Hydrophobic Polyethersulfone Membrane Research Articles

Nanofiltration fouling behaviors with different membrane materials induced by residual natural organics left over after ultrafiltration unit encountered with divalent cations

It is of practical significance to explore the fouling mechanism of nanofiltration membrane caused by residual natural organics left over after ultrafiltration unit. This paper systematically investigates nanofiltration membrane fouling behaviors induced by preserved humic acid components after ultrafiltration filtration (PHACUF) in the existence of Mg2+/Ca2+ ion from micro- and macro-level analyses. Those similarities and disparities in the roles of polyethersulfone or polyamide active layer to these issues were also studied comparatively. The results showed that there existed unneglectable standard blocking for polyethersulfone membrane when permeating bare PHACUF solution. However, with the addition of divalent cations, the main fouling mechanism changed to intermediate blocking. Fewer Mg2+ ions could fully link with the carboxylic groups of PHACUF molecules, leading to larger and more dense flocs by the “bridging” effect and the aggravated nanofiltration membrane fouling with more compact layer structure, especially for more hydrophobic polyethersulfone membrane. It could be inferred that in Mg2+/Ca2+ environment, actually, PHACUF-caused nanofiltration membrane fouling was mainly formed and constituted by hydrophobic acids and neutral fractions with much higher both hydrophobicity and content percentage, whether for the membrane-foulant interaction in the early stage or the foulant-foulant interaction in subsequent permeation stage.

Interfacial coordination mediated surface segregation of halloysite nanotubes to construct a high-flux antifouling membrane for oil-water emulsion separation

Forced surface segregation of hydrophilic nanoparticles on the hydrophobic polymer matrix is considered as the effective strategy to fabricate high performance hybrid membrane for oil/water separation. In this work, the halloysite nanotubes (HNTs) were successively modified with dopamine (PDA) and tannic acid (TA) coatings to obtain the hydrophilic nanoparticles (NPs) of HNTs-DA-TA. Next, the obtained HNTs-DA-TA NPs were blended with polyethersulfone (PES) to prepare the oil/water separation membrane via the phase inversion in the coagulation bath containing Fe3+. We have found that the interfacial coordination between TA and Fe3+ is able to enhance the surface segregation of hydrophilic HNTs-DA-TA NPs on hydrophobic PES membrane, which not only contributes to the formation of asymmetric porous membrane, but also can prevent the loss of nanotubes during the phase transitions. Thanks to these advantages, the water flux of nanocomposite membranes was significantly increased (up to 682 L m-2 h-1), which was ~3.4 times than that of the pristine PES membrane (199 L m-2 h-1), whereas the rejection was still kept at a high state. After three cycles of separation, the water flux recovery rate can reach up to 91%, which was also much higher than 56% of the pristine PES.

Hydrophobizing polyether sulfone membrane by sol-gel for water desalination using air gap membrane distillation

ABSTRACT The hydrophobic polyether sulfone membranes were prepared by the sol-gel method to be applied in an air gap membrane distillation setup for desalination. The surface modifications were carried out using Trimethylsilyl chloride (TMSCl) and Methyltrimethoxysilane (MTMS) solutions. The membranes were characterized using Attenuated Total Reflection Infrared (ATR-IR) spectroscopy, Scanning Electron Microscopy (SEM), and Optical Contact Angle (OCA) methods. The effects of membrane preparation as well as operating conditions such as temperature difference, salt concentration, feed rotation speed, and cold-side temperature on membrane performance were investigated using central composite design method. It was found that feed temperature has the largest effect among the parameters on the permeation flux. The flow rate and salt rejection of the membrane in the optimum conditions were 4.47 Kg m−2 h−1 and 99.37%, respectively.

Reducing ultrafiltration membrane fouling during potable water reuse using pre-ozonation

Wastewater reclamation has increasingly become popular to secure potable water supply. Low-pressure membrane processes such as microfiltration (MF) and ultrafiltration (UF) play imperative roles as a barrier of macromolecules for such purpose, but are often limited by membrane fouling. Effluent organic matter (EfOM), including biopolymers and particulates, in secondary wastewater effluents have been known to be major foulants in low-pressure membrane processes. Hence, the primary aim of this study was to investigate the effects of pre-ozonation as a pre-treatment for UF on the membrane fouling caused by EfOM in secondary wastewater effluents for hydrophilic regenerated cellulose (RC) and hydrophobic polyethersulfone (PES) UF membranes. It was found that greater fouling reduction was achieved by pre-ozonation for the hydrophilic RC membrane than the hydrophobic PES membrane at increasing ozone doses. In addition, the physicochemical property changes of EfOM, including biopolymer fractions, by pre-ozonation were systemically investigated. The classical pore blocking model and the extended Derjaguin−Landau−Verwey−Overbeek (XDLVO) theories were employed to scrutinize the fouling alleviation mechanism by pre-ozonation. As a result, the overarching mechanisms of fouling reduction were attributed to the following key reasons: (1) Ozone degraded macromolecules such as biopolymers like proteins and polysaccharides into smaller fractions, thereby increasing free energy of cohesion of EfOM and rendering them more hydrophilic and stable; (2) pre-ozonation augmented the interfacial free energy of adhesion between foulants and the RC/PES membranes, leading to the increase of repulsions and/or the decrease of attractions; and (3) pre-ozonation prolonged the transition from pore blocking to cake filtration that was a dominant fouling mechanism, thereby reducing fouling.

Removal of the nonionic surfactant Eumulgin ES from protein solutions by means of adsorption and ultrafiltration

Aqueous micellar two-phase extraction (AMTPE) is a promising technique for large-scale protein purification, however, it is unavoidable that a certain surfactant load will remain in the product stream. Therefore, an industrial application of AMTPE requires efficient and economic ways for the removal of surfactants as a polishing step. In view of this demand, the removal of the nonionic surfactant Eumulgin ES has been investigated by means of fixed bed adsorption and cross-flow ultrafiltration. The critical micelle concentration of an aqueous Eumulgin ES solution is 9.2mg/L with a hydrodynamic diameter of a micelle of approximately 15nm at 22°C. The adsorption of Eumulgin ES to hydrophobic polystyrene beads leads to high loading capacities, but proteins also bind with high affinity to the beads, making the technique of limited use. A better way is to remove the surfactant by means of ultrafiltration through a hydrophobic polyethersulfone membrane. In the course of the filtration process a viscous micelle phase at the membrane forms, by which the flux through the membrane is decreased drastically. While elevated temperatures and salt concentrations decrease the flux and the overall separation performance, the opposite conditions lead to improved surfactant removal efficiencies. Cross-flow ultrafiltration is finally applied for the separation of Eumulgin ES from a proteinaceous solution originating from a technical-scale AMTPE investigation. The filtration results in a total surfactant removal of >98.8% from the target protein solution within 8 exchanged volumes.

Investigating the relationship between model organic compounds and ultrafiltration membrane fouling

The aims of this study were to investigate the fouling mechanisms of model organic compounds (MOCs) on two ultrafiltration membranes [composite regenerated cellulose (YM100) and polyethersulfone (PES)] and the relationship between fouling and membrane characteristics, flux decline, and the streaming potential (SP). Two alginic acids (polymer and dimmer, AA), abietic acid (AbA), colominic acid (CA), and N-acetylneuraminic acid (NA) were selected as MOCs to test their membrane fouling potential through flux decline and SP. The fouling caused by the two AAs, which contained many polysaccharides, was the highest among MOCs, but this fouling was external (solute deposition on the membrane surface) and reversible as polysaccharides did not strongly adsorb onto the YM100 and PES membranes. CA also caused external fouling of the two membranes; however, AbA caused internal (solute adsorption on the pores wall of membrane) and irreversible fouling of the PES membrane. NA, which contained amino sugars, exhibited very low fouling of both membranes. The hydrophilic YM100 membrane experienced less fouling than the hydrophobic PES membrane with all MOCs. The measurement of the SP using a modified dead-end filtration cell was employed to evaluate the flux decline due to MOCs.

A Parametric Study on Protein‐Membrane‐Ionic Environment Interactions for Membrane Fouling

This work reports on protein‐membrane‐ionic environment interactions on the basis of chemical and electrochemical features of ultrafiltration membranes and the protein in the solution that affects the extent of protein adsorption onto the membrane, which is a measure of membrane‐fouling. Bovine serum albumin (BSA) was chosen as the model protein; and 10 kDa of hydrophobic polyethersulfone (PES) and hydrophilic cellulose triacetate (CTA) ultrafiltration membranes at the solution pH values of 3.78, 4.78, and 6.80, and ionic‐strengths of 0.01 M and 0.1 M were employed. Isotherms for BSA adsorption on both types of membranes were correlated by the Freundlich equation. More BSA was adsorbed on hydrophobic PES membranes than was adsorbed on hydrophilic CTA membranes. The highest degree of adsorption on PES membranes was obtained at pH=3.78 whereas the minimum adsorption occurred at the isoelectric point (IEP) (pH=4.78) of BSA. With increasing ionic strength, the adsorbed protein on both membranes decreased. The zeta‐potentials of the membranes and protein were determined by streaming potential measurements and theoretical calculations, respectively; and the electrostatic interactions and van der Waals energies between the membranes and the protein were calculated using the Deryagin‐Landau/Verivey‐Overbeek (DVLO) theory. To detect the structural changes that occurred, membrane surfaces were analyzed by Fourier transform infrared‐attenuated total reflectance (FTIR‐ATR) measurements, and scanning electron microscopy (SEM) and atomic force microscope (AFM) images.