Coarse bubble diffusers produce 1/4 to 1/2 inch (6.4 to 13 mm) bubbles which rise rapidly from the floor of a wastewater treatment plant or sewage treatment plant tank. They are typically used in grit chambers, equalization basins, chlorine contact tanks, and aerobic digesters, and sometimes also in aeration tanks. Generally they are better at vertically "pumping" water than at mass transfer of oxygen. Coarse bubble diffusers typically provide half the mass transfer of oxygen as compared to fine bubble diffusers, given the same air volume.