One of the critical issues limiting the successful application of membrane filtration for treatment of drinking water and wastewater is typically membrane fouling of contaminants caused by pore clogging of the membrane and cake layer formation on the membrane surface during filtration. The overall objective of this paper is to systematically provide a fundamental understanding of the underlying mechanisms governing membrane fouling during membrane filtration, with particular emphasis on the pore clogging of the membrane in colloidal filtration such as microfiltration and ultrafiltration. A generalized characteristic form of four classical blocking filtration laws, which had been most extensively used in the analysis of the pore clogging of the membrane, was theoretically derived. The model accounts for the variations of both the porosity and specific surface area of the interior of membrane associated with the progress of deep bed filtration, on the basis of the Kozeny–Carman equation. Several new combined models have recently been developed to describe complicated filtration behaviors in which pore clogging of the membrane and growth of the filter cake occur in series or in parallel. In the future, the development of a more accurate model to explain the behavior of the irreversible pore clogging of the membrane, which will not fully recover by the simple physical backwashing and other periodic dynamic operations, will become increasingly important, in order to establish efficient membrane-based water treatment technologies.

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A new crystallization process is proposed to recover phosphorus from wastewater treatment plants using waste cement particles generated in aggregate recycling processes. Batch experiments were conducted with the waste cement particles for the phosphate recovery from potassium dihydrogen phosphate (KH₂PO₄) solutions as a model of wastewater. For an initial concentration of the phosphate of 50 mgP L⁻¹, which is close to that in the water effluent produced in the sludge dewatering process, and an initial concentration of waste cement of 1.0 g L⁻¹, approximately 50% of the phosphate was removed from the solution in 360 min. From the change over time in the concentrations of the phosphate, protons, and calcium ions, two reaction mechanisms can be considered: reaction at the surface of the waste cement particles, and the aqueous-phase reaction of the dissolved calcium hydroxide (Ca(OH)₂) with the phosphate. The results of SEM and XRD analysis showed that the phosphorus was precipitated as hydroxyapatite (HAP) on the surface of the waste cement particles. The observed reaction rate of the phosphate recovery was comparable to those in the conventional HAP crystallization methods. Considering that costly additives such as a calcium source, e. g. calcium chloride, and seed materials are necessary for the conventional HAP crystallization methods, the present process is highly competitive due to the negligible cost of the waste cement.

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Nitrifying bacteria acclimated to tolerate concentrations of ammonium sulfate as high as 5300 mg/L were prepared from activated sludge (AS) or effective microorganism groups (EM) and physically immobilized on polymeric spherical hydrogel (KU, AL, AL [C], AL [F]), polymeric cubic hydrogel (ALCu, ALCu [C]), pelletized polypropylene (BCP [C]), or cylindrical polypropylene (ALT, ALT [C]). The supports AL [C], BCP [C], ALCu [C], and ALT [C], contain activated carbons (C), and AL [F] contains fly ash (F). Entrapped bacteria were also prepared by the crosslinked gelation of poly (vinyl alcohol) (PVA) with boric ion in the presence of C, F, or activated alumina (Al) to yield PVA [C], PVA [F], or PVA [Al], respectively.
Removal of high concentration of ammonium with acclimated nitrifying bacteria and stripping from model wastewater were carried out. Interestingly, entrapped bacteria produced NO₃⁻ from NH₄⁺ in series, while AS/PVA and physically immobilized bacteria produced only NO₂⁻ from NH₄⁺. In the case of high concentration of ammonium load, the acclimated bacteria cultured from EM/PVA [C] (bacteria/support) or AS/ALT [C] were able to remove about 57% of the ammonium ions with stripping from the 5300 NH₄–N mg/L model wastewater in 30 days. Complete nitrification reactions were examined by using immobilized bacteria, NO₂⁻-producing AS/ALT [C] and NO₃⁻-producing EM/PVA [Al]. High concentration of NH₄⁺ was almost completely nitrified to NO₂⁻ or NO₃⁻ after 35 or 50 days, respectively.

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This study examined the possibility of combined with MAP crystallization treatment using a reactor with compact settling zone combined with hydrocyclone treatment to achieve a high rate of treatment. e MAP reactors with a compact sedimentation basin or a baffled plate separator at top of reactor were discussed, hydro-retention time were 4.6 min and 1.6 min for the separator zone, respectively. The mean removal rate of total phosphorous T-P by MAP crystallization was 86.7% and 55.3%, respectively. The fine MAP particle in effluent from MAP reactor was separated by hydrocyclone. Overall T-P removal rate are reached 89.5% and 77.6%, respectively.

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Orange waste, a biomass waste, and pectic acid were loaded with zirconium(IV) to investigate its feasibility for phosphate removal from an aquatic environment. The amount of loaded zirconium was 0.25 and 0.70 mol/kg to orange waste gel and pectic acid gel, respectively. At pH 1–4, phosphate was quantitatively adsorbed onto Zr(IV)–loaded orange waste gel, whereas the adsorption onto Zr(IV)–loaded pectic acid gel was decreased with increasing pH. The maximum adsorption capacity of phosphate onto Zr(IV)–loaded orange waste gel and Zr(IV)–loaded pectic acid gel was evaluated as 0.25 and 3.4 mmol/g, respectively. Repeated use for adsorption followed by elution with 0.2 M NaOH was possible for Zr(IV)–loaded orange waste gel in a column mode.

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Carbonized material has a biological affinity and it is effective for the immobilization of microbes. This study examined the enhancement of biological nitrogen removal in the wastewater treatment by use of carbonized textile as the immobilizing carrier of nitrifying bacteria.
Carbonization experiments of cotton and rayon were performed, and rayon carbonized at relatively low temperature was selected as the immobilizing carrier. The performances of microbe adhesion and nitrogen decomposition were examined by using nitrifying bacteria. From these examinations, the carbonization of textile was recognized to be effective for the immobilization of nitrifying bacteria. In the wastewater treatment by using a small reactor and ammonia-rich model wastewater, the ammonia removal was higher for the reactor installed with carbonized textile than for that without it.
To examine the conditions of the immobilizing carrier for continuous treatment of wastewater, the flow characteristics of a large rectangular airlift bubble column were measured. Based on the energy balance, the liquid circulation flow rate was analyzed, and the distribution of dissolved oxygen in the column and the fraction of the anaerobic region were estimated. The continuous treatment of wastewater was conducted by using two large columns with and without carbonized textile installed. The BOD removal was unchanged, but the ammonia removal was higher for the reactor with carbonized textile than for that without it.

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Arsenic (III) and chromium (VI) are known to be harmful for human health. In this study, gibbsite (GB) was granulated using ethyl cellulose or alumina sol 520 for the removal of arsenic (III) and chromium (VI) . Two kinds of granular GBs had the ability to adsorb arsenic (III) and chromium (VI), with arsenic (III) being adsorbed in greater amount. Use of ethyl cellulose to prepare granular GB may not be economically suitable, because the production process is complex and requires the use of solvent. The amount of arsenic (III) and chromium (VI) adsorbed onto GB was slightly decreased by the granulation. The amount of arsenic (III) adsorbed onto granular GB in a binary solution system was greater than that in single solution system, while the amount of chromium (VI) adsorbed was similar in both systems. The adsorption mechanism of arsenic (III) and chromium (VI) is thought to dependent on the affinity between the metals and the surface or porosity of granular GB. The prepared GB could be utilized for removal of arsenic (III) or chromium (VI) in an aqueous environment.

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A simulation model of batch-wise operation of adsorption separation on a packed column was developed, which includes constants of the adsorption isotherm (a and b in the Freundlich equation) and the adsorption rate constant (K_fa; overall mass-transfer coefficient) of the system. By numerical solution of the model equations and using the laboratory experimental data obtained with a short adsorption column, a method was found to predict the steady-state adsorption breakthrough curve of the practical operation.
To obtain the steady-state breakthrough curve on the short column, the exit concentration of adsorption component at the starting time of fluid flow in the column C_n (t=0) must be zero and the column must have a definite length. Under such conditions, the same adsorption breakthrough curve as the practical operation can be obtained from the experimental test of the short adsorption column.
If C_n≠0, the steady-state adsorption breakthrough curve cannot be obtained in the short column. In this case, however, the adsorption rate constant (K_fa) and the constants of the adsorption isotherm (a and b) of the system can be determined from the analysis of the same short column test data. Therefore, by using the simulation model equations with these data, the breakthrough curve in the practical operation can be easily and correctly predicted.

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Because oxometallic ions (Mo(VI), W(VI), V(V), B(III), Cr(VI), Ge(IV)) are toxic for animals and plants, it is important to economically remove them from industrial wastewater.
In this paper, we examined whether the raw wood materials can adsorb oxometallic ions. It was found that wood particles such as cedar or bamboo can adsorb oxometallic ions. The optimum pHs of adsorption depended on the metal and wood particles used. The adsorption isotherm of metals correlated well with the Langmuir equation. The saturation adsorption capacities of metal ions on cedar were larger than those on bamboo.
In order to improve the adsorption ability, the wood particles were pre-treated with NaOH. Treatment with NaOH was effective for cedar.
Adsorption kinetics of metal ions on wood particles correlated well with a pseudo-second-order reaction model.
The unmodified raw wood material, especially cedar, was found to be promising adsorbent for the recovery of oxometallic ions.

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Toxic arsenical species include As(III) and As(V), of which As(III) species have specially strong toxicity. Because of this strong toxicity, contamination of groundwater by arsenic and arsenic-containing effluent from the semiconductor production process pose environmental problems. This study is concerned with the removal of As(III) and As(V) with four kinds of Mg/Al layered double hydroxides (LDH) containing CO₃²⁻, SO₄²⁻, Cl⁻ and NO₃⁻ as interlayer anionic species.
Anion exchange properties were found to differ according to the kind of layered double hydroxide. Mg–Al–NO₃⁻LDH was superior for exchange of As(III) and As(V) due to the nature of nitrate ion in the interlayer. For As(V) removal, pH of 7.1 or more was suitable. If the initial conditions are set as As(V) concentration of 10 mg/dm³, pH 7.1, 1 m³ of solution and 99% removal, the required amount of Mg–Al–NO₃⁻LDH is 0.27 kg for two step-batch operations. As(III) should be oxidized to As(V) before the removal processing.

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A biodegradable flocculant or bioflocculant was prepared from hen egg white protein. Egg albumin was ethyl-esterified in a 0.1 M HCl ethyl alcohol solution at room temperature. Ethyl-esterified egg albumin (EtOA) , having an esterification degree of 84%, was applied to the flocculation of diatomite. The flocculating ability of EtOA was evaluated by a clarification test and the sedimentation balance method. The diatomite suspension was effectively flocculated by the addition of small amount of EtOA (1 wt% of the diatomite weight) , and the flocculating ability of EtOA was higher than that of poly aluminum chloride at pH 4 to 10. The settling velocity of diatomite floc at the appropriate MeCS dosage (1–2 wt%) was about 0.005 m·s⁻¹ at pH <7, and it decreased to 0.003 m·s⁻¹ at pH >7.

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Flocs formed of polystyrene latex particles undergoing rapid Brownian coagulation were counted directly under an optical microscope to verify the validity of our previously proposed equation to predict the temporal evolution of the concentration of flocs developing fractal structure. Experiments were carried out by changing the diameter of the primary particle in order to emphasize the difference of excluded volume of formed flocs. The obtained results demonstrated the enhancement of the rate of coagulation in the later stage of coagulation, which verifies the validity of our previously proposed equation.

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The increasing thickening capacity in an inclined continuous thickener was theoretically analyzed by use of vertical and inclined solid flux curves obtained from vertical and inclined batch settling experiments with different calcium carbonate slurries. The model proposed in this study, which has a wedge-shaped layer of clear liquid developed at the upper surface of the inclined plate, can explain the difference between vertical and inclined settling velocities. Using these curves, the capacity of the thickener can be predicted based on graphical analysis of the critical loading operation under steady-state conditions. The capacity predicted by this analysis closely coincides with the results of experiments with the calcium carbonate slurry. Consequently, this procedure clearly provides an approach for analysis of an inclined continuous thickener, and also shows that the increasing thickening capacity for a thickener of any arbitrary vertical height can be determined graphically.

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Depth filters trap particles internally, and thus the compaction of the particle layer is partially repressed by the internal structure of the filter to yield a high permeation flux at a low transmembrane pressure. We filtered suspensions of three kinds of polystyrene latex particles (incompressible, spherical, 0.30, 0.54, and 0.70 μm in diameter) with an asymmetric depth filter, SE20 (nominal pore size=0.20 μm), at different transmembrane pressures and concentrations. The filtration resistance per unit weight of trapped particles with the depth filter was half of that with a screen filter in the filtration of latex particles. The particles were trapped first near the outlet side of the filter and then near the inlet side, unlike the standard blocking model for the membranes with cylindrical pores and the deep bed filtration model for sand filtration. A filtration model was proposed for the filtration of latex suspension with the depth filter. The model suggested that the asymmetric depth filter showed high performance because the filaments in the filter increased the porosity of the particle layer in contact with them.

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To gain a basic understanding of the ultrafiltration characteristics of suspensions containing both fine particles and macromolecules, dead-end ultrafiltration of mixtures of rutile titanium dioxide (TiO₂) and bovine serum albumin (BSA) was conducted under constant pressure, and the effects of pH and electrolyte concentration on the filtration properties were investigated from the standpoint of the interactions between particles and macromolecules. BSA molecules have a tendency to be adsorbed onto TiO₂ particles in the mixed suspension, which affects the stability of TiO₂ particles significantly. At pH conditions where TiO₂ and BSA carry opposite charges, BSA adsorption induces a marked change in the zeta potential of TiO₂, resulting in a dramatic change in the particle size. At pH conditions where TiO₂ and BSA carry the same electric charge, the particle size varies greatly upon addition of electrolyte due to its charge-shielding effect and the combined effect of electrolyte and BSA coexisting in liquid. Thus, it can be concluded that the ultrafiltration characteristics of particulate suspensions containing macromolecules are determined by the stability of particles.

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The effect of coagulant dosage on the filterability of coagulated humic acid solutions was studied by dosing polyaluminum chloride (PAC) as a coagulant. The experimental results showed that the conventional cake filtration theory (known as Ruh's filtration equation) can be applied to dead-end filtration analysis of dissolved humic acid solutions and/or coagulated humic acid suspensions. Increasing dosage of coagulant resulted in a decrease in the average specific filtration resistance of cake, and an optimum dosage was observed. For dissolved humic acid solutions, the average specific filtration resistance decreased significantly with an increase in solute concentration. The filterability of humic acid cake could be classified into three different regions, depending on humic acid concentration. Experimental results for coagulated humic acid suspensions coincided favorably with the calculated results based on the compressible cake filtration theory.

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The effect of BOD loading on solid–liquid separation properties of activated sludge in wastewater treatment process was investigated. The initial sedimentation velocity of activated sludge is highly dependent on BOD loading, and SVI decreased with increase of BOD loading and became smallest at the BOD loading of 0.4 kg/(MLSS-kg·d). In microfiltration of activated sludge, the dynamic behaviors were well described by the Ruth filtration rate equation. The average specific filtration resistance of filter cake became smallest at the BOD loading of 0.4 kg/(MLSS-kg·d), which is similar to the result of SVI. The filter cake composed of activated sludge has extremely high compressibility, indicating that increase in the filtration pressure does not necessarily lead to increase in the filtration rate. From the experimental data, it was found that the sedimentation and filtration properties of activated sludge correlate with the area mean diameter of sludge flocs. In addition, floc size of activated sludge was greatly influenced by BOD loading of the wastewater. Therefore, it seems reasonable to conclude that the solid–liquid separation properties of activated sludge are closely related to BOD loading of wastewater.

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In a submerged membrane activated sludge process that uses hollow fiber microfiltration for separation of activated sludge and the effluent, the suction pressure and the filtration resistance increase due to clogging of micro pores of the membrane and adhesion of sludge solids to the membrane surface, and the efficiency of the process decreases. In this study, wastewater treatment experiments were conducted with a wide range of initial sludge solids concentration (MLSS) under low BOD volumetric loading condition and constant membrane permeation flux condition to determine the effect of MLSS on various filtration resistances.
Suction pressure was found to increase rapidly when MLSS exceeds 12000 mg/L. In this condition, adhesion of sludge solids to the membrane surface increased. The filtration resistance of cake is proportional to the amount of adhering sludge solids, and the solid liquid separation process is based on Ruth's filtration equation. Therefore, for the long and stable operation of the submerged membrane activated sludge process, it is recommended that the process should be operated at MLSS of less than 12000 mg/L.

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Various types of cellulose acetate (CA), cellulose acetate propionate (CAP) and polyethersulfone (PES) hollow fiber membranes were prepared to evaluate energy consumption in submerged filtrations. It is possible to obtain CAP and PES microfiltration membranes with maximum pore size ranging from 0.3 to 2.0 μm by addition of hydrophilic non-solvent to polymer solution. Using CA membrane with pure water permeate velocity of 8.6×10⁻⁵m³·m⁻²·s⁻¹ at 0.1 MPa and molecular weight cut-off (MWCO) of 150 kDa, submerged filtration of waste carwash water after flocculation was performed at the treatment rate of 0.8 m³·h⁻¹ for 1 month. Average electric power consumption was 0.81 kWh·m⁻³ when backwashing and bubbling were conducted for 1 min after every 15 min of filtration. For comparison, cross-flow filtration using a conventional cross-flow CA membrane with MWCO of 150 kDa was performed under the same experimental conditions as in the case of the submerged filtration. When the cross-flow rate to permeate rate was 1, average electric power consumption was 1.2 kWh·m⁻³. This result indicates that energy consumption in submerged filtration is lower than that in cross-flow filtration. Using CAP and PES microfiltration membranes, energy consumption in submerged filtration was also measured under the same experimental conditions as in submerged filtration using CA membrane. The average electric power consumption was 0.78 kWh·m⁻³ for the CAP membrane with pure water permeate velocity at 0.1 MPa of 1.0×10⁻⁴, and 0.69 kWh·m⁻³ for the PES membrane with pure water permeate velocity at 0.1 MPa of 2.8×10⁻⁴m³·m⁻²·s⁻¹. It was found that energy consumption decreased more when the membrane with higher pure water permeate velocity was used.

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Hollow-fiber membranes were prepared using cellulose acetate butyrate (CAB) as a membrane material via thermally induced phase separation (TIPS) and the effects of preparation conditions (air gap and additives) on membrane characteristics were studied. The presence of the air gap was found to significantly affect the water permeability and microstructure of the hollow-fiber membrane. The hollow-fiber membrane prepared at an air gap of 0 mm has a microporous outer surface, while that prepared at an air gap of 5 mm has a skin layer close to the outer surface. As a result, the membrane prepared at an air gap of 0 mm showed high water permeability and relatively low mechanical strength. The membrane prepared at an air gap of 5 mm exhibited the opposite properties. Of the additives investigated the addition of poly (ethylene glycol) increased the porosity of the membrane surface, while polymeric surfactants (Tetronic^® 1307 and Pluronic^® F127) made the membrane surface hydrophilic.

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The intercrystalline pathway of MFI zeolite membranes was controlled for development of water purification membranes. The size of intercrystalline pathway was increased from nm order to μm order to obtain both microfiltration and absorbent effects. For the zeolite layer to be used as an absorbent, membrane thickness should be controlled. MFI zeolite membranes were prepared by using a dry gel conversion method on a porous alumina capillary substrate. Dried parent gel was coated on a porous substrate and the dried gel was converted to zeolite under high temperature steam. Membrane thickness can be controlled by changing the amount of dried gel coating on the substrate. Pore size of the intercrystalline pathways of MFI zeolite membranes was controlled by adding poly ethylene glycol (PEG) as a polymeric template. MFI zeolite XRD measurement confirmed that was successfully crystallized on the substrate regardless of the presence of PEG. Pore size the of intercrystalline pathway were measured by coupling a low temperature (350°C) calcination and a nano-permporometer. Without PEG addition the pore size was about 6 nm, and this was increased to more than 16 nm by adding PEG (M. W. 1000, PEG/SiO₂=0.1). This indicates that intercrystalline pathways can be controlled by adding PEG during crystallization procedures of zeolite membranes.

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Methane fermentation treatment of solids yields a digested sludge containing nitrogen and phosphorus in high concentrations. For the purposes of phosphorus load reduction of the water treatment system, anti-scaling of methane fermentation tanks and their surrounding apparatus, and phosphorus resource recovery, a system for positive crystallization and recovery of magnesium ammonium phosphate (MAP) from the digested sludge was devised. This system consists of a crystallization process, a separation process using the hydrocyclone and a low temperature drying process. The optimum operational conditions for MAP and the MAP drying conditions for a digested sludge containing solids at a concentration of several per cent were clarified, and a pilot-scale plant having a treatment capacity of 2 m³/h was built and subjected to 16-month demonstration tests.
For the separation of MAP using the hydrocyclone, it is necessary to suppress nucleation in the crystallization process. Based on the laboratory tests, it was found that MAP nucleation is suppressed and the crystal growth becomes predominant when a good fluidized condition of MAP is maintained in the reactor, the reactor is operated at a low supersaturation degree, and a suitable MAP crystallization loading per charged seed crystal amount is maintained. It was also found that, in the drying process, MAP can maintain its form without transition when the drying temperature is set below 70°C. In the demonstration tests of the series of processes, the PO₄–P removal efficiency in the crystallization process was above 85%, showing that the reactions proceeded well. Moreover, only about 10% of the reacted phosphorus was nucleated; that is, about 90% of reacted phosphorus grew on the seed crystal surfaces, and as a result, MAP could be separated well from the digested sludge. MAP recovered from the drying process had a moisture content below 0.1%, a purity of 92.6%, and a hazardous metal content below the standard values prescribed by the Fertilizer Regulation Act, and therefore, it could be confirmed that MAP has a high quality as a fertilizer product.

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The freeze concentration process with ultrasonic irradiation, which is very effective for concentration of solutes in solution, was applied to a suspension. Bentonite particles (median particle diameter = 0.80 μm) were used as a particle sample. The freezing treatment with ultrasonic irradiation was effective for concentration of the suspension, and this effect increased with the decrease of suspended solids (SS) concentration and the increase of irradiation power. The freeze concentration efficiency of SS was decreased by the presence of solutes (sodium chloride, L-phenyl alanine and saccharose), and this effect diminished as molecular weight of the solute increased. For sodium chloride, however, salting out occurred and SS coagulated. As a result, the freeze concentration efficiency of SS decreased greatly. Therefore we should pay attention to the kind of solute in freeze concentration treatment, and whether its addition of the solute might cause the salting out. While the SS addition into solution diminished the degree of the freeze concentration efficiency of the solutes in the solution, the order of this efficiency with SS was the same as that without SS.

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A novel process utilizing particle immobilization in alginate gels has been proposed for a solid-liquid separation of colloidal suspension. A mixture of sodium alginate aqueous solution and colloidal suspension is added to a calcium chloride aqueous solution, resulting in calcium alginate gels. The gel suspension is dehydrated gravitationally, followed by mechanical expression of the gel particles. During the expression, the colloidal particles remain in the gels and the expressed liquid is clear. The expressed cake is then discarded. The effect of the solution environment of the colloidal suspension on the process was studied. It was found that pH of the suspension does not affect the process, and sodium ions in the suspension also have little effect on the immobilization reaction. Calcium and aluminum ions in the suspension were found to interfere with the reaction, yielding metal-alginate gels before the sodium alginate solution and the colloidal suspension are mixed completely. For complete immobilization of colloidal particles, therefore, multi-valent ions in the suspension should be masked by use of a chelating agent.

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Polyelectrolytes are widely used as flocculants for water and waste-water treatment. To better control the flocculation, it is important to understand the structure of the layer of polyelectrolyte adsorbed on a colloidal particle. In the present study, electrophoretic mobilities of polystyrene latex particles with adsorbed polyelectrolytes were analyzed by applying Ohshima-Kondo's theory of soft particles to reveal the structure of the adsorbed polyelectrolyte. Electrophoretic mobilities leveled off to a nonzero value in the limit of high ionic strength of solution, which is a characteristic feature of soft particles. The charge density, ZN [mol/L], in the layer and the length scale parameter of permeability, 1/λ [nm], were obtained by applying the electrophoretic theory of soft particles. It was found that the mean distance between charged segments of adsorbed polyelectrolytes estimated by ZN was almost the same as 1/λ.

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Microcapsules containing tri-n-octylamine (hereafter TOA) as an extractant were prepared by using SPG membrane emulsification and in-situ polymerization. The morphology of microcapsules, the encapsulation efficiency of TOA, the extraction of palladium from hydrochloric acid solution and the back-extraction of palladium from microcapsules were investigated. The average diameter of the microcapsules was half of the pore diameter of the SPG membrane. The encapsulation efficiency of tri-n-octylamine was nearly 100%, and thus there was practically no loss of TOA during the preparation of microcapsules. Microcapsules pretreated with hydrochloric acid were equilibrated with palladium chloride hydrochloric acid solution, and the extraction properties were determined by measuring the concentration of residual palladium. The extraction of palladium occurred promptly, and all microcapsules prepared in this study reached equilibrium within 10 minutes. To examine the back-extraction of palladium from microcapsules, microcapsules were shaken in thiourea solution or hydrochloric acid until back-extraction equilibrium was reached. The results of extraction and back-extraction experiments indicated that TOA was completely encapsulated and there was no leakage of TOA, thus the microcapsules could be used repeatedly for extraction.

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A servo motor widely used in robot technology was applied to a mixing operation. Periodic interruption of rotation and a co-reverse periodic rotation of the impeller were very effective for liquid mixing without baffles in the turbulence region. Particularly with low viscosity liquid the co-reverse periodic rotation of the impeller was effective at a lower switch frequency for liquid mixing, although the mixing performance was not effective if the operation time was less than 2 s. The torque of the co-reverse periodic rotation was larger than that of the periodic interruption of rotation, but the mixing performance of unsteady mixing was more effective than the steady mixing because the mixing time was lower than that of steady mixing at the same specific power consumption.

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Two new type turbines which alternately combined flat blade with pitched blade were invented. They were a DOWN-impeller with down-flow-type pitched blades and an UP-impeller with up-flow-type pitched blades. The behavior of cavities and the mechanism of power transfer for the new type turbines were investigated by measuring the pressure distribution on the blade surface, and the effect on adjacent blades was clarified by comparing them for a paddle, a down-flow pitched blade turbine and an up-flow pitched blades turbine. Power per blade due to form drag was calculated from the pressure difference between the front and back side of a blade. Power transferred from blade to liquid for both flat and pitched blade of the new type turbines was greater than that for conventional turbines operating under the same conditions. It was found that the cavity behavior of new type turbines was very different from that of conventional turbines, and the reduction of power consumption due to aeration for the new type turbines was less than that for conventional turbines. The reduction of power consumption in a gassed condition was controlled with the form drag.

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The effects of the initial pH and ionic strength of a solution on the absorption rate, absorption efficiency, and selectivity of NO₂ absorption into magnesium/calcium sulfite slurry were experimentally investigated. A mixed gas containing NO₂ was sparged into a bubble column absorber, and the concentrations of nitrite and nitrate in the absorbing slurry were measured. Nitrite was selectively produced using magnesium/calcium sulfite slurry, which has a pH greater than approximately 5, while both nitrate production and nitrite desorption were suppressed. No effects of the magnesium/calcium sulfite concentration and ionic strength on the absorption rate and absorption efficiency were found in this study. The absorption performances of magnesium/calcium sulfite slurry were the same as those in a sodium sulfite solution.

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Blockage is a serious problem in practical use of microreactors, and detection of blockage is indispensable for their effective and stable operation. In this research, methods to locate channel blockage and estimate the degree of blockage were derived based on a simple pressure balance model of a microreactor. The proposed methods use the correlations between the pressure distribution data calculated by the pressure balance model and the actual pressure distribution data when blockage occurs. The results of computer simulation using fluid dynamics simulation software showed that the proposed methods can identify the blockage location and estimate the degree of blockage. The accuracy depends on the number and configuration of pressure sensors.

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An innovative multi-layer coating method has been developing for the production of graded refractive index lenses by repeated peripheral coating of a core fiber of higher refractive index with polymer solutions of progressively lower refractive indices. In this work, optimum operational conditions were investigated for the production of the core fiber of high refractive index by melt spinning technique. Favorable extrusion temperatures were determined by visual observation of the melt fracture in the extruded strands. The variance of the fiber diameter depended markedly on both the die temperature at the exit of the extruder and the chimney temperature of the fiber cooling section. In order to remove the small amount of oligomer contained in the copolymer, a vent was installed at the middle of the extruder to continuously evaporate the oligomer during extrusion. At an optimum melting temperature, the oligomer could be well removed without any loss of the polymer melts from the vent.

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During the rated continuous test of a PEFC stack under stationary PEFC system conditions, the potential of several cells fell remarkably and the test could not be continue. The cause of cell potential fall was confirmed to be thinning of the polymer electrolyte membrane (PEM) in the degraded cells and cross leakage of hydrogen from the anode. Rated continuous test under different condition of relative humidity revealed that low humidity conditions accelerate cell potential fall and PEM degradation. An, open circuit voltage (OCV) accelerated durability test further revealed that PEM degradation is chemical degradation caused by three factors (low humidity, presence of hydrogen and oxygen) . It is indicated that several radicals are concerned with PEM chemical degradation.

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In order to obtain knowledge for preventing water freeze in pipe in winter, we considered freezing phenomena in a pipe with small amount of water flow. The condition of flow rate Q established was 4.0×10⁻⁷–7.1×10^{−6 m}3/s, and freezing phenomena for two different-sized pipes were investigated. As a result, freeze at the condition of T_w (the temperature of the inside wall)=−2–−3°C was generated. It was found that freeze was likely to occur as the contact time between water and cold wall became longer. On the one hand, in the condition of a very low temperature (T_w<−3°C), it was shown that we were not able to avoid freezing by a method in which a small amount of water flow is continuously flowed. For such severe condition, countermeasures such as water drain and heating pipe etc are necessary.

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