[in Japanese]

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[in Japanese]

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In a tidal area at the estuary and the downstream of the Tamagawa river within 6km, five sampling sites were established. Moreover, two sites were established as reference, the Sekido bridge as nontidal area and the Nakayama bridge near the Lake Okutama as clean area.
The components of petrochemicals such as hexadecane, octylbenzene and 1-metylnaphthalene were added to each sample. Subsequently, they were cultivated at 20±1°C for intervals.
In result, these components were degraded to same extend at the tidal area in warm season. Hexadecane was degradaded about 80mg·l^-1 for 2days and 110120mg·l^-1 for 7days in summer, while octylbenzene was about 40mg·l^-1 for 3days and 6070mg·l^-1 for 7days in autumn. These were more degraded in warm season than cold.
And further, the biodegradation of these components were enhanced by addition of nutrients, which were constituted of NH₄Cl 100mg·l^-1, K₂HPO₄ 10mg·l^-1 and yeast extract 10mg·l^-1.
In the existence of pentadecane, the way of biodegradation was different between octylbenzene and 1-metylnaphtalene.

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The study was carried out in order to know the significance of the benthic animals as the indicator of water quality in stream. BOD and the diurnal change of DO were measured in the streams of Toyama prefecture and benthic animals were collected at the same time.
The benthic animals could be divided into two groups, namely group A and B. Group A includes Ephemeroptera, Plecoptera and Trichoptera, and indicates oligosaprobic level. Group B includes Physa fontinalis, Tubificidae, Erpobdella lineata, Asellus hilgendorfii and etc., and indicates α-mesosaprobic level. But in β-mesosaprobic level the species in group. A and B were found together.
The daily minimum DO was shown to be above 70% in summer or above 80% in autumn in the station in which the species of group A were found. And also BOD was above 1.0mg·l^-1 in summer or above 1.3mg·l^-1 in autumn in the station where those of group B were found.
The relation between BOD and the daily minimum DO was discussed and the diagrams about the ranges of the values of both the daily minimum DO and BOD in each of os, β-ms and α-ms were shown in summer and autumn respectively.

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Kinetic studies on the growth of Microcystis aeruginosa, Chlamydomonas sp. and Synedra acus were carried out on 2 member cultures in a microcosm system (diameter=1.0m, depth=3.0m) as well as small scale unialgal cultures to study the process of water-bloom formation by M. aeruginosa. In the microcosm cultures, aeration from the bottom was conducted to assess the effect of aeration/circulation on the water-bloom. The specific growth rate of M. aeruginosa was larger than that of Chlamydomonas under low light intensity (less than 1, 000 lux), whereas that of Chlamydomonas was larger under high light intensity at 20°C and 30°C. Thus Microcystis seemed to predominate over Chlamydomonas and subsequently form the water-bloom when light intensity underwater decreased sharply with depth of water due to light shielding by high concentration of suspended solids and/or phytoplankton. The specific growth rate of M. aeruginosa in 30°C was greater than that of S. acus, and therefore, predominated over S. acus.
Aeration and mixing of the whole water column in the microcosm delayed or prevented the dominance of M. aeruginosa. The artificial mixing and/or aeration seemed to be an effective way to control water-bloom formation by M. aeruginosa.

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The kaolinite suspension containing water glass is the one of the most popular waste water from chemical grouting tunnel constructions. In this study treatability of kaolinite suspension containing water glass in the coagulation process has been investigated. To make clear the effects of soluble or polymerized silicate on the coagulation process, various experiments were carried out. The polymerization rate and the value of electric charge of colloidal silica were measured under various pH and initial soluble silicate concentrations to characterize the nature of silicate.
The results obtained by the study can be summarized as follows.
(1) The highest polymerization rate of silicate is observed at pH 8.5 under the concentration of 300-1500 mg/l.
(2) Polymerized silica colloids show the largest negative charge at pH 9.2-9.5.
(3) The optimum pH range for the coagulation of kaolinite coexisting with water glass is between 4.5 and 7.0. The optimum pH value, however, changes depending upon the concentration of the soluble silicate and alum (aluminium sulfate) dosage.
(4) In the above mentioned optimum coagulation pH region, silicate exists mainly as the monomer. Therefore, polymerized silica dose not play an important roll for coagulation.
(5) Removal of soluble silica is very difficult by the both reasons that it requires high alum dosage and generates high sediment volume.

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