Installation for the treatment of wastewaters and biological disc for such an installation

An installation for the treatment of municipal and/or industrial wastewater, comprising a basin that receives the water to be treated and a series of disks with packing, said disks being parallel, vertical, mounted on a horizontal shaft, partially immersed in the water to be treated and being rotatable in such a way that the biomass that grows on the surface of the packing of the disks is alternately brought into contact with the water to be treated and with oxygen from the air, wherein the packing of the disks is configured in a plurality of zones, with radial spaces between adjacent zones, and the developed surface area of the packing in each zone of the disk increases with the distance of this zone from the rotation axis, thereby developing an increasing contact area on approaching the outside of the disk, wherein the packing has corrugations along a direction transverse to the mean plane of the disk, the corrugations opening up into the radial spaces between adjacent zones, and the frequency of the corrugations along the radial direction increases with the distance from the rotation axis, whereas the amplitude of the corrugations along a direction transverse to the mean plane of the disk remains approximately constant.