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• Membrane fouling caused by lipopolysaccharides (LPSs) was firstly assessed. • Evolution of fouling by LPSs could be several-fold faster than that by alginate. • Large molecules (>1 MDa) found in LPSs would be responsible for fouling. • QCM analysis showed that affinity of LPSs to PVDF polymer was remarkably high. • Addition of LPSs to MBR sludge apparently accelerated irreversible fouling. Polysaccharides were identified as key foulants in membrane bioreactors (MBRs) in previous studies. Polysaccharides used for MBR fouling research should represent real foulants, and alginate and dextran have often been used as model polysaccharides. However, their properties are not necessarily similar to those of polysaccharides that actually cause membrane fouling in MBRs. In recent studies, it was shown that polysaccharides causing membrane fouling in MBRs had the structures of lipopolysaccharides (LPSs), which are components of the cell wall of gram-negative bacteria. In the present study, therefore, membrane fouling caused by commercially available LPSs was investigated and was compared with that caused by model polysaccharides. In a series of batch filtration tests using four different microfiltration (MF) and ultrafiltration (UF) membranes, regardless of the membrane used, LPSs caused more severe membrane fouling than did alginate or dextran when they were filtered under the condition of the same organic carbon concentration. The properties of LPSs were found to be considerably different from those of alginate and dextran. In particular, affinity of LPS to PVDF polymer assessed by quartz crystal microbalance (QCM) mass measurement was remarkably high, and it would account for the severe fouling caused by LPSs. In experiments with filtering of mixtures of the model polysaccharides and a biomass suspension collected from a pilot-scale MBR, which were conducted to mimic the sudden increase in dissolved polysaccharides in real MBRs, LPS induced significant irreversible fouling, while alginate and dextran did not. The results obtained in this study clearly demonstrated high fouling potential of LPSs. Use of LPSs in future MBR fouling studies is therefore recommended. [ABSTRACT FROM AUTHOR]

Abstract Intensive membrane cleaning can be used with ceramic membranes since they are physically/chemically robust. It might therefore be possible for membrane bioreactors (MBRs) to be operated under the condition of a high membrane flux when ceramic membranes are used with such intensive membrane cleaning. In this study, bench-scale MBRs equipped with flat-sheet ceramic membranes were operated for long periods. Circulation of granular materials (cylindrical polyurethane) in the tank and frequent chemically enhanced backwash (CEB) were used as intensive physical cleaning and chemical cleaning in this study, respectively. Experiments were carried out with synthetic wastewater. The use of granular materials, which can cause significant damage to polymeric membranes (Kurita et al., 2015), was effective for controlling the formation of cake (deposition of microbial flocs) on the surface of the ceramic membranes. When both mechanical cleaning using the granular materials and CEB with 1000 ppm of sodium hypochlorite (NaClO) were applied, contrary to an expectation, evolution of reversible fouling (formation of a transparent gel layer on the membrane surface) became uncontrollable, whereas irreversible fouling was effectively controlled. The use of NaClO induced release of organic macromolecules via biomass decay, leading to the evolution of reversible fouling. When the intensity of CEB with NaClO was adequately lowered, with the aid of the mechanical cleaning using the granules, the bench-scale MBR could be operated stably under an elevated membrane flux for a long period (>70 days). It was postulated that the adjustment of CEB intensity preferably altered properties of organic macromolecules released from biomass: the structure of the gel layer was porous when the CEB intensity was lowered. When CEB is used in MBRs, it is thus important to balance cleaning efficiency and its harmful effect on biomass. When adequate CEB is used with intensive mechanical cleaning, MBRs with ceramic membranes can be operated under high flux conditions. Graphical abstract Image 1 Highlights • Use of flat-sheet ceramic membrane enabled intensive cleaning in MBR. • CEB induced release of organic macromolecules from biomass and accelerated fouling. • Characteristics of macromolecules released were different depending on CEB intensity. • Intensity of CEB must be carefully adjusted to avoid acceleration of fouling. • Flux could be significantly elevated with adequate CEB and granular materials. [ABSTRACT FROM AUTHOR]

With the widespread application of liquid chromatography with organic carbon detection (LC-OCD) to investigate membrane fouling in low-pressure membranes such as microfiltration (MF) and ultrafiltration (UF), membrane fouling by macromolecular hydrophilic biopolymer fraction has been recognized. In this study, a drinking water source was intensively investigated over 16 months. Membrane filtration using hollow-fiber MF membranes was carried out in constant flux mode with periodic backwashing, and two pretreatments (aluminum coagulation and anion exchange) were examined in terms of biopolymer removal and fouling mitigation. Higher biopolymer removal rates achieved by anion exchange than coagulation did not cause better control of membrane fouling in MF. Coagulation and anion exchange removed different types of biopolymers, which implied diversity in the biopolymer fraction. A modified set-up of LC-OCD analysis in which two different columns were sequentially connected was examined. It was demonstrated that the biopolymer fraction detected as a single peak with molecular weight of > 10,000 Da with the conventional LC-OCD set-up comprised of molecules with a variety of molecular weights including > 1,000,000 Da. It was found that coagulation removed large-size biopolymers with higher fouling potentials; while anion exchange preferentially removed small-size biopolymers with lower fouling potential. Concentration of large-size biopolymers in the feed water collected on different dates correlated with the degree of membrane fouling. In an attempt to generalize the conclusion drawn from the experiments using the specific drinking water source, batch MF tests filtering biopolymers isolated from different drinking water sources were also carried out. Importance of the large-size biopolymer fraction in the evolution of membrane fouling was also suggested with different drinking water sources. [ABSTRACT FROM AUTHOR]

Organic matter in municipal wastewater should be regarded as a resource for energy production in the future. Direct application of anaerobic digestion to municipal wastewater is easy if the concentration of organic matter is increased. Although microfiltration membranes can concentrate organic matter in raw municipal wastewater, severe membrane fouling is likely to occur. In this study, efficient physical cleaning methods for direct membrane filtration (DMF) of municipal wastewater were investigated. Agitation of the tank, vibration of membrane modules, and use of granular materials were examined. Aeration was not tested because it leads to microbial degradation of organic matter (loss of recoverable energy). No single cleaning method worked well for DMF. However, a combination of membrane vibration and agitation of the tank was found to be effective. When the effective physical cleaning was performed with chemically enhanced backwash using citric acid and an adequate membrane flux, DMF of real municipal wastewater could be continued for almost one month without conducting any off-line membrane cleaning. The increase in transmembrane pressure was almost perfectly controlled in the long-term operation, during which 75% of organic matter was successfully recovered and 50-fold concentration (based on volume) of wastewater was continuously achieved with hydraulic retention time of 3.1 h. [ABSTRACT FROM AUTHOR]

In recent studies on membrane fouling in microfiltration (MF) and ultrafiltration (UF) for drinking water production, hydrophilic macromolecular organics referred to as biopolymers have been shown to be major players in the fouling. In this study, various pretreatments were compared to maximize removal of biopolymers and to control membrane fouling efficiently. Multiple water samples were collected from different drinking water sources and were used in this study. Coagulation using polyaluminum chloride (PACl) was carried out under conditions of different dosages and different pHs and was also carried out in combination with the use of powdered activated carbon (PAC) or magnetic ion exchange (MIEX ® ) resin. The efficiency of removal of biopolymers was highest by the combination of MIEX ® and coagulation regardless of the type of sample. Efficient removal of biopolymers achieved by the combination of MIEX ® and coagulation led to efficient control of membrane fouling in MF, which was confirmed by bench-scale filtration tests conducted under a constant flux of 62.5 LMH using commercially available hollow-fiber membranes. Enhanced coagulation with increased coagulant dosage or acidic coagulation (pH = 6) also exhibited good removal of biopolymers in some cases and led to control of fouling. In contrast, the combination of PAC and coagulation sometimes caused more rapid evolution of fouling by forming cake layers on the membrane surface. Results of bench-scale tests showed that the concentration of biopolymers in the feed water correlated well with the degree of physically irreversible fouling, which was dominant in this study. The strong correlation was shown with multiple water samples treated by various pretreatments, demonstrating that biopolymer concentration in feed water is a good index for fouling studies. [ABSTRACT FROM AUTHOR]

In recent studies dealing with membrane fouling in microfiltration (MF)/ultrafiltration (UF) processes for drinking water production, biopolymers, which are hydrophilic macromolecules, have been identified as the key foulants. However, removal of biopolymers from water has been rarely focused on in previous studies. In this study, removal of biopolymers by coagulation, which is the most common pretreatment for MF/UF in existing full-scale facilities, was investigated. Surface water samples from three rivers used as raw water for drinking water production were examined in this study. Sampling was repeated in different seasons to examine a wide range of water quality. It was demonstrated that dosages commonly used in existing facilities were insufficient to maximize biopolymer removal by coagulation conducted at neutral pH. It was shown that an extremely high dosage of the coagulant was necessary to maximize biopolymer removal. A new dosage index, aluminum (Al, mg/L)/biopolymer (Bp, μg/L), was used in this study. Al/Bp of about 20 was found to be necessary at pH 7 to almost maximize biopolymer removal by coagulation regardless of the water tested. Maximized biopolymer removal brought about least evolution of membrane fouling, which was separately verified in bench-scale filtration tests. Efficiency of coagulation for biopolymer removal varied depending on the season: samples collected in the cold season exhibited poor removal of biopolymers. Detailed examinations of biopolymers in each sample suggested that properties of the biopolymers changed seasonally. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Evolution of irreversible fouling in pilot-scale membrane bioreactors (MBRs) treating municipal wastewater was studied. Three membrane modules were sacrificed to analyze foulants after they had been used for different durations (1 day, 8 days, 24 days). The module used for 1 day reflected fouling occurring at the initial stage, whereas the module used for 24 days reflected the later stage of fouling. After each module had been used for the predetermined period, it was disassembled and subjected to powerful chemical analysis such as Fourier transform infrared (FTIR) analysis. It was clearly shown that components involved in evolution of irreversible fouling gradually changed depending on the duration. The initial fouling (conditioning of membrane) was caused by humics, whereas later fouling was mainly caused by polysaccharides. A model for evolution of irreversible fouling in MBRs and implications for fouling control are discussed. [ABSTRACT FROM AUTHOR]

Abstracts A new approach for the analysis of polysaccharides in membrane bioreactor (MBR) is proposed in this study. Enrichment of polysaccharides by glyco-blotting, in which polysaccharides are specifically collected via interactions between the aldehydes in the polysaccharides and aminooxy groups on glycoblotting beads, enabled MALDI-TOF/MS analysis at a high resolution. Structures of polysaccharides extracted from fouled membranes used in a pilot-scale MBR treating municipal wastewater and those in the supernatant of the mixed liquor suspension in the MBR were investigated. It was found that the overlap between polysaccharides found in the supernatants and those extracted from the fouled membrane was rather limited, suggesting that polysaccharides that dominate in supernatants may not be important in membrane fouling in MBRs. Analysis using a bacterial carbohydrate database suggested that capsular polysaccharides (CPS) and/or lipo-polysaccharides (LPS) produced by gram-negative bacteria are key players in the evolution of membrane fouling in MBRs. [ABSTRACT FROM AUTHOR]

A membrane bioreactor (MBR) is not a mainstream wastewater treatment technology, mainly because the energy consumption in an MBR operation is high. This study investigated the mitigation of membrane fouling and the reduction in aeration through the introduction of granules into a pilot-scale baffled membrane bioreactor (BMBR) used to treat municipal wastewater. With granular materials, the BMBR could be stably operated, even when the filterability of the mixed liquor suspensions was considerably low due to low temperatures. The aeration rate could be reduced by more than 50% with the help of granules. However, it was found that the introduction of granules damaged parts of the membrane surface. The damage might be avoided by adjusting the contact intensity of the granules and the membrane surface. [ABSTRACT FROM AUTHOR]

Aeration to mitigate membrane fouling accounts for the largest fraction of energy consumed in membrane bioreactors (MBRs). To reduce the energy consumed during MBR operation, alternative methods must be developed to control membrane fouling. Granules should be introduced into submerged MBRs to mitigate membrane fouling due to their mechanical cleaning effect on the membrane surface. This study assessed the possible reduction in aeration for submerged MBRs through introducing granules and investigated membrane fouling characteristics from using granules. Two bench-scale MBRs operated in parallel with synthetic wastewater, and granules were introduced into one MBR. The MBR with granules operated stably even after aeration was reduced by 50%. Reversible fouling was almost entirely controlled through the introduction of granules. However, the granules promoted irreversible fouling due to cake elimination, which acted as a dynamic filter. The overall benefit from granules was apparent; although, reversible fouling dominated in the absence of granules. The foulant characteristics differed with granule use. These characteristic changes were also explained by the absence of the dynamic filtration effect. [ABSTRACT FROM AUTHOR]

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 1, 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. [ABSTRACT FROM AUTHOR]

Abstract: Although low-pressure membranes (microfiltration (MF) or ultrafiltration (UF)) have become viable options for drinking water treatment, problems caused by membrane fouling must still be addressed. The objective of this study was to compare five different surface waters and to identify a relevant index of water quality that can be used for prediction of the fouling potential of the water. Bench-scale filtration tests were carried out with commercially available hollow-fiber MF membranes. Fairly long-term (a few days) filtrations in the constant-flow mode were carried out with automatic backwash. Membrane fouling in this study was shown to be irreversible as a result of the periodic backwash carried out throughout of the operation. Easily accessible indexes of water quality including dissolved organic carbon (DOC), UV absorbance, Ca concentration and turbidity could not explain the degree of fouling encountered in the filtration tests. Fluorescence excitation-emission matrix (EEM) could provide information on the presence of protein-like substances in water, and peaks for protein showed some correlation with the membrane fouling. Biopolymer (characterized by high molecular weights and insensitivity to UV light absorption) concentrations in the five waters determined by liquid chromatography with organic carbon detection (LC-OCD) exhibited an excellent correlation with the fouling rates. Coagulation with polyaluminum chloride could mitigate membrane fouling in all cases. The extent of fouling seen with coagulated waters was also correlated with biopolymer concentrations. The relationship between biopolymer concentrations and the fouling rates established for the raw waters could also be applied to the coagulated waters. These results suggested that the contribution of biopolymers to membrane fouling in the present study was significant, an observation that was supported by the analysis of foulants extracted at the termination of each test. Biopolymer concentrations determined by LC-OCD might be used as a key indicator of fouling potential of water for low-pressure membranes. [Copyright &y& Elsevier]

Abstract: Membrane fouling remains a major obstacle for wider application of membrane bioreactors (MBRs) to wastewater treatment. Polysaccharides in mixed liquor suspensions in the reactors are thought to be mainly responsible for the evolution of membrane fouling in MBRs. However, details of polysaccharides causing membrane fouling in MBRs are still unknown. In this study, polysaccharides in a mixed liquor suspension of a pilot-scale MBR treating municipal wastewater were fractionated by using lectins, special proteins that bind to specific polysaccharides depending on their properties. Fouling potentials of the fractionated polysaccharides were assessed by bench-scale dead-end filtration tests. It was clearly shown that the degrees of fouling caused by fractionated polysaccharides were significantly different. The amounts of polysaccharides in each fraction could not explain the variations in the fouling, indicating the presence of polysaccharides with high specific fouling potentials. To investigate structures and origins of the polysaccharides with high fouling potentials, matrix-assisted laser desorption/ionization (MALDI)-time of flight (TOF)/mass spectrometry (MS) analysis was applied to the fractionated polysaccharides after partial hydrolysis. Several mass peaks obtained could be assigned to fragments of structures of polysaccharides (i.e., oligosaccharides) reported in a database/literature. This is the first report showing the plausible structures of polysaccharides in MBRs based on MS. A deeper understanding and effective control of membrane fouling in MBRs could be achieved with information obtained by the approach used in this study. [Copyright &y& Elsevier]

Abstract: Membrane bioreactors (MBRs) have become very attractive during the past decade owing to their advantages, although MBR operation has not been optimized yet. Recently, air-sparged side-stream MBRs (ASMBRs) have received much attention because they can overcome the drawbacks of submerged MBRs such as the difficulty of cleaning membrane modules. Widespread application of MBRs has been limited by problems associated with membrane fouling, and ASMBRs are not exceptions. Hydraulic conditions on the membrane surface used in an ASMBR are different from those in a submerged MBR, and this difference affects the characteristics of foulants. The aim of this study was to determine foulant characteristics in a pilot-scale ASMBR operated at an existing municipal wastewater treatment plant. Cylindrical membrane modules holding about 100 membrane tubes each were installed vertically in the ASMBR. Differences of foulants depending on tube positions in the horizontal cross section were investigated in the first experiment. There were no significant differences in the foulant characteristics regardless of the tube positions in the membrane module. This first experiment also showed that humic substances were dominant in the foulants extracted from the tubular membranes used in the ASMBR, whereas hydrophilic substances such as polysaccharides/proteins were reportedly dominant in foulants in the case of submerged MBRs. In the following experiment, a tiny hollow-fiber membrane module was submerged in the ASMBR’s reaction tank to filter the shared biomass suspension and enable direct comparison of foulant characteristics in different MBR configurations (i.e., air-sparged side-stream versus submerged). Humic substances were again found to be dominant in foulants extracted from the ASMBR’s tubular membranes, whereas hydrophilic organic matter was dominant in foulants extracted from the submerged hollow-fiber membranes. We hypothesize that different hydraulic conditions in the two configurations brought about the difference in foulants. The results obtained in this study suggest that effective measures to address membrane fouling will differ depending on the MBR configuration. [Copyright &y& Elsevier]

Abstract: Increasing attention has been given to pollution of the water environment by pharmaceutical compounds discharged from wastewater treatment plants. High-pressure driven membranes such as a nanofiltration (NF) membrane and a reverse osmosis (RO) membrane are considered to be effective for control of pharmaceuticals in wastewater treatment. In practical applications of NF/RO membranes to municipal wastewater treatment, feed water for the membranes always contains organic macromolecules at concentrations of up to 10mg-TOC/L, which are mainly composed of soluble microbial products (SMPs) produced during biological wastewater treatment such as an activated sludge process. In this study, influence of these organic macromolecules on removal of six pharmaceuticals by NF/RO membranes (UTC-60 and LF10) was investigated. Two types of biological treatment (conventional activated sludge process followed by media filtration (i.e., tertiary treatment) and treatment with a membrane bioreactor (MBR)) were examined as pretreatments for NF/RO membranes in this study. In the filtration tests with wastewater effluents, removal of the pharmaceuticals was higher than that seen with deionized pure water spiked with the pharmaceuticals. The increase was significant in the case of the NF membrane. Both alteration of membrane surface properties due to membrane fouling and association of the pharmaceuticals with organic macromolecules contributed to the increase in removal of pharmaceuticals by the membranes. Characteristics of the organic macromolecules contained in the wastewater effluents differed depending on the type of treatment, implying that removal of pharmaceuticals by NF/RO membranes is influenced by the type of pretreatment employed. [Copyright &y& Elsevier]

A membrane bioreactor (MBR) is a promising wastewater treatment technology, but there is a need for efficient control of membrane fouling, which increases operational and maintenance costs. Soluble microbial products (SMP) have been reported to act as major foulants in the operation of MBRs used for wastewater treatment. In this study, SMP in MBRs operated with different sludge retention times (SRTs) were investigated by means of various analytical techniques and their relations to the evolution of membrane fouling were considered. Bench-scale filtration experiments were carried out in a laboratory with synthetic wastewater to eliminate fluctuations that would occur with the use of real wastewater and that would lead to fluctuations in compositions of SMP. Three identical submerged MBRs were operated for about 50 days under the same conditions except for SRT (17, 51 and 102 days). Accumulation of SMP in the MBRs estimated by conventional analytical methods (i.e., the phenol–sulfuric acid method and the Lowry method) was significant in the cases of short SRTs. However, the degrees of membrane fouling in the MBRs were not directly related to the concentrations of SMP in the reactors estimated by the conventional analytical methods. Non-conventional analytical methods such as excitation-emission matrix (EEM) fluorescence spectroscopy revealed that characteristics of SMP in the three reactors considerably differed depending on SRT. Foulants were extracted from the fouled membranes at the end of the operation and were compared with SMP in each MBR. It was clearly shown that characteristics of the foulants were different depending on SRT, and similarities between SMP and the extracted foulants were recognized in each MBR on the basis of results of EEM measurements. However, such similarities were not found on the basis of results obtained by using the conventional methods for analysis of SMP. The results of this study suggest that the use of conventional methods for analysis of SMP is not appropriate for investigation of membrane fouling in MBRs. [Copyright &y& Elsevier]

Abstract: The main obstacle for a wider use of membrane bioreactors (MBRs) for wastewater treatment is membrane fouling, which increases operating costs. For a more efficient control of membrane fouling in MBRs, an understanding of the mechanisms of membrane fouling is important. We conducted two separate pilot-scale experiments using real municipal wastewater to investigate the influence of the membrane flux in MBRs on the characteristics of foulants, which were analyzed by Fourier transform infrared (FTIR) spectra, 13C nuclear magnetic resonance (NMR) spectra, monosaccharide composition and amino acid analyses. In each experiment, two identical membrane modules were submerged in the same MBR tank and were operated under different membrane fluxes. The results obtained in this study indicated that the membrane filtration flux significantly influenced membrane fouling in MBRs. Membrane fouling in the module operated with the higher flux was much greater than that of the other on the basis of the volume of filtered mixed liquor suspension. Analyses of the foulants desorbed from the fouled membranes revealed that the nature of the foulants significantly differed depending on the membrane flux despite the fact that the two modules filtered the same mixed liquor suspension at the same time. The difference in characteristics of the foulants caused by the difference in the membrane flux was similar in the two separate experiments, indicating that reproducibility of the data was sufficient. It was thought that different fractions of the mixed liquor suspension were transported to the surfaces of the membranes depending on the membrane flux and subsequently caused membrane fouling to different extents. The foulant desorbed from the membrane operated with a higher flux seemed to cause severer fouling than the foulant desorbed from the other membrane. [Copyright &y& Elsevier]

Abstract: 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 0.1μm. 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. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Submerged membrane bioreactors (MBRs) are now widely used for various types of wastewater treatment. One drawback of submerged MBRs is the difficulty in removing nitrogen because intensive aeration is usually carried out in the tank and the MBRs must therefore be operated under aerobic conditions. In this study, the feasibility of treating municipal wastewater by a baffled membrane bioreactor (BMBR), particularly in terms of nitrogen removal, was examined. Simultaneous nitrification/denitrification in a single and small reaction tank was possible by inserting baffles into a normal submerged MBR as long as wastewater was fed in the appropriate way. To examine the applicability of the BMBR, pilot-scale experiments were carried out using real municipal wastewater. Although neither external carbon addition nor mixed liquor circulation was carried out in the operation of the BMBR, average removal rates of total organic carbon (TOC), total phosphorus (T-P) and total nitrogen (T-N) reached 85%, 97% and 77%, respectively, with the hydraulic retention time (HRT) of 4.7h. Permeability of the membrane could be maintained at a high level throughout the operation. It was found that denitrification was the limiting step in removal of nitrogen in the BMBR in this study. Various types of monitoring carried out in the BMBR also demonstrated the possibility of further improvements in its performance. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

The elimination of six acidic pharmaceuticals (clofibric acid, diclofenac, ibuprofen, ketoprofen, mefenamic acid, and naproxen) in a real wastewater treatment plant (WWTP) using an activated sludge system and membrane bioreactors (MBRs) was investigated by using a gas chromatography/mass spectrometry (GC/MS) system for measurement of the compounds. Limited information is available for some of the tested pharmaceuticals at present. Solid retention times (SRTs) of the WWTP and the two MBRs were 7, 15, and 65 days, respectively. The elimination rates varied from compound to compound. The MBRs exhibited greater elimination rates for the examined pharmaceuticals than did the real plant. Dependency of the elimination rates of the pharmaceuticals on SRTs was obvious; the MBA operated with a longer SRT of 65 days clearly showed better performance than did the MBA with a shorter SAT of 15 days. The difference between the two MBRs was particularly significant in terms of elimination of ketoprofen and diclofenac. Measurements of the amounts of adsorbed pharmaceuticals on the sludge and aerobic batch elimination experiments were carried out to investigate the elimination pathways of the pharmaceuticals. Results of the batch elimination tests revealed that the sludges in the MBRs had large specific sorption capacities mainly due to their large specific surface areas. Despite the sorption capacities of sludges, the main mechanism of elimination of the pharmaceuticals in the investigated processes was found to be biodegradation. Biodegradation of diclofenac, which has been believed to be refractory to biodegradation, seemed to occur very slowly. [ABSTRACT FROM AUTHOR]

Abstract: There is a need for efficient control of membrane fouling in membrane bioreactors (MBRs), but there is still an insufficient understanding of the phenomena of membrane fouling and little is known about the influence of polymeric membrane materials on membrane fouling in MBRs. In this study, the influence of polymeric membrane materials on membrane fouling in MBRs was investigated on the basis of results of a pilot-scale experiment using real municipal wastewater. Two different polymers, polyethylene (PE) and polyvinylidene fluoride (PVDF), were examined side by side and the degree of fouling in each membrane was monitored. Also, analysis of the foulants in both membranes was carried out. The results obtained in this study demonstrated that PVDF is superior to PE in terms of prevention of irreversible fouling in MBRs used for treatment of municipal wastewater. Dissolved matter was mainly responsible for the irreversible fouling. Reversible fouling in the PVDF membrane might be related to an increase in sub-micron-sized organic matter that was mainly composed of carbohydrate. Composition of the foulants causing irreversible fouling differed considerably depending on the membrane polymeric materials. The results suggested that some fractions in organic matter in the mixed liquor have higher affinities with the membrane than do other fractions and consequently cause greater irreversible fouling. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 (FIR) and 13C 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 [ABSTRACT FROM AUTHOR]

Abstract: Unintentional indirect potable water reuse, where wastewater effluent is used as a part of a downstream drinking water source, has become a great concern. In this case, a variety of organic micro-pollutants contained in wastewater effluent could create problems. Membrane bioreactors (MBRs) have gained significant popularity as an advanced wastewater treatment technology and might be effective in removing such organic micro-pollutants. Available information on the performance of MBRs regarding removal of micro-pollutants, however, is currently limited. This study examined the ability of submerged MBRs to remove pharmaceutically active compounds (PhACs). Experiments were conducted at an existing municipal wastewater treatment facility, and the performance of the MBRs was compared with that of the conventional activated sludge (CAS) process. Six acidic PhACs (clofibric acid, diclofenac, ibuprofen, ketoprofen, mefenamic acid, naproxen) and one acidic herbicide (dichloprop) were investigated. Compared with CAS, MBRs exhibited much better removal regarding ketoprofen and naproxen. With respect to the other compounds, comparable removal was observed between the two types of treatment. Removal efficiencies of the PhACs were found to be dependent on their molecular structure such as number of aromatic rings or inclusion of chlorine. [Copyright &y& Elsevier]

As high quality drinking water becomes scarcer, unintentional indirect potable water reuse, where wastewater effluent is used as a part of a downstream drinking water source, has become a great concern throughout the world. In this case, a variety of organic micro-pollutants contained in wastewater effluent could create problems. High pressure-driven membranes such as nanofiltration (NF) or reverse osmosis (RO) might be a powerful option to deal with such micro-pollutants, however, a lack of information on their performance is apparent. This study examined the ability of RO membranes to retain neutral (uncharged) endocrine disrupting compounds (EDCs) and pharmaceutically active compounds (PhACs). A total of 11 compounds were chosen so that a certain range of molecular weights and octanol–water distribution coefficients (Kow) could be studied. With respect to membranes, two different materials (polyamide and cellulose acetate) were examined. Generally, the polyamide membrane exhibited a better performance in terms of the rejection of the selected compounds but the retention was not complete (57–91%). It was found that salt rejection or molecular weight cut-off (MWCO) that are often used to characterize membrane rejection properties did not provide quantitative information in terms of EDCs/PhACs rejection by NF/RO membranes. Molecular weight of the tested compounds could generally indicate the tendency of rejection for the polyamide membranes (size exclusion dominated the retention by the polyamide membrane) while polarity was better able to describe the retention trend of the tested compounds by the cellulose acetate membrane. The results obtained in this study imply that each membrane polymer material for NF/RO membranes, including ones that will be newly developed in the future, would exhibit different trends in terms of rejection of organic micro-pollutants, which is determined by physico-chemical properties of the compounds. [Copyright &y& Elsevier]

For more efficient use of membranes, the control of irreversible membrane fouling, which can be defined as fouling requiring chemical reagents to be mitigated, is of importance. In this study, irreversible fouling caused by constituents in surface water was investigated, based on a long-term pilot scale study. The membrane employed was a low-pressure hydrophobic ultrafiltration (UF) membrane made of polysulfone and having a molecular weight cutoff of 750,000 Da. Various chemical reagents were examined to overcome the irreversible fouling that had developed through 5 months of continuous filtration. Among the tested cleaning reagents, alkaline (NaOH) and oxidizing reagent (NaClO) showed good performance in the restoration of membrane permeability, which implied that organic matter played an important role in the development of the irreversible fouling in this study. Chemical analysis, adsorptive fractionation methods, fluorescence excitation–emission matrix (EEM) and Fourie-transformed infra-red (FTIR) spectra analysis were applied to elucidate which fraction of organic matter caused the irreversible fouling. All of the analysis indicated that polysaccharide-like organic matter was responsible for the evolution of the irreversible fouling. In addition to organic matter, presumably iron and manganese also contributed to the irreversible fouling to some extent. [Copyright &y& Elsevier]

The growing demand on water resources has increased interest in wastewater reclamation for potable reuse, in which rejection of organic micropollutants such as disinfection by-products (DBPs), endocrine disrupting compounds (EDCs), and pharmaceutically active compounds (PhACs) is of great concern. The objective of this study was to investigate the rejection of DBPs, EDCs, and PhACs by nanofiltration (NF) and reverse osmosis (RO) membranes as a function of their physico-chemical properties and initial feed water concentration. Experimental results indicated that negatively charged compounds could be rejected very effectively (i.e., >90%) regardless of other physico-chemical properties of the tested compounds due to electrostatic exclusion. No time-dependency was observed for rejection of charged compounds. In contrast, rejection of non-charged compounds was generally lower (<90% except for one case) and influenced mainly by the molecular size of the compounds. A clear time-dependency was observed for rejection of non-charged compounds, attributable to compound adsorption on the membrane. It was demonstrated that feed water concentration influenced rejection efficiency of the membrane. Experiments conducted at a low ng/l concentration range resulted in lower rejection efficiency as compared to experiments conducted at a μg/l range, suggesting the need to conduct experiments at the relevant concentration of interest. [Copyright &y& Elsevier]

This study addresses the adsorption of hydrophobic compounds at low concentration (∼100 ppb) onto NF/RO membranes. In this study, three surrogate compounds and three NF/RO membranes were tested under cross-flow conditions. Experimental results showed that the adsorption of hydrophobic compounds was significant for neutral compounds and ionizable compounds when electrostatically neutral. Also, operating conditions such as the permeate flow rate (flux) had a significant effect on the degree of compound adsorption. A comparison of the adsorption observed in dynamic filtration tests with that in static batch adsorption tests suggests that more adsorption sites are accessible for molecules during membrane filtration due to the pressurized advective flow. It was observed that the concentration of the tested compounds changed during filtration tests due to adsorption. Therefore, an accurate evaluation of a given membrane in terms of the rejection of a hydrophobic compound is not possible until saturation of the membrane with the compound of interest is accomplished. The experimental results demonstrated that a relatively large amount of the feed water needed to be filtered to reach saturation conditions. [Copyright &y& Elsevier]

In this paper, a new method for removal of nitrate from groundwater, in which elemental sulfur-based denitrification (autotrophic denitrification) and membrane separation are combined, is proposed. By using a membrane, autotrophic denitrifiers, whose growth rate is considerably low, can be kept at a high concentration. The performance of the proposed process was examined through a long-term experiment in the laboratory using synthetic feed water. A rotating membrane disk module equipped with UF membrane (750,000 Da) was used in this study. Complete removal of nitrate (25 mg N/L) was achieved under the conditions of a biomass concentration of about 1000 mg protein/L and HRT of 160 min. Dissolved oxygen concentration and sulfur/biomass ratio in the membrane chamber were found to be the key factors in maintenance of high-process performance. Deterioration in membrane permeability was insignificant. It was found that membrane filtration could be continued with a water flux of 0.5 m3/m2/day for about 100 days without any chemical membrane cleaning. The proposed process, however, caused a slight increase in assimilable organic carbon. Sulfide was not detected in the denitrified water. [Copyright &y& Elsevier]

The recovery and utilization of organic matter in municipal wastewater are essential for the establishment of a sustainable society, such that these factors have drawn significant recent attention. The up-concentration of organic matter via direct membrane filtration (DMF), followed by anaerobic digestion, is advantageous over the treatment of the entire wastewater by an anaerobic process, such as an anaerobic membrane bioreactor (AnMBR). However, the occurrence of severe membrane fouling in the DMF is a problem. In this study, DMF was carried out at an existing wastewater treatment plant to attempt long-term operation. A combination of vibration of membrane modules, short-term aeration, and chemically enhanced backwash (CEB), with multiple chemicals (i.e., the alternative use of citric acid and NaClO), was found to be effective for the mitigation of membrane fouling in DMF. Furthermore, switching the feed from influents to effluents in the primary sedimentation basin significantly mitigated membrane fouling. In this study, in which microfiltration membrane, with a nominal pore size of 0.1 μm, was used, ∼75% of the organic matter in raw wastewater was recovered, with the volumetric concentration of wastewater by 50- or 150-fold. Organic matter recovered by DMF had significantly higher potentials for biogas production than the excess sludge generated from the same wastewater treatment plant. An analysis of the energy balance (i.e., the energy used for DMF and recovered by DMF) suggests that the proposed DMF can produce a net-positive amount of electricity of ∼0.3 kWh from 1 m3 of raw wastewater with a typical strength (chemical oxygen demand of 500 mg/L). [Display omitted] • Membrane fouling in DMF hinders organic matter recovery from wastewater. • Fouling was mitigated by short-term aeration and chemically enhanced backwash. • Recovered organic matter had a high methane gas production potential. • Energy to drive the proposed DMF system was low and can be compensated by biogas. [ABSTRACT FROM AUTHOR]

Discusses the filtration resistant induced by ammonia oxidizers accumulating on the rotating membrane disk. Continuous operations of the biofilm-membrane reactor (BMR); Analysis of the deposit on the membrane; Evaluation and distribution of membrane filtration resistance.

This study investigated the efficiency of intensive membrane cleaning for membrane bioreactors (MBRs) using a combination of mechanical scouring with granules and chemically enhanced backwashing (CEB). The implementation of such intensive cleaning was possible with ceramic flat-sheet membranes. Experiments were carried out using bench-scale MBRs at an existing wastewater treatment plant. First, CEB with NaClO was investigated in terms of the CEB frequency, duration, and concentration of the chemical reagent. CEB carried out for 60 min every 6 h, with 50 ppm of NaClO, was found to be effective, and it enabled an MBR to operate at 50 LMH, two to three times higher than the flux of full-scale MBRs. However, these CEB conditions were insufficient when the temperature was low (i.e. in winter), when an adhesive gel layer formed on the membrane surface. Its high resistance to cleaning might be explained by the increased levels of soluble microbial products and/or the presence of algal cells. Alkaline-assisted CEB, with NaClO (pH 12) and an increase in the volume of granules in the membrane tank, solved this problem. With the modified cleaning method, the fouling could be almost perfectly controlled at low-temperature conditions, such as 13 °C. MBRs may be regarded as fouling-free MBRs when the proposed cleaning method is used with ceramic flat-sheet membranes. Most real-world MBR operations operate with lower fluxes than the flux examined in this study, and at higher temperatures. Image 1 • Ceramic flat-sheet membranes were used with intensive cleaning. • Fouling was perfectly controlled by the combination of granular scouring and CEB. • MBRs could be operated with 2 to 3-times higher flux than that set in full-scale MBRs. • The gel layer that formed in winter had unique features and was very adhesive. • The proposed method for cleaning was also effective in winter (13 °C). [ABSTRACT FROM AUTHOR]

In this study, microfiltration (MF) and ultrafiltration (UF) of surface water were compared in terms of irreversible fouling and effective pretreatment. Hollow-fiber MF/UF membranes made from the same polymer (polyvinylidene fluoride (PVDF)) were examined with multiple samples of surface water used for drinking water production. Experiments were carried out in a realistic style: with a constant flow rate and periodic backwashing. Regardless of the source of the feed water, evolution of fouling was less significant in the case of UF. In the case of MF, anion exchange followed by coagulation using poly-aluminium chloride (PACl) efficiently mitigated membrane fouling, whereas PACl coagulation alone was sufficient for UF. Artificial alteration of the composition of natural organic matter (NOM) in the feed water was carried out by MF/UF with different pore sizes, and it was revealed that different fractions of NOM were responsible for evolution of irreversible fouling in MF and UF: large biopolymers and small biopolymers were responsible for irreversible fouling in MF and UF, respectively. The mechanism of fouling mitigation by coagulation was also investigated. Cake (coagulated flocs) deposited on the membrane surface mitigated irreversible fouling in UF, whereas it did not affect irreversible fouling in MF. It was postulated that advection flow caused by membrane filtration made more adsorption sites available inside the flocs for removal of small biopolymers (i.e., UF foulants). Image 1 • Occurrence of irreversible fouling in UF was less significant than that in MF. • Pretreatment by coagulation was very effective for UF but not for MF. • Large biopolymers were mainly responsible for irreversible fouling in MF. • Small biopolymers were mainly responsible for irreversible fouling in UF. • Cake on the membrane controlled irreversible fouling in UF but not in MF. [ABSTRACT FROM AUTHOR]

The article introduces reports published within the issue including one on the performance of a ceramic microfiltration (MF) device, one on the impact of the speciation of manganese on the removal of manganese and organic matter by nanofiltration (NF), and one on computation fluid dynamics (CFD) to estimate sheer stress on a membrane.

It has been reported that the combination process of biofilm and submerged membrane bioreactors (MBRs) can mitigate membrane fouling. In this study, the influence of using three different biofilm carriers (fixed rope carrier, moving granular carrier and moving sponge carrier) on the operation and membrane fouling of MBRs was investigated. Using rope or sponge carriers with MBR processes improved the removal efficiency of nitrogen via the creation of an anoxic part inside the carriers. However, membrane fouling became very severe when rope carriers were used. Using granular or sponge carriers effectively mitigated membrane fouling because they mechanically cleaned the membrane surface. The cake/gel layer on the membrane surface was perfectly removed by granular or sponge carriers. However, the deterioration of the filterability of the mixed liquor suspensions was significant with granular carriers, leading to the evolution of physically irreversible fouling, whereas such deterioration was insignificant with the sponge carrier. The characteristics of the soluble microbial products (SMP) significantly varied depending on the types of carriers used, which could influence the filterability of mixed liquor suspensions and the development of irreversible membrane fouling. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Direct membrane filtration (DMF) of municipal wastewater using a microfiltration membrane was investigated to capture organic matter. In contrast to the expectation that membrane fouling cannot be controlled in DMF of domestic wastewater, it was possible to stably continue membrane filtration with relatively high membrane fluxes (∼20 LMH) for >200 h by applying chemically enhanced backwash (CEB), whereas approximately 75% of the organic matter in wastewater could be recovered. Off-line chemical membrane cleaning could completely restore membrane permeability, indicating the possibility of a much longer operation of DMF. Selection of chemical reagents used for CEB was found to influence the amount of organic matter recovered by DMF. Based on the experimental results, feasibility of DMF was discussed by a comparison with a conventional wastewater treatment plant treating the same wastewater as studied in this study. [ABSTRACT FROM AUTHOR]

Abstract: The proteins that caused membrane fouling in a continuous operation of membrane bioreactors (MBRs) treating real municipal wastewater were investigated in detail. We continuously operated two identical pilot-scale MBRs under different solid retention times (SRTs) and extracted the foulants at the end of the operation. Regardless of the operating conditions, proteins were dominant components in the foulants extracted from the fouled membranes. The extracted proteins were subjected to the separation with two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and the identification through the N-terminal amino acid sequencing analysis. The proteins concentrated by the combination of the crude concentration using an ultra-filtration (UF) membrane and trichloroacetic acid (TCA) precipitation were separated and visualized well on 2D-PAGE gels. The results of 2D-PAGE analysis indicated that the compositions of proteins that caused membrane fouling significantly differed depending on the SRT, although such differences cannot be seen in the amino acid composition analysis. Analyzing selected 2D-PAGE spots by N-terminal amino acid sequencing analysis led to the identification of two well-characterized outer membrane proteins originating from Pseudomonas genus, namely OprF and OprD. To our knowledge, this is the first successful identification of proteins that have caused membrane fouling in continuous operations of MBRs treating real wastewater. [Copyright &y& Elsevier]

• Low dose oxidant can abate membrane fouling in GDM filtration. • Biopolymers were removed from influent water by dosed oxidants. • Dosed oxidants significantly altered biofilm bacterial community structure. • Formed δ-MnO 2 nanosheets layer protected membrane pore from contamination. Membrane fouling is the principal factor that currently limits the performance of gravity-driven membrane (GDM) filtration systems in drinking water treatment. In this study, the benefits of applying a low dose (approximately 0.1 mg · L − 1 ) of environmentally benign oxidants, both H 2 O 2 and KMnO 4 , as a pretreatment to GDM filtration system has been evaluated in terms of reduced membrane fouling and treated water quality. While both oxidants improved permeate flux, the effect of KMnO 4 was greater than H 2 O 2. Both oxidants reduced the size of influent organic substances and those of large molecular weight (>20 kDa), such as biopolymers, disappeared. The thickness of the fouling layers was substantially reduced after oxidation, and the KMnO 4 system had a markedly different physical structure of fouling layer, with an apparent sub-layer of δ-MnO 2 nanosheets below a fouling sub-layer. The formation of the δ-MnO 2 nanosheets sub-layer appeared to protect the underlying membrane pores from contamination by influent organics. Oxidation pretreatment reduced the presence of proteins and polysaccharides in the fouling layers and significantly altered the bacterial community structures (p < 0.01) and decreased biodiversity. The microbial species that secreted amounts of extracellular polymeric substances (EPS), such as Xanthobacter, were not eliminated in the H 2 O 2 fouling layer, while for the KMnO 4 system, the manganese oxidizing bacteria (MOB; e.g., Pseudoxanthomonas) and metal-resistant genus Acidovorax, dominated the community. [Display omitted] [ABSTRACT FROM AUTHOR]

Water treatment using microfiltration (MF)/ultrafiltration (UF) membranes is gaining in popularity all over the world but the problem of membrane fouling needs to be addressed. In this study, the influence of 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. [ABSTRACT FROM AUTHOR]

Abstract: 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 13C) 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. [Copyright &y& Elsevier]

• Organic matter was recovered in direct membrane filtration of municipal wastewater. • Anaerobic digestibility of organic matter was investigated in batch experiments. • Biogas production from organic matter was comparable to that of mixed sludge. • Biogas production from organic matter containing polyaluminum chloride was highest. Direct membrane filtration (DMF) process is a promising technology for up-concentration and recovery of organic matter (OM) from municipal wastewater. This study investigates anaerobic digestibility of up-concentrated OM obtained from the DMF process. Effluent from a primary sedimentation basin was used as feed water. Effect of polyaluminum chloride (PACl) addition to the DMF process on the anaerobic digestibility of obtained up-concentrated OM was also investigated because PACl is sometimes used as a coagulant in the DMF process for improving effluent quality and OM recovery, and for mitigating membrane fouling. Batch anaerobic digestion experiments were conducted to achieve these objectives. Fitting the obtained data to the reaction curve model revealed that maximum biogas production based on feed volatile solids (VS fed) from up-concentrated OM containing PACl reached 0.56 L-Biogas/g-VS fed , which was higher than from up-concentrated OM without PACl (0.47 L-Biogas/g-VS fed), waste activated sludge (0.35 L-Biogas/g-VS fed), and mixed sludge (0.48 L-Biogas/g-VS fed). Methane yield based on degraded VS (VS deg) of up-concentrated OM containing PACl was 0.56 L-CH 4 /g-VS deg , which was also highest. These results indicate the up-concentrated OM obtained from the DMF process has high potential for biogas production, and the addition of PACl in the DMF process (∼4.3 mg-Al/L) could enhance the biogas production. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • An anaerobic digestion bioreactor was setup for FO concentrated sewage treatment. • Inhibitory batch tests were carried out for the impact of NaCl and NH 4 +-N. • Single existence of NaCl had negative influence on methane production. • Single existence of NH 4 +-N had different impacts due to the its concentration. • The inhibition was severer with the co-existence of NaCl and NH 4 +-N. Abstract Sewage can become a valuable source if its treatment is re-oriented. Forward osmosis (FO) is an effective pre-treatment for concentrating solutions. A laboratory-scale anaerobic digestion (AD) bioreactor was setup for the treatment of concentrated real sewage by FO membrane to investigate the removal of chemical oxygen demand (COD) and biogas production. Inhibitory batch tests were carried out for the impact of NaCl and NH 4 +-N. Results showed that the concentrated sewage could be purified with 80% COD removal, and energy recovery could be achieved. But the process was inhibited. The results of inhibitory batch test showed that (i) when the NH 4 +-N concentration was lower (<200 mg/L), the biogas production was promoted, when it went high, the inhibition appeared; (ii) single existence of NaCl had negative influence on methane production; (iii) the inhibition was more severe with co-existence of NaCl and NH 4 +-N. The AD performance could be recovered via sludge acclimation. [ABSTRACT FROM AUTHOR]