PURPOSE: To efficiently purify night soil, by returning a part of liquid obtained by treating the night soil in the first denitrifying step and the first aerating step to the first denidtrifying step, and treating the mixed liquid of the remainder of the treated liquid with sludge from a purifying cell in the second denitrifying step and the second aerating step.
CONSTITUTION: Night soil, circulating liquid and returned sludge are supplied to a denitrifying cell 11, denitrified therein and then aerated in the first aerating cell 12. A part of the treated liquid is returned as the circulating liquid to the denitrifying cell 11, while the remainder is fed to another denitrifying cell 13. On the other hand, sludge in a purifying cell and the circulating liquid together with the liquid from the first aerating cell 12 are introduced into a denitrifying cell 11. The mixed liquid is denitrified in the denitrifying cell 13 and aerated in the second aerating cell 14. A part of the liquid flowing out of the second aerating cell 14 is returned to the denitrifying cell 13, while the remainder is fed to a precipitating cell 15. Diluting water is introduced into the second aerating cell 14 at needs.
TAKEMOTO YUTAKA
ITOU TAKASHI
HAYASHI IKUKO
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