Abstract: A method for treating liquid-waste utilizing carriers having microorganisms immobilized thereon employs an aerobic treatment tank. At least one underwater agitation type aeration apparatus having an air-diffusing mechanism on a discharge side of an impeller is provided in the treatment tank. While supplying atomized air into the liquid-waste, the carriers and the liquid-waste are circulated through the treatment tank by the underwater agitation type aeration apparatus, to thereby substantially uniformly distribute the carriers in a floating state in the treatment tank. The discharge opening of the underwater agitation type aeration apparatus is provided in the vicinity of a bottom surface of the treatment tank or at an intermediate position with respect to the depth of liquid in the treatment tank.

Abstract: A carrier-separating and liquid-collecting mechanism in a liquid-waste treatment apparatus having a treatment tank in which carriers having microorganisms immobilized thereon are suspended. The carrier-separating and liquid-collecting mechanism includes a cylindrical screen (13) and a liquid-collecting devices (14) disposed in the cylindrical screen. The cylindrical screen is provided in the treatment tank, such that the axis of the cylindrical screen extends in a substantially horizontal direction. The liquid-collecting device is a pipe or a gutter having liquid-collecting holes, and is capable of collecting liquid at a plurality of positions through the cylindrical screen. The carrier-separating and liquid-collecting mechanism may further include a rotation mechanism for supporting the cylindrical screen and intermittently rotating the cylindrical screen on the axis thereof and a brush (18) which is fixed so as to be in parallel to the cylindrical screen in contact with the cylindrical screen.