Air diffuser

A method of treating water with an air diffuser, the air diffuser comprising:

• a bottom panel provided in a horizontal direction in a tank in which water is filled, the bottom panel including longitudinal edges extending in a longitudinal direction and width-direction edges at longitudinal ends of the bottom panel;
• an air diffusion body formed as a soft film and installed to cover the bottom panel from above;
• a frame that covers the longitudinal edges and the width-direction edges of the bottom panel, the soft film being sandwiched between the bottom panel and the frame;
• and
• air diffusion holes arranged to penetrate through the soft film, wherein
• a gap is defined between the bottom panel and the soft film within an area defined by the frame, the gap being in communication with the air diffusion holes and allowing gas fed into the gap to be discharged into water through the air diffusion holes,
• the air diffuser allows pressure of the gas to deform the soft film upward at all points within the frame, and
• an air diffusion region of the soft film where the air diffusion holes are arranged has a width equal to or larger than 10 mm and smaller than 120 mm,
• the method comprising supplying air to the air diffuser at a volume of equal to or smaller than 60 [Nm3/(m2·hr)].