Taro Miyoshi

Mitigated membrane fouling of anammox membrane bioreactor by microbiological immobilization.

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.

Preparation of robust braid-reinforced poly(vinyl chloride) ultrafiltration hollow fiber membrane with antifouling surface and application to filtration of activated sludge solution

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.

Rejection of nutrients contained in an anaerobic digestion effluent using a forward osmosis membrane

AbstractThe possibility of applying a forward osmosis (FO) membrane filtration process for the post-treatment of an anaerobic membrane bioreactor (AnMBR) was investigated in this study. The FO membrane filtration test, using a surrogate AnMBR effluent prepared by supernatant obtained from a real anaerobic digester, demonstrated excellent rejection of phosphate ions. On the other hand, the rejection of ammonium ions was moderately effective and depended heavily on the operating conditions of the FO membrane (e.g. orientation of the FO membrane) solute concentration in the draw solution (DS) and ammonium ion concentration in the feed solution (FS). The flux of ammonium ions across the FO membrane decreased as the solute concentration in the FS increased. The reverse solute flux from the DS to FS also increased as the solute concentration in the DS increased. The above-mentioned trend was particularly remarkable in the FO filtration with an active layer facing DS (AL-DS) orientation, in which the reverse sol...

Discrepant membrane fouling of partial nitrification and anammox membrane bioreactor operated at the same nitrogen loading rate.

In this study, two times more serious membrane fouling was found in anammox membrane bioreactor, compared to partial nitrification membrane bioreactor (PN-MBR) operated at the same nitrogen loading rate. By protein, polysaccharide, amino acids and functional groups analysis, it was found that the discrepancy in membrane fouling was virtually due to the difference in microbial products of nitrifiers and anammox bacteria. Protein and polysaccharide were main foulants on membrane surface; meanwhile theirs content and ratio in the EPS, supernatant and membrane surface were significantly different in PN-MBR and anammox-MBR. The anammox metabolism products contained much more hydrophobic organics, hydrophobic amino acids, and hydrophobic functional groups than nitrifiers. A mass of anammox bacteria as well as hydrophobic metabolism products deposited on the hydrophobic membrane surface and formed serious fouling. In further, hydrophilic modification is more urgently needed to mitigate membrane fouling when running anammox-MBR, than PN-MBR.

Characteristics of foulants of forward osmosis membranes used in municipal wastewater concentration processes

AbstractThis 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.

Sub-1-μs start-up time, 32-MHz relaxation oscillator for low-power intermittent VLSI systems

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.

A fully integrated, 1-µs start-up time, 32-MHz relaxation oscillator for low-power intermittent systems

This paper proposes a fully integrated 32-MHz relaxation oscillator (ROSC) capable of fast 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 1.66-nW/kHz, 32.7-kHz, 99.5ppm/°C fully integrated current-mode RC oscillator for real-time clock applications with PVT stability

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.

Low-cost water treatment system using submerged membrane filtration in developing countries

AbstractIn 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 45xa0L/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...