TREATMENT OF SEWAGE

PURPOSE:To well and stably remove phosphorus by mixing sewage with activated sludge to alternately execute aeration treatment and non-aeration treatment and preliminarily stirring sewage in a non-aeration state or an anaerobic state within a flow rate adjusting tank when biological phosphorus removed by activated sludge. CONSTITUTION:When sewage 1 is treated, at first, sewage 1 flows in a flow rate adjusting tank 2 to be stirred by a stirrer 15 in order to prevent the sedimentation of a solid component or corrosion. At this time, the sewage 1 is stirred under a non-aeration condition or an anaerobic condition. Therefore, it is prevented that soluble org. matter in sewage is decomposed and reduced by bacteria. Next, the stirred sewage 1 is supplied to an aeration tank 3 while the flow rate thereof is uniformized to be subjected to activated sludge treatment of an intermittent aeration system repeating aerobic and anaerobic treatments by timer control. Continuously, the sewage 1 is introduced into a sedimentation tank 8 to be separated into supernatant water 9 and settled sludge 10. By this constitution, sewage containing a large amt. of soluble org. matter is supplied to the aeration tank 3 to accelerate the discharge of biological phosphorus at the time of non-aeration.