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Membrane fouling is still a significant drawback of membrane technology. Irreversible fouling can be alleviated only by chemical cleaning. Guidelines for determining the methods and efficiency of chemical cleaning, such as those for timing and chemical category, are still not available because of the lack of knowledge about foulants during membrane filtration. In this study, a new in situ observation method, i.e., three-dimensional solid-phase fluorescence excitation–emission matrix spectroscopy (SPF-EEM), was used to characterise the chemical cleaning efficiency of irreversible fouling. Caustic, acidic and hypochlorite chemical solutions were tested as cleaning agents used in different sequences. Progression trends of irreversible fouling were then characterised by in situ and online SPF-EEM. Chemical cleaning efficiency observed by SPF-EEM was consistent with that observed by conventional infrared spectroscopy analysis, which only can be conducted ex situ. By performing SPF-EEM analysis, the optimal chemical cleaning procedure, which exhibited a result consistent with that obtained for the recovery of pure water permeability, could be determined. Hence, SPF-EEM is effective for the in situ characterisation of irreversible fouling, and it is beneficial for the determination of the timing and chemical category for cleaning based on the SPF-EEM of foulants.

DOI： 10.1016/j.memsci.2020.118296

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

The optimization of the coagulation of floc remains challenging because it is affected by various factors, including the pH, turbidity, and alkalinity. A jar test is a reliable method to optimize the coagulation conditions; however, it is time-consuming and requires an experienced technician. A convolutional neural network (CNN) can be used to extract the specific image characteristics via learning processes to construct image classification models. In this study, we applied a CNN for predicting the jar test performance. Artificial water adjusted with kaolin and commercial humic acid was initially used. The floc image was recorded using a video camera during the jar test, and models for predicting the turbidity of the supernatants were constructed by inputting the recorded floc images and the level of turbidity as the training dataset. The learning curve denoted that all the models exhibited 100% accuracy during the learning process, clearly indicating that the CNN worked appropriately with respect to the extraction of the characteristics of the floc images and the determination of their settleability. Subsequently, the overfitting level was investigated by inputting the test data into the models. The maximum prediction accuracy of all the models exceeded 96%. The initial 100 s of the model's learning of the floc images achieved a maximum accuracy of 99.6%, i.e., the images captured during rapid mixing were sufficient to ensure the reliability of the model. The applicability of the model to natural water samples was also investigated using samples obtained during different months. Even though the accuracy for natural water was lower than that for artificial water, 90% accuracy was achieved even when fluctuating natural water was used, demonstrating the applicability of a CNN to extract the characteristics of the floc governing its settleability and to immediately as well as automatically predict the state of coagulation.

DOI： 10.1016/j.seppur.2019.116467

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.watres.2019.114928

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

In coagulation-membrane filtration water treatment processes, it is still difficult to determine the optimal coagulation condition to minimize irreversible membrane fouling. In microfiltration (MF), mesa particles (i.e., 20 nm-0.5 mu m) are thought to play an important role in irreversible membrane fouling, especially their characteristics of particle number (PN) and zeta potential (ZP). In this study, a new nanoparticle tracker combined a high-output violet laser with a microscope was developed to identify the physicochemical characteristics of these microscopic and widely dispersed meso-particles. The effects of pH and coagulant dose on ZP and PN of micro-particles (i.e., >0.5 mu m) and meso-particles were investigated, and then coagulation-MF tests were conducted. As the result, irreversible membrane fouling was best controlled for both types of membranes, while meso-particle ZP approached zero at around pH 5.5 for both types of natural water. Since PN was greatest under these conditions, ZP is more important in determining the extent of irreversible membrane fouling than PN. However, the acidic condition to neutralize meso-particles is not suitable for actual operation, as considering residual aluminum concentration, pipe corrosion, and chlorination efficiency. It is therefore necessary to investigate coagulants or other methods for the appropriate modification of meso-particle characteristics. (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

DOI： 10.1016/j.watres.2016.05.076

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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 mu m), 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. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.watres.2014.01.024

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

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.

DOI： 10.1021/es800406j

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

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 C-13 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.

DOI： 10.1021/es0629054

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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 C-13) 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. (c) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.watres.2007.05.060

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Language：Japanese   Publisher：公益社団法人 計測自動制御学会  

<p>The objective of this paper is to predict the turbidity after flocculation from floc images in jar-test deep convolutional neural network (DCNN). Our goal is to develop a system to control the water purification process using the predictive model. In conventional studies, chemical parameters such as pH and alkalinity are generally used to predict turbidity. However, our proposed method does not use chemical parameters. It uses images of floating matter, called “floc”, generated during the flocculation process as input to the DCNN. We performed experiments using DCNN to predict turbidity after flocculation from images of “flocs” generated in jar-tests. We used VGG-16 as the DCNN for our experiments. Furthermore, we conducted experiments to compare the proposed method with the baseline method using chemical parameters.</p><p>As a result, 1) we revealed that the turbidity after flocculation can be predicted by using the image during flocculation as input to VGG-16; 2) we revealed that the optimal period to be used for the prediction model was the data 200 second after the start of the jar-tests; 3) we revealed that our proposed method can predict turbidity with better accur

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Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

DOI： 10.2208/jscejer.78.7_iii_73

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In this study, we have proposed an indentation method to characterize a surface degraded layer due to UV light irradiation of polymers. Here, we assume that the degraded layer has a homogeneous and isotropic nature, and that the target material is a bilayer system (i.e., the degraded layer is formed on the substrate of the non-degraded base material). This method enables the quantitative measurement of mechanical properties (Young's modulus E and yield strength σY) and thickness of the degraded layer. In the first step, we conducted a shallow indentation in order to ignore the effect of substrate (non-degraded base material). This method deduces the mechanical property of degraded layer itself. The second step is deep indentation (i.e. indentation depth is deeper to capture substrate effect) for measuring the thickness of the degraded layer. To establish these methods, reverse analysis with the dimensionless function was newly proposed. We conducted a parametric study using the finite element method, in which the material cases cover various polymers, degradation properties, and layer thickness. Experimental verification was finally carried out, and the degraded layer due to UV light for polycarbonate (PC) was successfully characterized. Because this method is simple, convenient, and non-destructive, it might be useful for characterization of weathering degradation in other engineering polymers.

DOI： 10.1016/j.mtcomm.2020.101873

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Language：Japanese   Publisher：日本水環境学会 ; 1992-  

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Language：Japanese   Publisher：日本下水道協会  

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本研究の目的は浄水場の凝集プロセスにおける凝集剤の注入量を最適化するために、凝集剤を注入した処理水の初期の画像から最終的な凝集後濁度を予測することである。凝集プロセスでは凝集剤を注入し攪拌することによって時間を追うごとにフロックと呼ばれる多量の集塊が形成される。このフロックの形成初期段階の処理水の画像から機械学習を用いて凝集後濁度を予測する。深層畳み込みネットワークを利用し、河川水を用いた実験を行った結果、(1)特徴が出やすいと思われる凝集の時間帯を明らかにし、(2)河川水の凝集中の画像からおよそ90%前後の精度で予測可能であることを明らかにした。

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Language：Japanese   Publisher：公益社団法人 日本水道協会  

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Language：Japanese   Publisher：公益社団法人 日本水道協会  

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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.

DOI： 10.3390/ijerph16111907

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© 2019 by the authors. Licensee MDPI, Basel, Switzerland. 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.

DOI： 10.3390/ijerph16111907

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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.

DOI： 10.1016/j.biortech.2018.09.147

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.watres.2018.01.034

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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 hi 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/cm(2) (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. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.watres.2017.08.005

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Engineering polymers generally exhibit asymmetric yield strength in tension and compression due to different arrangements of molecular structures in response to external loadings. For the polymeric materials whose plastic behavior follows the Drucker-Prager yield criterion, the present study proposes a new method to predict both tensile and compressive yield strength utilizing instrumented spherical indentation. Our method is decomposed into two parts based on the depth of indentation, shallow indentation, and deep indentation. The shallow indentation is targeted to study elastic deformation of materials, and is used to estimate Young's modulus and yield strength in compression; the deep indentation is used to achieve full plastic deformation of materials and extract the parameters in Drucker-Prager yield criterion associated with both tensile and compressive yield strength. Extensive numerical computations via finite element method (FEM) are performed to build a dimensionless function that can be employed to describe the quantitative relationship between indentation force-depth curves and material parameters of relevance to yield criterion. A reverse algorithm is developed to determine the material properties and its robustness is verified by performing both numerical and experimental analysis.

DOI： 10.1115/1.4035268

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DOI： 10.18898/1217.00016648

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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 25,400 mg/L after 92 d. A high chemical oxygen demand (COD) removal efficiency, i.e., 98%, was achieved during operation. A hydraulic retention time of 34 d and a pulse organic loading rate of 2200 mg-COD/(L-reactor) gave a biogas production rate and biogas yield of 1.33 L/(reactor d) and 0.08 L/g-CODinput, respectively. The external membrane unit worked well without membrane cleaning for 90 d. The transmembrane pressure reached 25 kPa and the filtration flux decreased by 80% because of membrane fouling after operation for 90 d. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.biortech.2016.06.124

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DOI： 10.5360/membrane.41.142

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The tensile deformation behavior of polyvinylidenedifluoride (PVDF) symmetrical microfiltration hollow-fiber (HF) membranes was studied. The membranes had submicron pores with a three-dimensional open-cell structure. The surface and cross section of the porous membranes were observed by FESEM (field emission scanning electron microscope) to investigate the microstructure of the cell, namely, its size and ligament geometry. During uniaxial tensile tests, the membranes underwent elastic deformation and plastic deformation. Large deformation induced pore growth along the tensile direction, resulting in an increase in water permeability. In order to establish a mechanical model for tensile deformation, the finite element method (FEM) was employed. In this model, the Kelvin polyhedron (truncated octahedron structure) was used to mimic a three-dimensional open-cell structure. A one-unit cell based on this structure was created, and a periodical boundary condition was employed for the FEM computation. The FEM model could reproduce the overall elastoplastic deformation behavior of the porous membrane and provide useful insight into the fabrication of porous membranes and reliable operation of water purification. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.memsci.2015.09.048

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.watres.2015.09.018

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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. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.watres.2015.08.039

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The effects of membrane module configuration and membrane flux on specific air demand per permeate (SAD(p)) required for stable operation of a submerged membrane bioreactor (MBR) for treating municipal wastewater were investigated. An intensively aerated membrane module was developed to reduce the membrane fouling in submerged membrane bioreactors. In this module, coarse bubbles can be introduced at higher density in the vicinity of the membrane fibers, made of polytetrafluoroethylene (PTFE), which has a very high tensile strength (90-110 N/fiber) even though it has high porosity (about 80%). By applying the intensively aerated membrane module developed in this study to pilot-scale MBRs, very low membrane fouling rate was achieved during the continuous MBR operation. The observation of fiber movements using high speed camera revealed that the membrane-fiber vibration in the intensively aerated module were apparently intensified compared with those in a conventional membrane module. Reducing membrane flux was also beneficial for reducing SAD(p). When the MBR equipped with the intensively aerated module, stable continuous MBR operation without any membrane cleaning for two months under low SAD(p) (8.8 m(3)-air/m(3)-permeate) was achieved by lowering membrane flux to 16 L/m(2) h (or 0.4 m(3)/m(2)/day), even in the short membrane height of 0.5 m. These results strongly suggest that there is still great room for improving the efficiency of membrane aeration by optimizing hydrodynamics around membrane modules. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.seppur.2015.04.030

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DOI： 10.2208/jscejer.71.III_447

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Water treatment using ultrafiltration (UF) membranes is gaining popularity world-wide, but the problem of membrane fouling needs to be addressed. We investigated the characteristics of membrane foulants by conducting two long-term filtration experiments using surface water from the Chitose River. The membrane was made of polyacrylonitrile and had a molecular weight cut-off of 100 kDa. The experiments were conducted in February 2004 Winter operation (Run 1) and October 2005 Summer operation (Run 2), when feed water characteristics were considerably different. Despite this, rates of physically irreversible fouling were similar. By measuring pure water permeability before and after chemical cleaning, we found that acidic or chelate solutions were most effective for cleaning the membrane from Run 1, whereas an alkaline solution was more effective for that from Run 2. Analysis of the chemical solutions that effective worked for canceling the fouling revealed that acidic cleaning in Run 1 extracted iron, carbohydrate and humic acid, while alkaline cleaning in Run 2 extracted carbohydrates. These results indicates that the iron, carbohydrates and humic acid caused the physically irreversible fouling in Run I, and carbohydrates were mainly responsible in Run 2. Based on the findings obtained in this study, it was suggested that the most important foulants and the most effective chemical cleaning agents may differ substantially between seasons. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.seppur.2014.04.043

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IWA PUBLISHING  

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.

DOI： 10.2166/wst.2014.104

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IWA PUBLISHING  

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.

DOI： 10.2166/wst.2014.364

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Language：Japanese   Publisher：日本水環境学会  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：SOC FIBER SCIENCE TECHNOLOGY  

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Language：Japanese   Publisher：繊維学会  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IWA  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Performance and fouling characteristics of two pilot-scale polyvinylidene fluoride hollow fiber microfiltration membranes for drinking water treatment were studied under the same flux and physical cleaning conditions. It is expected that this paper can provide insights into the functions of operation mode (one pressurized and one submerged) of the membrane in process performance and fouling evolution. As a result, it was found that the two membranes showed similar performance in terms of removal efficiencies of organic and inorganic substances. However, the pressurized membrane showed relatively more severe membrane fouling than the submerged membrane because the cake compressibility and thickness seemed to have been increased due to the hard-to-remove cake layer of the pressurized membrane containing relatively large amounts of humic substances, carbohydrate, and Fe than that of the submerged membrane, especially under high turbidity conditions without any pre-treatment. Under low turbidity conditions with pre-coagulation/sedimentation, the two membranes showed similar behaviors for increase of transmembrane pressure. After the chemical cleaning that was carried out after removing the cake layers from the membrane, surface flux restoration of the two membranes was not much different.

DOI： 10.1016/j.desal.2008.05.025

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Aseanian membrane society  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

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 char 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. (c) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.colsurfb.2008.05.017

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Chemical coagulation has been widely used as a method to mitigate membrane fouling in MF/UF membranes used for drinking water treatment. Optimization of coagulation as pre-treatment of membrane processes has not been achieved yet: the optimum condition of coagulation for conventional treatment systems is not necessarily applicable to membrane-based treatment systems. This study investigated (physically) irreversible membrane fouling in an MF membrane used with pre-coagulation by aluminum salt. In a series of bench-scale filtration tests, feed water containing commercially available humic acid or organic matter isolated from surface water was coagulated with polyaluminum chloride (PACl) under various conditions and subsequently filtered with an MF membrane with the nominal pore size of 0.1 mu m. It was found that coagulation conditions had great impacts on the degree of physically irreversible fouling. Acidic conditions improved the quality of treated water but generally caused greater physically irreversible fouling than did neutral or alkaline conditions. Also, dosage of coagulant was found to be influential on the degree of membrane fouling: high dosage of coagulant frequently caused more severe irreversible fouling. Sizes of flocs seemed to become small under acidic conditions in this study, which was indicated by high concentrations of aluminum in the permeate under acidic conditions. It is thought that small flocs produced under acidic conditions could migrate into micropores of the membrane and caused physically irreversible fouling by plugging or adsorption. These findings obtained in the bench-scale tests were verified in a long-term pilot-scale test. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.memsci.2008.04.018

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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 adversly 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. (C) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.watres.2007.12.011

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

A long-term filtration experiment with a microfiltration membrane was carried out at an existing water purification plant and the influence of pre-coagulation on the evolution of physically irreversible fouling was investigated. Coagulation carried out at pH 7 mitigated the evolution of physically irreversible fouling. It was found that the degree of physically reversible fouling increased as a result of coagulation. Chemical analysis of the foulant desorbed by NaOH or HCl solution showed that pre-coagulation could prevent the fouling caused by iron, but could not control the fouling caused by organic matters. Particle size distribution of iron in the feed water implied that physically irreversible fouling was caused by the iron of size close to the micro-pores of the membrane (around 0.1μm) when coagulationwas not carried out. The pre-coagulation enlarged the size of iron particles, and would prevent the evolution of physically irreversible fouling. Based on the results obtained in this study, for the control of physically irreversible fouling, the optimum condition of coagulation is determined as follows: the one that can enlarge particles in the feed water with the size that is close to opening of membrane micro-pores.

DOI： 10.11532/proes1992.44.135

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：I W A PUBLISHING  

Water treatment using microfiltration (MF)/ultrafiltration (UF) membranes is gaining in popularity all over in this study the influence of problem of membrane fouling needs to be addressed the world but the, calcium on irreversible fouling in MF/UF membrane filtering natural organic matter (NOM) was investigated on the basis of a series of bench-scale filtration tests. Two types of feed water, solution of commercially available humic acid and surface water used for drinking water source, were filtered with four different MF/UF membranes. It was found that the influence of calcium on the evolution of irreversible fouling would differ depending on the feed water characteristics. Calcium facilitated the aggregation of small molecules with hydrophobic nature contained in commercially available humic acid and the aggregate probably plugged the micropores, resulting in severe irreversible fouling. The effect of calcium was not obvious in the case of the surface water used in this study. This result implies that the use of commercial humic acid for the examination of membrane fouling would be inappropriate.

DOI： 10.2166/aqua.2007.018

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This paper describes the demulsification of olive-oil/ SDS emulsion (DOSE) method for selective isolation of environmental mycobacteria. A soil sample was suspended in olive oil and centrifuged. The supernatant was emulsified on plates together with SDS solution. After incubation, the colonies that had developed on the plates were surrounded by clear zones. The isolates were identified as genus Mycobacterium, and as belonging to a fast-growing group, by 16S rRNA gene sequence analysis.

DOI： 10.1271/bbb.60687

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Other Link： http://orcid.org/0000-0003-2103-7796

Language：English   Publishing type：Research paper (scientific journal)   Publisher：日本水環境学会  

Two pilot-scale polyvinylidene fluoride (PVDF) microfiltration (MF) membranes with different structures (i.e. symmetric and asymmetric) were operated after coagulation/sedimentation, sand filtration, and chlorination. Turbidity was removed completely. Moreover, humic substances, Al, and Fe were removed very well by the pilot-scale system. An asymmetric membrane (HFS membrane) having a nominal pore size of 0.05 &mu;m showed relatively high removal efficiency of the small organic matter (about 6,000 Da) than a symmetric membrane (HFM membrane) having a nominal pore size of 0.1 &mu;m. However, the extracted inorganic concentrations of the HFM membrane were relatively higher than that of the HFS membrane. Therefore, it could be concluded that the HFS membrane better reduced membrane fouling than the HFM although the nominal pore size of the former was half of the latter. To control microbial growth and mitigate membrane fouling, a NaOCl solution was injected into the effluent of sand filtration before the both membranes. However, it adversly affected membrane fouling due to the oxidization of inorganic substances such as Al, Fe, and Mn.

DOI： 10.2965/jwet.2007.79

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS INC  

For more efficient use of membrane technology in water treatment, it is essential to understand more about the fouling that requires chemical cleaning to be eliminated (i.e., irreversible fouling). In this study, five different MF/UF membranes and four types of organic matter collected from different origins were examined in terms of the degree of irreversible membrane fouling. Experimental results demonstrated that the extent of irreversible fouling differed significantly depending on the properties of both the membrane and organic matter. Among the tested membranes, UF membranes made of polyacrylonitrile (PAN) exhibited the best performance in terms of prevention of irreversible fouling. In contrast, MF membranes, especially one made of polyvinylidenefluoride (PVDF), suffered significant irreversible fouling. Conventional methods for characterization of organic matter such as specific ultraviolet absorption (SUVA), XAD fractionation, and excitation-emission matrix (EEM) were found to be inadequate for prediction of the degree of irreversible fouling. This is because these analytical methods represent an average property of bulk organic matter, while the fouling was actually caused by some specific fractions. It was revealed that hydrophilic fraction of the organic matter was responsible for the irreversible fouling regardless of the type of membranes or organic matter.

DOI： 10.1080/01496390600634665

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Language：Japanese   Publisher：北海道大学衛生工学会  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The main obstacle for wider use of membrane bioreactors (MBRs) for wastewater treatment is membrane fouling (i.e., deterioration of membrane permeability), which increases operating costs. For more efficient control of membrane fouling in MBRs, an understanding of the mechanisms of membrane fouling is important. However, there is a lack of information on membrane fouling in MBRs, especially information on features of components that are responsible for the fouling. We conducted a pilot-scale experiment using real municipal wastewater with three identical MBRs under different operating conditions. The results obtained in this study suggested that the food-microorganisms ratio (F/M) and membrane filtration flux were the important operating parameters that significantly influenced membrane fouling in MBRs. Neither concentrations of dissolved organic matter in the reactors nor viscosity of mixed liquor, which have been thought to have influences on fouling in MBRs, showed clear relationships with membrane fouling in this study. Organic substances that had caused the membrane fouling were desorbed from fouled membranes of the MBRs at the termination of the operation and were subjected to Fourier transform infrared (FTIR) and C-13 nuclear magnetic resonance (NMR) analyses. These analyses revealed that the nature of the membrane foulant changes depending on F/M. It was shown that high F/M would make the foulant more proteinaceous. Carbohydrates were dominant in membrane foulants in this study, while features of humic substances were not apparent.

DOI： 10.1021/es0502425

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DOI： 10.11532/proes1992.41.257

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