An integrated sewage biochemical treatment plant containing mechanical treatment devices, a sewage-and-sludge mixing chamber with a circulation pump and a combined biological treatment device, includes a plane feed biofilter, a spray line, collecting trays and drain collectors connected to water-jet aeratic columns sunk in the aeration zones, and aftertreatment devices. The combined biological treatment device whose capacity is 5 to 15,000 m3/day has a biofilters spray line that includes trays with emptying fittings and reflecting disks, the distance from the trays emptying fittings upper ends to the disk reflectors is 0.8 to 2 m, and the distance between the trays centers and the distance between the trays fittings axes is 0.6 to 1.8 m.