PROBLEM TO BE SOLVED: To inexpensively realize the regeneration and increase in vital force of a microorganism phase by charging symbiotic bacteria, which are based on aerobic bacteria in which facultative anaerobic bacteria and anaerobic bacteria are allowed to coexist, in the aeration tank of an activated sludge treatment apparatus having generated the lowering of a removal ratio of BOD and COD components to perform stirring and aeration. SOLUTION: In an activated sludge treatment apparatus equipped with an aeration tank, a sedimentation tank, a discharge tank and a sludge tank, when the regeneration and increase in vital force of a microorganism phase in the aeration tank having generated the lowering of a removal ratio of BOD and COD components are achieved, symbiotic bacteria which are based on aerobic bacteria in which facultative anaerobic bacteria and a number of anaerobic bacteria are allowed to coexist are charged in the aeration tank to perform stirring and aeration. When the temp. of introduced raw waste water is 25-35 deg.C, mesophiles functioning actively within this temp. region are mainly employed as symbiotic bacteria and, when the temp. of introduced raw waste waster is 25 deg.C or lower, low temp. bacteria functioning actively within this temp. region are mainly employed.
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