Biodegradation of phthalic acid esters (di-n-butyl phthalate, DBP ; diheptyl phthalate, DHP ; di-2-ethylhexyl phthalate, DEHP) was investigated in the water of the Kako River by using the method by incubation with 0.1% peptone.
DBP was easily degraded in the water of all sampling sites except for the most upper stream. The biodegradation rates of DHP and DEHP increased gradually from upper stream to lower reaches although decrease of rates was observed at middle reaches where waste water from several dye works flowed into.
On the other hand, concentrations of DBP and DEHP in the river water decreased gradually with distance from upper stream. The correlation coefficient between biodegradation rates and concentrations in the river water was -0.75 in case of DBP.
It was concluded that the overall of the Kako River has a function of selfpurification for phthalic acid esters, although there was a little suppression of the function at middle reaches.

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Flow volume and water qualities of ten drains in urban area, Kawasaki-city, were measured all day over two years, and overall runoff ratio of BOD was analyzed.
The flow volume and water qualities were much influenced with wastewater from household, but all the drains were kept in aerobic conditions. The overall runoff ratios of BOD from 6 to 22 o'clock were in the range from 0.2 to 1.0, and they were analyzed by simulation that catchment area of the each drain was regarded as a homogenious aerobic bio-reactor. And the following equation for the runoff ratio α was obtained by the relation with the catchment area S(km²)and mean flow volume Q (m³/h) ; α=1/{1+5exp(4.4S)/Q}

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The characteristics of waste water discharged from an under tunnel construction site using chemical grouting of water glass and colloidal cement has been studied in order to develop a guideline of design the waste water treatment plant.
The characteristics of waste water was examined at excavating, grouting and pausing stage of the construction. The results obtained by this study can be summerized as follows.
(1) Amout of the waste water discharged in a day was observed maximun in the excavation stage. It was about ten fold of the minimum discharged volume.
(2) Daily average value of pH and turbidity in a day were 11.3± 0.9 and 2020± 1110TU respectively.
(3) Daily average concentration of soluble silicate and calcium ion were 114± 6lmgSiO₂·l^-1 and 58±33mg·l^-1 respectively.
(4) Daily average value of P-alkalinity and electric conductivity in a day were observed to be 140± 180mg CaCO₃·l^-1 and 390±473μs·cm^-1 (25°C) respectively.
(5) A guideline for designing waste water treatment plant in the construction site could be recommended as follows : Allowable amount of discharge is to be 2.5 times of the daily average in excavation stage ; pH, turbidity and soluble silicate are 11.3, 3100TU and 230mg SiO₂·l^-1 respectively.

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In the course of diffuser performance measurement with the standard method under unsteady state used sodium sulfite, concentration change of oxygen in the aerated off gas can be observed by means of off gas method.
In early stage of the measurement oxygen concentration of off gas is gradually reduced and it arrives at minimum value while dissolved oxygen concentration in the liquid is suddenly brought down to zero.
The overall oxygen transfer coefficient KLa which is a typical parameter of diffuser performance can be derived from this minimum oxygen concentration. Experiment on diffuser performance measurement of the ceramic perforated plate has been conducted and the both values obtained from experimental results by off gas and sodium sulfite method under the same condition have been compared and they have agreed as a result of statistics test. This conclusion is very significant for diffuser performance measurement under operating condition because off gas method is actually only useful method for measurement of operating aeration tanks.

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