To provide a sewage treatment method and apparatus in confluent type sewerage capable of sharply reducing the outflow amount of a pollutant in discharge water at the time of rainy weather and capable of reducing an injection amount of chlorine.
An ascending flow type high speed filter tank 10, which is filled with a floating filter medium wherein apparent specific gravity is 0.1-0.4 and 50% compression hardness is preferably 0.1 MPa or more, is arranged in place of a conventional first sedimentation basin. Confluent type sewage is introduced into the high speed filter tank 10 at the times of fine weather and rainy weather to remove SS and the treated water is guided to a rear stage reation tank 11 and a final sedimentation basin 12 at the time of fine weather to be treated successively. At the time of rainy weather, water exceeding designed water quantity Q of the treated water in the high speed filter tank 10 is sterilized if necessary to be directly discharged. Since an SS removing ratio reaches 70%, the pollutant in the discharged water at the time of rainy weather can be sharply reduced.
MIYATA ATSUSHI
HIROTA JUNICHI
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