Simultaneous Injection of Contrast and Saline Using Spiral Flow-Generating Tube for Hepatic Dynamic Computed Tomography: Effect on Enhancement of Liver Parenchyma and Metastases to the Liver.

PURPOSE: Recently, there have been a few reports regarding the usefulness of a novel saline injection technique using a spiral flow-generating tube. The purpose of this study was to evaluate whether simultaneous saline injection using a spiral flow-generating tube was able to improve hepatic contrast enhancement and lesion conspicuity of metastatic liver tumors. METHODS: We randomized a total of 411 patients with various liver diseases including metastases by total body weight (A, n = 204) and contrast dilution protocol (B, n = 207). Group A received 400 mgI/kg of contrast medium alone without a spiral flow-generating tube; group B received contrast medium 400 mgI/kg simultaneous with injection of a 0.57-ml/kg physiologic saline solution through a spiral flow-generating tube. Abdominal aorta computed tomography (CT) number, hepatic enhancement (ΔHU), percentage of tests demonstrating an enhancement effect of the liver parenchyma exceeding Δ50 HU in 3 measured segments (S2, S6, and S8), and the contrast-to-noise ratio of the metastatic liver tumors were measured. RESULTS: The mean aortic CT number of group B (417.0 HU ± 61.7; P < 0.01) was approximately 10% higher than that of group A (384.6 ± 79.1 HU). The average ΔHU was 59.8 ± 11.4 HU for group A and 61.7 ± 11.7 for group B. The ΔHU for group B was significantly higher than that for group A (P = 0.017). The percentage of tests demonstrating with the enhancement effect of group B was more than 80% in all subgroups; however, that of group A was less than 80% in all subgroups. The contrast-to-noise ratio of group B (7.8 ± 3.3 HU) was significantly higher compared to that of group A (6.5 ± 2.8 HU) (P < 0.05). CONCLUSIONS: Because of the volume effect, injecting a contrast medium diluted with normal saline improved the degree of hepatic and aortic contrast enhancement and achieved better visualization of liver metastases. CLINICAL IMPACT: The use of spiral flow-generating tube may help diagnostic of hepatic and aortic contrast enhancement and liver metastases. IMPORTANCE: The use of a spiral flow-generating tube improved the degree of hepatic and aortic contrast enhancement and achieve better visualization of liver metastases. POINTS: The use of low-concentration syringe formulations is limited by body weight. However, the use of spiral flow-generating tube provides low-concentration contrast medium regardless of body weight.

Tensile deformation of polytetrafluoroethylene hollow fiber membranes used for water purification.

The tensile deformation behavior of polytetrafluoroethylene (PTFE) hollow fiber membranes is studied. PTFE membranes at present have sub-micron pores with an open cell structure, which plays a critical role in water purification. One of the main challenges in water purification is that the pore structure becomes covered with biofouling, leading to blocked pores. To maintain the capacity for water purification, physical cleaning along with mechanical deformation is usually conducted. Thus, it is crucial to understand the mechanical properties, in particular the deformation behavior, of the membrane fibers. Using uniaxial tension experiments, we established a fundamental discrete model to describe the deformation behavior of a porous structure using a finite element method. The present model enables the prediction of the macroscopic deformation behavior of the membrane, by taking into account the changes of pore structure. The insight may be useful for porous membrane fabrication and provide insights for the reliable operation of water purification.

Influence of extracellular polysaccharides (EPS) produced by two different green unicellular algae on membrane filtration in an algae-based biofuel production process.

In the present study, two strains of green algae named S1 and S2, categorized as the same species of Pseudo-coccomyxa ellipsoidea but showing 99% homology, were cultivated under the same conditions and filtrated with a microfiltration membrane. On the basis of the results of the extracellular polysaccharides (EPS) characteristics of these two green algae and the degree of fouling, the influence of these characteristics on the performance of membrane filtration was investigated. There was no difference in the specific growth rate between the S1 and S2 strains; however, large differences were seen in the amount and quality of EPS between S1 and S2. When the S1 and S2 strains were filtered with a membrane, the trend in the increase in transmembrane pressure (TMP) was quite different. The filtration of the S1 strain showed a rapid increase in TMP, whereas the TMP of the filtration of the S2 strain did not increase at all during the operation. This clearly demonstrated that the characteristics of each strain affect the development of membrane fouling. On the basis of the detailed characterization of solved-EPS (s-EPS) and bound-EPS (b-EPS), it was clarified that s-EPS mainly contributed to irreversible fouling for both operations and the biopolymer-like organic matter contained in b-EPS mainly contributed to reversible fouling.

Solid-phase fluorescence: Reproducibility and comparison with the solution states.

Solid-phase fluorescence excitation-emission matrix (SPF-EEM) spectroscopy has potential for non-extractive, non-destructive, and non-contact analytical measurements of powder and solid-state samples, as well as front-face EEM spectroscopy for suspensions of high optical density. However, as there is no unified measurement method for SPF spectroscopy, comparing samples measured in different research fields is difficult. Therefore, this study designs a cell that can be created by a 3D printer and examines reproducibility on measuring fluorescent powders. The developed cell is applied to proteins (ovalbumin, BSA, gliadin, gluten, powdered collagen, casein), amino acids (tryptophan, tyrosine, and phenylalanine), soybean ingredients (daidzein, and genistein), and fluorescent chemicals (rhodamine B, fluorescein sodium salt, pyrene, and quinine sulfate dihydrate) and their spectra are compared with those in the solution states. When samples are refilled into the cell three times, the cell exhibits high reproducibility in terms of fluorescence peak wavelength and intensity. The solid proteins exhibit peaks attributed to the fluorescent amino acid residues, and broad peaks which are not detected for the proteins in the solution states. Powdered rhodamine B and fluorescein sodium salt do not exhibit fluorescence, possibly due to the inner-filter effect (IFE). Some non-colored molecules also exhibit loss of fluorescence or a remarkable difference between the solid and solution states, possibly due to the interaction of the fluorescent structure with the surrounding local environment, similar to the solvent effect, which is possibly affected by the molecular proximity, three-dimensional structure, and moisture absorption capacity.

Quantification of organic fluorophores in absorbing media by solid-phase fluorescence excitation-emission matrix (SPF-EEM) spectroscopy of modeled mixtures containing bovine serum albumin (BSA) and colorants.

Solid-phase fluorescence excitation-emission matrix (SPF-EEM) spectroscopy is beneficial for investigating the characteristics of natural organic matter (NOM) in the solid phase without extraction procedures. However, inner filter effect (IFE) due to the presence of dark components in samples can make it difficult to quantify the fluorophore concentration. To establish a new method to determine unknown concentrations of a fluorescent material in a sample containing various absorbing materials by SPF spectroscopy, modeled mixtures containing bovine serum albumin (BSA) and colorants at different ratios were examined. Fluorescence intensities of BSA against various concentrations afforded different saturation curves for different colorants in the mixtures, suggesting that it is difficult to use the SPF intensity for quantifying the concentration of fluorescent samples in which IFE has occurred, because one cannot obtain a single calibration curve that does not depend on the absorbing medium that it is mixed in. However, products of the fluorescence intensity and Kubelka-Munk (KM) function at the excitation wavelength were proportional to the first order of BSA weight concentrations, regardless of the colorant type. By using this trend as a calibration curve, it may be possible to quantify the amount of BSA from its SPF-EEM spectrum. In this study, the KM function was obtained using an ultraviolet-visible (UV-Vis) spectrometer with an integrating sphere. To reduce the labor and equipment cost of UV-Vis spectroscopy, a substrate of the KM function also was obtained from the Rayleigh scattering in an SPF-EEM spectrum, which could be used as a parameter for calibration curves that quantify the BSA concentration. Although further studies are required, this study proposed that the product of the SPF intensity and KM function at the excitation wavelength can be partially used for an empirical formula to quantify a variety of fluorescent materials mechanically mixed with various absorbing materials.

Important properties of anion exchange resins for efficient removal of PFOS and PFOA from groundwater.

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) present in various water sources have raised a serious concern on their health risk worldwide. Anion exchange is known to be one of the effective treatment methods but the resin properties suitable for theses contaminants have not been fully understood. We examined four commercially available anion exchange resins with different properties (DIAION™ PA312, HPA25M, UBA120, and WA30) and one polymer-based adsorbent (HP20), for their PFOA and PFOS removal in the batch experiment. All or a part of the selected resins were further characterized for their functional group, surface morphology and pore size distribution. The 72 h batch experiment with the 100 mg/L PFOA or PFOS in the laboratory pure water matrix showed a superior capacity of the strong base anion exchange resins, the porous-type HPA25M and PA312, and the gel-type UBA120, for PFOA removal (92.6-97.9%). Among those resins, the high porous HPA25M was suggested most effective due to its remarkably high reaction rate and effectiveness to PFOS (99.9%). In the groundwater matrix, however, the performance of the those anion exchange resins was generally suppressed, causing up to 71% decrease in their removal rates. The least matrix impact was observed for PFOS removal by HPA25M, which indicated the resin's high selectivity to the contaminant. The physiochemical analysis indicated that the presence of relatively large pores (1 nm-10 nm) over HPA25M played an important role in the PFAS removal.

Solid-phase fluorescence excitation emission matrix for in-situ monitoring of membrane fouling during microfiltration using a polyvinylidene fluoride hollow fiber membrane.

Controlling membrane fouling is challenging and information regarding the causes of fouling is critical for this. While liquid-phase fluorescence spectroscopy excitation emission matrix (LPF-EEM) has previously been applied to identify the characteristics of membrane foulants, we applied EEM measurements to solid samples to identify foulants accumulated on the membrane. This solid-phase fluorescence EEM (SPF-EEM) enables sensitive and nondestructive identification of different organic solids. LPF-EEMs and SPF-EEMs were used on natural organic matter (NOM) isolated from secondary-treated wastewater, which revealed differences in peak positions and in spectral shapes. SPF-EEMs and LPF-EEMs of hydrophobic (HPO), transphilic (TPI) and hydrophilic (HPI) fractions showed that peaks of HPO fraction disappeared while those of TPI and HPI fractions shifted to a longer excitation and emission position through solidification. Then, the surface of the membrane fiber was continuously monitored using SPF-EEM during filtration. Three peaks appeared as expected during membrane fouling progression, indicating that in-situ monitoring of foulants was successful. Comparison of the EEM peaks between foulants and isolated NOM fractions shows the presence of both liquid-phase proteinaceous substances and gels formed from HPI and TPI fractions. Changes in peak intensity confirmed that the former proteinaceous substances were responsible for both reversible and irreversible fouling, while the latter gels mainly contributed to the irreversible fouling. We demonstrated the functionality of the SPF-EEM as an in-situ fouling monitoring tool.

Application of Graphene Oxide for Adsorption Removal of Geosmin and 2-Methylisoborneol in the Presence of Natural Organic Matter.

We investigated the adsorption characteristics of geosmin and 2-methylisoborneol (MIB) on graphene oxide (GO) in the absence and presence of natural organic matter (NOM). The graphene oxide had fast adsorption kinetics for both compounds because of its open-layered structure, with adsorption equilibrium being achieved within 15 min of contact. Although NOM did not affect the adsorption of geosmin on GO, it delayed that of MIB, probably because of competition for adsorption sites. The adsorption isotherms show that GO had a greater capacity for geosmin adsorption than for MIB because geosmin was more hydrophobic. Moreover, NOM interfered with the adsorption of MIB onto the GO, but increased the amount of adsorbed geosmin, which likely occurred because NOM increased the dispersibility of GO, which then increased the number of GO adsorption sites. The difference in the effects of NOM on GO adsorption of geosmin and MIB may be explained by their hydrophobicity. Although the adsorption of geosmin and MIB by GO was fast, its capacity to adsorb both compounds was substantially lower than that of activated carbon because of its higher hydrophilicity.

Digestion performance and contributions of organic and inorganic fouling in an anaerobic membrane bioreactor treating waste activated sludge.

This study evaluates the performance of an anaerobic membrane bioreactor (AnMBR) digesting waste activated sludge. A digestion reactor equipped with an external hollow fiber microfiltration membrane module was operated in continuous-mode for 248 days. The system demonstrated 56% volatile solids degradation at an organic loading rate of 0.40 g-VS/(L·d) in 15 days of hydraulic retention time. The average methane content in the biogas produced was 76% which is considerably high compared to that from a typical continuously stirred tank reactor. The transmembrane pressure remained under 12 kPa without membrane cleaning during the experimental period due to low filtration flux (0.01-0.07 m/d) and cross-flow-mode filtration. Ex situ membrane cleaning revealed that physically irreversible fouling was the dominant form of membrane fouling. Inorganic and organic fouling accounted for 16% and 45% of total membrane fouling, respectively.

Comparison of fouling characteristics of two different poly-vinylidene fluoride microfiltration membranes in a pilot-scale drinking water treatment system using pre-coagulation/sedimentation, sand filtration, and chlorination.

Two pilot-scale hybrid water treatment systems using two different poly-vinylidene fluoride (PVDF) microfiltration (MF) membranes (i.e. symmetric and composite) were operated at a constant permeate flux of 104.2l m(-2)h(-1) (=2.5 md(-1)) with a pre-coagulation/sedimentation, sand filtration (SF), and chlorination to produce potable water from surface water. Turbidity was removed completely. And humic substances, Al, and Fe were removed very well by the pilot-scale membrane system. To control microbial growth and mitigate membrane fouling, a NaOCl solution was injected into the effluent from SF before reaching the two membranes (pre-chlorination). However, it adversely affected membrane fouling due to the oxidization and adsorption of inorganic substances such as Al, Fe, and Mn. In the next run, the NaOCl was introduced during backwash (post-chlorination). As compared with the result of pre-chlorination, this change increased the operating period of the symmetric and the composite membranes from about 10 and 50 days to about 60 and 200 days, respectively.

Directed aggregation and fusion of lipid vesicles induced by DNA-surfactants.

We investigated DNA-directed aggregation of vesicles using DNA-surfactants. Following tethering of single-stranded DNA oligonucleotides to vesicles using DNA-surfactant, the tethered vesicles were assembled with other vesicles bearing complementary strands. The vesicle aggregation was strongly affected by the salt concentration and by temperature according to the characteristics of DNA hybridization. Restriction enzyme, which can hydrolyze the double-stranded DNA used in the present study, dissociated the vesicle aggregates. Exploration using fluorescently labeled vesicles suggested that the DNA-directed vesicle aggregation took place in a sequence-specific manner through DNA-duplex formation. Interestingly, the DNA-directed aggregation using short DNA-surfactant induced the fusion of vesicles to produce giant vesicles, resulting in an enzymatic reaction in the giant vesicle.

Differences in behaviour of three biopolymer constituents in coagulation with polyaluminium chloride: Implications for the optimisation of a coagulation-membrane filtration process.

Coagulation is often applied as a pre-treatment for membrane processes to reduce dissolved organic matter and to prevent membrane fouling. Biopolymers (BPs) have repeatedly been reported as major organic foulants, and coagulation conditions such as pH or dose have been optimised to minimise the remaining BPs. Optimisation however remains problematic because of the complex and heterogenetic nature of BP. In this study, the behaviour of several BP fractions in a coagulation process was investigated by excitation-emission matrix-parallel factor analysis (EEM-PARAFAC) following liquid chromatography (LC)-fractionation. Using a series of jar tests, we found that BP removal depends on the type of source water, reflecting differences in charge neutralisation conditions in three samples of natural water despite nearly identical processes for removing humic substances. This result demonstrates the complexity of optimisation for BP coagulation. Fractionation of EEM-PARAFAC to BP by LC showed that at least three organic component groups (C1, C2 and C3) constitute BP. C1 is tryptophan-like organic matter that is often found in wastewater effluent, C2 is tyrosine-like organic matter that has a phenolic chemical structure, and C3 is a humic-like substance. C1 was removed thoroughly at acidic pH but not at neutral pH, while the removal of C2 was inefficient even with a significant change in pH or dose, indicating similar difficulties in a coagulation process. The difference in components C1 and C2 may partly explain the difference in efficiencies of removal of BP in water from different sources. Our investigation suggests that the optimisation or selection of appropriate pre-treatment processes for membrane systems should be substantially based on the composition of BPs (e.g., C1 and C2 components).

Transition in fouling mechanism in microfiltration of a surface water.

The main disadvantage of membrane filtration is membrane fouling, which remains as the major obstacle for more efficient use of this technology. Information about the constituents that cause fouling is indispensable for more efficient operation. We examined the changes in both foulant characteristics and membrane morphology by performing the pilot-scale filtration test using one microfiltration membrane. During the operation, we cut the membrane fibers three times, and the components that caused irreversible fouling were extracted by acid or alkaline solution. We found that the characteristic of inorganic matter extracted by acid solution completely differed depending on the filtration period. A large amount of iron was extracted in the second chemical cleaning, while manganese was the dominant component of the extracted inorganic matter in the third chemical cleaning. The analysis of Fourier transform infrared (FTIR) and cross polarization magic angle spinning carbon-13 (CPMAS (13)C) nuclear magnetic resonance (NMR) demonstrated that the contribution of humic substances and carbohydrate in the organic foulant had increased as fouling developed. The changes in the major foulant have no relation with the fluctuation in feed water. The analysis of membrane morphology illustrated that the cake layer started to build up after the blockage of membrane pores. Based on the above results, we hypothesized the following fouling mechanism: the pores were covered or narrowed with relatively large particles such as iron, carbohydrate or protein; small particles such as manganese or humic substances blocked the narrowed pores; and finally an irreversible cake layer started to build up on the membrane surface.

Development of novel polysulfone membranes with embedded zirconium sulfate-surfactant micelle mesostructure for phosphate recovery from water through membrane filtration.

We prepared novel membranes that could adsorb phosphate from water through membrane filtration for use in a phosphate recovery system. Zirconium sulfate surfactant micelle mesostructure (ZS), which was the phosphate adsorbent, was embedded in a polysulfone matrix and flat sheet ultrafiltration membranes were made by nonsolvent induced phase separation. Scanning electron microscopy showed that the ZS particles existed on both the top surface and in the internal surface of the membrane. Increases in ZS content led to greater pure water flux because of increases in the surface porosity ratio. The amount of phosphate adsorbed on the membrane made from the polymer solution containing 10.5 wt% ZS was 0.071 mg P/cm2 (64.8 mg P/g-ZS) during filtration of 50 mg P/L synthetic phosphate solution. The membrane could be repeatedly used for phosphate recovery after regeneration by filtration of 0.1 M NaOH solution to desorb the phosphate. We applied the membrane to treat the effluent from an anaerobic membrane bioreactor as a real sample and successfully recovered phosphate.

Performance of anaerobic membrane bioreactor during digestion and thickening of aerobic membrane bioreactor excess sludge.

In this study, we evaluated the performance of an anaerobic membrane bioreactor in terms of digestion and thickening of excess sludge from an aerobic membrane bioreactor. A digestion reactor equipped with an external polytetrafluoroethylene tubular microfiltration membrane module was operated in semi-batch mode. Solids were concentrated by repeated membrane filtration and sludge feeding, and their concentration reached 25,400mg/L after 92d. A high chemical oxygen demand (COD) removal efficiency, i.e., 98%, was achieved during operation. A hydraulic retention time of 34d and a pulse organic loading rate of 2200mg-COD/(L-reactor) gave a biogas production rate and biogas yield of 1.33L/(reactor d) and 0.08L/g-CODinput, respectively. The external membrane unit worked well without membrane cleaning for 90d. The transmembrane pressure reached 25kPa and the filtration flux decreased by 80% because of membrane fouling after operation for 90d.

Interactions of dissolved humic substances with oppositely charged fluorescent dyes for tracer techniques.

To investigate interactions between oppositely charged fluorescent dyes and dissolved humic substances, fluorescence quenching of fluorescein and rhodamine 6G with dissolved humic substances was performed. Binding coefficients were obtained by the Stern-Volmer equation. The fluorescence of rhodamine 6G was largely quenched by the addition of humic acid and a non-linear Stern-Volmer plot was obtained. This strong quenching may be caused by the electrostatic interaction between cationic rhodamine 6G and humic acid and strengthened by the hydrophobic repulsion. In contrast, the quenching and interactive effects of dissolved humic substances for fluorescein were relatively weak.

Tracking inorganic foulants irreversibly accumulated on low-pressure membranes for treating surface water.

While low-pressure membrane filtration processes (i.e., microfiltration and ultrafiltration) can offer precise filtration than sand filtration, they pose the problem of reduced efficiency due to membrane fouling. Although many studies have examined membrane fouling by organic substances, there is still not enough data available concerning membrane fouling by inorganic substances. The present research investigated changes in the amounts of inorganic components deposited on the surface of membrane filters over time using membrane specimens sampled thirteen times at arbitrary time intervals during pilot testing in order to determine the mechanism by which irreversible fouling by inorganic substances progresses. The experiments showed that the inorganic components that primarily contribute to irreversible fouling vary as filtration continues. It was discovered that, in the initial stage of operation, the main membrane-fouling substance was iron, whereas the primary membrane-fouling substances when operation finished were manganese, calcium, and silica. The amount of iron accumulated on the membrane increased up to the thirtieth day of operation, after which it reached a steady state. After the accumulation of iron became static, subsequent accumulation of manganese was observed. The fact that the removal rates of these inorganic components also increased gradually shows that the size of the exclusion pores of the membrane filter narrows as operation continues. Studying particle size distributions of inorganic components contained in source water revealed that while many iron particles are approximately the same size as membrane pores, the fraction of manganese particles slightly smaller than the pores in diameter was large. From these results, it is surmised that iron particles approximately the same size as the pores block them soon after the start of operation, and as the membrane pores narrow with the development of fouling, they become further blocked by manganese particles approximately the same size as the narrowed pores. Calcium and silica are assumed to accumulate on the membrane due to their cross-linking action and/or complex formation with organic substances such as humic compounds. The present research is the first to clearly show that the inorganic components that contribute to membrane fouling differ according to the stage of membrane fouling progression; the information obtained by this research should enable chemical cleaning or operational control in accordance with the stage of membrane fouling progression.

Hydrophilic fraction of natural organic matter causing irreversible fouling of microfiltration and ultrafiltration membranes.

Although membrane filtration is a promising technology in the field of drinking water treatment, persistent membrane fouling remains a major disadvantage. For more efficient operation, causative agents of membrane fouling need to be identified. Membrane fouling can be classified into physically reversible and irreversible fouling on basis of the removability of the foulants by physical cleaning. Four types of natural organic matter (NOM) in river water used as a source of drinking water were fractionated into hydrophobic and hydrophilic fractions, and their potential to develop irreversible membrane fouling was evaluated by a bench-scale filtration experiment together with spectroscopic and chromatographic analyses. In this study, only dissolved NOM was investigated without consideration of interactions of NOM fractions with particulate matter. Results demonstrated that despite identical total organic carbon (TOC), fouling development trends were significantly different between hydrophilic and hydrophobic fractions. The hydrophobic fractions did not increase membrane resistance, while the hydrophilic fractions caused severe loss of membrane permeability. These results were identical with the case when the calcium was added to hydrophobic and hydrophilic fractions. The largest difference in NOM characteristics between hydrophobic and hydrophilic fractions was the presence or absence of macromolecules; the primary constituent causing irreversible fouling was inferred to be "biopolymers", including carbohydrates and proteins. In addition, the results demonstrated that the extent of irreversible fouling was considerably different depending on the combination of membrane materials and NOM characteristics. Despite identical nominal pore size (0.1 µm), a polyvinylidene fluoride (PVDF) membrane was found to be more rapidly fouled than a PE membrane. This is probably explained by the generation of strong hydrogen bonding between hydroxyl groups of biopolymers and fluorine of the PVDF membrane. On the basis of these findings, it was suggested that the higher fouling potential of the hydrophilic fraction of the dissolved NOMs from various natural water sources are mainly attributed to macromolecules, or biopolymers.

Affinity of functional groups for membrane surfaces: implications for physically irreversible fouling.

Fouling in membranes used for water treatment has been attributed to the presence of natural organic matter (NOM) in water. There have been reports recently on the contribution of hydrophilic fractions of NOM (e.g., carbohydrate-like substances) to fouling, but there is still little information about the physicochemical interactions between membranes and carbohydrate-like substances. In this study, the affinity of carbohydrate-like substances to two different microfiltration (MF) membranes was investigated by using atomic force microscopy (AFM) and functionally modified microspheres. Microspheres were attached to the tip of the cantilever in an AFM apparatus and the adhesion forces working between the microspheres and the membranes were determined. The microspheres used in this study were coated with either hydroxyl groups or carboxyl groups to be used as surrogates of carbohydrate-like substances or humic acid, respectively. Measurements of adhesion force were carried out at pH of 6.8 and the experimental results demonstrated that the adhesion force to membranes was strong in the case of hydroxyl groups but weak in the case of carboxyl groups. The strong adhesion between the hydroxyl group and the membrane surface is explained by the strong hydrogen bond generated. It was also found that the affinity of the hydroxyl group to a polyvinylidenefluoride (PVDF) membrane was much higher than that to a polyethylene (PE) membrane, possibly due to the high electronegative nature of the PVDF polymer. The time course of changes in the affinity of hydroxyl group to a membrane used in a practical condition was investigated by repeatedly carrying out AFM force measurements with PE membrane specimens sampled from a pilot plant operated at an existing water treatment plant. Microspheres exhibited strong affinity to the membrane at the initial stage of operation (within 5 days), but subsequently exponential reduction of the affinity was seen until the end of operation, as a result of fouling development. However, the magnitude of affinity of hydroxyl-modified microspheres was much higher than that of carboxyl-modified microspheres even after the significant reduction of affinity of hydroxyl-modified microspheres to the membranes was seen. The results obtained in this study partially explain why hydrophilic NOM dominated over humic substances in foulants of membranes used for water treatment in recent studies on fouling.

Mechanism involved in the evolution of physically irreversible fouling in microfiltration and ultrafiltration membranes used for drinking water treatment.

Control of membrane fouling is important for more efficient use of membranes in water treatment. Control of physically irreversible fouling, which is defined as fouling that requires chemical cleaning to be cancelled, is particularly important for reduction of operation cost in a membrane process. In this study, a long-term filtration experiment using three different types of MF and UF membranes was carried out at an existing water purification plant, and the evolution of physically irreversible fouling was investigated. The experimental results demonstrated that the extent of physically irreversible fouling differed significantly depending on the membrane type. Cleaning of the fouled membranes with various chemical reagents demonstrated that organic matter was mainly responsible for physically irreversible fouling. Organic matter that had caused physically irreversible fouling in the long-term operation was desorbed from the fouled membranes and was subjected to Fourier transform infrared and 13C nuclear magnetic resonance analyses. These analyses revealed that carbohydrates were dominant in the membrane foulant regardless of the type of membrane. Based on measurements of molecular weight distribution of organic matter in the feedwater and the permeates from the membranes, a two-step fouling mechanism is proposed to explain the dominance of carbohydrates in the foulant: hydrophobic (humic-like) components with small molecular weight are first adsorbed on the membrane and, consequently, narrow the size of micro-pores of membranes, and then hydrophilic (carbohydrate-like) compounds with larger molecular weight plug the narrowed pores or the hydrophilic compounds are adsorbed onto the membrane surface conditioned by the hydrophobic components.