Ultrafiltration of Humic Acid Solution: Effects of Self‐dispersible Carbon Black and Cations

Abstract

Effects of carbon black (CB) addition on membrane fouling and rejection of macromolecular humic acids (HA) were evaluated by a stirred‐cell ultrafiltration unit. Stable CB dispersions increased filtration resistances, but enhanced HA rejection by the membranes. Monovalent and divalent ions affected the filtration resistance of CB solution differently; namely, NaCl solution showed a very high resistance due to the concentration of CB in the diffusion boundary layer near the membrane surface, whereas CaCl₂ and MgCl₂ solutions showed only cake resistance. The cake layer containing both CB and HA was more easily removed from the membranes than HA‐cake layer.     

Influence of Water Compositions and Conditioning on Flux Enhancement in an Immersed Membrane System

Abstract

The objective was to quantify the importance of operational conditions, aeration, and physico‐chemical conditioning on membrane fouling intensity. The suspension filterability was also analysed by using frontal filtration and a cake filtration model. Results pointed out the moderated role of aeration to reduce compound accumulation on the membrane surface. It did not appear as a determining criterion to prevent membrane fouling. In contrast, the physico‐chemical conditioning appeared as a determining criterion to increase critical flux. According to the experimental conditions 200 l/m²/h/bar membrane permeability could be maintained transmembrane pressure (TMP) when filtering stored rainwater. This permeability value was 2–3 times higher than the values obtained without conditioning. Moreover, according to the low turbidity of such stored rainwater and because of the high selectivity of the membrane, the coagulation step, a very low amount of 10 mg/l FeCl₃, was sufficient to intensify the filtration step. This conditioning interest appeared less significant when filtering salted water in immersed membrane systems, but a 20 mg/l FeCl₃ addition appeared sufficient to double the value of critical flux. Nevertheless filtration in frontal mode pointed out the significant impact of physico‐chemical conditioning in reducing the cake deposit hydraulic resistance.     

Sustainable Flux Fouling in a Membrane Bioreactor: Impact of Flux and MLSS

Abstract

The long term sustainable flux behavior of a submerged membrane bioreactor operated under a steady state conditions at a range of mixed liquor suspended solids (MLSS) concentrations has been examined. Comparison of fouling rates at a number of imposed fluxes has been made between long term filtration trials and short term tests using the flux step method. Results indicate an exponential relationship between fouling rate and flux for both long and short term trials, although the value was an order of magnitude lower during long term tests. Moreover, operation during long term trials is characterised by a period of pseudo stable operation followed by a catastrophic rise in TMP at a given critical filtration time (t_filt) during trials at 6 g · L^?1. This time of stable operation, t_filt, is characterised by a linear relationship between fouling rate and flux. Results have been compared with the literature. Data for membrane fouling prior to the end of t_filt yielded a poor fit with a recently proposed model. Trends recorded at t>t_filt revealed the fouling rate to follow no definable trend with flux, contrary to the notion that fouling beyond the critical filtration time relates to solids deposition.     

A Review of Membrane Fouling in MBRs: Characteristics and Role of Sludge Cake Formed on Membrane Surfaces

Abstract

Membrane bioreactor (MBR) has been deemed to be a promising technology for wastewater treatment and reclamation; however, the MBR filtration performance inevitably decreases with filtration time attributed to the deposition of soluble and particulate materials onto and into the membrane under the interactions between activated sludge components and the membrane. Cake layer formation on membrane surfaces has been a major challenge in the operation of MBRs under supra-critical flux operation, and/or caused by uneven distribution of aeration intensities, etc.; however, it was argued that a thin cake layer might improve filtration operation by some researchers. This paper provides a critical review on the formation mechanisms, properties, the role of sludge cake in membrane filtration, and the corresponding strategies of controlling cake fouling in MBRs. Drawbacks and benefits of the formation of sludge cake were also discussed in order to better understand the characteristics and role of sludge cake formation in MBRs.     

Bulk and interfacial physical properties of aqueous solutions of sodium lauryl sulphate: Part IV: Dilute aqueous solution behavior by electron spin resonance studies and by pH and surface tension measurements

The electron spin resonance spectrum of the nitroxide label 2,2,6,6 – TetraMethyl – 4 – Piperidone – Oxide (TEMPO) has been investigated in aqueous solutions of a purified and commercially available impure samples of sodium lauryl sulphate (NaLS) for a wide range of concentrations. The spectra were recorded at 24°C as a function of surfactant concentration. The reorientational correlation times T_θ of the TEMPO label in aqueous solutions were calculated using the Kivelson's theory. Using the T_θ data qualitative analysis has been carried out in an attempt to understand the microscopic effects produced by the hydrophobic part of the surfactant on the water structure and the hydrophobic-hydrophobic interactions in water. Four major discontinuities in the τ_θ results have been identified with the purified NaLS system. They are found to occur at NaLS concentrations of 0.008 wt.%, 0.015 wt.%, 0.23 and 1.73 wt.%. The latter two concentrations represent the first and the second critical micelle concentration (CMC) of the surfactant while the first two concentrations reveal the existence of premicellar association and dissociation processes, respectively. These discontinuities have been also confirmed by the pH data and by surface tension results from the du Noüy ring method. The effect of addition of lauryl alcohol and sodium chloride on τ_θ values was also studied. The additive action has been found to produce an additional discontinuity, corresponding to the mixture CMC, in the τ_θ versus concentration plot. Analysis of other effects such as solution aging and hydrolysis of NaLS are also included. The applicability of the spin labelling technique for the study of aqueous solution behavior of NaLS is discussed by comparing data reported in the literature.     

Electrolysis of Sodium Silicate Solutions Using Cation-Exchange Membranes

Abstract

The electrolysis of sodium silicate solutions was studied at various temperatures, current densities, and concentrations. By using a cation-exchange membrane, NaOH was recovered at high current efficiency in the cathodic compartment. Sodium silicate solutions in the anodic compartment were upgraded to products of higher SiO₂/Na₂O ratios. The deposition of silica on anodes strongly inhibits smooth operation during electrolysis, and a semibatch method is described to overcome this difficulty.     

Use of Poly(methyl methacrylate-co-methacrylic acid) Membranes in the Ultrafiltration of Aqueous Fe3+ Solutions by Complexing with Poly(vinyl pyrrolidone) and Dextran

Abstract

In this study water soluble complexible polymers, poly(vinyl pyrrolidone) (PVP) and dextran, were used for the ultrafiltration (UF) of aqueous Fe⁺³ solutions by using poly(methyl methacrylate-co-methacrylic acid) (PMMA-co-MA) membranes. Effects of polymer concentration and pH on the volume collected in the filtration of Fe⁺³ solutions and percent retentions (R%) were examined. It was determined that increase in polymer concentration decreased the permeability of PMMA-co-MA membrane and pH increased the retention of Fe³⁺ solutions. R% for Fe³⁺ solutions were obtained as 62% and 48% with PVP and dextran respectively at pH 3.0, for a filtration period of 80 minutes and retention for Fe³⁺ solution without using any complex forming polymer was found as 14%. Membranes were characterized by AFM analysis and contact angle measurements.     

Poly(phenylacetylene) with bulky chiral germyl groups: synthesis and effects of measuring solvents and temperature on chiroptical properties

(+)-p-[{Methyl(1-naphthyl)phenyl}germyl]phenylacetylene, an acetylene with a bulky chiral germyl group, was polymerized with [(nbd)RhCl]₂-Et₃N to give a high-molecular-weight polymer in good yield. The CD spectrum of the polymer exhibited very large molar ellipticities [θ] in the UV region in non-aromatic solvents (e.g. THF and CHCl₃). In contrast, the CD signals of the polymer in aromatic solvents (e.g. toluene, tetralin, and benzene) became appreciably smaller: [θ]_max=6.4×10⁴ (330 nm) and −4.7×10⁴° cm² dmol⁻¹ (370 nm) in CHCl₃; [θ]_max=1.1×10⁴ (330 nm) and −0.7×10⁴° cm² dmol⁻¹ (370 nm) in toluene. The [θ]_max values of the polymer in aromatic solvents increased when the solutions were heated, which is attributed to decreased π-π interaction between the solvents and side groups.     

Modified Polyethersulfone (PES) Ultrafiltration Membranes for Enhanced Filtration of Whey Proteins

Abstract

Application of membrane technology to whey protein separation is an interesting development that has seen growth in recent years. In particular, modification of existing membranes to impart charge properties on the membrane surface or in the pores has been shown to improve membrane selectivity, product purity, and throughput of protein solutions. This paper focuses on exploring the effects of membrane charge and solution pH on filtration of the major whey proteins α‐lactalbumin (14.1 kDa) and β‐lactoglobulin (18.4 kDa) using functionalized PES membranes. The membranes have an open pore structure containing charged sulfonated grafted polymer chains that allows for greater protein retention. The modified membranes were synthesized by polymerization of styrene in the membrane pores followed by sulfuric acid treatment of the resulting polystyrene grafts. The charged membrane gave a calculated selectivity of five times better than the raw membrane at pH 7.2 based on data from single protein transmission experiments. The enhanced selectivity of the tailor‐made membrane was due to increased retention of β‐lactoglobulin due to a reduction in molecular sieving combined with electrostatic repulsion between negatively charged β‐lactoglobulin and the negatively charged membrane.     

Using a simple method to prepare UiO-66-NH2/chitosan composite membranes for oil–water separation

Chitosan (CS) was used as a cross-linking agent to modify UiO-66-NH₂, and the modified UiO-66-NH₂ was fixed on the mixed cellulose membrane (MCE) through vacuum filtration technology to prepare a new type of membrane. The membrane exhibited excellent hydrophilicity in the air and excellent super-oleophobic performance underwater, and effectively separated various oil–water emulsions. When separating petroleum ether-water emulsion, the filtration flux of the modified membrane was 2000 L m⁻² h⁻¹ higher than that of MCE, and the separation efficiency can reach more than 95%. After 10 cycles, the flux of the modified membrane was about four times of that MCE, which was 500 L m⁻² h⁻¹. Most importantly, the membrane still maintained underwater superoleophobicity in the environment of strong acid, strong base, and salt solution.     

Electrochemical Analysis of Ion-Exchange Membranes with Respect to a Possible Use in Electrodialytic Decontamination of Soil Polluted with Heavy Metals †

Abstract

Transport numbers in different metal chloride solutions were estimated using the emf method for two ion-exchange membranes: Ionics CR67 HMR412 (cation-exchange membrane) and Ionics AR204 SXRA 7639 (anion-exchange membrane). The cation-exchange membrane was found to work nearly ideally for NaCl and CaCl₂ solutions even at high concentrations, whereas deviation from ideality was seen for ZnCl₂ and CuCl₂ solutions. The anion-exchange membrane showed transport numbers for the anion around 0.95 for NaCl, CaCl₂ and ZnCl₂ solutions for the concentration range investigated. Electrodialytic desalting experiments taken as a simplified simulation of the electrokinetic decontamination method showed that it was possible to remove all ions in the simulated soil volume, with a sharp increase in the potential difference over the soil volume as a result, and that it was possible to control the metal content in the different solutions in the electrodialytic decontamination method.

     

Electrokinetic characterization of the Al2O3 ceramic MF membrane by streaming potential measurements

The alumina microfiltration(MF) membrane was modified with nanocrystalline TiO₂ in the pore wall. The electrokinetic properties of unmodified and modified alumina membranes were characterized by streaming potential measurements during tangential filtration at various conditions of pH, ionic concentration and ionic species in solutions. The modified membrane reveals a more acidic characteristic. The influence of pH value on the streaming potential of both membranes is explained by the shifting of the proton equilibrium that occurs at the surface of the membrane. The modification of the alumina membrane with TiO₂ leads to the decrease of its isoelectric point (IEP) from 6.1 to 4.0 when filtered with NaCl solution. The ionic concentration and electrolyte species also have influence on the streaming potential of both membranes. The reversal of the streaming potential sign and the change of the isoelectric point of the membrane when filtered with CaCl₂ and Na₂SO₄ solutions show specific adsorption of Ca²⁺ and SO₄^2- ions onto the surface.     

Removal of Metal Ions from Liquid Solutions by Crossflow Microfiltration

Abstract

The applicability of crossflow microfiltration (CFMF) to the removal of metal ions from liquid solutions was studied. Three treatment processes were employed in this study. The first process was filtration of liquid solutions containing metal ions by CFMF. The second process was CFMF with membranes precoated by CaCO₃ cake. The third process used suspension flocculation as a pretreatment step before CFMF. It was found that CFMF or CFMF with precoated membranes could not remove the metal ions (Cu²⁺, Mn²⁺ and Fe²⁺) from water efficiently. On the contrary, CFMF with suspension flocculation as a pretreatment could remove the metal ions from water completely under suitable pH values. The unsteady-state permeate flux for CFMF with suspension flocculation increased with an increase in temperature but decreased with an increase in pH of the liquid solutions. In addition, an optimal permeate flux existed in the relationship among the permeate flux, crossflow velocity, membrane pore size, and pressure drop. Furthermore, the unsteady-state permeate flux obtained experimentally for CFMF with suspension flocculation could be predicted by a mathematical model developed previously if an equivalent diameter of the flocs in the suspension was used in the model.     

Ultrafiltration of W/CO2 Microemulsions in Ceramic Membranes

Abstract

Water‐in‐CO₂ (W/CO₂) reverse microemulsions stabilized with 1100 Da poly(ethylene glycol)‐poly(propylene glycol)‐poly(ethylene glycol) block copolymer were recovered using an ultrafiltration ceramic membrane in a custom high‐pressure cross‐flow separation unit. Viscosity‐corrected liquid CO₂ flux (298 K) through the membrane was investigated as a function of time and surfactant concentration to determine the cake layer mass transfer resistance. Rapid CO₂ flux decline was observed with increasing surfactant concentration, denoting cake layer buildup on the membrane surface. For instance, at 0.09 and 0.55 wt% surfactant, the ratio of cake resistance to membrane resistance was 0.4 and 3.8, respectively. Based on our previous work, the reverse‐micelles retain their aqueous core and are not altered during filtration. Ultimately, inorganic membrane separations can reduce energy consumption associated with compression/expansion cycles typically used in CO₂‐based processes.     

Polyethersulfone (PES)–silver composite UF membrane: Effect of silver loading and PVP molecular weight on membrane morphology and antibacterial activity

Polyethersulfone–silver composite membranes were fabricated via a simple phase inversion method by using silver nitrate (AgNO₃) as an antibacterial agent and polyvinylpyrollidone (PVP) of molecular weight 10,000, 40,000 and 360,000 Da as dispersant in the dope formulation. The effect of AgNO₃ loading on the resulting membrane was studied using field emission scanning electron microscope (FESEM), energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) techniques. The silver loss during fabrication and pure water filtration was measured using inductive-coupled plasma mass spectrometer (ICP-MS). From XPS and EDX examinations, it was observed that the resulting membrane prepared from 2 wt.% AgNO₃ and PVP of 360,000 Da exhibited high concentration of Ag mainly due to the high Ag-particle entrapment in the membrane structure. The uniform distribution of Ag particles has contributed significantly to 100% inhibition against Escherichia coli (E. coli) growth within 24 h incubation. In addition, the results of pure water filtration test showed minimum silver loss during operation, indicating better stability of membrane produced in terms of Ag-entrapment in membrane structure. Based on the findings, it can be concluded that PES–silver composite membrane with PVP of 360,000 MW offers huge potential membrane for bacteria removal and disinfection.     

Huggins' constant and unperturbed parameter of dilute polymer solutions

A novel method developed to evaluate the unperturbed parameter K_θ from the viscometric data of dilute polymer solutions can be considerably simplified by making the reasonable assumption that the Huggins' constant under theta conditions, k_Hθ, is equal to ½ for a number-average degree of polymerization of over about 2000. Two linear equations are derived pertaining to the present analysis, one to deal with the experimental data, and the other specially to estimate the intrinsic viscosity [η]θ which corresponds to κ_Hθ. All calculations were done by the linear least-squares method. The K_θ was computed by the Mark–Houwink–Sakurada equation. It is shown that reliable results on K_θ can be obtained for polystyrene and poly(vinyl acetate).     

Novel low pressure drop and easy regeneration ceramic whisker membrane for submicron particulate matter filtration

Aiming to efficiently remove submicron particulate matter (PM), a low pressure drop ceramic whisker membrane was prepared via precursor solution dip coating followed by high temperature firing. Aluminum nitrate 9-Hydrate and boric acid were used as the precursors for the formation of aluminum borate. A highly porous film comprising interconnected single phase 9Al₂O₃·2B₂O₃ whiskers of high aspect ratio, was successfully formed on an alumina support. Flue gas filtration tests indicated that as-fabricated ceramic whisker membrane exhibited outstanding filtration performance. More than 95 % PM in 0.3–1 µm was removed by using the as-prepared ceramic whisker membrane, and the pressure drop after three rounds of back blow regeneration remained stably at approximate only 1.3 times of the air pressure drop. This work provided a feasible approach to the preparation of a novel ceramic membrane with low pressure drop, and a novel strategy for high efficiency removal of submicron PM.     

The Rheology of Wetting By Polymer Melts

Theoretically, the rate of capillary penetration of a polymer melt into a slit, a model for a surface irregularity, has been shown to depend on γcosθ/η) where γ refers to the surface tension of the liquid, η its viscosity and θ a time-dependent contact angle. Analytical expressions relating the depth of penetration with time have been experimentally verified by observations of the penetration of molten polyethylene and poly-(ethylene-vinyl acetate) into aluminum channels. Values of η, calculated from the observed data, agree closely with independent determinations of this material parameter. A theoretical treatment has also been developed which describes the velocity of spreading of a liquid drop over a flat surface. Flow equations for the flow of free films were adapted for this purpose. The spreading velocity is predicted to depend on the product of three factors (1) a scaling factor, (γ/η1R_o), where R_o is the initial radius of curvature, (2) cosθ_∞. (l-cosθ/cosθ_∞) where θ_∞ refers to the equilibrium value of θ, and (3) geometric terms. After demonstrating that a drop of molten polymer may be treated as a spherical cap, the predicted dependence of spreading rate on drop size, cosθ_∞ (nature of the substrate) and the scaling factor was experimentally verified. Some discrepancies noted at long times and high temperatures are discussed.     

PEG/GO/TiO2纳米复合材料改性PVDF膜的制备及其抗污性能

为改善聚偏氟乙烯(PVDF)膜的抗污性能,以聚乙二醇2000接枝的GO/TiO₂(PEG/GO/TiO₂)纳米复合材料为添加剂,通过非溶剂诱导沉淀相分离法制备了一系列PEG/GO/TiO₂/PVDF复合超滤膜。采用FTIR、SEM和接触角测试仪对其结构和形貌进行了表征,采用超滤法评价其纯水通量和抗污性能。结果表明,当PEG/GO/TiO₂纳米复合材料质量分数为0.60%时,制备的PEG/GO/TiO₂/PVDF复合超滤膜(记为0.60%PEG/GO/TiO₂/PVDF)表现出最佳的亲水性和抗污性能,其接触角比PVDF膜下降8.2°,总孔隙率增加13.40%,PEG/GO/TiO₂纳米复合材料在PVDF膜中分散较均匀。在0.08 MPa的工作压力下,0.60%PEG/GO/TiO₂/PVDF的纯水通量高达282.44 L/(m²·h),对腐植酸溶液的过滤通量为131.96 L/(m^2...     

Diffusion Dialysis. Effect of Membrane Composition on Acid/Salt Separation

Abstract

In order to highlight the relationship between membrane composition and ability to separate acid/salt mixtures by diffusion dialysis, a few anion-exchange membranes were examined. Experiments on solubility/diffusivity phenomena were carried out in contact with hydrochloric acid and sodium chloride solutions (single-and two-solute experiments). Computations using Glueckauf and Tye models have indicated high nonuniformity in the distribution of fixed charges within the membranes and different accessibilities of the internal membrane volumes for the acid and salt. The Neosepta AFN-7 membrane (Tokuyama Soda Co.) has proved effective in differentiating the permeants by sorption (_{k HCl}/k _NaCl ?2) and diffusivity (D _HCl/D _NaCl up to 10). This membrane is also the only one which, when in contact with two-solutes solutions, absorbs the acid preferentially to the salt. For this membrane the perferential sorption and transport of the acid depends not only on the physical structure of the membrane but also on the chemical nature of the polymer which contains pyridine moieties.