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Background/purpose Although mandibular advancement oral appliances (OAs) are the most widely used and accepted therapeutic modality for obstructive sleep apnea (OSA), whether these maxillary and mandibular appliances should be semi-fixed or fixed remains uncertain. This randomized crossover pilot study compared the efficacy, side effects, and patient preference of semi-fixed and fixed OAs for the treatment of OSA. Materials and methods Patients with mild to moderate OSA were recruited and randomly assigned to either the semi-fixed or fixed OA group, whereby they used their assigned OA for the first 4 weeks, followed by assessments for sleep parameters (including the Apnea-Hypopnea Index [AHI]) and temporomandibular joint pain as a side effect. After a two-week washout period, patients were switched to the alternative OA for 4 weeks, followed by repeated assessments. Patient preference was assessed at the end of the completed treatment period. Results Fifteen patients were enrolled and completed the full study protocol. Both types of OAs were efficient in reducing the patient's AHI in comparison to baseline (i.e., without OA). However, there was no significant difference in AHI reduction between the semi-fixed and fixed OA devices. Regarding the side effect of temporomandibular joint pain and patient preference, the semi-fixed OA device was superior to the fixed OA device on both measures. Conclusion While both semi-fixed and fixed OAs are effective in treating patients with OSA, semi-fixed OAs are superior in regards to both patient preference and reduced side effects. Thus, semi-fixed OAs may be the preferred therapeutic modality for OSA.

Many studies on membrane fouling have been made and reported, and it has been revealed, based on liquid chromatography organic carbon detection (LC-OCD), that biopolymer is the main foulant in the drinking water treatment process, in which the raw water is taken from a river or a dam. However, measurement by LC-OCD is time-consuming and costly. Therefore, continuous measurement of biopolymer concentration by LC-OCD is not feasible. For this reason, we have not been able to monitor biopolymer continuously and control membrane fouling. The purpose of this study is to find a new fouling index (FR) to control membrane fouling without measuring the biopolymer concentration. Then, we tried to find a correlation between biopolymer and other water components by a multiple regression analysis. As the result, we have suggested the new fouling index (FR) which consists of the sum of the fluorescence intensity within the Region III domain measured by excitation emission matrix (EEM) fluorescence spectroscopy and the concentration of dissolved organic carbon measured by the total organic carbon (TOC) measurement. TOC and EEM are measured easily and continuously. Thus, we can control membrane fouling by monitoring the FR continuously.

We investigated the operating conditions of a baffled membrane bioreactor (B-MBR) under which long-term stable operation can be achieved through the continuous operation of a pilot-scale B-MBR. Under appropriate operating conditions, the B-MBR was capable of achieving excellent treated water quality in terms of biochemical oxygen demand and concentration of total nitrogen. Excellent removal of total phosphorus was also achieved. In addition, the degree of membrane fouling was acceptable, indicating that stable continuous operation of a B-MBR is possible under the operating conditions adopted in the present study. Estimation of the specific energy consumption in hypothetical full-scale B-MBRs operated under the conditions recommended by the findings was also performed in this study. The results suggest that energy consumption in full-scale B-MBRs would be in the range of 0.20–0.22 kWh/m3. These results strongly suggest that energy consumption in MBR operation can be significantly reduced by applying the concept of a B-MBR.

In this study, we investigated the effects of recirculation and separation times on removals of organic matter, nitrogen, and phosphorus in a baffled membrane bioreactor (B-MBR) treating real municipal wastewater. A pilot-scale B-MBR experimental apparatus was operated under two different sets of recirculation and separation times. The results revealed that, irrespective of operating conditions, the biochemical oxygen demand (BOD) and concentration of total nitrogen (T-N) in the treated water can be lowered to less than 3 and 5 mg/L, respectively. Although T-N was effectively removed in the two different operating conditions, increase in the fraction of recirculation time results in tiny deterioration of nitrogen removal efficiency in the B-MBR. Phosphorus removal efficiency was also slightly decreased as the fraction of recirculation time (ratio between recirculation and separation times) was increased. The results of the measurement of dissolved oxygen (DO) profiles at different points of the B-MBR apparatus indicate that the increase in DO concentration in the anoxic zone of the B-MBR becomes much more pronounced by increasing recirculation intensity. On the basis of the results obtained in this study, it can be concluded that efficient removal of BOD, T-N, and total phosphorus can be achieved by the B-MBR as long as appropriate recirculation intensity is selected.

This paper presents a fully integrated 32-MHz relaxation oscillator (ROSC) capable of sub-1-µs start-up time operation for low-power intermittent VLSI systems. The proposed ROSC employs current mode architecture that is different from conventional voltage mode architecture. This enables compact and fast switching speed to be achieved. By designing transistor sizes equally between one in a bias circuit and another in a voltage to current converter, the effect of process variation can be minimized. A prototype chip in a 0.18-µm CMOS demonstrated that the ROSC generates a stable clock frequency of 32.6 MHz within 1-µs start-up time. Measured line regulation and temperature coefficient were ±0.69% and ±0.38%, respectively.

A 44-year-old male was diagnosed with acute myeloid leukemia with a complex karyotype. He underwent bone marrow transplantation using an HLA 6/6 antigen-matched sibling donor, but developed chronic graft-versus-host disease (cGVHD) with skin erythema and oral and esophageal lichen planus changes. Treatment with a combination of prednisolone and cyclosporine was initiated on day 646 after transplantation, but oral symptoms persisted. The patient developed bilateral osteonecrosis of the lower jaw after extraction of the lower left and right molars on days 2,861 and 3,339, respectively. As the disease gradually progressed, segmental mandibular osteotomy was performed. Biopsy specimens demonstrated proliferation of squamous epithelial carcinoma cells in the bilateral gingiva and lower jaw bone, which confirmed the diagnosis of bilateral gingival squamous cell carcinoma. Thus, gingival squamous cell carcinoma should be considered as a differential diagnosis in post-transplant patients with refractory osteonecrosis of the jaw during the course of cGVHD.

In this study, we investigated the organic matter responsible for reverse osmosis (RO) membrane fouling in seawater desalination. In addition, pretreatments by which fouling organic fractions causing severe membrane fouling can be removed effectively were investigated. The results from continuous operation of a pilot-scale sand filter indicated that the changes in the concentrations of specific organic fractions, such as transparent exopolymer particles (TEP) and biopolymers determined by liquid chromatography with organic carbon detection (LC-OCD), cannot be evaluated by comprehensive water quality indices (e.g., total organic carbon (TOC) or dissolved organic carbon (DOC) concentrations). In addition, the changes in the degree of membrane fouling cannot be explained by the comprehensive TOC and DOC concentrations. Among the water quality indices examined in this study, the concentration of TEP with relatively large particle size (i.e., > 1.0 μm) and content of protein-like organic matter that can be detected by fluorescence excitation-emission matrix (EEM) spectral analysis were well correlated to RO membrane fouling levels. The results obtained in this study strongly suggest that developing a pretreatment method that can effectively eliminate TEP and proteinaceous compounds contained in seawater is important for the stable operation of a seawater desalination plant utilizing an RO membrane.

Goniodomin A is a marine polyether macrolide natural product isolated from the dinoflagellate Alexandrium hiranoi. In this paper, we report stereocontrolled, convergent synthesis of a fully functionalized C12-C36 fragment of goniodomin A. The synthesis of the C12-C25 vinylstannane involved a Wittig reaction and a reductive cycloetherification for the construction of the dihydropyran ring. The C26-C36 thioester was synthesized via a Nozaki-Hiyama-Kishi reaction of an aldehyde and an iodoalkyne, the former of which was easily prepared from (R)-malic acid as a chiral source by taking advantage of substrate-controlled diastereoselective reactions. Finally, a palladium-catalyzed coupling of the C12-C25 vinylstannane and the C26-C36 thioester completed the synthesis of the target compound.

In this study, we investigated the possibility of installing membrane-based water treatment technology in Indonesia. Due to high turbidity in river water, tremendous amount of chemicals (mainly coagulants) are often used in the water treatment process in Indonesia. Consumption of such chemicals can be alleviated using membrane filtration since complete rejection of particulate matter can be achieved by membranes without the necessity of coagulation. A pilot-scale membrane filtration unit was continuously operated for more than three months at an existing drinking water treatment plant in Bandung, Indonesia. The results indicated that the operation under a membrane flux of 45 L/m2/h and chemical maintenance cleaning frequency of once per two days was very stable, and almost no detectable membrane fouling was seen at this operating condition. At this condition, the operating expenditure of the membrane-based water treatment system was estimated to be nearly equal to that of a conventional water trea...

Forward osmosis (FO) membrane processes have attracted much attention because of their versatile potential in water treatment applications. However, further development of FO membranes is required to make them suitable for advanced FO applications. In this study, we used polyketone porous membranes as a novel support layer for the fabrication of thin-film composite (TFC) FO membranes. Highly porous polyketone membranes were prepared by phase separation and subsequent interfacial polymerization was carried out on the polyketone membrane surface. The prepared TFC-FO membranes showed excellent osmotically driven performance with one of the highest water fluxes in those of commercially available FO membranes because of the lower structural parameter (S-value) of less than 300 μm. The comparison of five types of prepared and three types of commercial FO membranes provided an understanding of the impact of the support layer structure on osmotically driven membrane performance when internal concentration polarization is involved. By tuning the porosity and pore size near the active layer, we successfully prepared an FO membrane with high performance, which showed a water flux exceeding 29.3 L m−2 h−1 with 0.065 mol m−2 h−1 reverse salt flux in the AL-FS orientation when 0.6 M NaCl solution and pure water were used, respectively, as the draw and feed solutions.

In this study, the details of proteins causing membrane fouling in membrane bioreactors (MBRs) treating real municipal wastewater were investigated. Two separate pilot-scale MBRs were continuously operated under significantly different operating conditions; one MBR was a submerged type whereas the other was a side-stream type. The submerged and side-stream MBRs were operated for 20 and 10 days, respectively. At the end of continuous operation, the foulants were extracted from the fouled membranes. The proteins contained in the extracted foulants were enriched by using the combination of crude concentration with an ultrafiltration membrane and trichloroacetic acid precipitation, and then separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). The N-terminal amino acid sequencing analysis of the proteins which formed intensive spots on the 2D-PAGE gels allowed us to partially identify one protein (OmpA family protein originated from genus Brevundimonas or Riemerella anatipestifer) from the foulant obtained from the submerged MBR, and two proteins (OprD and OprF originated from genus Pseudomonas) from that obtained from the side-stream MBR. Despite the significant difference in operating conditions of the two MBRs, all proteins identified in this study belong to β-barrel protein. These findings strongly suggest the importance of β-barrel proteins in developing membrane fouling in MBRs.

Recently, forward osmosis (FO) has received much attention as an advanced water treatment technology. Although the FO process has begun to spread widely worldwide, it still has some problems – such as the low water permeation rate compared with those required for some applications – that must be solved for its commercial application. To achieve the higher water flux and lower reverse salt flux, pressure assisted osmosis (PAO), in which pressure is applied to a feed solution (FS), has recently been proposed. In this work, experiments were carried out to investigate membrane structures and operating conditions in the PAO process by using three types of cellulose triacetate (CTA) — hollow fiber (HF) membranes. The HF membranes are preferable in the FO process because a high packing density and a large specific surface area can be obtained in the HF module. In addition, the HF membrane module has four ports and does not require a spacer between the membranes. The effects of the applied pressure, the draw solution concentration, and the structure parameter of the HF membranes on the PAO performance were investigated. The water flux in the PAO process was theoretically analyzed. The calculated results satisfactorily agreed with experimental data.

The effects of membrane module configuration and membrane flux on specific air demand per permeate (SADp) 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 SADp. When the MBR equipped with the intensively aerated module, stable continuous MBR operation without any membrane cleaning for two months under low SADp (8.8 m3-air/m3-permeate) was achieved by lowering membrane flux to 16 L/m2 h (or 0.4 m3/m2/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.

Recent development in forward osmosis (FO) membranes is promising in providing a versatile potential application for further advance in the water treatment and energy production sectors. Using FO hollow fiber membranes to achieve wide application of FO at an industrial level is advantageous because of their large specific membrane area and easy module construction for large-scale applications. In this study, three types of cellulose triacetate (CTA) hollow fiber (HF) forward osmosis membranes with diameters of less than 200 μm were evaluated under various operating conditions i.e., draw solution concentration, cross flow velocity, membrane orientation, and temperature. The osmotically driven performance evaluation revealed that the CTA HF membranes featured high water flux-to-reverse salt flux ratios, J w FO / J s FO , exceeding 800 L/mol. These values are much higher than those of commercial and reported FO membranes. The performance of the obtained FO membranes was also analyzed theoretically and the theoretical results agreed well with the experimental data.

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.

We investigated the effect of different membrane polymeric materials on the relationship between membrane pore size and development of membrane fouling in a membrane bioreactor (MBR). Membranes with different pore sizes were prepared using three different polymeric materials, cellulose acetate butyrate (CAB), polyvinyl butyral (PVB), and polyvinylidene fluoride (PVDF), and the development of membrane fouling in each membrane was evaluated by batch filtration tests using a mixed liquor suspension obtained from a laboratory-scale MBR. The results revealed that the optimal membrane pore size to mitigate membrane fouling differed depending on membrane polymeric material. For PVDF membranes, the degree of membrane fouling decreased as membrane pore size increased. In contrast, CAB membranes with smaller pores had less fouling propensity than those with larger ones. Such difference can be attributed to the difference in major membrane foulants in each membrane; in PVDF, they were small colloids or dissolved organics in which proteins are abundant, and in CAB, microbial flocs. The results obtained in this study strongly suggested that optimum operating conditions of MBRs differ depending on the characteristics of the used membrane.

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.

We propose a sub-1-μs start-up time, fully integrated 32-MHz relaxation oscillator (ROSC) for intermittent VLSI systems. Our proposed ROSC employs current mode architecture that is different from conventional voltage mode architecture. This enables compact and fast switching speed to be achieved. The measurement results demonstrated that the ROSC achieved sub-1-μs start-up time and generated stable output frequency of 32.6 MHz. Measured line regulation, temperature coefficient, and variation coefficient in 10 samples were ±0.69, ±0.38, and 0.62%, respectively.

Membrane fouling needs to be mitigated for widespread use of membrane bioreactors (MBRs). It has been pointed out that particles with small sizes found in supernatants (sub-micron particles) of mixed liquor suspensions of MBRs are important in the evolution of membrane fouling of this technology. However, information on characteristics of sub-micron particles in MBRs is still insufficient. In this study, a pilot-scale MBR treating municipal wastewater was used to investigate and characterize sub-micron particles in an MBR and to identify the size fraction(s) responsible for irreversible fouling in an MBR. It was clearly shown that characteristics of sub-micron particles in the MBR varied considerably depending on their sizes. Results of Fourier transform infrared (FTIR) analysis and monosaccharide analysis suggested that irreversible fouling in this study was mainly caused by the specific size fraction of 0.1–0.45 μm, which was close to the size of micropores of the membrane used. Pore plugging might explain this to some extent.

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.

Braid-reinforced hollow fiber membranes with high mechanical properties and considerable antifouling surface were prepared by blending poly(vinyl chloride) (PVC) with poly(vinyl chloride-co-poly(ethylene glycol) methyl ether methacrylate) (poly(VC-co-PEGMA)) copolymer via non-solvent induced phase separation (NIPS). The tensile strength of the braid-reinforced PVC hollow fiber membranes were significantly larger than those of previously reported various types of PVC hollow fiber membranes. The high interfacial bonding strength indicated the good compatibility between the coating materials and the surface of polyethylene terephthalate (PET)-braid. Owing to the surface segregation phenomena, the membrane surface PEGMA coverage increased upon increasing the poly(VC-co-PEGMA)/PVC blending ratio, resulting in higher hydrophilicities and bovine serum albumin (BSA) repulsion. To compare the fouling properties, membranes with similar PWPs were prepared by adjusting the dope solution composition to eliminate the effect of hydrodynamic conditions on the membrane fouling performance. The blend membranes surface exhibited considerable fouling resistance to the molecular adsorption from both BSA solution and activated sludge solution. In both cases, the flux recovered to almost 80% of the initial flux using only water backflush. Considering their great mechanical properties and antifouling resistance to activated sludge solution, these novel membranes show good potential for application in wastewater treatment.

A compact and low-power current-mode RC oscillator (RCO) with process, voltage, and temperature (PVT) stability has been developed. The circuit employs a current-mode RCO architecture without using a conventional comparator based voltage-mode architecture. The current-mode architecture enables a compact RCO and faster switching speed to be achieved. By designing transistor sizes equally between one in a bias circuit and another in a voltage to current converter, the effect of process variation can be minimized. A prototype chip in a 0.18-µm CMOS process demonstrated that the RCO generates a stable clock frequency of 32.7 kHz with a small area of 0.19 mm2 and low-power dissipation of 54.2 nW at 0.85-V power supply, which achieves a figure of merit (FoM) of 1.66 nW/kHz. The measured temperature coefficient and line regulation were 99.5ppm/°C and 8.9ppm/mV, respectively.

This study investigated the organic matter that causes fouling in the forward osmosis (FO) membrane filtration system used in wastewater concentration processes. The development of the fouling of FO membranes caused by actual municipal wastewater was compared with that of the fouling caused by solutions containing artificial foulants (i.e. Aldrich humic acid, bovine serum albumin, and sodium alginate). This comparison shows that the development of the fouling was underestimated when using the artificial foulants. The characteristics of the foulants were investigated using fluorescence excitation-emission matrix spectra and liquid chromatography-organic carbon detection analyses. The results obtained by these advanced analytical methods indicated that the so-called biopolymers (i.e. organic macromolecules mainly comprising polysaccharides and proteins) were the major components of the foulants. In contrast, hydrophobic organic matter, such as humic substances, was not a dominant component.

We conducted a high-load operation of a baffled bio-reactor equipped with air-sparged side-stream tubular membrane modules for treating actual municipal wastewater at two different periods (high- and low-temperature). Although nitrogen removal efficiency slightly decreased at the low-temperature period, this baffled bio-reactor showed excellent nitrogen and phosphorus removal efficiencies. We also investigated the developments of both physically reversible and irreversible fouling during operation with two-phase flow (mixed-liquor and gas) at various gas velocities and the mixed-liquor velocity was fixed at 0.50 m/s. The membrane flux was fixed at 80 L/m2/hour throughout the experiments. Regardless of the difference in temperature, the trends in the development of these two types of membrane fouling caused by the difference in gas velocity were similar. For physically reversible fouling, an optimum gas velocity, in which the development of this type of fouling was minimized, was found to be around 0.42 m/...

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.

We investigated the relationship between the nature of proteins and their fouling propensities in pilot-scale membrane bioreactors (MBRs) treating real municipal wastewater with two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). In 2D-PAGE, proteins are separated based on their isoelectric points and molecular weights, and therefore, information can be obtained on the nature of the proteins. Foulants extracted from fouled membranes at the end of continuous operation and organic matter contained in mixed liquor suspension were analyzed by 2D-PAGE, and the results were compared. This analysis was performed for two identical MBRs operated under different solid retention times (SRT) to investigate the effect of the operating condition on the types of proteins with high fouling propensities. In the MBR operated with a long SRT, the presence of proteins that appeared in the neutral pH range was more pronounced in the extracted foulant. Because the pH of the mixed liquor suspension was in the range of...

Membrane fouling is a serious problem in drinking water treatment systems. Biological contact filters (BCFs) are often used as a pretreatment to remove ammonia, dissolved organic matter (DOM), and metal ions such as iron and manganese. In this study, the effect of BCF as a pretreatment for membrane fouling was evaluated using a laboratory-scale mini module consisting of a mini BCF column and a mini MF column. Initially, it was confirmed that the main foulant was a biopolymer (at low concentration) in the raw water. Subsequently, the biopolymer concentrations in the BCF influent and effluent were measured with the excitation emission matrix (EEM) fluorescence spectroscopy and the liquid chromatograph organic carbon detector (LC-OCD). The fouling potential of the BCF influent and effluent was also measured to evaluate MF membrane fouling rate. The results demonstrate that application of the BCF reduced the biopolymer concentration of the effluent and reduced membrane fouling. The effect of BCF was also established in an actual drinking water treatment plant. It was found that optimizing the contact time of raw water with the BCF was crucial to reduce membrane fouling.

We investigated seasonal variation in membrane fouling in membrane bioreactors (MBRs) treating municipal wastewater regarding the difference between physically reversible and irreversible fouling. Two separate MBRs with different solid retention times (SRTs) operated in parallel for about 200 days including high- and low-temperature periods to evaluate the effect of operating conditions on seasonal variation of membrane fouling. Seasonal variations of both types of membrane fouling (i.e., physically reversible and irreversible fouling) were observed for the MBR with short SRT (13 days). However, in the MBR with long SRT (50 days), there were no significant seasonal variations in both types of membrane fouling. In the MBR with short SRT, the trends in the seasonal variation in the development rates of physically reversible and irreversible fouling were different. Physically reversible fouling was more significant in the low-temperature period, while physically irreversible fouling developed more rapidly in the high-temperature period. The development rates of physically reversible fouling can be related to the concentration of dissolved organic matter in the mixed liquor suspension of MBRs; whereas those of physically irreversible fouling could not be explained by the concentration of dissolved organic matter. The characteristics of dissolved organic matter differed depending on the temperature period, and the trends of dissolved organic matter variation in mixed liquor were similar with those of foulants that caused physically irreversible fouling. The results obtained in this study indicated that seasonal variation in physically reversible and irreversible fouling is related to changes in quantity and quality of organic matter, respectively.

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.

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.

In this study, membrane fouling behavior of anammox MBR with or without carriers made by magnetic porous carbon microspheres was investigated. The results show that Trans Membrane Pressure was an order of magnitude lower after 50days due to use of carriers, which did not directly contact with membrane surface. Scanning Electron Microscope analysis indicates that abundance of anammox bacteria formed biofilm on membrane surface. Fourier transform infrared spectroscopy combined with amino acids contents analysis for membrane surface deposition show that metabolite released by anammox bacteria contains more hydrophobic groups than hydrophilic, which was considered as important reason for its abundant existence on hydrophobic membrane surface. Microbiological immobilization not only reduces biological membrane fouling, but also mitigates organic fouling including organic matter containing COO, hydrophobic groups (CH3, CH2 and CH etc), as well as inorganic deposition. Our finding provides an effective method for mitigating MBR membrane fouling in anammox process.

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.