Abstract: A hollow fiber membrane module adapted to be immersed in water to provide filtered water has hollow fibers bundled in a U shape and a securing part that secures the free end portion of the hollow fiber bundle such that the free end portion communicates with a water collecting part provided adjacent to the securing part. A support member is provided inside the U-shaped end portion of the hollow fiber bundle and supports and engages the hollow fibers such that each hollow fiber has a relatively wide U-shaped end portion and the hollow fibers are dispersed over the support member. A spacer is provided near the securing part and retains the hollow fibers such that the hollow fibers extend outward of the axis of the securing part and such that longitudinally extending portions of each hollow fiber are spaced apart from each other. Thus, suspended matter entering the bundle of the hollow fibers can be easily removed by washing and there is no possibility of the hollow fibers adhering together.

Abstract: Aeration apparatus for aerating a liquid to be treated in an aeration tank. The aeration apparatus has an impeller by means of which the liquid is displaced through an annular discharge passage defined between an outer casing and an inner casing disposed coaxially in the outer casing at a predetermined distance from the latter. The outlet end of the annular discharge passage opens in a substantially horizontal direction and radially outwardly. A gas supplying device provided in the annular discharge passage is adapted to supply an oxygen-containing gas to the liquid flowing in the annular passage.