PURIFYING TANK

摘要

PURPOSE: To prevent the concn. of the solid component in a membrane separation tank from becoming too high by providing an intermediate treatment tank receiving water to be treated through an anaerobic treatment tank between the anaerobic treatment tank and the membrane separation tank and holding the balance between the return amt. of treated water and the sum of returned water to be treated and water to be treated after membrane separation. CONSTITUTION: An anaerobic treatment tank N1 and a membrane separation tank E2 equipped with a membrane separator M are provided and an intermediate treatment tank E1 receiving water to be treated through the anaerobic treatment tank N1 is provided between the anaerobic treatment tank N1 and the membrane separation tank E2. A transfer pump A transferring water to be treated to the membrane separation tank E2 is provided to the intermediate treatment tank El and the overflow water of the water to be treated in the membrane separation tank E2 is returned not only to the intermediate treatment tank E1 through a first return passage 21 but also to the anaerobic treatment tank N1 through a second return passage 22. This return is controlled so that excessive water to be treated is sent to the anaerobic treatment tank M1 when the water to be treated returned to the intermediate treatment tank E1 exceeds a set amt.