町田 基

Abstract In this study, aiming to address the issue of phosphate contamination in water, a novel activated carbon adsorbent with excellent adsorption performance for phosphate ions was designed and synthesized through a nitrogen-doped surface modification method. The adsorption experiment results revealed that the sample obtained after the second activation at 600 °C (MeUrGlu-6.0Z0.5-2nd) exhibited a high adsorption capacity of up to 0.42 mmol/g for phosphate ions. The surface modification method using nitrogen-doping significantly enhanced the adsorption capacity of the adsorbent for phosphate anions. The surface characteristics of the sample were analyzed by Brunauer-Emmett-Teller method, elemental analysis, and X-ray photoelectron spectroscopy (XPS). The characterization results indicated that the increase in adsorption capacity primarily attributed to the successful introduction of quaternary nitrogen (N-Q) onto the activated carbon surface. Additionally, the adsorbent demonstrated high adsorption capacity for phosphate ions in acidic solution (pH <4.5), overcoming the limitation of commercial anion exchange resin HP555 which cannot be used effectively in acidic environment. The Langmuir isotherm model was found to accurately describe the adsorption process which is a monolayer adsorption. Finally, the regenerability of MeUrGlu-6.0Z0.5-2nd and the recovery of phosphate ions were investigated in a continuous flow adsorption mode.

Abstract In this study, polyacrylonitrile (PAN)-based carbon fiber with high nitrogen content was activated at 800 °C with sodium carbonate and heat-treated at 950 °C to prepare activated carbon fiber (ACF), and the results of nitrate ion adsorption on the prepared ACF are presented. CHN elemental analysis, XPS measurement, and Boehm titration were used to determine the nitrogen content and surface functional groups of ACF. It is discussed that the total amount of nitrogen decreases, whereas quaternary nitrogen (N-Q) increases upon heat treatment. The decrease in adsorption capacity of the prepared activated carbon under different storage conditions is shown. It is observed that the adsorption capacity of nitrate ion at equilibrium pH (pH_e) 5 is halved after 5 weeks, and the decrease in adsorption capacity at pH_e 3 is suppressed. The adsorption isotherms of the prepared ACF are shown using the Langmuir equation. The effect of pH on the adsorption capacity of the prepared ACF is compared with that of ACF before heat treatment and zinc chloride-activated powdered activated carbon. The adsorption capacity of ACF without heat treatment at 950 °C decreases as the pH_e of the solution increases, and the pH of the nitrate solution including ACF after heat treatment is stable at pH_e 4–5.

Abstract Although water transfer as an efficient method to improve water quality and control Microcystis blooms in lakes has been executed for several decades, few studies have examined effective dilution rates depending on various water qualities. Therefore, to clarify the effective dilution rate to suppress Microcystis blooms, a competitive growth simulation model developed for eutrophic conditions was utilized. A competition experiment between Microcystis sp. and Cyclotella meneghiniana under limited phosphorus and sufficient nitrogen concentration was conducted to investigate the mechanism of dilution effect and verify the broad applicability of the simulation model. Experimental results revealed that there was no remarkable discrepancy in Microcystis sp. cell density among different dilution groups (p>0.05), while C. meneghiniana cell density was significantly different between groups (p<0.05). The accuracy of the simulation model under limited phosphorus as well as sufficient nitrogen concentration was verified by comparing the simulated value with experimental results. Based on the simulated results, it was suggested that a dilution rate of over 13.3% can suppress Microcystis blooms effectively in Lake Tega, Japan, as a case study. The predicted data was also compared with the field data collected over years in Lake Tega, and its effectiveness has been confirmed.

On the surface of Microcystis cells, there is a carbohydrate called extracellular polysaccharides (EPS) playing a significant role in the colony formation of Microcystis. EPS consists of tightly cell-bound EPS (TB-EPS), and both of these substances are considered to be strongly related to the colony formation and buoyancy of Microcystis. In this study, Microcystis aeruginosa (strain: NIES-843) was used to examine the effects of EPS, TB-EPS, and divalent metal cations such as calcium and magnesium on the buoyancy and colony formation of M. aeruginosa NIES-843. Under various light conditions, the addition of TB-EPS into the culture medium induced M. aeruginosa NIES-843 to obtain high buoyancy at concentrations of Ca²⁺ and Mg²⁺ concentrations of 10 mg/L and 30 mg/L, respectively. Under the absence of light, the addition of EPS could lead M. aeruginosa to form a colony and obtain buoyancy, and the addition of TB-EPS could not significantly change the buoyancy of M. aeruginosa NIES-843. The colony size analysis showed that at the same cationic concentration, the addition of TB-EPS could induce M. aeruginosa to form the largest colony and present strong buoyancy. This study suggested that temperature and illumination are conducive to colony formation and present higher buoyancy of M. aeruginosa.

Nitrogen-free phenol resin fiber was used to examine the effect of nitrogen-introduction via thermal chemical vapor deposition (CVD) using nitrogen-containing chemicals. In this study, a combination of heat treatment, steam activation, aniline CVD was conducted to prepare the nitrogen-doped activated carbon (AC) and the effective procedure was studied to enhance arsenic adsorption capacity. As a result, consecutive treatment of steam activation as pre-treatment, aniline CVD, steam activation for porous structure, and at least heat treatment was the best processing order for the preparation of ACs. Heat-treated samples demonstrated their robustness against steam activation; therefore heat treatment should be conducted as post treatment for effective CVD process. One of the samples which was prepared by this procedure, 8ST30-8ANL10-8ST50-9.5HT30 (sample #5) showed 0.112 mmol/g of arsenate adsorption capacity, and it was at least 70% higher than that of any other prepared samples. To inspect the high adsorption capacity of this sample, the effect of solution pH, pore structure parameters, elemental analysis, and Boehm titration was conducted comparing with the other prepared samples.

In this study, N-doped activated carbon BDC-STM30-10.0HT was prepared from bean dreg by using steam activation and heat treated at 1000 degrees C under helium gas flow for the removal of Cr(VI). The properties of the prepared carbon catalysts were characterized by CHN elemental analyzer, SEM, N-2 adsorption and XPS techniques, and the obtained bean dreg activated carbon BDC-STM30-10.0HT had a high specific surface area (1004 m(2)/g) and high quaternary nitrogen content (1.11 %). Activated carbon with different specific surface areas was prepared by changing the temperature during high temperature treatment and the order of high temperature treatment and steam activation. The results of batch adsorption experiments showed that the Cr(VI) adsorption capacity of activated carbon was positively correlated with the specific surface area, but it does not only depend on the specific surface area, but also quaternary nitrogen. The adsorption equilibrium data were well described by the Langmuir model, and BDC-STM30-10.0HT had excellent adsorption capacity for Cr(VI) (3.30 mmol/g). BDC-STM30-10.0HT showed superior recyclability, and after five times regenerations, the adsorption capacity of BDC-STM30-10.0HT still had 54 % of the initial adsorption capacity.<bold> </bold>

Abstract In this study, N-doped biochar BZ-9.5AG-30 min was prepared from bamboo by using ZnCl2 as activator and heat treated at 950 °C under NH3 gas flow for the removal of Cr(VI). The adsorbent was characterized by BET, and the amount of introduced nitrogen content and nitrogen species on BZ-9.5AG-30 min was examined by CHN elemental analyzer and X-ray photoelectron spectroscopy, respectively. Herein, the obtained BZ-9.5AG-30 min had a high specific surface area (1,610 m2/g) and high N content (4.52%). The pH of the solution had a great influence on the adsorption process, indicating that the acid condition is conducive to the adsorption process of Cr(VI). Adsorption equilibrium data of Cr(VI) were analyzed by the Langmuir and the Freundlich models. The adsorption equilibrium data were well described by the Langmuir model, and BZ-9.5AG-30 min has excellent adsorption capacity for Cr(VI) (4.31 mmol/g). BZ-9.5AG-30 min showed superior recyclability, and after five times regenerations, the adsorption capacity of BZ-9.5AG-30 min still had 63% of the initial adsorption capacity.

By comparing the two types of activated carbon fibers (ACFs), characteristics of adsorption sites for nitrate ion other than quaternary nitrogen (N-Q) were investigated. Using phenol resin as precursors, activation with ZnCl2 was performed, and then heat treatment at 950°C was carried out to prepare ACFs without N-Q, while ACFs with N-Q was prepared in the same method using polyacrylonitrile-based carbon fiber as precursors. We assessed the amount of functional groups, elemental composition, porous properties, and model of unit crystal size of graphene. For both ACFs with N-Q and without N-Q, equilibrium adsorption amount was not always simply proportional to surface area, but to the average number of benzene rings (Bz-rings) of graphene universally. PhR-5.0Z4 had only 20 benzene rings per graphene unit, but after heat treatment at 950°C, the number drastically increased to 1088 (PhR-5.0Z4-9.5HT30). However, when the ACFs contained a large amount of oxygen, the number of Bz-rings was limited to 792 (PhR-5.0Z4-Ox-9.5HT30) even after heat treatment at 950°C, and did not increase sufficiently. Cπ sites are more susceptible to oxygen inhibition than N-Q in adsorbing nitrate ions. For ACFs having Cπ sites as main adsorption sites, the heat treatment at 950°C without oxidation can enhance the nitrate ion adsorption capacity.

It is well recognized that gas vesicles influence the buoyancy of Microcystis and control the migration in the water column. Some of Microcystis strains do not have gas vesicles, so these strains cannot obtain buoyancy from them. In this study, we used two types of Microcystis strains such as the non-gas vesicle synthesizing strain M. aeruginosa UTEX-2061 and the gas vesicle synthesizing strain M. aeruginosa NIES-843 in the buoyancy control experiments of M. aeruginosa. By inducing colony formation and calculating the relative buoyancy rate of each strain, it was proven that the colony formation was strictly related to the buoyancy of both Microcystis strains. M. aeruginosa NIES-843 possessing gas vesicles could obtain buoyancy under the lower concentration of calcium and magnesium than M. aeruginosa UTEX-2061 possessing no gas vesicles. With the addition of the extracellular polysaccharides (EPS) extracted from Microcystis blooms into the culture medium, M. aeruginosa NIES-843 and UTEX-2061 could present higher buoyancy at the lowest concentrations of calcium and magnesium. It was suggested that EPS combined with the divalent metal cations such as calcium and magnesium made Microcystis form colony effectively. Calcium and magnesium ions enhanced the ability of colony formation of Microcystis and had a significant influence on buoyancy.

Cd(II) and Cr(VI) are highly toxic heavy metal ions, which commonly coexist in industrial wastewater. In this study, simultaneous removal of Cd(II) and Cr(VI) by a bamboo-based oxidized biochar (BZ-APS24h) was investigated. The biochar was modified by ZnCl 2 and oxidized with (NH4)(2)S2O8, and its structures as characterized by SEM, BET, elemental composition and X-ray photoelectron spectroscopy. Batch adsorption experiments for Cd( II) and Cr(VI) were carried out to explore the effects of oxidation time, pH, contact time, temperature and coexisting ions on its adsorption process. The results showed that the BZ-APS24h exhibited excellent adsorption performance for the removal of Cd(II) (0.27 mmol/g) and Cr(VI) (0.65 mmol/g). The adsorption data were fitted well with pseudo-second-order model and Langmuir isotherm. The pH of the solution had a great influence on the adsorption process. The coexistence of Cd(II) and Cr( VI) affected the equilibrium pH after adsorption, and synergistic adsorption was also observed.

In this study, commercial activated carbon fibers (ACFs) KF1500 was modified by thermal chemical vapor deposition (CVD) method using acetonitrile and steam to adsorb nitrate ions in aqueous solution. Physical properties and surface chemical characteristics of each modified ACF were examined to reveal the surface modification mechanism of modified ACFs. Adsorption kinetics and influence of solution pH were also examined to investigate the adsorption properties. The sample of KF-8ST10-8AN20-9.5HT30-8ST30 showed maximal nitrate adsorption capacity of 0.74 mmol/g at solution pH 3, and surface area was calculated to be 1358 m(2)/g and 1483 m(2)/g by Brunauer-Emmett-Teller (BET) method and subtracting pore effect (SPE) method using alpha(s) plots, respectively. By means of modification, the quaternary N (or graphitic N) (N-Q) configuration, which is a strong site to adsorb nitrate ion, represented nearly 5 times greater value than that of KF1500. The N-Q configuration reached up to 1.86% in total elemental composition from 0.4% of KF1500. The adsorptive kinetic data of KF-8ST10-8AN20-9.5HT30-8ST30 ACFs were highly well described with pseudo-second-order (R-2 = 0.998) model. The adsorption capacity of nitrate decreased rapidly with the increase of the alkalinity in nitrate solution, which indicated that hydroxyl groups rather than nitrate ions in the aqueous solution were more attractive and competitive to the N-Q and other adsorptive sites on the surface of ACFs.

© 2019, Islamic Azad University (IAU). This study attempted to promote the colony formation and enlarge the colony size of wild Microcystis strain by adjusting extracellular polysaccharides and cationic ion concentrations in culture medium, and then, using the enhanced floating velocity (Stokes’ law), wild Microcystis at the water surface was removed. In order to examine the difference between extracellular polysaccharides mixture and tightly cell-bound extracellular polysaccharides used in this study, the component composition and physical properties were also examined. The results showed that tightly cell-bound extracellular polysaccharides contained the greater amounts of cations (Ca 2+ and Mg 2+ ), phosphorus, carboxy group and monosaccharides than extracellular polysaccharides mixture. There were greater amounts of carboxy groups and mannose residue in tightly cell-bound extracellular polysaccharides than extracellular polysaccharides mixture, which would contribute to the stronger cell–cell adhesion of wild Microcystis to make colony formation and expand colony size. The adjustment of extracellular polysaccharides and cationic ion concentrations was effective method to promote the colony formation and enlarge the colony size of wild Microcystis, and that the control of Microcystis buoyancy by enhancing the colony size would be one of the options for the suppression of Microcystis blooms from the viewpoint of cost-effective, low-energy, environmentally-friendly, and non-destructive of Microcystis cells.

High sulfur petroleum coke (HSPC, 7.6 wt-S%) was employed to prepare activated carbons (ACs) using KOH to develop pore structure with remaining sulfur content for supplying post oxidation treatments to effectively generate sulfo groups which could be a stronger adsorption sites of cationic heavy metal ions in aqueous solutions than carboxy groups. KOH activation was conducted at 550-800 degrees C by two methods of physical mixing (KOH and HSPC solid-solid mechanical mixture) and impregnation (KOH solution and HSPC liquid-solid mixture and then dried in oven). Prepared samples were characterized with nitrogen adsorption-desorption isotherms and elemental analysis. Physical mixing was effective for HSPC of large particle size, whereas impregnation was effective for small particle. Based on the experimental results, mild activation conditions such as KOH/HSPC ratio of 1 and temperature of 550 degrees C were preferable; specific surface areas and remaining sulfur contents of the resultant ACs by physical mixing and impregnation methods could be achieved 651 m(2)/g, 2.9 wt-S% and 812 m(2)/g, 5.2 wt-S%, respectively. Post oxidation of the ACs and the consecutive Ni(II) adsorption experiments implied that sulfo groups that could work even in acidic region might be generated on ACs from HSPC comparing with ACs from low sulfur petroleum coke.