| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for treating organic sewage at a low running cost while the generated amount of waste sludge is remarkably reduced in a process for purifying the sewage using activated sludge. SOLUTION: In the step to purify biologically the organic sewage by an activated sludge process, this method comprises returning a part A of the activated sludge obtained by the process to an aeration tank 2 of the process after subjected to alkali treatment and supplying a part B of the activated sludge to an alkali treatment tank 7 after oxidized by ozone so that the solid amounts in the parts A and B satisfy the condition SA>SB (wherein SA is the solid amount in the sludge of A; SB is that of B). As the other method, B is supplied to the aeration tank after oxidized by ozone.
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