To provide an air diffuser for high-concentration sewage which is capable of improving the oxygen supply efficiency to an aerator liquid mixture without increasing an aerator capacity.
This sewage treatment device has an aerator 2 which biologically treats the organic matter and the organic sewage of a high nitrogen concentration, an immersion type membrane separator 7 immersed into the aerator 2, an air diffusion pipe 8 which is arranged below the immersion type membrane separator 7, and air supply system 10 which supplies air to the air diffusion pipe 8 and a sewage supply system 3 which supplies the organic sewage to the aerator 2. The sewage supply system 3 is provided with an external diffusion section 6 and an air supply system 10 is connected to the upstream side of the external diffusion section 6 and the external diffusion section 6 is provided with a sharply expanding flow passage section 6b which rapidly expands in the flow passage section as compared to the upstream side pipeline.
IZUMI SEIJI
KAMISAKA TAICHI
