天野 佳正

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.

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>

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.

This paper presents two new kinds of calcium-silicate composites adsorbents KMnO4 modified alkali-treated calcium silicate composite (KASC and Fe3O4@KASC) to investigate adsorption capacity of adsorbing phosphate. The synthesized adsorbents were studied systematically by X-ray fluorescence analysis, nitrogen absorption-adsorption analyzer, X-ray diffraction, zeta potential analyzer, scanning electron microscopy and Fourier-transform infrared spectroscopy (FTIR) spectrophotometer. Factors affecting phosphate adsorption including kinetics, isotherm, pH, coexistent anions, and adsorbent dosage were investigated in batch experiments. The adsorption processes were best described by pseudo-second-order and Langmuir model, and the amount of adsorbed phosphate calculated using Langmuir model was 182 mg g(-1) for KASC and 145 mg g(-1) (f)or Fe3O4@KASC. Besides, Fe3O4@KASC also contained magnetic property. Adsorption of phosphate by KASC and Fe3O4@KASC were also performed by fixed-bed column experiments and the results were well described by Yoon-Nelson model and Thomas model. Almost all the adsorbed phosphorus could be recovered by 2% citric acid solution. The phosphate fractionation and FTIR spectra analysis indicated that (CaO)(2)PO2 was generated during the phosphate adsorption process.

Rayon-based activated carbon fiber (ACF) was modified with several methods: acetonitrile thermal chemical vapor deposition at 800 degrees C (8AN) to dope nitrogen element on carbon surface, heat treatment at 950 degrees C (9.5HT) to convert doped nitrogen species into quaternary nitrogen (N-Q) and steam activation at 800 degrees C (8ST) to additionally develop pore structure. The modified samples were evaluated as adsorbents for the removal of nitrate from NaNO3 aqueous solution at equilibrium solution pH (pH(e)) around 3.0. Sequential modification of ACF with 8AN, 9.5HT and 8ST achieved the greatest adsorption capacity at 0.7 mmol/g in all prepared samples.The modified adsorbent was probably included in the greatest group in nitrogen-doped carbonaceous adsorbents for nitrate removal. To inspect the high adsorption capacity, specific surface area, elemental analysis and X-ray photoelectron spectroscopy measurements were conducted comparing with the other prepared adsorbents. Based on the data analysis, some specific surface area and N-Q might play an important role in the adsorptive removal of nitrate.

In this study, two types of extracellular polysaccharides (EPS), namely, mixed EPS (MX-EPS) and tightly bound EPS (TB-EPS), were extracted from cyanobacterial blooms using different methods. To evaluate their compositional differences, elemental composition, FTIR, and TG/DTA profile were measured for both EPS samples. Following that, unicellular Microcystis aeruginosa was cultured in a medium containing EPS, Ca2+ ion, and Mg2+ ion, and the effect of each type of EPS on the colony formation of M. aeruginosa was examined. Results showed that TB-EPS had more carboxy groups than MX-EPS, and that the TB-EPS medium contained Ca2+ and Mg2+ ions. These cations were not detected in the MX-EPS medium. During the colony formation experiment, colonies were observed when Ca2+ and Mg2+ ions were present at 250 mg/L concentration each. In addition, colony density increased when TB-EPS was added, compared to that of MX-EPS. Colonies were also observed in the medium containing only TB-EPS (100 mg/L), indicating that M. aeruginosa can form colonies using Ca2+ ion present in TB-EPS. During the MX-EPS extraction, Ca2+ ion chelated with EDTA was removed during ethanol precipitation. Therefore, the extraction protocol followed for TB-EPS was better than that of MX-EPS for maintaining Ca2+ ions, and thereby maintaining an EPS composition that enables for colony formation.