Yoshimasa Amano

Adsorption of heavy metals onto activated carbons derived from polyacrylonitrile fiber

The aim of this research is to produce activated carbons derived from polyacrylonitrile (PAN) fiber and to examine their feasibility of removing heavy metals from aqueous solution. Thermogravimetric analysis was used to identify the suitable conditions for preparing oxidized fiber and coke as activated carbon precursors. Steam and CO(2) were used to activate the precursors. Activated carbons were characterized by their pore texture, elemental compositions and surface functionalities. Batch adsorption and desorption studies were carried out to determine the metal-binding ability of activated carbons. Two commercial activated carbon fibers (ACFs), i.e., A-20 and W10-W, were employed to compare the removal performance of PAN derived activated carbons. Influence of oxidation treatment of PAN fiber prior to steam activation was also explored and discussed. Results indicated that steam produced a higher surface area but a lower resultant yield as compared to CO(2). Also, precursors activated by steam showed a greater removal performance. For both activation methods, fiber displayed a better metal-binding ability than coke. A small nitrogen loss from PAN fiber as a result of oxidation treatment assisted a greater removal of Cu(II) and Pb(II), but the interaction to Cu(II) was found stronger. It is proposed that the formation of cyclized structure by oxidation treatment minimized the nitrogen loss during steam activation, hence increased the uptake performance.

Effect of phosphorus fluctuation caused by river water dilution in eutrophic lake on competition between blue-green alga Microcystis aeruginosa and diatom Cyclotella sp.

Tega-numa (Lake Tega) is one of the eutrophic lakes in Japan. For the improvement of water quality in Lake Tega, the North-chiba Water Conveyance Channel was constructed in 2000, which transfer water from Tone River into the lake. After 2000, the dominant species of diatoms, mainly Cyclotella sp., have been replacing blue-green algae, mainly Microcystis aeruginosa in Lake Tega. This transition of dominant species would be due to the dilution, but the detail mechanism has not been understood yet. This study examined the relationship between phosphorus fluctuation caused by river water dilution to Lake Tega and dominance of algal species, M. aeruginosa or Cyclotella sp. based on the single-species and the mixed-species culture experiments. The single-species culture experiment showed that the half-saturation constant and uptake rate of phosphorus were one order lower and seven times higher for M. aeruginosa than those for Cyclotella sp. These findings implied that M. aeruginosa would possess a potential for the growth and survival over Cyclotella sp. in the phosphorus limited condition. The superiority of M. aeruginosa was reflected in the outcome of the mixed-species culture experiment, i.e., dominance of M. aeruginosa, even phosphorus concentration was lowered to 0.01 mg-P/L. Therefore, it could be concluded that the decrease in phosphorus concentration due to the river water dilution to Lake Tega would be interpreted as a minor factor for the transition of dominant species from M. aeruginosa to Cyclotella sp.

Arsenic Adsorption by Activated Carbon with Different Amounts of Basic Sites under Different Solution pH and Coexistent Ions

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 and ions. The effective arsenic species for As(V) adsorption was , 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 ( ).

Enhanced lead(II) binding properties of heat-treated cattle-manure-compost-activated carbons

AbstractConsiderable 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, pHPZC 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 w...

Adsorptive Behavior of Phosphate onto Activated Carbons Varying Surface Physicochemical Properties

This study demonstrated the modification of commercially available activated carbons (CS and R1) by de-ashing (DA), oxidation (Ox) and outgassing (OG) treatment to possess different surface area, pore volume, and the amount of surface functional groups, and these parameters were related to the efficiency of phosphate removal. The results showed that positively charged carbon surface due to the adsorption of protons to the basic sites resulted in the promotion of phosphate adsorption, that is, the extent of the surface area with the basic sites such as Cπ electrons and/or basic oxygen groups would enable to enhance the efficiency of phosphate adsorption.

ENVIRONMENTAL CONDITION INDEX FOR ESTIMATION ON EUTROPHIC STATE OF ENCLOSED AQUIFER ECOSYSTEM

To evaluate the effect of sediment treatment on aquifer ecosystem, a new ecological index that is composed of water quality, sediment quality and biota quantity was proposed in this study. According to ECI (Environmental Condition Index), DAF treatment (Dissolved Air Flotation) + MgO sprinkling was assessed as the most efficiency method for improvement of eutrophicated ecosystem, that is, this method can make the organic matter quantity in aquatic ecosystem minimum level in comparison with other sediment treatment method. Also, for application of this method to real field remediation such as eutrophicated lake, marsh, reservoir and so on, more detailed analysis for treatment function and optimum condition of sediment treatment was considered to be necessary.

Effect of heat treatment on copper removal onto manure-compost-activated carbons

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.

Influence of Phosphorus and Silicon on Competitive Interaction between Microcystis aeruginosa and Cyclotella sp. by Monoculture and Competitive Biculture Experiments

In Lake Teganuma, the shift of dominant species from blue-green algae (Microcystis aeruginosa [M. aeruginosa]) to diatoms (Cyclotella sp.) has been observed since 2000 as a result of the discharge of Tone River water into Lake Teganuma through the North-chiba Water Conveyance Channel. In this study, the influence of phosphorus fluctuation under relatively high silicon concentration, reflecting the condition in Lake Teganuma after 2000, on the shift of dominant species was experimentally examined through individual monoculture and competitive biculture experiments. The results from monoculture experiment showed that the half-saturation constant and uptake rate of phosphorus for M. aeruginosa was respectively lower and faster than that for Cyclotella sp., representing that M. aeruginosa possesses much higher growth potential than Cyclotella sp. under the phosphorus limited condition. The outcome of competitive biculture experiment obviously reflected these results, i.e., dominance of M. aeruginosa with a proportion of 99 % in total cell. Therefore, phosphorus fluctuation under the high silicon concentration could be interpreted as a minor factor for the shift of dominant species, from M. aeruginosa to Cyclotella sp. as observed in Lake Teganuma.

Adsorption of nitrate onto nitrogen-doped activated carbon fibers prepared by chemical vapor deposition

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 °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.

Evaluation and Suppression of Microcystis aeruginosa by Photocatalyst Coatings with Visible Light Photocatalytic Activity

Photocatalyst coatings had been successfully fabricated by molten salt treatment at 673 K for 3 h for titanium (Ti) coatings, which coated on alumina (Al2O3) balls by mechanical coating technique with Ti powder. The influence of molten salt treatment on the formed compounds, surface morphology and photocatalytic activity under visible light irradiation on degradation of MB solution and suppression of Microcystis aeruginosa of photocatalyst coatings was investigated. XRD results show that potassium titanate (K2Ti6O13) forms on the surface of Ti coatings during molten salt treatment. The visible light photocatalytic activity of photocatalyst coatings has been effectively enhanced by molten salt treatment.