Effects of Filtration Mode on the Performance of Gravity-Driven Membrane (GDM) Filtration: Cross-Flow Filtration and Dead-End Filtration

Gravity-driven membrane (GDM) filtration technology has been extensively in the employed drinking water treatment, however, the effect filtration mode (i.e., dead-end mode vs. cross-flow mode) on its long-term performance has not been systematically investigated. In this study, pilot-scale GDM systems were operated using two submerged filtration mode (SGDM) and cross-flow mode (CGDM) at the gravity-driven pressures 120 mbar and 200 mbar, respectively. The results showed that flux stabilization was observed both in the SGDM and CGDM during long-term filtration, and importantly the stabilized flux level of CGDM was elevated by 3.5–67.5%, which indicated that the filtration mode would not influence the occurrence of flux stability, but significantly improve the stable flux level. Interestingly, the stable flux level was not significantly improved with the increase of driven pressure, and the optimized driven pressure was 120 mbar. In addition, the GDM process conferred effective removals of turbidity, UV254, CODMn, and DOC, with average removals of 99%, 43%, 41%, and 20%, respectively. With the assistance of cross flow to avert the overaccumulation of contaminants on the membrane surface, CGDM process exhibited even higher removal efficiency than SGDM process. Furthermore, it can be found that the CGDM system can effectively remove the fluorescent protein-like substances, and the intensities of tryptophans substance and soluble microbial products were reduced by 64.61% and 55.08%, respectively, higher than that of the SGDM. Therefore, it can be determined that the filtration mode played an important role in the flux stabilization of GDM system during long-term filtration, and the cross-flow filtration mode can simultaneously improve the stabilized flux level and removal performance.

Real time imaging of single extracellular vesicle pH regulation in a microfluidic cross-flow filtration platform

Extracellular vesicles (EVs) are cell-derived membranous structures carrying transmembrane proteins and luminal cargo. Their complex cargo requires pH stability in EVs while traversing diverse body fluids. We used a filtration-based platform to capture and stabilize EVs based on their size and studied their pH regulation at the single EV level. Dead-end filtration facilitated EV capture in the pores of an ultrathin (100 nm thick) and nanoporous silicon nitride (NPN) membrane within a custom microfluidic device. Immobilized EVs were rapidly exposed to test solution changes driven across the backside of the membrane using tangential flow without exposing the EVs to fluid shear forces. The epithelial sodium-hydrogen exchanger, NHE1, is a ubiquitous plasma membrane protein tasked with the maintenance of cytoplasmic pH at neutrality. We show that NHE1 identified on the membrane of EVs is functional in the maintenance of pH neutrality within single vesicles. This is the first mechanistic description of EV function on the single vesicle level.

Stability of Polymeric Membranes to UV Exposure before and after Coating with TiO2 Nanoparticles

The combination of photocatalysis and membrane filtration in a single reactor has been proposed, since the photocatalytic treatment may degrade the pollutants retained by the membrane and reduce fouling. However, polymeric membranes can be susceptible to degradation by UV radiation and free radicals. In the present study, five commercial polymeric membranes were exposed to ultraviolet (UV) radiation before and after applying a sol–gel coating with TiO2 nanoparticles. Membrane stability was characterized by changes in hydrophilicity as well as analysis of soluble substances and nanoparticles detached into the aqueous medium, and by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and energy-dispersive X-ray spectrometry (EDS) for structural, morphological, and elemental distribution analysis, respectively. The TiO2 coating conferred photocatalytic properties to the membranes and protected them during 6 h of UV radiation exposures, reducing or eliminating chemical and morphological changes, and in some cases, improving their mechanical resistance. A selected commercial nanofiltration membrane was coated with TiO2 and used in a hybrid reactor with a low-pressure UV lamp, promoting photocatalysis coupled with cross-flow filtration in order to remove 17α-ethinylestradiol spiked into an aqueous matrix, achieving an efficiency close to 100% after 180 min of combined filtration and photocatalysis, and almost 80% after 90 min.

Optimization of a High-Performance Poly(diallyl dimethylammonium chloride)-alumina-perfluorooctanoate Intercalated Ultrafiltration Membrane for Treating Emulsified Oily Wastewater via Response Surface Methodology Approach

This research aimed to investigate the ultrafiltration of water from emulsified oily wastewater through the application of surface-functionalized ceramic membrane to enhance its water permeability based on optimized parameters using a cross-flow filtration system. The interactive effects of feed concentration (10–1000 ppm), pH (4–10), and pressure (0–3 bar) on the water flux and oil rejection were investigated. Central composite design (CCD) from response surface methodology (RSM) was employed for statistical analysis, modeling, and optimization of operating conditions. The analysis of variance (ANOVA) results showed that the oil rejection and water flux models were significant with p-values of 0.0001 and 0.0075, respectively. In addition, good correlation coefficients of 0.997 and 0.863 were obtained for the oil rejection and water flux models, respectively. The optimum conditions for pressure, pH, and feed concentration were found to be 1.5 bar, pH 8.97, and 10 ppm, respectively with water flux and oil rejection maintained at 152 L/m2·h and 98.72%, respectively. Hence, the functionalized ultrafiltration ceramic membrane enables the separation efficiency of the emulsified oil in water to be achieved.

Superparamagnetic Fe3O4@CA Nanoparticles and Their Potential as Draw Solution Agents in Forward Osmosis

In this study, citric acid (CA)-coated magnetite Fe3O4 magnetic nanoparticles (Fe3O4@CA MNPs) for use as draw solution (DS) agents in forward osmosis (FO) were synthesized by co-precipitation and characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), dynamic light scattering (DLS), transmission electron microscopy (TEM) and magnetic measurements. Prepared 3.7% w/w colloidal solutions of Fe3O4@CA MNPs exhibited an osmotic pressure of 18.7 bar after purification without aggregation and a sufficient magnetization of 44 emu/g to allow DS regeneration by an external magnetic field. Fe3O4@CA suspensions were used as DS in FO cross-flow filtration with deionized (DI) water as FS and with the active layer of the FO membrane facing the FS and NaCl as a reference DS. The same transmembrane bulk osmotic pressure resulted in different water fluxes for NaCl and MNPs, respectively. Thus the initial water flux with Fe3O4@CA was 9.2 LMH whereas for 0.45 M NaCl as DS it was 14.1 LMH. The reverse solute flux was 0.08 GMH for Fe3O4@CA and 2.5 GMH for NaCl. These differences are ascribed to a more pronounced internal dilutive concentration polarization with Fe3O4@CA as DS compared to NaCl as DS. This research demonstrated that the proposed Fe3O4@CA can be used as a potential low reverse solute flux DS for FO processes.

Tunable membranes incorporating artificial water channels for high-performance brackish/low-salinity water reverse osmosis desalination

Membrane-based technologies have a tremendous role in water purification and desalination. Inspired by biological proteins, artificial water channels (AWCs) have been proposed to overcome the permeability/selectivity trade-off of desalination processes. Promising strategies exploiting the AWC with angstrom-scale selectivity have revealed their impressive performances when embedded in bilayer membranes. Herein, we demonstrate that self-assembled imidazole-quartet (I-quartet) AWCs are macroscopically incorporated within industrially relevant reverse osmosis membranes. In particular, we explore the best combination between I-quartet AWC and m-phenylenediamine (MPD) monomer to achieve a seamless incorporation of AWC in a defect-free polyamide membrane. The performance of the membranes is evaluated by cross-flow filtration under real reverse osmosis conditions (15 to 20 bar of applied pressure) by filtration of brackish feed streams. The optimized bioinspired membranes achieve an unprecedented improvement, resulting in more than twice (up to 6.9 L⋅m−2⋅h−1⋅bar−1) water permeance of analogous commercial membranes, while maintaining excellent NaCl rejection (>99.5%). They show also excellent performance in the purification of low-salinity water under low-pressure conditions (6 bar of applied pressure) with fluxes up to 35 L⋅m−2⋅h−1 and 97.5 to 99.3% observed rejection.

An Investigation Into The Fouling Phenomena Of Polycarbonate Membranes Used In The Treatment Of Latex Paint Wastewater

The treatment of latex paint wastewater with ultrafiltration allows for the reuse of the filtrate as process water or for cleaning purposes, as well as the potential for reclamation of the valuable paint solids. In this study, the utilization of polycarbonate membranes for the ultrafiltration of dilute latex dispersions was evaluated. Hydrophilic, flat sheet ultrafiltration membranes with a mean pore size of 0.1 μm were used. All filtration experiments were conducted under constant pressure operation, in a circular, centre-fed, cross-flow filtration cell. The effect of feed flow rate was investigated, and the steady-state permeate flux achieved showed an increase of 294% between 1.0 and 3.0 L/min. Increasing the operating pressure also resulted in an increased permeate flux, with a 320% increase from 1.5 to 5.5 psi. Also considered was the effect of the feed solid concentration on the permeate flux. When compared to the clean water flux (0% solids) of 5.5×10- Surfactant-enhanced ultrafiltration was also studied, with concentrations ranging from 25% to 200% of the literature values of the surfactant's critical micelle concentration (CMC) in pure water. The addition of an anionic surfactant, sodium dodecyl sulphate (SDS), reduced the effectiveness of the filtration. However, the addition of a cationic surfactant, cetyl trimethylammonium bromide (CTAB), increased the permeate flux of the latex dispersion up to 130% when twice its CMC was used, with evidence of a reduction in the effect of fouling of the membranes. This may be due to repelling interactions between the surface of the membrane and the surface of the formed micelles, as well as a reduced cake resistance due to the larger particle size of the constituents forming a less dense cake layer.

An Investigation Into The Fouling Phenomena Of Polycarbonate Membranes Used In The Treatment Of Latex Paint Wastewater

The treatment of latex paint wastewater with ultrafiltration allows for the reuse of the filtrate as process water or for cleaning purposes, as well as the potential for reclamation of the valuable paint solids. In this study, the utilization of polycarbonate membranes for the ultrafiltration of dilute latex dispersions was evaluated. Hydrophilic, flat sheet ultrafiltration membranes with a mean pore size of 0.1 μm were used. All filtration experiments were conducted under constant pressure operation, in a circular, centre-fed, cross-flow filtration cell. The effect of feed flow rate was investigated, and the steady-state permeate flux achieved showed an increase of 294% between 1.0 and 3.0 L/min. Increasing the operating pressure also resulted in an increased permeate flux, with a 320% increase from 1.5 to 5.5 psi. Also considered was the effect of the feed solid concentration on the permeate flux. When compared to the clean water flux (0% solids) of 5.5×10- Surfactant-enhanced ultrafiltration was also studied, with concentrations ranging from 25% to 200% of the literature values of the surfactant's critical micelle concentration (CMC) in pure water. The addition of an anionic surfactant, sodium dodecyl sulphate (SDS), reduced the effectiveness of the filtration. However, the addition of a cationic surfactant, cetyl trimethylammonium bromide (CTAB), increased the permeate flux of the latex dispersion up to 130% when twice its CMC was used, with evidence of a reduction in the effect of fouling of the membranes. This may be due to repelling interactions between the surface of the membrane and the surface of the formed micelles, as well as a reduced cake resistance due to the larger particle size of the constituents forming a less dense cake layer.