MEMBRANE-SEPARATION ACTIVE SLUDGE SYSTEM TO BE LOCATED OUTSIDE TANK

摘要

It is intended to provide a membrane-separation active sludge system to be located outside a tank which would not excessively lower the MLSS concentration in a biological reaction tank, requires no separate drainage device for the drainage of reverse washing and ensures a high stability of the filtration performance of the separation membrane. Namely, a membrane-separation active sludge system to be located outside a tank wherein drainage of reverse washing formed by reverse washing a separation membrane (2), which contains materials clogging the membrane face, is combined in a tank (7) for drainage of reverse washing, treated with ozone and then returned into a biological reaction tank (1). Owing to this constitution, the materials clogging the membrane face having a size similar to the membrane pore size of the separation membrane are finely divided or easily incorporated into an active sludge flock in the biological reaction tank. When returned into the biological reaction tank (1), therefore, the sludge never worsen the filtration performance of the separation membrane. Moreover, the MLSS concentration in the biological reaction tank can be maintained by the sludge thus returned.