PROCESS FOR TREATING FILTHY WATER

PURPOSE:To enable treatment of filthy water having high BOD and high SS load by carrying out reactions between filthy water and activated sludge in a first and second aeration tanks, leaving always a fixed amt. of sludge in the first aeration tank to cause reactions between microorganisms grown in the residual sludge and org. matters in the filthy water. CONSTITUTION:pH of filthy water contg. org. matters is adjusted to a pH permitting easy growth of microorganisms. The filthy water is introduced into a first aeration tank 5 wherein it is mixed with activated sludge contg. the microorganisms leaving a fixed amt. of said activated sludge previously in the aeration tank 5. During the storage of the filthy water in the tank 5, the org. matters are removed while performing stirring and aeration. When the level of the filthy water reaches a fixed level of the tank 5, the filthy water is transferred to a second aeration tank 10. The level of the filthy water of the tank 5 is lowered by the transfer of the filthy water. When the level reaches a predetermined level suitable for permitting a fixed amt. of sludge to remain as seed sludge, the transfer of the filthy water to the tank 10 is stopped. Then, aeration is continued in the seed sludge remaining in the tank 5, and the filthy water contg. org. matters having a pH adjusted to a value permitting easy growth of microorganisms is introduced into the tank 5 while continuing aeration, to continue further stirring and aeration. The filthy water is further aerated in the tank 10, and a flocculating agent is injected into a tank 12, and the filthy water is separated into supernatant water and sludge in a tank 14.