COMBINED TREATMENT METHOD FOR IMPROVING EXISTING SINGLE TREATMENT SEPTIC TANK INTO COMBINED TREATMENT TANK, AND THE COMBINED TREATMENT TANK OBTAINED BY THIS METHOD

PROBLEM TO BE SOLVED: To provide a combined treatment tank by improving an existing single treatment septic tank, and the combined treatment tank obtained by this method. SOLUTION: A membrane treatment tank E is installed near the existing single treatment septic tank D having an inflow port 1, plural treating chambers and an outflow port. A pump 32 and a transfer pipe 33 for transferring sewage are connected between a prescribed chamber of the tank D and the tank E. As a result, such a combined treatment septic tank is completed, as has the two tanks D and E where the sewage can be treated successively. Therefore, even when miscellaneous waste water from a bath room, a kitchen, a washing machine, a washroom, or the like, as well as waste water from a lavatory are made to flow in the combined treatment tank, they can be purified by separating solids by precipitation in a precipitation chamber 3 of the tank D, treating the liquid separated in the chamber 3 with activated sludge in the tank E and filtering solids contained in the water treated with the activated sludge by a membrane in the tank E.