| 摘要 |
<p>PURPOSE:To make it possible to suppress the re-release of a phosphorus component into treated water and to remarkably enhance the removal efficiency of phosphorus from sewage, by shortening the stay time of precipitated sludge in a precipitation tank as possible. CONSTITUTION:Sewage and activated sludge are mixed to be subjected to aeration treatment in an aeration tank 2 and sludge is precipitated in a precipitation tank 3 to flow treated water out of a system while the part of precipitated sludge is returned to the mixing and aeration treatment process with sewage. In this sewage treatment method, the stay time of the precipitated sludge in the precipitation tank 3 is shortened as possible. For the sake of shortening stay time, for example, it is expedient that an inclined plate type precipitation tank is employed but, as other means, a mechanical concentrating process 7 due to a centrifugal concentrator is provided between the tank 3 and a sludge tank 4. As the result, the re-release of a phosphorus component into treated water caused by making the tank 3 anaerobic can be prevented and the removal efficiency of phosphorus from sewage can be extremely enhanced.</p> |
