To provide a waste water treatment apparatus which is made compact enough to be installed inside the outer periphery of a common house and the running cost of which is reduced, and to provide a method for operating the waste water treatment apparatus.

An air spouting disk 7 consisting of a porous material is disposed at the bottom of a separation pit 3 and a multiple microbe culture solution is supplied from a sink of a kitchen to the separation pit in such a state that air bubbles are discharged from the air spouting disk 7 with the frequency of once or more times a day. The outside diameter of the air spouting disk 7 is adjusted to 70% of the inside diameter of the bottom of the separation pit 3, the diameter of each hole of the air spouting disk 7 is adjusted to 25-50 m, the height of air bubbles discharged from the air spouting disk 7 is adjusted to 1-5 mm and the amount of air bubbles to be discharged is adjusted to 25-35 L/minute so that the inside of the separation pit 3 is agitated satisfactorily, the decomposition of oil, fat or organic matter by multiple microbes is optimized and waste water is cleaned.