Fine bubble diffusers
Encyclopedia
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 mass transfer of oxygen to the water. The oxygen, combined with the food source, sewage
, allows the bacteria to produce enzymes which help break down the waste so that it can settle in the secondary clarifiers or be filtered by membranes. A fine bubble diffuser is commonly manufactured in various forms: tube, disc, plate, and dome.
water. Furthermore, fine bubble diffusers evenly spread out (often referred to as a 'grid arrangement') on the floor of a tank, provide the operator of the plant a great deal of operational flexibility. This can be used to create zones with high oxygen concentrations (oxic or aerobic), zones with minimal oxygen concentration (anaerobic
) and zones with no oxygen (anoxic). This allows for more precise targeting and removal of specific contaminants.
The importance of achieving ever smaller bubble sizes has been a hotly debated subject in the industry as ultra fine bubbles (micrometre size) are generally perceived to rise too slowly and provide too little "pumpage" to provide adequate mixing of sewage in an aeration tank. On the other hand, the industry standard "fine bubble" with a typical discharge diameter of 2 mm is probably larger than it needs to be for many plants. Average bubble diameters of 0.9 mm are possible nowadays, using special polyurethane (PUR) or special recently developed EPDM membranes.
Fine bubble diffusers have largely replaced coarse bubble diffusers
and mechanical aerators in most of the developed world and in much of the developing world. The exception would be in secondary treatment phases, such as activated sludge processing tanks, where 85%-90% of any remaining solid materials (floating on the surface) are removed through settling or biological processes. The biological process uses air to encourage bacterial growth that would consume many of these waste materials, such as phosphorus and nitrogen that are dissolved in the wastewater. The larger air release openings of a coarse bubble diffuser helps to facilitate a higher oxygen transfer rate and bacterial growth. One disadvantage of using fine bubble diffusers in activated sludge tanks is the tendency of floc (particle) clogging the small air release holes.
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 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 mass transfer of oxygen to the water. The oxygen, combined with the food source, sewage
Sewage
Sewage is water-carried waste, in solution or suspension, that is intended to be removed from a community. Also known as wastewater, it is more than 99% water and is characterized by volume or rate of flow, physical condition, chemical constituents and the bacteriological organisms that it contains...
, allows the bacteria to produce enzymes which help break down the waste so that it can settle in the secondary clarifiers or be filtered by membranes. A fine bubble diffuser is commonly manufactured in various forms: tube, disc, plate, and dome.
Bubble Size
The subject of bubble size is important because the aeration system in a wastewater or sewage treatment plant consumes an average of 50 to 70% of the energy of the entire plant. Increasing the oxygen transfer efficiency decreases the power the plant requires to provide the same quality of effluentEffluent
Effluent is an outflowing of water or gas from a natural body of water, or from a human-made structure.Effluent is defined by the United States Environmental Protection Agency as “wastewater - treated or untreated - that flows out of a treatment plant, sewer, or industrial outfall. Generally refers...
water. Furthermore, fine bubble diffusers evenly spread out (often referred to as a 'grid arrangement') on the floor of a tank, provide the operator of the plant a great deal of operational flexibility. This can be used to create zones with high oxygen concentrations (oxic or aerobic), zones with minimal oxygen concentration (anaerobic
Hypoxia (environmental)
Hypoxia, or oxygen depletion, is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system...
) and zones with no oxygen (anoxic). This allows for more precise targeting and removal of specific contaminants.
The importance of achieving ever smaller bubble sizes has been a hotly debated subject in the industry as ultra fine bubbles (micrometre size) are generally perceived to rise too slowly and provide too little "pumpage" to provide adequate mixing of sewage in an aeration tank. On the other hand, the industry standard "fine bubble" with a typical discharge diameter of 2 mm is probably larger than it needs to be for many plants. Average bubble diameters of 0.9 mm are possible nowadays, using special polyurethane (PUR) or special recently developed EPDM membranes.
Fine bubble diffusers have largely replaced coarse bubble diffusers
Coarse bubble diffusers
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...
and mechanical aerators in most of the developed world and in much of the developing world. The exception would be in secondary treatment phases, such as activated sludge processing tanks, where 85%-90% of any remaining solid materials (floating on the surface) are removed through settling or biological processes. The biological process uses air to encourage bacterial growth that would consume many of these waste materials, such as phosphorus and nitrogen that are dissolved in the wastewater. The larger air release openings of a coarse bubble diffuser helps to facilitate a higher oxygen transfer rate and bacterial growth. One disadvantage of using fine bubble diffusers in activated sludge tanks is the tendency of floc (particle) clogging the small air release holes.