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Soluble algal organic matter (AOM) resulting from cyanobacterial blooms can cause severe fouling for water treatment membranes as it contains a large proportion of high molecular weight (MW) organics such as biopolymers and humic-like substances. UV/H 2 O 2 advanced oxidation of feedwater containing AOM derived from Microcystis aeruginosa was investigated as a means of mitigating the fouling of a ceramic microfiltration (MF) membrane and degrading the algal toxin microcystin-LR. The result was compared with the pre-treatment using coagulation with ACH. UV/H 2 O 2 treatment and coagulation achieved a marked and comparable reduction in total fouling resistance, however coagulation led to considerably lower irreversible fouling. The significant reduction in membrane fouling by the pre-treatments was attributed to the effective breakdown/removal of the very high MW biopolymers (≥20,000 Da) and high MW organic substances (~10,000 Da) in the AOM. UV/H 2 O 2 treatment resulted in the generation of lower MW substances due to partial oxidation of the large molecules, and consequently greater irreversible membrane fouling compared with coagulation. Microcystin-LR was completely inactivated by UV/H 2 O 2 , whereas coagulation was ineffective for removing it. [ABSTRACT FROM AUTHOR]

In this paper, we report that fast evaporation of volatile solvent from cellulose acetate (CA) solution layer containing a proper nonvolatile alcohol can lead to the formation of relatively uniform nanoporous CA membrane. We propose that in the phase-separation process, the molecules of the nonvolatile alcohol aggregate to constitute the polymer-lean nuclei (PLN). These PLN exist stably (but not evaporate), grow continuously, and develop finally into the pores on the membrane. Relevant evidences are provided to support the proposed mechanism. This work implies a possible approach to generate uniform nanopores on polymer membrane. [ABSTRACT FROM AUTHOR]

Abstract: Macrovoids are defects that are frequently encountered in phase inversion as well as in other solution-cast membranes. Macrovoid formation continues to hold many surprises despite several decades of pertinent studies and frequent claims for definitive answers. We have discovered conditions leading to macrovoid growth parallel to a transparent membrane skin (horizontal macrovoids, HMVs); the benefits from the macrovoid-study point of view are slow growth, easy observation and possibility of designing modes of interference that facilitate the understanding of the parameters that affect the initiation and growth (including orientation) of macrovoids. Our study emphasizes the case of dopes consisting of atactic PMMA dissolved in acetone and solidified in a hexane non-solvent bath but dopes of other polymers also exhibit the same features. While a host of parameters affect the occurrence of HMVs we find that they are ultimately a possible response to the mechanical force field that evolves during progressing solidification of the concentrated polymeric solution; as a result HMVs can occur, under appropriate conditions, regardless if there is phase separation (which leads ultimately to a macroporous bulk membrane microstructure) or not. [Copyright &y& Elsevier]

Abstract: Integrally skinned asymmetric crosslinked polyimide (PI) nanofiltration membranes suitable for organic solvent nanofiltration (OSN) were formed via the phase inversion method. A better understanding of how membrane formation parameters (such as composition of the dope solution, the evaporation step, and chemical properties of the polymer) affect membrane performance (flux and rejection) was sought. The findings were reported in three parts. In this paper, Part A of the study, the importance of the choice of polyimide and solvent system was studied. Membranes prepared from Ultem 1000 and Matrimid 5218 were much more open as compared to membranes prepared from P84 and HT P84. Increasing share of 1,4-dioxane used as a co-solvent did not improve rejection of membranes prepared from Ultem 1000 and Matrimid 5218. An introduction of a simple tool based on mutual solubility parameters allowed to qualitatively predict the effect of polyimide choice and solvent composition used in the dope solution on membrane performance. Lower value of the introduced total solubility parameter was very well correlated with lower rejection. [Copyright &y& Elsevier]

Abstract: This paper is Part B of a three paper series seeking better understanding of how formation parameters (such as composition of the dope solution, the evaporation step, and chemical properties of the polymer) affect the performance of polyimide (PI) membranes for organic solvent nanofiltration (OSN). In this work, the impact of the evaporation step, taking place prior to phase inversion, on membrane performance was analysed. In the next step, the ultimate role of a co-solvent was investigated. The study has shown that PI OSN membranes prepared from volatile 1,4-dioxane could be successfully formed when no evaporation was allowed. Moreover, good rejecting PI OSN membranes were also prepared when only non-volatile co-solvents, such as diethylene glycol dimethyl ether and dimethyl phthalate, were used. The results have shown that the evaporation step should be avoided in the studied system as it worsened the flux while having no effect on rejection. The presence of a co-solvent, regardless if it is volatile or not, was found to be crucial for tight skin layer formation, as it increases the solvent to non-solvent diffusion rate ratio during the immersion step. This triggers formation of a skin layer via vitrification. [Copyright &y& Elsevier]

Abstract: A phenolphthalein based poly(ether ether ketone) (PEEKWC) has been used for the preparation of asymmetric membranes for organic solvent nanofiltration, chemically stable membranes showing high retention of organic solute molecules. Integrally skinned asymmetric PEEKWC membranes were fabricated from concentrated solutions by phase separation induced by non-solvent. Two organic solutes with molecular weight in the range of NF application (i.e. 200–1000g/mol) have been selected: safranine (MW 351g/mol) and Rose Bengal, (MW 1017g/mol). The membrane performance has been studied using water and alcohols as solvents (methanol, ethanol, iso-propanol and n-butanol). A nearly complete rejection for Rose Bengal in isopropanol (99.8%), higher than that observed in water (86%) and methanol (90%) has been obtained. However, an opposite trend has been found for the smaller safranine: the retention in water (71%) is higher than that in isopropanol (52%). The NF results have been interpreted in terms of membrane–solute, membrane–solvent and solute–solvent interactions. [ABSTRACT FROM AUTHOR]

Abstract: Chemically crosslinked polyimide organic–inorganic composite nanofiltration membranes suitable for application in harsh organic solvents were successfully prepared by phase inversion of dope solutions. TiO2 nanoparticles were dispersed in these dope solutions, comprising polyimide (PI) in N,N-dimethylformamide/1,4-dioxane. The impact of TiO2 on the resulting PI membranes was investigated using SEM, TGA, water contact angle, dope viscosity measurements and mechanical strength. The presence of TiO2 nanoparticles within the membrane matrix was proved by the detection of a peak characteristic of TiO2 in the WAXS pattern. SEM pictures of the cross-section of the PI/TiO2 membranes showed dramatically changed morphology compared to reference membranes with no TiO2 addition. Macrovoids present in reference membranes were suppressed by increasing loading of TiO2 nanoparticles, and eventually disappeared completely at a TiO2 loading above 3wt.%. Decreasing water contact angle and an increase in ethanol flux indicated that hydrophilicity increased as nanoparticle loading increased. The effect of TiO2 on the functional performance of the membranes was evaluated by measuring flux and rejection using cross-flow filtration. Perhaps surprisingly, the presence of TiO2 improved the compaction resistance of the membranes, whereas rejection and steady flux were almost unaltered. [Copyright &y& Elsevier]

Abstract: The potential of 3-phenyl-4-benzoylisoxazol-5-one (HPBI) as metal extractant has been evaluated for the first time for Cu(II) transport from aqueous nitrate solutions by supported liquid membrane (SLM) in the solvents chloroform, 2-nitro phenyl octyl ether (NPOE) and dodecyl nitro phenyl ether (DNPE). The efficiency of the membrane transport was optimized as a function of pH, temperature, aqueous phases and membrane composition. It follows the sequence CHCl3 >DNPE>NPOE. The results suggested that the transport mechanism was mainly controlled by the diffusion of the Cu(PBI)2 complex in the membrane core. A comparative investigation of Cu(II) transport ions has been made between SLM and polymeric plasticized membrane (PPM), containing HPBI with NPOE and DNPE as organic solvents or plasticizers in order to evaluate the feasibility of PPM with HPBI. [Copyright &y& Elsevier]

Abstract: This work examines flux and rejection performances under cross-flow for several concentrated (5–30wt.%) methanol–dimethyl methylsuccinate (DMMS) solutions permeating through two commercially available organic solvent resistant nanofiltration membranes (Starmem™ 122 (S-122) and MPF-50). The experimental flux/rejection data for the flat sheet membranes was fitted using pore-flow and solution-diffusion models for membrane transport, coupled with film theory for liquid mass transfer effects. It was found that solution-diffusion gives a better description of some of the experimental trends. In the practical range of concentrations studied, rejection should be seen as a variable, dependent on the mass transfer characteristics of the nanofiltration system in use. [Copyright &y& Elsevier]

Abstract: This paper describes improvements to an apparatus for in-situ determinations of swelling where a linear inductive probe and electronic column gauge with an overall resolution of 0.1μm was used for measurements of seven variants of polyacrylonitrile (PAN)/polydimethylsiloxane (PDMS) composite nanofiltration membranes in a range of alkane, aromatic and alcohol solvents. The unswollen membranes incorporated PDMS layers between 1 and 10μm nominal thickness and were manufactured with a radiation and/or thermal crosslinking step. The tested membranes exhibited a range of swelling dependent on the degree of crosslinking, the initial PDMS layer thickness and the type of solvent. With no applied pressure the PDMS layer on some radiation cross-linked membranes swelled as much as ∼170% of the initial thickness whilst other membranes were restricted to a maximum swelling of ∼80%. When a pressure up to 2000kPa was applied to a membrane then swelling could be reduced to ∼20% of the value obtained at zero applied pressure. By vertically stacking up to three membrane samples it was possible to determine the swelling of PDMS layers as thin as 1μm, although higher imposed pressures rendered some results unreliable as the measurement resolution of the apparatus was approached. The results of the swelling experiments are contrasted with crossflow nanofiltration performance in terms of solvent flux and solute rejection. [Copyright &y& Elsevier]

Abstract: This paper reports rejection of organic solutes with molecular weight (MW) in a range of 180–600 in aqueous and organic solvents through several commercial solvent resistant nanofiltration membranes (SRNF). The organic solutes investigated include charged and neutral molecules and the selected solvents are water, water–methanol mixture, methanol, ethanol, acetone and ethyl acetate. The higher rejection in water than in organic solvents was observed for Desal-DK, MPF-44 and STARMEM™ series membranes. However, MPF-50 showed “uncommon” rejection characteristics of higher rejection in organic solvents (methanol, ethanol and acetone) than in water for neutral molecules compared to charged molecules. The rejection was analysed in accordance with the charge effect and hydration/solvation mechanism. [Copyright &y& Elsevier]

Abstract: The separation characteristics of a dense polydimethylsiloxane (PDMS) membrane were studied using mixtures comprising xylene, cyclohexane or n-heptane with oxygenate components at concentrations up to 75% by weight. The effects of polarity on flux and rejection performance were determined through a test matrix of solvent type, concentration, filtration pressure, crossflow rate and the degree of membrane crosslinking. In all cases involving alcohols, the more polar compound in the feed mixture was partially rejected by the membrane and the extent of rejection was dependent on the polarity as quantified by solubility parameter. The rejection–concentration profiles for several alcohol/solvent mixtures exhibited a maximum, with the highest rejection being around 30%. Mixtures containing MTBE did not separate, i.e. no rejection was observed. Rejection increased with increasing pressure and crossflow rate but was largely unaffected by the degree of membrane crosslinking. Component flux was affected by the oxygenate concentration in the mixture, which was attributed in part to changes in the degree of membrane swelling with composition. Experimental findings suggest that the separation is primarily governed by multicomponent solvent/oxygenate/membrane swelling equilibria, and results compare favourably with swelling isotherms available in the open literature. [Copyright &y& Elsevier]

Abstract: Solvent transport in organic solvent nanofiltration membranes has been studied in a lab-scale cross-flow nanofiltration rig over extended periods using the common solvents methanol, toluene, ethyl acetate and their mixtures. The organic solvent nanofiltration membranes STARMEM™ 122 1 [1] STARMEM™ is a trademark of W.R. Grace and Co. (W.R. Grace and Co.) and MPF50 (Koch Membrane Systems) were investigated. It was found that it took a few days to obtain stable solvent flux using STARMEM™ 122, and that the solvent flux in this membrane showed good repeatability between different sample discs. MPF50 did not provide reproducible results, therefore, no modelling/data analysis was performed for this membrane. Our experimental data shows that both solution-diffusion and pore-flow models can be used to predict permeation of solvent mixtures, using only the permeabilities of the pure solvents to obtain input parameters to each model. The solution-diffusion model gave more accurate predictions. Our conclusion is that for the solvents studied, it is possible for reasonable predictions of solvent mixture flux to be made over the whole concentration range, based on the data for pure solvents. [Copyright &y& Elsevier]