In the air diffusion process, air is introduced from blowers through diffusion tubes suspended in a spiral flow tank, or in some cases, through diffuser plates in the bottoms of the aeration tanks or channels. An aeration period of 15 minutes is normally adequete, including proper mixing of chemicals. Tank cross sections should be square or with maximum up to two times the depth. Depths from flow lie should be from 10 to 12 feet. The quantity of air needed varies from 0.005 to 2.0 cubic feet of air per gallon of water.