天野 佳正

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.

The work investigated the potential application of Mg-laden biochar prepared from Mg-enriched bamboo to remove and recover phosphate from water. The Mg-laden biochar samples were synthesized at 400 degrees C, 500 degrees C and 600 degrees C. With the increasing synthesized temperature, the production rate of adsorbent decreased but the Mg content and specific surface area increased. Factors on phosphate adsorption including kinetic, isotherm, pH, dosage were examined through batch experiments. The maximum phosphate adsorption amount was 344, 357 and 370 mg/g for biochar-Mg-400, biochar-Mg-500 and biochar-Mg-600, respectively. The effect of phosphate adsorption on Mg-laden biochar samples was also investigated by fixed-bed column experiments, and the maximum adsorption amount calculated by Thomas model was 60.7, 61.2 and 62.2 mg/g, respectively. The adsorbed phosphate could be successfully desorbed by 3M NaOH solution and the regenerated Mg-laden biochar samples could be reused at least 5 times for phosphate adsorption. The bioavailability of postsorption biochar was proved very well through the Mehlich 3 method. Phosphate adsorption characteristic and FTIR analysis indicated that the adsorption was mainly controlled by two mechanisms: ligand exchange and electrostatic attraction.

Hexavalent chromium Cr(VI) pollution problem has become increasingly serious. In this study, activated carbon CGP-K3-800 was prepared from commercial Norit CGP by using KOH as activator for the removal of Cr(VI). The surface area of CGP-K3-800 was increased up to 3,098 m(2)/g. The adsorbent CGP-K3-800 exhibited an adsorption capacity of 4.99 mmol/g (259.5 mg/g) in the solution pH of 2 at 25 degrees C, which was 1.64 times larger than that of the original CGP. Adsorption equilibrium data were described and analyzed by the Langmuir models, indicating that Cr(VI) adsorption on CGP-K3-800 tended to be monolayer adsorption. The calculated thermodynamic parameters showed that the adsorption process of Cr(VI) onto CGP-K3-800 was an endothermic process. By investigating the effect of pH, the acid condition is conducive to the adsorption and reduction process of Cr(VI). CGP-K3-800 had good regeneration performance, and the reduction ability of Cr(VI) on the CGP-K3-800 would be gradually lost. CGP-K3-800 shows a higher adsorption capacity and better regeneration performance in removal of Cr(VI), can be applied as a promising adsorbent for the removal of Cr(VI) from wastewater.

Nitrogen-doped activated carbon fibers (ACFs) were prepared by chemical vapor deposition using melamine powder and acetonitrile for introducing quaternary nitrogen on the commercial ACFs, subsequently heated at 950 degrees C and activated by steam. Adsorption experiments of nitrate in aqueous solution were also conducted to evaluate adsorption capacity of the prepared ACFs using ion chromatography. The amount of introduced nitrogen content and nitrogen species on activated carbon fibers was examined by CHN elemental analyzer and X-ray photoelectron spectroscopy, respectively. As a result, adsorption capacity of quaternary nitrogen-doped ACF (ST-ML-AN-ST) was 0.75 mmol/g, indicating ca. two-times higher than that of untreated ACF (0.38 mmol/g). According to the adsorption data, the Langmuir isotherm model was the best fit. The prepared samples were also regenerated using hydrochloric acid. After regeneration, the adsorption capacity of the nitrogen-doped ACF (ST-ML-AN-ST) showed ca. 80% on average, implying that a portion of nitrates was adsorbed on the prepared ACFs irreversibly.

In this study, we confirmed the effects of light and K+ concentration on the buoyancy of the cyanobacterium Microcystis aeruginosa (Kutzing) Lemmermann (NIES-843), and the relationship between the gas vesicle and buoyancy of M. aeruginosa was revealed through the culture experiment. The results showed that under laboratory conditions, light illumination and K+ concentration strongly affected the flotation and settlement of M. aeruginosa, and that the floating and settling cycle of M. aeruginosa could be reproduced in a test tube by controlling light illuminance. The ability of M. aeruginosa buoyancy weakened with the increase in the K+ concentration, and M. aeruginosa could not exhibit buoyancy at the K+ concentration of 0.03mol/L. The phase-contrast microscope observation revealed that M. aeruginosa that floated on the water surface had gas vesicles, while none of the gas vesicles was detected for M. aeruginosa at the bottom of a test tube.

Approximately three grams of black colored air-stabilized polyacrylonitrile (PAN) fiber, namely PYROMEX (PYR), containing nitrogen element was activated by steam at 800 degrees C to develop porosity and thermally treated at 900-1000 degrees C in helium to convert a part of nitrogen species to quaternary nitrogen (N-Q) using various combinations of the steam and thermal treatments in a 25 phi inner diameter quartz tube, and adsorption capacity of nitrate anion from aqueous solution was measured. Steam activation at 800 degrees C by 20 mL water charge and consecutive heat treatment at 950 degrees C for 30 min (PYR-8ST20-9.5HT30) showed the largest nitrate adsorption capacity of 0.64 mmol/g among all prepared adsorbents. Effect of solution pH on nitrate adsorption was also investigated at the initial nitrate concentrations of 0.85-5.06 mmol/L for PYR-8ST20- 9.5HT30 compared with thermal treated cellulose based ACF at 950 degrees C for 30 min (KF1500-9.5HT30). The adsorption amount of nitrate on PYR-8ST20-9.5HT30 was always greater than that on KF1500-9.5HT30 at any condition examined in the experiments in spite of specific surface area of PYR-8ST20-9.5HT30 being less than half of KF1500-9.5HT30. Langmuir type adsorption isotherms of nitrate could be applied at pH range from 3 to 6.Maximum adsorption capacities of PYR-8ST20-9.5HT30 and KF1500-9.5HT30 calculated from the isotherms were 0.56-0.72 and 0.50-0.61 mmol/g, respectively, altering the values depending on the solution pH. The higher adsorption capacities could come from the greater amount of nitrogen, particularly quaternary nitrogen (N-Q),and the less oxygen that would work as inhibitor sites for nitrate adsorption, on PYR-8ST20-9.5HT30 than KF1500-9.5HT30.

The present study investigates isolated extracellular polysaccharides (EPS) from algal blooms, and then concentrations of EPS and cationic ions in culture medium of disaggregated Microcystis aeruginosa were controlled by adding the EPS and cationic ions to make M. aeruginosa colonies under laboratory conditions. We examined the respective effects of Mg2+ ion, Ca2+ ion, and EPS on the colony formation, and subsequently the interaction of these factors was investigated to lower cationic ion concentration levels (i.e. < 1000 mg/L for Ca2+) in our previous study. The results showed that M. aeruginosa formed colonies in the Ca2+ + Mg2+ and the EPS + Ca2+ + Mg2+ media, and large colonies were found only in the EPS + Ca2+ + Mg2+ medium. Although M. aeruginosa required a high amount of Ca2+ ion (1000 mg/L) to form colonies in the previous study, the present work revealed that Mg2+ ion (250 mg/L) could decrease the Ca2+ ion concentration to 250 mg/L. Thermal analysis (TG/DTA analysis) of the EPS indicated that the EPS possessed surface functional groups such as carboxy groups. As the roles of cationic ions for the colony formation of M. aeruginosa, the present study suggests that Ca2+ ion contributes to the cross-linking reaction between negatively charged carboxy group on the EPS and M. aeruginosa cells, and Mg2+ ion acts as an agent capable of decreasing the Ca2+ ion concentration for the colony formation. It was also revealed that the EPS could induce the colony formation and expand the colony size of M. aeruginosa.

The removal and recovery of phosphate from water by Fe3O4@alkali-treated calcium-silicate composite (Fe3O4@ASC) was investigated. The adsorbent was characterized by XRF, BET, XRD and zeta-potential analyses. The characterization results showed the successful synthesis of Fe3O4@ASC with a high specific surface area (129 m(2)/g). In batch experiments, the kinetic data and isotherm data fitted well to the pseudo-second-order model and Langmuir model, respectively, and the maximum adsorption capacity calculated by Langmuir model was 128 mg/g. The phosphate adsorption of Fe3O4@ASC performed well over a wide pH range from 2.5 to 13 and exhibited a good selective property even with 10 times higher molar concentration of other anions. Fe3O4@ASC could remove nearly 100% phosphate from real lake solution with phosphate concentration of 10 mg/L at the dosage of 0.25 g/L. In the column experiment, the breakthrough point of Fe3O4@ASC column was nearly 6000 mL for the initial phosphate concentration of 18.02 mg/L. Experimental data showed a good agreement with Yoon and Nelson model and Thomas model, the saturation adsorption capacity was 92 mg/g. Phosphate fractionation, XRD, and FTIR spectra analysis indicated that Ca-P precipitation generated during the phosphate adsorption process. Besides, the adsorbed phosphate could be successfully recovered by 2% citric acid solution, which implied that recovered phosphate could be reused as fertilizer.

In this study, the activated polyacrylonitrile (PAN) -based carbon fibers were evaluated as phosphate ion adsorbents in water. The activated PAN-based carbon fibers were prepared from commercially available oxidized black colored PAN fiber by ammonia gas activation at 950 degrees C, and KOH activation and/or steam activation at 800 degrees C under helium gas flow. The adsorption amount of phosphate ion was improved from 0.1 mmol/g for ammonia gas activated PAN-based carbon fiber to 0.24 mmol/g for ammonia gas and steam activated PAN-based carbon fiber. Characterizations of activated PAN-based carbon fibers were carried out using the nitrogen adsorption-desorption analysis at. 196 degrees C and elemental analysis. The BET surface area and pore volumes were increased by any activation method employed, but the pore diameter and nitrogen content tended to be decreased during the high temperature treatment. Using the fiber showing the highest adsorption capacity, the adsorption isotherm, the effect of pH, and the reusability of the adsorbent were investigated. The steam activated PAN-based carbon fibers with pre- and post-ammonia treatment had higher adsorption capacity and Langmuir adsorption affinity than other prepared adsorbents, and the adsorption amount of phosphate ion achieved the highest at the equilibrium pH range of 6.7.

Preparation of anion exchangers using melamine sponge (MS) and adsorption of nitrate ion was investigated. Carbonized melamine sponge was prepared at 500 degrees C with ZnCl2 impregnation (Z6) to develop the pore structure. Z6 was further treated by CH3I to introduce quaternary nitrogen onto the carbon surface and referred to as Z6-Q. Based on the result of X-ray photoelectron spectroscopy (XPS), Z6-Q contained more quaternary nitrogen than MS and Z6. Adsorption of nitrate ion on Z6-Q reached an equilibrium state the most quickly among the prepared samples. Adsorption kinetic curves indicated that the rate-limiting process was diffusion inside the pore for the adsorption of nitrate ion. In the adsorption of nitrate ion ranging 0.1-0.7 mmol/g, Z6-Q released equimolar chloride ion, suggesting that Z6-Q could have anion exchange sites to adsorb nitrate ion.

In our previous publication, we discussed the ammonium persulfate oxidation conditions of an activated carbon fiber and its use for the removal of aqueous lead. Results showed that oxidation at long times and at mild oxidant concentrations gave a high adsorption capacity for Pb(II) (2.7 mmol g(-1)), but at the same time, the porous structure of the fiber was highly decreased (385 m(2) g(-1)). In the present study, we present recent results that showed that using higher concentrations of oxidant at shorter times could give similar high adsorption capacities, with the difference that the big specific surface area of the fibers remained almost unchanged (ca. 1500 m(2) g(-1)). Moreover, the oxidized activated carbon fibers were characterized by their amount of soluble compounds in NaOH (oxidation debris), and it was determined to be less for samples produced at shorter oxidation times. Additionally, column adsorption-desorption experiments were done for a single metal solution of Pb(II) and for a mixture solution of Pb(II), Cd(II) and Ni(II), where Pb(II) ion was found to be preferably adsorbed by the oxidized activated carbon fiber.

Although dilution of lake water has been used for improvement of water quality and algal blooms control, it has not necessarily succeeded to suppress the blooms. We hypothesized that the disappearance of algal blooms by dilution could be explained by flow regime, nutrient concentrations, and their interaction. This study investigated the effects of daily renewal rate (d), nitrogen (N) and phosphorus (P) concentration, and their interaction on the domination between Microcystis aeruginosa and Cyclotella sp. through a monoxenic culture experiment. The simulation model as functions of the N: P mass ratio and dilution rate (D) (calculated from d) was constructed, and the dominant characteristics of both species were predicted based on the model using parameters obtained in a monoculture experiment and our previous study. Results of monoxenic culture experiment revealed that M. aeruginosa dominated in all conditions (d = 5 or 15%; N = 1.0 or 2.5 or 5.0 mg-N L-1; P = 0.1 or 0.5 mg-P L-1) and the predicted cell densities were substantially correspondent to experimental data. Under various N: P ratios and D values, characteristics of domination for each species were predicted, indicating that Cyclotella sp. tended to be dominant under high P concentrations (P = 0.36 mg-P L-1) when the N: P ratio was less than 7.0, and M. aeruginosa could not form algal blooms at the N: P ratio = 7.0 (N = 0.7 mg-N L-1). It was also suggested that the dilution rate leading to the Cyclotella sp. domination required 0.20 day(-1) or higher regardless of the N: P ratios.

The removal and recovery of phosphate from water by calcium-silicate composite (CSC) and alkali-treated calcium-silicate composite (ASC) was investigated. ASC had a higher specific surface area and total pore volume, and exhibited better performance of phosphate adsorption than CSC. In the batch mode adsorption studies, the isotherm adsorption experiments data fitted well the Langmuir isotherm model and the maximum adsorption capacities were 120 and 73.0 mg/g for ASC and for CSC, respectively. For the kinetic study, the experimental data fitted very well the pseudo-second-order kinetic model. The uptake of phosphate could be performed well over a wide pH range, from 3.0 to 13.0 for ASC and from 4.0 to 13.0 for CSC. The adsorption of phosphate by ASC was very selective even with 10 times higher concentration of other coexistent anions. For the adsorption of low phosphate concentration (10 mg/L), ASC could efficiently remove phosphate at the dosage of 0.8 g/L, while CSC was even difficult to remove phosphate at the dosage of 4.0 g/L. Phosphate fractionation results and FTIR spectra showed that phosphate-Ca complex was formed through phosphate adsorption process. The adsorbed phosphate could be successfully desorbed by 2% citric acid solution, indicating that the adsorbent after adsorbed phosphate could be reusable as fertilizer in the agricultural field.

Colony formation of Microcystis aeruginosa, a bloom-forming cyanobacteria, is closely associated with algal blooms in eutrophic freshwater systems worldwide. To develop effective methods for controlling excess algal growth, it is important to evaluate mechanisms underlying how M. aeruginosa forms colonies. In this study, extracellular polysaccharides (EPS) was isolated from algal blooms that mainly consisted of the genus Microcystis in eutrophic lakes and powdered EPS was prepared. This powdered EPS was used to control the EPS concentration in culture medium; then, the relationship among EPS, calcium (Ca2+), and colony formation of dispersed unicellular M. aeruginosa was investigated under alkaline conditions (pH 8.0). Experimental data indicated that the addition of powdered EPS (200mg/L) alone did not induce colony formation of M. aeruginosa cells at pH 8.0, however; high concentration of calcium ion (1,000mg/L) did contribute to colony formation. Moreover, when both EPS (200mg/L) and calcium ion (1,000mg/L) were added, the average cell number per colony increased by 2.6 times and particle size was enlarged compared with the culture medium in which calcium ion (1,000mg/L) alone was added. The average total sugar content per colony and/or single cell of M. aeruginosa was found to be 62.7pg/colony and 1.28pg/cell for Ca2+ added medium, and 730pg/colony and 5.74pg/cell for the EPS+Ca2+ medium, indicating that an increase in cellular EPS content caused colony formation of M. aeruginosa.

<p>Melamine sponge was used to prepare carbonized materials for the adsorption of nitrate ions. Carbonization and ZnCl₂ activation of the melamine sponge were simultaneously conducted at 500 °C to develop porosity. In addition, a subsequent CH₃I treatment was used to modify its surface. A ZnCl₂ impregnation ratio of 6 g/g (Z6) was the best condition for the removal of nitrate ions and a further increase in nitrate adsorption was observed as a result of the CH₃I treatment (Z6-Q). Z6-Q exhibited a superior nitrate ion adsorption capacity of 0.81 mmol/g which was approximately 1.3 times that of Z6. The adsorption of nitrate ions on the prepared samples was found to be the highest under acidic conditions, while basic conditions were not suitable due to inhibition by the hydroxide ions. In the pH range 1.5 to 2.5, the initial concentration of chloride ions increased and caused competition with nitrate ion adsorption. Based on the adsorption isotherms of nitrate ions, the adsorption processes were well fitted to the Langmuir equation. The TG/DTG profile revealed thermal decomposition of quaternary ammonium and adsorbed nitrate ions. After 3 regeneration cycles, the amounts of adsorbed nitrate ions for Z6 and Z6-Q were respectively 95 and 98% of the initial values, implying that the adsorbents are recyclable.</p>

This study isolated extracellular polysaccharides (EPS) as a powder material from cyanobacterial blooms and the powdered EPS was used to trigger colony formation of dispersed unicellular M. aeruginosa by controlling EPS concentration in culture medium. The effect of Ca2+ ions on the colony formation of M. aeruginosa was also investigated, then the interaction between EPS and Ca2+ ions on colony formation was discussed. The results showed that the addition of the powdered EPS into the medium did not cause morphological changes of M. aeruginosa, suggesting that EPS alone would not induce the colony formation of M. aeruginosa. On the other hand, a high concentration of calcium ions (1000 mg/l) caused colony formation. When EPS and Ca2+ ions in the culture medium were adjusted to 200 and 1000 mg/l, respectively, the colony density, the average cell number per colony and the particle size of M. aeruginosa showed ca. 1.7-2.0 times greater values than those in the Ca2+ added medium. Calcium ion contributed to the aggregation of M. aeruginosa via crosslinked reaction with negatively charged M. aeruginosa cells, and the addition of EPS possessing negatively charged functional groups such as carboxy groups could enhance the reaction, promoting the crosslinked reaction between EPS and Ca2+ ions.

Various agricultural residues such as bamboo chips, bagasse bottom ashes, corncobs and macadamia nutshells were used to prepare activated carbon by steam activation. These materials were further treated by Ca(OH)(2) and HCl solution, and the sample originated from bamboo was the best for nitrate removal from water. In addition, the bamboo activated carbon was treated with high concentrations of CaCl2 and HCl solution (BC-CL-A), showing a greater adsorption amount for nitrate removal. BC-CL-A exhibited a nitrate adsorption capacity (0.45 mmol g(-1)) approximately twice as much as that of the untreated sample. The nitrate adsorbed on BC-CL-A was easily desorbed from the surface by KCl solution due to ion exchange between NO3- and Cl-. Regeneration test for BC-CL-A by KCl solution was also examined. After three cycles of regeneration, the adsorbed nitrate could be removed by 88.6%, implying that some nitrates were irreversibly adsorbed on BC-CL-A.

An activated carbon fiber was oxidized with ammonium persulfate solutions (APS) and used for the adsorption of Pb(II) from aqueous solutions. A comprehensive study on the effect of the oxidation process conditions-oxidant concentration, oxidation temperature and time-on the obtained fibers Pb(II) adsorption capacity and their chemical and physical properties was done. Samples were characterized by elemental analysis, Boehm titration, N-2 adsorption-desorption isotherms and infrared spectroscopy. Adsorption isotherms were obtained for the activated carbon fibers and for two commercial ion-exchange resins, and they showed good agreement with the Langmuir model. For the first time, an activated carbon fiber with a high adsorption capacity for aqueous Pb(II) was obtained (2.70 mmol g(-1), ca. 559 mg g(-1)). This value was more than 10 times higher than that of the pristine fiber and superior to those of the commercial ion-exchange resins. The adsorption kinetics data of the oxidized activated carbon fiber were studied by different kinetic models and found to be better described by the pseudo-second order model, while the adsorption equilibrium could be reached in less than 2 h. It was confirmed that the adsorption process mainly occurred by an ion-exchange mechanism. The obtained results showed that APS oxidation is capable of producing activated carbon fibers with high adsorption capacities for aqueous Pb(II), making them promising materials for industrial wastewater treatment applications. (C) 2016 Elsevier Ltd. All rights reserved.

Commercially available oxidized black colored polyacrylonitrile (PAN) fiber was heat treated above 900 degrees C under helium or ammonia gas flow. Ammonia gas treatment made specific surface area of the oxidized PAN increase from 7 m(2)/g to 1000 m(2)/g or more, becoming activated carbon fiber (ACF), whereas helium treatment resulted in the maximum surface area of only 60 m(2)/g. Adsorption of phosphate improved from 0.022 mmol/g for oxidized PAN to 0.057 mmol/g for the helium treatments at pH range of 5-6. In case of ammonia treatment, the adsorption amount of phosphate attained 0.056 to 0.17 mmol/g in maximum, depending on the treating temperature ranging from 925 to 975 degrees C. The adsorption sites for negatively charged phosphate could be estimated to be positively charged quaternary nitrogen species generated on PAN fiber surface by the heat treatment. Langmuir adsorption affinity of PAN-ACF was derived from isotherms to be 0.6 L/mmol or more; moderate adsorption affinity was exhibited.

Activated carbon (AC) has been widely applied for adsorptive removal of organic contaminants from aqueous phase, but not for ionic pollutants. In this study, nitrogen doped AC was prepared to increase the adsorption capacity of nitrate from water. AC was oxidized with (NH4)(2)S2O8 solution to maximize oxygen content for the first step, and then NH3 gas treatment was carried out at 950 degrees C to aim at forming quaternary nitrogen (N-Q) species on AC surface (Ox-9.5AG). Influence of solution pH was examined so as to elucidate the relationship between surface charge and adsorption amounts of nitrate. The results showed that Ox-9.5AG exhibited about twice higher adsorption capacity than non-treatment AC at any initial nitrate concentration and any equilibrium solution pH (pH(e)) investigated. The more decrease in pH(e) value, the more adsorption amount of negatively charged nitrate ion, because the surface charge of AC and Ox-9.5AG could become more positive in acidic solution. The oxidation and consecutive ammonia treatments lead to increase in nitrogen content from 0.35 to 6.4% and decrease in the pH of the point of zero charge (pH(pzc)) from 7.1 to 4.0 implying that positively charged N-Q of a Lewis acid was created on the surface of Ox-9.5AG. Based on a Langmuir data analysis, maximum adsorption capacity attained 0.5-0.6 mmol/g of nitrate and adsorption affinity was 3.5-4.0L/mmol at pH(e) 2.5 for Ox-9.5AG.

In Lake Tega, Japan, the shift of dominant algal species was caused as a result of discharging water from the adjacent river into the lake. The transition from cyanobacteria (mainly the genus Microcystis) to diatoms (mainly the genus Cyclotella) resulted in a disappearance of algal blooms. Although some environmental conditions such as flow rate, nutrient concentration, and transparency were changed by the project, the decisive factor for the transition has not been clarified yet. For the effective control of algal blooms by water discharge, this study aimed to elucidate the effects of daily renewal rate and nitrogen concentration on the interspecific competition between Microcystis aeruginosa and Cyclotella sp. Monoculture experiments were conducted to obtain growth characteristics for each species and mixed culture experiments were performed to examine their competitive abilities under various daily renewal rates of the culture medium (15 and 30 %) and nitrate concentrations (71.4, 178, and 357 mu M). In addition to prepared medium, Lake Tega water was also used for mixed culture experiments. The results showed that the increase in a daily renewal rate contributed to the dominance of Cyclotella sp., while a nitrate concentration had little influence on the competition. We conclude that algal blooms composed of the genus Microcystis would be controlled by maintaining a daily renewal rate up to 30 % or more, which corresponded to the dilution rate of 0.36 day(-1), under a nitrate concentration of <= 357 mu M. The study would include essential information for the management of lakes suffering from frequent occurrences of algal blooms.

When the water quality in Lake Tega was the worst among Japanese lakes in the 1970s, cyanobacteria (mainly the genus Microcystis) were observed to be the dominant species in the summer. Since 2000, for water quality improvement, a large amount of the Tone River water was discharged into Lake Tega, resulting in an improvement in the water quality together with transition of algal dominant species from cyanobacteria to diatoms (mainly the genus Cyclotella). Although several factors including nutrient concentration and daily renewal rate (d) could have been related to the succession of algal dominant species, these effects have not been understood very well. This study investigated the effects of the daily renewal rate and nitrate-nitrogen (hereafter nitrogen) concentration (N) on the competition between the cyanobacterium Microcystis aeruginosa and the diatom Cyclotella sp. through monoculture and monoxenic culture experiments. Based on the experimental results, a simulation model was constructed to predict the competitive growth pattern of each species. Monoxenic culture experiments showed that M. aeruginosa outcompeted Cyclotella sp. under conditions of N = 0.5 (1.0 mg-N L-1) and d = 5, 15, and 20%. The domination of M. aeruginosa could be attributed to smaller values for the half-saturation constant and the minimum nitrogen cell quota for this species with respect to Cyclotella sp. However, Cyclotella sp., possessing higher values of nitrogen cell quota and nitrogen uptake rate, dominated by an increasing nitrogen concentration (N = 1.0 mg L-1) and daily renewal rate (d = 30%). The competitive growth patterns of M. aeruginosa and Cyclotella sp. could roughly be predicted by the simulation model. These results suggested that the daily renewal rate as well as the nitrogen concentration, could affect the competition and be influential factors as to which species dominates between M. aeruginosa and Cyclotella sp.

Bamboo chars and bamboo activated carbons prepared by steam activation were applied for ink wastewater treatment. Bamboo char at 800 degrees C was the best for the removal of color and chemical oxygen demand (COD) from ink wastewater compared to bamboo chars at 300 to 700 degrees C due to higher surface area and mesopore volume. Bamboo activated carbon at 600 degrees C (S600) was the best compared to bamboo activated carbon at 800 degrees C (S800), although S800 had larger surface area (1108 m(2)/g) than S600 (734 m(2)/g). S600 had higher mesopore volume (0.20 cm(3)/g) than S800 (0.16 cm(3)/g) and therefore achieved higher color and COD removal. All bamboo activated carbons showed higher color and COD removal efficiency than commercial activated carbon. In addition, S600 had the superior adsorption capacity for methylene blue (0.89 mmol/g). Therefore, bamboo is a suitable material to prepare adsorbents for removal of organic pollutants.

© 2016 The Society of Chemical Engineers, Japan. Activated carbons (ACs) were prepared from sulfur-containing petroleum coke (PC, sulfur content 8%) and oxidized to introduce sulfo groups. The effect of specific surface area of ACs on the amount of Ni(II) adsorbed on oxidized ACs was examined. PC was first activated with potassium hydroxide (KOH) at a KOH/PC mass ratio of 1-3, an activation temperature of 400-850°C, and an activation time of 0.5-2.0 h. The specific surface area and total pore volume of the ACs prepared were 510-1,890 m2/g and 0.25-1.07 cm3/g, respectively. In the second step, ACs were oxidized with concentrated nitric acid under the same conditions, and Ni(II) adsorption from water onto oxidized ACs was compared with that onto oxidized commercial bead shaped activated carbon (BAC, sulfur content less than 0.02%). The results showed that Ni(II) adsorption onto oxidized ACs increased linearly with the increase in specific surface area of ACs from 500 to 1,000 m2/g and reached saturation at 3.5 mmol/g in the range of 1,000-1,900 m2/g. Oxidized ACs adsorbed Ni(II) even at low solution pH of 1.0, whereas no adsorption onto oxidized BAC was observed, suggesting that sulfo groups were present on the surface of oxidized AC prepared from sulfur-containing PC.

In this study, introduction of acidic functional groups onto a carbon surface and their removal were carried out through two oxidation methods and outgassing to investigate the adsorption mechanism of aromatic compounds which have different polarity (benzene and nitrobenzene). Adsorption experiments for these aromatics in aqueous solution and n-hexane solution were conducted in order to obtain the adsorption isotherms for commercial activated carbon (BAC) as a starting material, its two types of oxidized BAC samples (0Xs), and their outgassed samples at 900 degrees C (OGs). Adsorption and desorption kinetics of nitrobenzene for the BAC, OXs and OGs in aqueous solution were also examined. The results showed that the adsorption of benzene molecules was significantly hindered by abundant acidic functional groups in aqueous solution, whereas the adsorbed amount of nitrobenzene on OXs gradually increased as the solution concentration increased, indicating that nitrobenzene can adsorb favourably on a hydrophilic surface due to its high dipole moment, in contrast to benzene. In n-hexane solution, it was difficult for benzene to adsorb on any sample owing to the high affinity between benzene and n-hexane solvent. On the other hand, adsorbed amounts of nitrobenzene on OXs were larger than those of OGs in n-hexane solution, implying that nitrobenzene can adsorb two adsorption sites, graphene layers and surface acidic functional groups. The observed adsorption and desorption rate constants of nitrobenzene on the OXs were lower than those on the BAC due to disturbance of diffusion by the acidic functional groups.

Activated carbon fiber (ACF) was oxidized by different concentrations of HNO3 solution and different contact time. Both the original and the oxidized ACFs were tested to adsorb Pb(II) from aqueous solution. Properties of ACFs were characterized by BET surface area, elemental analysis, Boehm titration and the pH of the point of zero charge (pH(pzc)). The results showed that the maximum adsorption ability of Pb(II) on the oxidized ACF was 0.34 mmol/g at pH 3.0, which was 3 times larger than that on the original ACF, and was enhanced to 0.96 mmol/g by increasing the solution pH from 3.0 to 5.9. The adsorption isotherm of all ACFs obeyed the Langmuir isotherm model. Moreover, the Pb(II) adsorption rate for the oxidized ACF was about 3-fold faster than that of the original ACF.

Batch and column adsorption of divalent cadmium ions from aqueous solution using oxidized activated carbon (OAC) was investigated. Commercially available bead-shaped activated carbon (BAC) was oxidized with ammonium persulfate, and Cd(II) adsorption experiments were performed in batch and flow systems. The total amount of Cd(II) adsorbed in the flow system was 1.7 mmol/g, which was asymptotically equal to the maximum amount adsorbed in the batch system. Regeneration of the adsorbent was evaluated via Cd(II) desorption from OAC using 0.1 M nitric acid. The total Cd(II) desorbed was approximately 1.9 mmol/g, which was nearly equivalent to the total Cd(II) adsorbed in the flow system. The amount of Cd(II) adsorbed using regenerated OAC in the 2nd-cycle was not significantly different from that adsorbed in the 1st-cycle. These results imply that OAC is prospectively reusable for Cd(II) adsorption applications.

A commercially available activated carbon (AC) was oxidized using 1M H2SO4 solution containing 2 M (NH4)(2)S2O8 oxidant with the solution to carbon ratio of 50 cm(3) g(-1) by changing oxidation period ranging 1 to 10 days at ambient temperatures of 20 or 30 degrees C to introduce carboxy groups onto the carbon surface to capture Pb(II) ions. Adsorptive removal of Pb(II) ions from aqueous solution was also examined with the oxidized ACs. The Pb(II) ion adsorption progressed via ion exchange with protons of carboxy groups bound to graphite and 2.2 mmol g(-1) of Pb(II) could be accommodated at equilibrium pH above 4.0 for ACs oxidized for at least 10 days at 20 degrees C and 4 days at 30 degrees C. Decrease in specific surface area and yield and increase in oxygen and hydrogen content in ACs also observed during the (NH4)(2)S2O8 treatment implied that the oxidation could convert graphite sheets to smaller size by hydrolysis while many carboxy groups would be introduced to the peripherals of the graphite sheets to scavenge Pb(II) ions.

Considerable concerns have been raised over the presence of lead(II) in water bodies. In this work, the performance of heat-treated cattle-manure-compost-activated carbons were investigated to remove lead(II) from aqueous solution. Activated carbons were prepared by one-step ZnCl2 activation followed by heat treatment at different temperatures. They were characterized according to BET surface area, pore size distribution, elemental analysis, pH(PZC) and Boehm's titration. It was found that the increase of treatment temperature resulted in a decrease in both the BET surface area as well as the concentration of phenolic groups. However, such decreases were compensated by an increase of lead(II) by more than three times to a value of 0.110 mmol/g, and this was also true for commercial F400-activated carbon. Lead(II) adsorption onto heat-treated activated carbons could be described by Langmuir isotherm with weaker interaction to active sites. Results also suggested that the increase in lead(II) uptake was due to the rich electron clouds of the C pi-system, regardless of the difference in the surface area upon heat treatment.

The bamboo-based and bead-shaped activated carbon (BAC) were used to examine the effects of textural properties and surface chemistry, respectively, on As(V) adsorption. The relationships between solution pH, coexistent ions and/or arsenic species and As(V) adsorption by BAC were also investigated. The Langmuir and pseudo-second order kinetics models were employed to evaluate the prepared activated carbon for As(V) adsorption. The results showed that As(V) adsorption was strongly attributed to surface properties, that is, basic sites rather than textural properties. The fittings of adsorption data to the kinetics models revealed that As(V) adsorption would be governed by diffusion process rather than collision process. Among various acidity regulators (HCl, HNO3, and H2SO4), the pH adjustment by HCl induced the highest adsorption amount at pH 5.5, indicating that the inhibition effect of Cl- ion for As(V) adsorption was much less than NO3- and SO42- ions. The effective arsenic species for As(V), adsoprtion was H2AsO4, and the decrease in the adsorption amount in acidic condition would be due to the inhibition by excess of Cl- ion, while the decrease in the adsorption at pH more than 5.5 would be attributed to the increase in OH- ion or to the influence of increased hydrogen arsenate species(HAsO42-).

栄養塩 (窒素・リン) 濃度および光照射が継代培養株M. aeruginosa (UTEX LB 2061) の浮揚性と，バラストとして機能する細胞含有多糖類量に及ぼす影響を検討した。その結果，M. aeruginosa継代培養株は，野生株ほど明瞭ではないものの鉛直移動を示すことがわかった。M. aeruginosa 継代培養株の浮揚性は光照射よりも栄養塩濃度の影響を受け，栄養塩制限下で細胞が沈降する傾向にあった。一方，細胞含有多糖類量は明暗周期によって変動したが栄養塩濃度には依存せず，継代培養株のM. aeruginosaの浮揚性はバラストではなく主にガス胞により制御されていると予想された。

The objective of this study is the synthesis of activated carbon derived from cattle manure compost (CMC) causing environmental problems using zinc chloride (ZnCl2) activation and to examine the suitability and performance of the prepared activated carbon (PAC) in removing 2-methylisoborneol (2-MIB) from aqueous solution. The influence of ZnCl2/CMC ratios and outgassing from the PACs on the removal of 2-MIB were studied. Pore texture and surface functional groups were obtained to characterize the PACs. It is suggested that the increase of micropore surface area and volume as a result of the activation favored the removal of 2-MIB, while activated carbon rich in acidic functional groups showed poor 2-MIB adsorption. The preferable removal of 2-MIB depended on the poor acidic functional groups and the higher micropore surface area in the PACs. A sample of the PACs was synthesized at a lower temperature (around 550 degrees C) compared to commercially available activated carbon (CAAC) (around 900 degrees C). The sample showed a performance for 2-MIB removal for drinking water purification as well as CAAC. Furthermore, from the results of N-2 adsorption-desorption isotherms and 2-MIB adsorption isotherm in aqueous solution, pore structure of PACs and 2-MIB adsorption mechanism on it were suggested.

In this study, the bamboo charcoals and the bamboo-based activated carbons were prepared from Moso bamboo (Phyllostachys pubescens) by N-2 carbonization, CO2 activation and NH3 ammonization at 500-900 degrees C and HNO3 oxidation at room temperature followed by air oxidation at 350 degrees C. The structural and surface chemical characteristics of prepared activated carbons were determined by N-2 adsorption-desorption isotherms and Boehm titration, respectively. The water vapor adsorption capacity of each prepared activated carbon was examined with varying the pore structure, surface acidic functional groups and nitrogen contents of samples. Water vapor adsorption-desorption of the bamboo charcoals showed that very small micropores which could adsorb water vapor but be impossible for nitrogen molecule to be accessed would be formed when the carbonization was performed above 700 degrees C. The water vapor adsorption capacity at low humidity region was found to be obviously improved by the oxidation with HNO3. The elemental analysis demonstrated that nitrogen was abundantly introduced into the activated carbon through ammonization at 700-900 degrees C. Also, thermogravimetric analysis for NH3-treated activated carbons which were saturated in relative humidity (RH) of 90% indicated that the interaction between water vapor and activated carbon could be strengthened by surface nitrogen. Ammonization at 900 degrees C significantly developed the specific surface area and pore volume and showed the highest capacity of water vapor adsorption. (C) 2013 Elsevier B.V. All rights reserved.

In this study, the removal of acidic functional groups and introduction of basic groups/sites on activated carbons (ACs) by outgassing and ammonia gas treatment were respectively carried out to enhance the nitrate ion adsorption in aqueous solution. Then, the relationships between nitrate ion adsorption and solution pH as well as surface charge of AC were investigated to understand the basic mechanisms of nitrate ion adsorption by AC. The result showed that the nitrate ion adsorption depended on the equilibrium solution pH (pH(e)) and the adsorption amount was promoted with decreasing pH(e). The ACs treated by outgassing and ammonia gas treatment showed larger amount of nitrate ion adsorption than that by untreated AC. These results indicated that, since basic groups/sites could adsorb protons in the solution, the AC surface would be charged positively, and that the nitrate ion would be electrically interacted with positively charged carbon surface. Accordingly, it was concluded that basic groups/sites on the surface of AC could promote nitrate ion adsorption.

The work was aimed to investigate the effect of heat treatment of manure-compost-based activated carbons on the adsorption of copper from aqueous solution. Activated carbons were characterized according to physical structures and surface functional groups. All equilibrium data of activated carbons formerly treated at different temperatures obeyed Langmuir model to linear approximation. Results showed that copper ions favorably adsorbed onto the mesopores at lower equilibrium concentrations and subsequently changed to the micropores at higher equilibrium concentrations. It was found that the increase in electron density upon heat treatment offered higher tendency for the uniform amount of protons to occupy the surface sites. Analysis of Scatchard plots suggested that the affinity driven by the mesopores toward copper ions was stronger than that of the micropores.

Adsorptive removal of nitrate ions in aqueous solution using activated carbons (ACs) was examined. After ash was removed from Filtrasorb 400 AC, oxidation and outgassing and several heat treatments were carried out to modify the textural and surface properties of ACs. AC oxidized with 8 M nitric acid followed by outgassing at 900 degrees C (Ox-9OG) exhibited the greatest Langmuir adsorption capacity and affinity for nitrate removal among the total 7 ACs examined. Influence of coexisting chloride and sulfate ions was investigated as well to inspect the nitrate adsorption sites. The highest amount of sites which adsorbed nitrate ions exclusively could be observed for Ox-9OG adsorbent even though as great as 250 times greater number of chloride or sulfate ions over nitrate ions were present in the same aqueous system. Some basic oxygen species on carbon were estimated to work as selective adsorption sites for nitrate ions. (c) 2013 Elsevier B.V. All rights reserved.