Abstract: A rotary multitube biocontactor has a plurality of tubes of a predetermined length and diameter. The tubes are bundled in a pillar like form and are connected with each other and with an axle at the sectional center thereof by means of welding or the like. The plurality of tubes are at angles to the axle, the axle being mounted in bearings provided on a trough at the top of two sidewalls thereof so as to enable the axle to be located close to the surface of water contained in the trough. The axle is rotated by a motor connected thereto thereby rotating the multitube biocontactor so that the tubes move in and out of the water contained in the trough.