PURPOSE: To activate the filtrate of waste excretion water of raised hogs efficiently and satisfactorily by spraying said filtrate from the upper part of a spray tower erected in the central part of an aeration basin, storing the water in the aeration basin and releasing the water after purifying.

CONSTITUTION: The filtrate (a) of the waste excretion water of raised hogs is scattered and released in the form of mists from the upper part of a spray tower erected in the central part of an aeration basin 1 to the circumference and is stored in the basin 1, from which the water is released after purification. The filtrate (a) sprayed like mists from the upper part of the tower 2 contacts with air uniformly in the air and in this stage, a large amt. of oxygen is contained in the filtrate (a). Particularly since the filtrate is sprayed like mists, large contact areas are taken, and as compared to conventional bubbling system, the filtrate is activated with high higher efficiency.