutrophication and yielding valuable and sustainable resources. [Copyright &y& Elsevier]

• Metal-organic coordination complex coating effectively tailors surface property of nanofiltration membrane. • The nanofiltration membrane yields a molecular weight cutoff of 297 Da after 15-s coating. • The coated nanofiltration membrane shows impressive fractionation of humic substances and salts. • Nanofiltration-diafiltration can enrich and purify humic substances from landfill leachate concentrate. Sustainable treatment of the highly saline landfill leachate concentrate for application as green fertilizer calls for effective fractionation of the existing humic substances and inorganic salts; advanced selective nanofiltration membranes are proposed for this. One-step, rapid assembly of a tannic acid-Fe3+ coordination complex is a promising strategy to endow the membranes with an enhanced nanofiltration performance. In this study, a robust and homogeneous tannic acid-Fe3+ coordination complex layer was effectively coated onto the surface of a loose nanofiltration substrate in an extremely short time (15 s). After the coating of the tannic acid-Fe3+ coordination complex layer, the nanofiltration membrane showed a significantly reduced molecule weight cutoff (i.e., reduction from 601 to 279 Da) and thus enhanced selectivity towards humic substances. Specifically, the rejection to humic substances of the coated nanofiltration membrane increased from 95.31±0.54% to 99.32±0.18% with negligible rise in salt rejection, demonstrating an enhanced fractionation efficacy for humic substances and salts. Assisted by a diafiltration operation with the coated nanofiltration membrane, humic substances in the landfill leachate concentrate were effectively purified and extracted with 96.60% recovery. Particularly, the humic substances were linearly enriched by ca. 7.8 folds (i.e., from 1837 to 13970 mg·L−1) with a purity of 98.91% for potential application as liquid fertilizer. The one-step rapid tannic acid-Fe3+ coordination complex coating exhibits an impressive efficacy to engineer advanced nanofiltration membranes that could be applied at a large scale for sustainable resource extraction from landfill leachate concentrate. [Display omitted] [ABSTRACT FROM AUTHOR]

• Superhydrophobic PVDF membrane was fabricated by spray-coating of fluorinated SiO 2 NPs. • Superhydrophobic PVDF membrane had a water contact angle of 171.8 ± 1.1° and sliding angle of 1.69 ± 0.13°. • The modified PVDF membrane maintained stable superhydrophobicity under harsh conditions. • The prepared membrane has consistent separation efficiencies up to 99.88 ± 0.03% in water-in-oil emulsions over 40 cycles. • Scale-up fabrication of superhydrophobic PVDF membrane was successfully performed. Hydrophobic anti-wetting membranes have many applications, such as oily wastewater treatment via oil/water separation, desalination via membrane distillation, and carbon capture via gas-liquid membrane contactors. Herein, we used a simple and scalable method to fabricate robust superhydrophobic polyvinylidene fluoride (PVDF) based membranes by one-step spray-coating of fluorinated SiO 2 nanoparticles. The prepared PVDF membrane was systematically characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and contact angle measurements. The modified PVDF membrane had excellent superhydrophobicity with an extremely high water contact angle up to 171.8 ± 1.1° and a low sliding angle of 1.69 ± 0.13°, due to the fluorinated close-packed hydrophobic SiO 2 nanoparticles on the surface. The modified PVDF membrane maintained its relatively stable superhydrophobicity under various harsh conditions, i.e., exposure in hot water, NaOH and HCl, ultrasonication and high-speed flushing, indicating the superior robustness and stability. The prepared membrane also exhibited consistent separation efficiencies up to 99.88 ± 0.03% in water-in-oil emulsions, and superior recyclability and durability over 40 cycles. In addition, spray-coating showed its great promise in engineering various superhydrophobic surfaces on different substrates and excellent scalability in fabricating large-size membranes. This study demonstrates a facilely scalable spray-coating method for engineering robust superhydrophobic surfaces and membranes that can be potentially used for various gas, vapor and water/oil separations. [ABSTRACT FROM AUTHOR]