Coarse bubble diffusers
Encyclopedia
Coarse bubble diffusers are a pollution control technology used to aerate and or mix wastewater for sewage treatment
. They 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.
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
.http://www.wastewater.com/pdf/101.pdf Maufacturers of diffused aeration systems claim that converting from coarse bubble to fine bubble system should yield a 50% energy cost savings.http://www.wastewater.com/pdf/105.pdf Specifically, in aeration tanks, a system that utilizes coarse bubble diffusers requires 30 to 40% percent more process air than a fine bubble diffused air system to provide the same level of treatment. The exception would be in secondary treatment (or side processing) phases. In these processing tanks, floc particles, sediment and carbonate buildup tend to plug or clog the small air release openings on the fine bubble diffusers. Because of their small air openings, fine bubble diffusers cease to have an advantage. Currently, coarse bubble diffusers are the mainstay solution.
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 elastomer
ic 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. When comparing disc-shaped diffusers, the majority fail to withstand specific challenges http://www.coarsebubblediffuser.com/compare-diffuser-differences.html, beyond 1 or 2 years, which include: clogging, blowing off and cracking. Any coarse bubble diffuser that eliminates these problems would deliver a huge cost-savings, not only in product replacement, but in system downtime to facilitate their exchange. Definitely a motivating factor of budget-sensitive operators at municipal waste water treatment processing plants.
Sewage treatment
Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...
. They 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
Fine bubble diffusers
Fine bubble diffusers are a pollution control technology used to aerate wastewater for sewage treatment. They produce a plethora of very small air bubbles which rise slowly from the floor of a wastewater treatment plant or sewage treatment plant aeration tank and provide substantial and efficient...
, given the same air volume.
Application
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
Fine bubble diffusers
Fine bubble diffusers are a pollution control technology used to aerate wastewater for sewage treatment. They produce a plethora of very small air bubbles which rise slowly from the floor of a wastewater treatment plant or sewage treatment plant aeration tank and provide substantial and efficient...
.http://www.wastewater.com/pdf/101.pdf Maufacturers of diffused aeration systems claim that converting from coarse bubble to fine bubble system should yield a 50% energy cost savings.http://www.wastewater.com/pdf/105.pdf Specifically, in aeration tanks, a system that utilizes coarse bubble diffusers requires 30 to 40% percent more process air than a fine bubble diffused air system to provide the same level of treatment. The exception would be in secondary treatment (or side processing) phases. In these processing tanks, floc particles, sediment and carbonate buildup tend to plug or clog the small air release openings on the fine bubble diffusers. Because of their small air openings, fine bubble diffusers cease to have an advantage. Currently, coarse bubble diffusers are the mainstay solution.
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 elastomer
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...
ic 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. When comparing disc-shaped diffusers, the majority fail to withstand specific challenges http://www.coarsebubblediffuser.com/compare-diffuser-differences.html, beyond 1 or 2 years, which include: clogging, blowing off and cracking. Any coarse bubble diffuser that eliminates these problems would deliver a huge cost-savings, not only in product replacement, but in system downtime to facilitate their exchange. Definitely a motivating factor of budget-sensitive operators at municipal waste water treatment processing plants.