PURPOSE: To execute the easy and efficient primary treatment of crude refuse and to lessen the labor of housework and the burden of self-governing bodies by pulverizing the crude refuse thrown in together with the city water from a sink by means of a disposer, treating the sewage mixed with the city water with microorganisms and releasing the treated water to a sewer.

CONSTITUTION: While the crude refuse of a kitchen is thrown into the disposer 4 from a throwing section 1b, the city water is discharged from the sink section 1a to the sewer. A solenoid valve 5 is thereafter opened to transfer the sewage mixed with the pulverized crude refuse into an anaerobic tank 7 of a treating section 6. The sewage in the anaerobic tank 7 is decomposed to an org. acid by anaerobic bacterium beds and is made to flow as an org. acid soln. over a contact aeration tank 8. On the other hand, the org. acid soln. is convectionally passed between aerobic bacterium beds 8a together with the air bubbling out of a diffusion pipe 9 in the contact aeration tank 8. The org. acid soln. is oxidation decomposed by the effect of the microorganisms sticking thereon and is discharged as low BOD sewage together with suspended and activated sludge to the sewer through an effluent port 11.