A wastewater treatment facility with one or more rotating biological contactors, the wastewater treatment facility comprising: - a tank; - a rotatable shaft that is supported by the tank; - one or more stages for purifying incoming wastewater, at least one of the one or more stages (12, 16, 18) being oriented transversely to the rotatable shaft and having one or more disk assemblies, each disk assembly having a number of disks, at least some of the disks having: - a front face and a back face; - a plurality of turbulating posts extending from the front face and the back face of the disks for agitating wastewater and offering surfaces to which microorganisms may attach for consuming contaminants from the wastewater and degrading the microorganisms; and - a plurality of connecting extensions extending from the front face and back face, the connecting extensions having tips and tip heights that exceed a height of the plurality of turbulating posts so that adjacent disks in a disk assembly are connected and spaced apart by a mating relationship between the tips of the connecting extensions; at least some of the disks being formed from multiple concentric rings of ring segments with an inner ring, an intermediate ring and an outer concentric ring; the inner ring having a bore that receives the rotatable shaft; the ring segments of the intermediate ring being joined to the ring segments of the inner ring and of the outer concentric ring; the ring segments being provided with: - two generally radially extending edges; - two circumferential edges that extend between the two radially extending edges; - a first engagement feature extending from a side of a ring segment; and - a second engagement feature extending from a side of another ring segment that enables adjacent ring segments to be fastened and thus cooperate to form at least a portion of a disk; characterized in that the first engagement feature and the second engagement feature are snap fit features; the plurality of connecting extensions being hollow and tubular and forming flow channels defined between connecting extensions from and across opposing faces (31, 32) of a disk, so as to allow water to be transmitted through flow channels in a manner that jets of water slough off the dead biomass at the end of a stage (12, 16, 18). - a tank; - a rotatable shaft that is supported by the tank; - one or more stages for purifying incoming wastewater, at least one of the one or more stages (12, 16, 18) being oriented transversely to the rotatable shaft and having one or more disk assemblies, each disk assembly having a number of disks, - a front face and a back face; - a plurality of turbulating posts extending from the front face and the back face of the disks for agitating wastewater and offering surfaces to which microorganisms may attach for consuming contaminants from the wastewater and degrading the microorganisms; and - a plurality of connecting extensions extending from the front face and back face, the connecting extensions having tips and tip heights that exceed a height of the plurality of turbulating posts so that adjacent disks in a disk assembly are connected and spaced apart by a mating relationship between the tips of the connecting extensions; - two generally radially extending edges; - two circumferential edges that extend between the two radially extending edges; - a first engagement feature extending from a side of a ring segment; and - a second engagement feature extending from a side of another ring segment that enables adjacent ring segments to be fastened and thus cooperate to form at least a portion of a disk;