| 摘要 |
PROBLEM TO BE SOLVED: To reduce dependence of concentration on filtering pressure and on the formation of a cake layer on a membrane surface while enhancing membrane separation capacity by adjusting the pH of a separated liquid obtained by flocculating and dehydrating excretion sewage to biologically treat the separated liquid and adjusting this treated liquid in pH to subject the same to flocculation treatment by an inorg. flocculant before applying membrane separation treatment thereto. SOLUTION: A polymeric flocculant is added to excretion sewage in a flocculation tank 12 to flocculate a suspended substance, an oil component, a heavy metal compd. or the like and the sludge dehydrated and separated by a dehydrator 13 is discharged out of the system by a dehydrated sludge taking-out means 14. The separated liquid is nitrified and denitrified by nitrifying bacteria, nitrite bacteria and denitrifying bacteria and the treated liquid high in the concn. of a suspended substance is sent to a flocculating and mixing equipment 16 without being subjected to solid-liquid separation treatment. An inorg. flocculant is added to the treated liquid in a flocculating and mixing equipment 16 and the pH of the treated liquid is also adjusted to flocculate hardly decomposable org. matter. This treated liquid is sent to a membrane separation equipment 18 to be separated into sludge and a membrane separated liquid and the membrane separated liquid is supplied to an activated carbon treatment equipment 21 to remove residual COD or org. matter such as COD, a chromaticity component or the like. |
