A rotating biological contactor is formed about a polygonal shaft. The contactor includes a hub formed of a series of hub rings disposed side by side along the length of the shaft with each hub ring formed of hub segments which are joined end to end. In one embodiment the hub segments are identical and there is one hub segment for each corner of the polygonal shaft. In a second embodiment there is one hub segment for each two corners. The hub segments also include a mounting portion which has welded to it alternating flat and formed thin walled sectors of contactor media. The sectors are joined to each by welding and successive layers of the sectors are angularly offset from each other so that some of the sectors span the joints between adjacent hub segments of a hub ring.

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