To estimate the interference action of chemicals, to the activated sludge, we established a method of measuring the toxicity (LC₅₀) of these chemicals to the micro-organisms, using the oxygen absorption rate of this activated sludge as a parameter. Simultaneously, as a convinient method, we tried to acquire a toxicity value, using the mortality of protozoa as a parameter, and compared the results with the former.
We observed that the latter shows generally smaller values of LC₅₀ (stronger toxicity). The above mentioned convinient method may be used to determine the rule of action in the case of an accident of the own sewage plant.

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A basic study on the desorption of volatile compounds dissolved in water from water to air was conducted for the purpose of predicting the desorption rate of volatile compounds in the wastewater treatment system.
1. A theory explaining that the ratio, β, of the liquid mass transfer coefficients of two different compounds is constant was developed.
2. The constantances of β for the methylene chloride / oxygen combination was experimentally found to be correct.
3. The liquid mass transfer coefficient of a compound (y) can be calculated using the theory provided the coefficient of another compound is known under the particular hydraulic conditions.
4. The desorption rate of a compound (y) can be calculated by putting the liquid mass transfer coefficient of y into the mass transfer equation.

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The Tokyo port area, which is a tidal area situated between The Sumida River and Tokyo Bay, was investigated for two years for the purpose of revealing the water dynamics and water quality.
The results are summarized as follows.
(1) Strong stratification owing to the difference of density was formed at about 5 meters depth from April to September.
(2) As water temperature rose, surface water became turbid and particulate organic carbon and chlorophyll-a increased and became about ten-fold and one hundred-fold as much as in winter respectivly, which was similarly observed generally in a eutrophic lake or innar bay.
(3) At the low tide fresh water from the Sumida River flowed down along west side piers in the port and sea water rose through the central part of channel at the high tide.
(4) The fresh water was eutrophic also, and the ratio of particulate organic carbon to chlorophyll-a was about 60 in summer, almost the same as that of phytoplankton,

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