Effect of aluminum speciation on ultrafiltration membrane fouling by low dose aluminum coagulation with bovine serum albumin (BSA)

Effect of Al2O3 on Nanostructure and Ion Transport Properties of PVA/PEG/SSA Polymer Electrolyte Membrane

Polymer electrolyte membrane (PEM) fuel cells have the potential to reduce our energy consumption, pollutant emissions, and dependence on fossil fuels. To achieve a wide range of commercial PEMs, many efforts have been made to create novel polymer-based materials that can transport protons under anhydrous conditions. In this study, cross-linked poly(vinyl) alcohol (PVA)/poly(ethylene) glycol (PEG) membranes with varying alumina (Al₂O₃) content were synthesized using the solvent solution method. Wide-angle X-ray diffraction (XRD), water uptake, ion exchange capacity (IEC), and proton conductivity were then used to characterize the membranes. XRD results showed that the concentration of Al₂O₃ affected the degree of crystallinity of the membranes, with 0.7 wt.% Al₂O₃ providing the lowest crystallinity. Water uptake was discovered to be dependent not only on the Al₂O₃ group concentration (SSA content) but also on SSA, which influenced the hole volume size in the membranes. The ionic conductivity measurements provided that the samples were increased by SSA to a high value (0.13 S/m) at 0.7 wt.% Al₂O₃. Furthermore, the ionic conductivity of polymers devoid of SSA tended to increase as the Al₂O₃ concentration increased. The positron annihilation lifetimes revealed that as the Al₂O₃ concentration increased, the hole volume content of the polymer without SSA also increased. However, it was densified with SSA for the membrane. According to the findings of the study, PVA/PEG/SSA/0.7 wt.% Al₂O₃ might be employed as a PEM with high proton conductivity for fuel cell applications.

Enhanced membrane fouling control and trace organic compounds removal during microfiltration by coupling coagulation and adsorption in an electric field

Coupling electric field, coagulation, and powdered activated carbon (PAC) adsorption in the microfiltration (MF) process was an effective strategy for membrane fouling alleviation and trace organic compounds (TrOCs) elimination. In the electric field, the surface charges of bovine serum albumin (BSA) molecules and kaolin particles distributed along the direction of the electric field and formed electric dipoles, which lowered electrostatic repulsion between BSA-BSA, BSA-kaolin, and kaolin-kaolin, resulting in enhanced particle aggregation and turbidity reduction. Electrophoretic migration also strengthened the interaction between particles and polyaluminum chloride (PACl). Protein removal showed a significant linear correlation with the transmembrane pressure (TMP), and the slope variation of the fitting curves reflected the role of the electric field in the BSA removal and membrane fouling control. Under the synergistic function of electric field, coagulation, and PAC adsorption, the MF system achieved an 80.7% reduction on membrane fouling, an average BSA removal of 76.4%, and TrOCs elimination of 65.3%-81.7%. Electrochemical oxidation was the main contributor to the TrOCs removal when 2.5 V voltage was applied, and could also prolong the service life of PAC.

Chitosan-Based Nanocomposite Polymeric Membranes for Water Purification-A Review

During the past few years, researchers have focused their attention on developing innovative nanocomposite polymeric membranes with applications in water purification. Natural and synthetic polymers were considered, and it was proven that chitosan-based materials presented important features. This review presents an overview regarding diverse materials used in developing innovative chitosan-based nanocomposite polymeric membranes for water purification. The first part of the review presents a detailed introduction about chitosan, highlighting the fact that is a biocompatible, biodegradable, low-cost, nontoxic biopolymer, having unique structure and interesting properties, and also antibacterial and antioxidant activities, reasons for using it in water treatment applications. To use chitosan-based materials for developing nanocomposite polymeric membranes for wastewater purification applications must enhance their performance by using different materials. In the second part of the review, the performance's features will be presented as a consequence of adding different nanoparticles, also showing the effect that those nanoparticles could bring on other polymeric membranes. Among these features, pollutant's retention and enhancing thermo-mechanical properties will be mentioned. The focus of the third section of the review will illustrate chitosan-based nanocomposite as polymeric membranes for water purification. Over the last few years, researchers have demonstrated that adsorbent nanocomposite polymeric membranes are powerful, important, and potential instruments in separation or removal of pollutants, such as heavy metals, dyes, and other toxic compounds presented in water systems. Lastly, we conclude this review with a summary of the most important applications of chitosan-based nanocomposite polymeric membranes and their perspectives in water purification.

Synergistic fouling behaviors and mechanisms of calcium ions and polyaluminum chloride associated with alginate solution in coagulation-ultrafiltration (UF) process

Effects of calcium ions and polyaluminum chloride (PACl) on membrane fouling in coagulation-ultrafiltration (UF) process were investigated in this study. Filtration tests demonstrated three interesting filtration behaviors: 1) high specific filtration resistance (SFR) of alginate solution with low CaCl₂ or PACl addition (e. g. 3.51×10¹⁵ m·kg ^-1 under the condition of 1.5 mM CaCl₂ addition); 2) unimodal pattern of alginate SFR with PACl or CaCl₂ addition alone; 3) synergistic effects between CaCl₂ and PACl on alginate SFR. It was found that, the foulant morphological changes driven by the thermodynamic mechanisms based on Flory-Huggins lattice theory take the critical roles in these filtration behaviors. Density functional theory (DFT) calculations showed that initial coordination of Ca²⁺ and Al³⁺ ions with alginates tended to form tetrahedron geometry and geometry of coordinating three terminal carboxyl groups, respectively, which facilitated to elongate the alginate chains (without clustering the flocs) and form more stable gel, increasing SFR. Improving Ca²⁺ and Al³⁺ dosages triggered transition to other geometries for clustering polymeric network and flocculation, reducing SFR. Due to the higher binding affinity of Ca²⁺ over Al³⁺, Ca²⁺ and Al³⁺ sequentially take roles of enlarging polymeric network and clustering the coordination compounds, and then facilitate to form large size flocs and reduce SFR, causing the synergistic effects between CaCl₂ and PACl additions. The proposed thermodynamic mechanisms satisfactorily explained these interesting fouling behaviors, allowing to further optimize coagulation-UF process.

The role of transparent exopolymer particles (TEP) in membrane fouling: A critical review

Transparent exopolymer particles (TEP) as gel-like particulate acidic polysaccharide have been commonly found in marine, surface water and wastewater. Currently, increasing interest has been devoted to TEP-associated membrane fouling in different membrane systems for water and wastewater treatment, thus this review attempts to provide a holistic view and critical analysis with regard to the definition, formation, detection and properties of TEP, which could ultimately determine its fouling potential. It appears that there is not a common consensus on the actual role of TEP in membrane fouling development due to the subjective definition and highly debatable detection method of TEP. It was clearly demonstrated in this review that the formation of TEP was largely related to cations in water and wastewater which indeed determined the cross-linking degree of precursor materials (e.g. polysaccharides) via intermolecular interactions, and subsequently the quantity of TEP formed. The binding between cations ions (e.g. monovalent, divalent and trivalent cations) and polysaccharide not only depends on the functional groups of polysaccharide, but also its spatial configuration. These in turn suggest that the formation, property and ultimate fouling potential of TEP would be closely related to the type and concentration of cations, while well explaining the controversial reports on TEP-associated fouling in the literature. In addition, the fouling mechanisms of TEP are also elucidated with details in this review, including (i) the formation of TEP-associated gel layer on membrane surface; (ii) carrying microorganisms to membrane surface via protobiofilm and (iii) trapping of deformable TEP in membrane pores. Consequently, it is apparent that TEP is an ignored determinant of membrane fouling, which has not yet been seriously addressed in the design and operation of membrane systems for water and wastewater treatment.

Effects of protein properties on ultrafiltration membrane fouling performance in water treatment

Protein-like substances always induce severe ultrafiltration (UF) membrane fouling. To systematically understand the effect of proteins, regenerated cellulose UF membrane (commonly used for protein separation) performance was investigated in the presence of bovine serum albumin (BSA) under various water conditions. Results showed that although trypsin enhanced the membrane flux via proteolysis, catalysis took a long time. Membrane fouling was alleviated at high solution pH and low water temperature owing to the strong electrostatic repulsion force among BSA molecules. Both Na⁺ and Ca²⁺ could increase membrane flux. However, Ca²⁺ played a bridging role between adjacent BSA molecules, whereas membrane fouling was alleviated via a hydration repulsion force with Na⁺. The order of influence on membrane fouling was as follows: Ca²⁺ concentration > Na⁺ concentration > pH > temperature > trypsin concentration. Furthermore, a polyvinylidene fluoride UF membrane experiment showed that Ca²⁺ could reduce the fouling induced by BSA. Thus, the differences in UF membrane performance will have application potential for alleviating UF membrane fouling induced by proteins during water treatment.

Progress of Nanocomposite Membranes for Water Treatment

The use of membrane-based technologies has been applied for water treatment applications; however, the limitations of conventional polymeric membranes have led to the addition of inorganic fillers to enhance their performance. In recent years, nanocomposite membranes have greatly attracted the attention of scientists for water treatment applications such as wastewater treatment, water purification, removal of microorganisms, chemical compounds, heavy metals, etc. The incorporation of different nanofillers, such as carbon nanotubes, zinc oxide, graphene oxide, silver and copper nanoparticles, titanium dioxide, 2D materials, and some other novel nano-scale materials into polymeric membranes have provided great advances, e.g., enhancing on hydrophilicity, suppressing the accumulation of pollutants and foulants, enhancing rejection efficiencies and improving mechanical properties and thermal stabilities. Thereby, the aim of this work is to provide up-to-date information related to those novel nanocomposite membranes and their contribution for water treatment applications.

Comparison of the effects of aluminum and iron(III) salts on ultrafiltration membrane biofouling in drinking water treatment

Coagulation plays an important role in alleviating membrane fouling, and a noticeable problem is the development of microorganisms after long-time operation, which gradually secrete extracellular polymeric substances (EPS). To date, few studies have paid attention to the behavior of microorganisms in drinking water treatment with ultrafiltration (UF) membranes. Herein, the membrane biofouling was investigated with different aluminum and iron salts. We found that Al₂(SO₄)₃·18H₂O performed better in reducing membrane fouling due to the slower growth rate of microorganisms. In comparison to Al₂(SO₄)₃·18H₂O, more EPS were induced with Fe₂(SO₄)₃·xH₂O, both in the membrane tank and the sludge on the cake layer. We also found that bacteria were the major microorganisms, of which the concentration was much higher than those of fungi and archaea. Further analyses showed that Proteobacteria was dominant in bacterial communities, which caused severe membrane fouling by forming a biofilm, especially for Fe₂(SO₄)₃·xH₂O. Additionally, the abundances of Bacteroidetes and Verrucomicrobia were relatively higher in the presence of Al₂(SO₄)₃·18H₂O, resulting in less severe biofouling by effectively degrading the protein and polysaccharide in EPS. As a result, in terms of microorganism behaviors, Al-based salts should be given preference as coagulants during actual operations.

Effect of aluminum speciation on fouling mechanisms by pre-coagulation/ultrafiltration process with different NOM fractions

Ultrafiltration is an emerging technology for drinking water production, but the membrane fouling is still a challenge. This study was carried out to investigate the effect of aluminum speciation on UF membrane fouling behavior by different NOM fractions-humic substances and proteins, as represented by humic acid (HA) and bovine serum albumin (BSA), respectively. The interesting results showed that the total fouling resistance of the mixture of HA-BSA-kaolinite solution without coagulant demonstrated a slight decrease in comparison with those of the individually filtered substances, indicating a mitigatory fouling effect. The hydrolysis of aluminum products was various as pH and membrane fouling was related to aluminum speciation. The average size of flocs dramatically increased and fractal dimension of flocs decreased with the increasing of pH value independent on water quality, which indicated that aluminum speciation had a significant impact on floc properties. For the mixture of HA-BSA-kaolinte, the slightly larger of flocs average size in comparison with the individual organic fraction after coagulation was probably attributing that BSA was encapsulated by HA to enlarge the molecular length and floc size further increased. The membrane performance also showed that coagulation effluent of HA-BSA-kaolinite mitigated membrane fouling. The strong linear relationship was observed between flocs fractal dimension and final membrane flux in this research. From the results, the control of flocs fractal dimension should be considered as a new technique for traditional hybrid coagulation/ultrafiltration system, which resulted in minimized total and irreversible fouling and has a meaningful engineering application value.

Development of High-Antifouling PPSU Ultrafiltration Membrane by Using Compound Additives: Preparation, Morphologies, and Filtration Resistant Properties

In this study, flat sheet asymmetric polyphenylsulfone (PPSU) ultrafiltration membranes with enhanced antifouling properties were prepared with a non-solvent induced phase separation (NIPS) method through compound additives containing a polymeric pore-forming agent, a small molecular non-solvent and a surfactant. The formation processes of the porous asymmetric membranes with different kinds of additives were studied in detail, and the microstructure controllable preparation of membrane was achieved by establishing a bridge between the membrane preparation parameters and separation performances. All prepared membranes were characterized by using a scanning electron microscope (SEM), contact angle analysis, porosity, maximum pore size, water and BSA solution permeability studies. The performance efficiency of the membrane was evaluated by using BSA as a model foulant in terms of permeability, solute rejection (R), Rm (membrane inherent resistance), Rc (cake layer resistance), and Rp (pore plugging resistance). The results showed that when the compound additives were used, the inter-connected pores were observed, maximum pore size, contact angle and membrane filtration resistance decreased, while the porosity increased. When PVP compound additives were added, the water flux increased from 80.4 to 148.1 L/(m²·h), the BSA rejection increased from 53.2% to 81.5%. A similar trend was observed for membranes with added PEG compound additives; the water flux and BSA rejection simultaneously increased. The filtration resistance decreased as a result of compound additives. The uniformity of membrane and the number of effective pores could be enhanced by adding compound additives through the cooperation of different additives.