Kaoru Fujinaga

Nitrous oxide in brackish Lakes Shinji and Nakaumi, Japan

Abstract Nitrous oxide (N2O) was measured monthly from September 1997 to August 1998 in the brackish Lakes Shinji and Nakaumi, Japan. N2O (5–37 μg N l−1) was supersaturated in the overlying water on lake sediments from October 1997 to January 1998. The N2O concentration in the hypolimnion was higher than that in the epilimnion on 17 October 1997, when N2O was first observed in a water column of Lake Nakaumi. Afterward, N2O was almost uniform throughout the water column and then disappeared on 16 February 1998. On the one hand, large amounts of N2O were found throughout the year in the interstitial water in Lake Shinji, where a high concentration of nitrate was discharged from the Hii River. On the other hand, in Lake Nakaumi, stratified by halocline, a high concentration of N2O was observed in the interstitial water only from winter to spring. N2O concentrations in the interstitial water were about 10 to 1000 times as large as those in the overlying water. These results imply that N2O was mainly produced at the sediment-water interface and was diffused to the overlying water. It was also suggested that the accumulation of N2O in the sediment-water system was accelerated by a high concentration of hydrogen sulfide.

Preconcentration method for phosphate in water using activated carbon loaded with zirconium

ZusammenfassungEin einfaches und wirkungsvolles Anreicherungsverfahren für Phosphat in wässriger Lösung beruht auf der Verwendung von Zr-beladener Aktivkohle (Zr-C*), die durch Vermischen (3 Tage) von 100 ml Zirkonylnitratlösung (1 g Zr, pH 1,6) mit 10 g Aktivkohle, Filtern und Trocknen hergestellt wurde. 10 g des Materials enthielten 0,5–0,6 g Zirkonium. Adsorption und Desorption von Phosphat sind nur vom pH-Wert der Lösung abhängig und erfolgen quantitativ bei pH < 8,0 bzw. pH > 13,5. Die wässrige Probelösung vom pH 1,5 wird durch das auf einem Membranfilterpapier befindliche Zr-C*-Bett gesaugt und das zurückgehaltene Phosphat durch Elution mit 40 ml 1 M NaOH-Lösung wiedergewonnen. Pyrophosphat, Tripolyphosphat und Metaphosphat verhalten sich ähnlich wie Orthophosphat.SummaryAn effective and simple method for preconcentration of phosphate in aqueous solution has been developed, using activated carbon loaded with zirconium (Zr-C*). The Zr-C* was prepared by mixing 100 ml of zirconyl nitrate solution (1 g Zr, pH 1.6) with 10 g of activated carbon at 25 ° C for three days, filtering and drying the residue in air. 10 g of the resulting material included 0.5 g to 0.6 g of zirconium. The adsorption of phosphate and its desorption depend only on the pH of solution. They occur quantitatively and instantaneously at pH below 8.0 and above 13.5, respectively. An aqueous solution with the pH adjusted to 1.5 is passed through the Zr-C* bed formed on a membrane filter paper with the aid of suction. The collected phosphate is then recovered by eluting with 40 ml of 1 M sodium hydroxide solution. Pyrophosphate, tripolyphosphate and metaphosphate behave as similar as orthophosphate.

Liquid-liquid extraction of some transition metals with a mixed solvent system

Abstract A carbon disulphide-isoamyl alcohol-pyridine ternary solvent was found to be applicable to the extraction of transition metal ions such as Zn2+, Co2+, Ni2+, Cd2+ and Cu2+, but not Mn2+, Fe3+, CrO2−4 and MoO2−4. The ions were extracted as isoamylxanthates from aqueous sulphate medium. The optimum extraction conditions, such as mixing ratio of solvents, pH and shaking time for equilibrium, and the extraction mechanism were established.

Seasonal variation in nutrients and chlorophyll a in the stratified brackish Lake Nakaumi, Japan

The major inorganic nitrogenous compounds in aquatic environments are nitrate, ammonium and sometimes nitrite. Previously we studied the uptake of ammonium and nitrate by natural phytoplankton (SEIKE et al. 1986a), denitrification (SEIKE et al. 1986b, l986c ), nitrification (SEIKE et al. 1986c, 1997), the behavior of nitrate (SEIKE et al. 1990) and nitrous oxide (SENGA et al. 2001, 2002) in the brackish Lake Nakaumi, Japan. The present study was undertaken to explain seasonal variation in inorganic nitrogen compounds in the water column of Lake Nakaumi, on the basis of existing knowledge of nitrogen cycling in the lake. Data on nitrogenous nutrients such as nitrate, nitrite and ammonium in the lake were collected monthly during 1990-1999. Chlorophyll a was analyzed from data collected at monthly intervals from 1990 to 2002. A further aim of this paper was to evaluate the importance o f coupled nitrifi-

A pretreatment method for the determination of nitrate in brackish water and seawater based on the hydrazinium reduction technique

Abstract The hydrazinium reduction technique has so far been inapplicable to the determination of nitrate in brackish water and seawater due to interference from magnesium ions. We developed a pretreatment method for brackish water and seawater samples for the determination of nitrate based on the hydrazinium reduction technique. Magnesium ions in water samples were converted to a precipitate of a complex with oxine (8-quinolinol) at pH 9.5, and then the precipitate was centrifuged at 3000 rpm for 20 min. The extra oxine in the resulting sample (the supernatant liquid), which inhibits the reduction of nitrate to nitrite, was removed using a Sep-Pak C18 cartridge. Thus we achieved the preparation of a magnesium-free water sample. Using the hydrazinium reduction technique with the proposed pretreatment method, nitrate in brackish water and seawater as well as fresh water was quantitatively determined with high accuracy.

Adsorption Behavior of Metal Ions with β-Diketone Type Chelating Agents Supported on Hydrophobized Mesoporous Silicate MCM-41

To investigate the adsorption behavior of metal ions with β-diketone type chelating agents, thenoyltrifluoroacetone (Htta) and benzoyltrifluoroacetone (Hbfa) supported on mesoporous silicate MCM-41 that has been hydrophobized (hMCM-41) using trimethylchlorosilane was synthesized. The hexagonally arranged pore structure of MCM-41 was not significantly changed by the hydrophobic treatment and attachment of chelating agents, although the pore size, pore volume and surface area were slightly smaller than those of untreated MCM-41 as a result of the chemical modification of the surface. The amount of chelating agents adsorbed on hMCM-41 was 0.47 for Htta and 0.33 mmol g for Hbfa, respectively. All metal ions examined, except for Cd, were quantitatively adsorbed on hMCM-41 as metal complex, M(tta)2 or M(bfa)2. The order of the adsorption selectivity of the metal ions was similar to the stability constants of metal ions with Htta or Hbfa. Furthermore, most of the metal ions adsorbed onto hMCM-41 at lower pH compared with the results of having used MCM-41 as a support of chelating agents. This suggests that the adsorption ability of metal ions with chelating agents was improved by the hydrophobic treatment of MCM-41.

The Simple Design Method of Ammonium Ion Removal Equipment with Packed Natural Zeolite.

The NH4+ exchange capacity of natural zeolite depends on the location of extraction and on the ion contents of the waste water to be treated. The NH4+ exchange capacity is determined for each zeolite and waste water sample individually in the current design method of NH4+ removal equipment. Therefor, these results cannot be generally applied to other cases. In this study, the equation to obtain the design velocity of treatment through the zeolite packed cloumn by the cation exchange capacity and particle size of zeolite as well as the ammonium concentration and temperature of water was investigated. In addition, the experimental equation to show the ion exchange equilibrium from cation contents was obtained. On the basis of the investigation, the simple method to obtain the design variables was developed.

Portable Simplified Photometer for in Situ Environmental Water Analysis

Abstract The portable simplified photometer, in which high-luminous light emitting diode (LED) was used as a lamp, was manufactured as an useful tool for in situ environmental water analysis. This photometer is applicable to various spectrophotometric methods for the determination of chemical species exhibiting an absorption λmax of the colored complex spectrum around 660 nm and/or 560 nm.