METHOD FOR DENITRIFICATION TREATING WASTE WATER AND TREATING SYSTEM

PROBLEM TO BE SOLVED: To obtain a compact denitrification treating method. SOLUTION: Plural anaerobic treating zones 5a and 5b and aerobic treating zones 6a and 6b are alternately arranged in the flow direction headed with the anaerobic treating zone 5a to a treating device 1. By using the treating device 1, waste water to be treated is supplied in steps to the plural anaerobic treating zones 5a and 5b including the head and passed successively through the downstream zones to biologically treat nitrogen compds., then, the treated effluent is introduced into a solid-liq. separator 2 to separate sludge, and the separated sludge is returned to the anerobic treating zone 5a at the head. A movable bed upflow sand filter 3 is preferably used in combination with the device 1 for finish treatment. A device having the capacity in accordance with a standard activated-sludge process is used, and an efficient and high removal performance can stably be maintained for a long period while maintaining at least the conventional waste water treating capacity without circulating a large amt. of a nitrified soln.