Coarse bubble diffusers

Coarse bubble diffusers produce 1/4 to 1/2 inch 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.

These diffusers are typically made in the shape of a perforated rectangular pipe called a wide band, or a cap of 3" in diameter with an elastomeric membrane.  Other varieties of coarse bubble diffusers exist though it is generally accepted that all of them perform similarly with respect to mass oxygen transfer.

Often in non-newtonian/pseudoplastic fluids, such as a digester with high solids concentration, it does make sense to use coarse bubble diffusers rather than fine bubble diffusers, due to the larger bubbles ability to shear through more viscous wastewater.

However over the past two decades, coarse bubble diffusers have been used less frequently primarily due to the ever increasing cost of energy, and the availability of more reliable, highly efficient fine bubble diffusers

Source

 * [SSI Aeration http://www.stamfordscientific.com]