| 摘要 |
PROBLEM TO BE SOLVED: To increase the treating quantity of sewage without decreasing the purifying ability for water by treating the sewage after biologically treated in 2 stages with membranes each having a specific average pore diameter to suppress the construction and operation cost. SOLUTION: The 1st stage treatment is carried out by sending the sewage treated with aerobic microorganism in a biologically treating tank 10 to the membrane 11 using a flat membrane, a hollow fiber membrane or a ceramic membrane and having >=0.5μm average pore diameter with a pump 20 operated. The filtrate after flocculation treatment in a flocculation treatment tank 12 is sent to the membrane 13 using a hollow fiber membrane, a cylindrical membrane or the like and having <0.5μm average pore diameter to be treated in the 2nd stage. The filtrate treated with the membrane 13 is discharged to the outside or reutilized and the concentrated liquid is returned to the flocculation treatment tank 12. As a result, the treating rate is acceleated by reducing the load on and after next process without filtering no large solid material in the 1st stage treatment to increase the treating quantity without lowering the level of the treated water.
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