Fujio Takahashi

BOD sensor using magnetic activated sludge

Abstract A biochemical oxygen demand (BOD) sensor, consisting of a Pb(−)|NaOH|Pt|O 2 (+) electric cell, was constructed. The sensor is basically one application of a dissolved oxygen electrode. Magnetic sludge was prepared by mixing magnetite powder with acclimated activated sludge. A magnetic cathode, comprised of a Sm-Co magnet plated with platinum, was covered by a Teflon membrane; magnetic sludge was simply layered on the membrane by magnetic attraction. The magnetic sludge decomposed the BOD component with consumption of oxygen. The BOD could therefore be determined by measuring the electric current produced by the BOD sensor. This current was then converted into the concentration change of oxygen transported through the Teflon membrane from the magnetic sludge layer.

Immobilized enzyme reaction controlled by magnetic heating : γ-Fe2O3-loaded thermosensitive polymer gels consisting of N-isopropylacrylamide and acrylamide

Abstract Invertase and γ-Fe 2 O 3 (8–24%) were immobilized in a copolymer gel of N -isopropylacrylamide (NIPA) and acrylamide (AAm) ( NIPA AAm gel). Sucrose hydrolysis was studied using a column packed with NIPA AAm gel immobilized enzyme under exposure to a magnetic field (effective value 830 Oe, maximum value 1,170 Oe, 1.68–2.66 kHz). The column temperature rose from 24–25 to 31–56°C due to the heat generated from magnetic hysteresis loss. When the magnetic field was applied, the overall concentration of reducing sugars in the outlet solution increased initially and then decreased due to thermal shrinkage of the gel support. This result clearly demonstrates the potential utility of the present gel-entrapment system in the magnetic control of immobilized enzyme reactions.

Magnetic forced sedimentation of flocs in activated sludge supplemented with ferromagnetic powder of iron oxide

Aiming to increase the sedimentation rate of flocs prepared by the activated sludge process, the effect of the application of ferromagnetic powder of iron oxide (magnetic powder) and a gradient magnetic field on the sedimentation process was examined. The volumetric loading rate of Polypepton was kept to 200–1,000 mgl−1 d−1 during 7 d in the activated sludge supplemented with 2,000 mg l−1 of magnetic powder. When a gradient magnetic field was applied, the initial zone settling velocity in the case of the Polypepton loading rate of 1,000 mg l−1 d−1 was found to be 36 times faster than that in the case of the control.

Sewage Treatment under Conditions of Balancing Microbial Growth and Cell Decay with a High Concentration of Activated Sludge Supplemented with Ferromagnetic Powder

Abstract In order to decrease excess sludge production, the treatment of synthetic sewage was carried out under conditions of balancing microbial growth and cell decay with a high concentration of activated sludge supplemented with a ferromagnetic powder (magnetic sludge). The leakage of magnetic sludge was prevented by the combined treatment of magnetic separation and gravitational sedimentation. COD Cr , removal and effluent suspended solids concentrations were maintained at 85–94% and 5–24 mg l −1 , respectively, over 30 d. Meanwhile, mixed-liquor volatile suspended solids concentration in the aeration tank remained virtually constant and excess sludge was not produced.

Simultaneous removal of organic and nitrogen compounds in intermittently aerated activated sludge process using magnetic separation

Magnetic separation was introduced to an activated sludge process to improve the solid-liquid separation characteristics of the sludge. The process was operated with the intermittent aeration method and applied for the removal of organic matter and nitrogen in wastewater. The activated sludge supplemented with magnetite (Fe3O4) powder (magnetic sludge) exhibits a ferromagnetic property and deposited on the surface of magnetic disks due to magnetic force. The magnetic separation apparatus (composed of rotary magnetic disks and scrapers) separated treated water from the sludge suspension of 13–22 g VSS l−1 within 5 min. Compared with the sedimentational separation process, the magnetic separation technique showed better performance. Simultaneous removal of about 89% of TKN and about 92% of soluble CODCr in influent was performed under loading rates of 0.92 g CODCr l−1 d−1 and 0.10 g TKN l−1, respectively, with a non-aeration/aeration cycle of 40/20 min.

Enzyme reaction controlled by magnetic heating due to the hysteresis loss of γ-Fe2O3 in thermosensitive polymer gels immobilized β-galactosidase

Abstract Control of the immobilized enzyme reaction was investigated by using a magnetic heating. β-Galactosidase and 24% γ-Fe2O3 were entrapped in a copolymer gel of N-isopropylacrylamide and acrylamide. The heat was generated inside the gel due to the hysteresis loss of γ-Fe2O3 under exposure in an alternating magnetic field (effective value 840 Oe, 2.3 kHz), and the temperature elevated above the lower critical solution temperature of the gel. The intermittent exposure of the magnetic field (0.5 min on, 15 min off) could control the temperature cycle between 20.2 and 31.4°C. The process of deswelling–swelling of the gels was repeated by the thermal cycling operation. The product concentration increased no more than 5% in the enzyme reaction. This was smaller than the result reported in the isothermal operation (heating from outside of the gel). It was considered that the hydraulic pump effect was not observed by heating from inside the gel: As compared with the isothermal operation at 31.4°C (around 4.2 kJ/h for heating the solution in the column), the thermal cycling operation was found to need less energy for intermittent heating (1.2 kJ/h) in order to keep the same conversion in the enzyme reaction.

Enhancement of ethanol formation by immobilized yeast containing iron powder or Ba-ferrite due to eddy current or hysteresis

Abstract Heat generation due to eddy currents and hysteresis induced by alternating magnetic field was utilized for the enhancement of ethanol formation catalyzed by immobilized yeast. A gel containing 2% sodium alginate, 4.2% dry yeast and 15, 30 or 50% iron powder (or Ba-ferrite) was prepared in CaCl 2 solution to immobilize the yeast. The gel was cut into cylindrical pieces of φ 2 mm × 2 mm. The cylindrical pieces of gel were placed inside a column through which culture medium flowed at a constant temperature. The ethanol concentration increased by 12% with immobilized yeast containing 50% iron powder at 5,000 Hz and 200 Oe of alternating magnetic field due to eddy currents. A similar result was obtained (14% increase) using immobilized yeast containing 50% Ba-ferrite at 2,000 Hz and 400 Oe of alternating magnetic field due to hysteresis. These effects corresponded to a 4°C rise in temperature in the gel.

The electrochemical asymmetric reduction of α-keto acids in the magnetic fields

Abstract It was found that mandelic or lactic acid, which was produced by the electrolytic reduction of phenylglyoxylic or pyruvic acid in the magnetic fields of 980–1680 Gauss, was dextrorotatory. The optical yield increased proportionally to the magnetic flux density. The electrochemical asymmetric reduction occurred when the direction of magnetic flux was parallel to the normal of the surface of mercury electrode. The same results were obtained if the magnet was placed upside down, that is, north and south poles were replaced reversely. No rotatory power appeared when the magnetic flux was directed horizontally. In the case of phenylglyoxylic acid reduction, the maximum optical yield was 21% under the conditions of pH 3.8, 10°C, 1680 Gauss and the controlled potential with −1.25 V vs sce . Pyruvic acid was similarly reduced to form excessive l -isomer when the electrolysis was carried out at pH 4.4, 25°C, 1680 Gauss and −1.3 V vs sce .

Continuous citric acid fermentation by magnetic rotating biological contactors using Aspergillus niger AJ 117173

Abstract The use of magnetic rotating biological contactor (MRBC) was introduced in citric acid fermentation. Two types of contactors, disk and drum systems, were used. The effect of magnetite (Fe 3 O 4 ) on citric acid fermentation in the surface culture method was examined. Dissolution of magnetite during fermentation did not show major adverse effects. Batch fermentation using the disk and the drum showed the maximum citric acid concentration of 68.9 g· l −1 and 73.1 g· l −1 at the period of 31 and 36 d, respectively. In the disk system, a specific biofilm area of 4.2 cm −1 against working volume was found to be effective, while 1.8 cm −1 was observed in the drum system, yielding higher citric acid production. A combination of an 8 d period of acclimatization and 2 ml·h −1 flow rate was a suitable condition for continuous citric acid fermentation. In the drum system, citric acid was produced with a higher productivity (4.3 g· l −1 ·d −1 ) compared with that in the disk system (2.2 g· l −1 ·d −1 ) and biofilm capable of maintaining its stable activity for about 50 d of continuous operation.

Enhancement of enzyme reaction of magnetically anisotropic polyacrylamide gel rods immobilized with ferromagnetic powder and β-D-galactosidase in an alternating magnetic field

An immobilized polyacrylamide gel containing beta-D-galactosidase and Sr-Ba-ferrite was magnetized in a static magnetic field. The gel rods (10 mm long, O 2 mm) exhibiting magnetic anisotropy could move at lower than 100 Hz but not at higher than 250 Hz in an alternating magnetic field of 200 Oe. In case of immovability of gel rods, the apparent enzymic activity increased 3 times higher under exposure of an alternating magnetic field of 500 Oe (570 Hz). It could be explained that the ferromagnetic powder inside the gel might vibrate under the influence of elasticity of gel in the alternating magnetic field of 100 or 500 Oe and 0.2-12 kHz. This might facilitate faster diffusion of the substance inside the gel and transportation of the substrate and the product through the surface of gel. Consequently, the enzyme reaction was apparently activated.