Biological waste water treatment system having a sedimentation tank vertically combined with an aeration tank therein

A waste water treatment system comprising:

• an anaerobic tank for treating phosphorous, which is contained in waste water and introduced into the anaerobic tank by anaerobic microorganisms;
• a first anoxic tank and a second anoxic tank for treating nitrate contained in the waste water from the anaerobic tank by denitrification microorganisms;
• a holding tank for containing therein the waste water from the second anoxic tank;
• an aeration tank for treating an organic material contained in waste water from the holding tank by microorganisms and pure oxygen and for treating ammonia by microorganisms to turn ammonia into the nitrate, the aeration tank being a substantial cylindrical body mounted on a concrete bottom provided with an inclined eccentric slope formed thereon for causing the waste water to eccentrically flow within the aeration tank, the aeration tank having a diffuser for diffusing compressed air into the waste water contained in said aeration tank, and means for supplying pure oxygen to the waste water in the aeration tank, wherein the anaerobic tank, the pair of anoxic tanks and the holding tank are mounted around the aeration tank to surround the aeration tank with substantially identical height with one another;
• a sedimentation tank vertically combined with an upside of the aeration tank and communicated with said aeration tank through a through-hole, the sedimentation tank having a clarified water outlet through which clarified water is discharged from the sedimentation tank, the sedimentation tank having a sludge pit;
• means for slowing down the flow of the waste water introduced into the sedimentation tank from the aeration tank, the slowing-down means including a reversed funnel-shaped guider for guiding the flow of the waste water introduced into the sedimentation tank to converge flow lines of the waste water to a central line of the sedimentation tank, the reversed funnel-shaped guider having a guide baffle mounted inside the reversed funnel-shaped guider, and an outer guider for guiding a flow of the waste water having passed the reversed funnel-shaped guider to allow the waste water to flow between an external surface of the reversed funnel-shaped guider and an internal surface of the outer guider, the outer guider having a larger diameter than the reversed funnel-shaped guider;
• means for re-introducing the waste water in an upper portion of the aeration tank into the first anoxic tank;
• and
• means for re-introducing sludge in said sedimentation tank to the anaerobic tank.