Activated sludge treatment method, and method for upgrading existing waste water treatment equipment using said method

An activated sludge treatment method for treatment of wastewater by a circulation system equipped with a waste water aeration-conditioning tank, a pressurized flotation concentration-separation tank, a dilute activated sludge aeration tank, a bioreactor, and a sedimentation tank, sludge being circulated among the tanks, wherein the activated sludge treatment method is characterized by comprising:

• a step 1 in which sludge 2 produced in the sedimentation tank is supplied to the waste water aeration-conditioning tank supplied with waste water prior to treatment;
• a step 2 in which waste water into which the sludge 2 has been mixed is subjected to aeration-conditioning in the waste water aeration-conditioning tank, to bring the oxidation-reduction potential to a positive value, and the conditioned waste water is then supplied to the pressurized flotation concentration-separation tank;
• a step 3 in which the sludge 1 produced through treatment in the pressurized flotation concentration-separation tank is supplied to the bioreactor;
• a step 4 in which the treated waste water 1 separated from the pressurized flotation concentration-separation tank is supplied to the dilute activated sludge aeration tank;
• a step 5 in which released water and the sludge 3 produced by treatment in the bioreactor are supplied to the dilute activated sludge aeration tank;
• and
• a step 6 in which the treated waste water 2 separated from the dilute activated sludge aeration tank is supplied to the sedimentation tank.