The contact aeration processes have many applications in small sewage treatment plants in rural areas. The processes favour the nitrogen removal ability even during the winter season when waste water temperature is low. It has been observed that the nitrification did not occur vigorously when the temperature of waste water was less than 15°C. Hence, to increase the nitrification capability, the flow pattern of the treatment process was renewed in such a way that the aeration tanks were placed before the anaerobic tanks. In contrast, the anaerobic tanks were previously placed before the aeration tanks. Return flow circulation was introduced within the aeration tanks rather than the treated water after aeration process would return to the first anaerobic tank. The waste water temperature was maintained around 13°C because it was not below from 13°C even in the Tohoku and Hokkaido regions. This type of arrangement lead to almost complete nitrification. However, denitrification did not progress under the condition. Therefore, intermittent aeration in the first aeration tank and circulation flow of 1-Q within the aeration tanks were used. In addition, the anaerobic tanks had circulation flow equivalent to 4-Q. Results reveal passably good agreement of nitrogen removal that T-N concentration of effluent less than 10mg·l-1 was observed. From the results, we would like to propose a system of the Experiment 5 for nitrogen removal of contact aeration process.

View full abstract

A precise and sensitive method was examined for the determination of thallium in environmental sediments by electrothermal atomic absorption spectrometry. The ground sample was digested with HF/HNO₃/HClO₄/H₂SO₄, then thallium was determined by standard addition method. Both use of a pyrolytic graphite-coated tube and addition of matrix modifier (Pd²⁺ 2000ppm+5% hydroxylammonium hydrochloride in 1 mol·l^-1 sulfuric acid solution) were effective in increasing sensitivity and precision. Constant absorbance was obtained in the charring temperature ranging from 900 to 1100°C.
Analytical results of thallium obtained by proposed method showed in good agreement with the certified values for the environmental (sediments, rocks, soil and coal fly ash) reference materials. The precision was 2.5-5.2%. Similar analytical results were obtained by digested with HF/HNO₃/HClO₄ to the proposed digestion method.
Thallium concentrations in river, lake and marine sediments from Kanagawa prefecture were detected in the range from 0.140 to 0.565μg·g^-1 (average 0.299μg·g^-1) by digestion with HNO₃/HCl/HClO₄ and from 0.171 to 0.624μg·g^-1 (average 0.375μg·g^-1) by digestion with HF/HNO₃/HClO₄/H₂SO₄.
The detection limit of the proposed methods was 0.063μg·g^-1 for 0.5g of sediment.

View full abstract

Nitrification of ammonium in wastewater was investigated by a bio-electro reactor process under low DO conditions. A flat carbon plate attached nitrifying bacteria was used as anode and a stainless plate was used as cathode. In order to investigate the effect of bulk liquid DO concentration on nitrification, the experiments were carried out under both high DO (5.0 g·m^-3) and low DO (0.1 g·m^-3) conditions. Electric current applied was changed from 0.0075A to 0.03A.
Under the low DO condition, nitrification rate increased with an increase in applied electric current. However, under the high DO condition, the effect of applying electric current on nitrification was small. Production of nitrite was very small under both the high and low DO conditions. Effects of electric field on the nitrification rate was not observed within the experimental range.

View full abstract

The removal of sulfides in seawater under anaerobic condition by using powder converter slag (particle size, 53-75μm) was examined. The release of ammonium from coastal bottom sediments by the slag was also examined.
Sulfides were quantitatively removed by the slag. The amount of removal was 31.7mgS.g^-1 and 14.5mgS.g^-1 at pH 8.2 and 9.0, respectively. The sulfide removal decreased with an increase in pH and was 1.7 mgS.g^-1 at pH 9.9. Surface analysis of slag by a X-ray microanalyzer indicated that sulfides were removed mainly at C region which consisted mainly of CaO and SiO₂ without any inhibition of phosphorous removal.
The addition of the slag to bottom sediments may enhance the release of ammonium from the sediments with an increase in pH due to dissolution of free calcium oxide in slag.

View full abstract

In order to establish standard rearing method of Red Seabream (Pargus major) for testing bioconcentration of hazardous pollutants, optimal population density, water temperature and amount of food were investigated. Necessary parameters investigated were dissolved oxygen, ammonia and pH in rearing seawater, lipid and protein contents in experimental fish, their growth ratio and their conditioning factor. The most critical parameters were dissolved oxygen and lipid content. The optimal conditions obtained using a 60l aquarium with a running water system were less than 0.59g·l^-1·d^-1 for population density, 20-25°C for water temperature, 4% of body weight given per day for the amount of food and 6 times a week for the frequency of feeding.

View full abstract

In order to clarify the movement of nitrogen (N) and phosphorus (P) between the sediment and overlying water in the eutrophic Lake Koyama in Tottori, the change in the cocentration of the different forms of N and P was investigated in 1993 and 1994.
The total N (T-N) concentration in the overlying water was fairly lower than that of the porewater. The ammonium-N (NH₄-N) produced in the sediment was immediately diffused and/or was changed into organic N (Org.-N). The mineralization of N in the sediment was not controlled by the concentration of T-N or Org.-N of the sediment, but by the water temperature. The organic matter derived from the dead body of planktons seemed to be the main N supply to the sediment.
The concentration of T-P in the porewater was far lower than that of the overlying water and the P in the sediment existed in the form of Inorg.- P, which suggested that the elution of P from the sediment into the water was not probable, except for the period of the low dissolved oxygen concentration of the water in summer.

View full abstract