Coarse Bubble - High Rate Mixing and Aeration Systems
Tideflex Technology’s Coarse Bubble Aeration Systems provide the operators with extreme flexibility in operational methods for their process systems. Now the process requirements of the system can drive the operational methods not the limitations of the equipment within the tank. Tideflex’s innovative duckbill check valve diffuser is not dependant upon maintaining a positive system pressure or continuous blower operation nor is it affected by the increase in solids concentration of the process fluid.
For Waste Sludge Holding Tanks and Aerobic Digesters, further Denitrification is desirable and can be achieved by providing extended anoxic periods through the holding process. This requires discontinuing the airflow (oxygen supply) to the tank resulting in a loss of the positive pressure within the air distribution system subjecting the diffuser unit to backflow conditions of the process sludge. The Tideflex Coarse Bubble Diffuser is inherently a duckbill check valve where hydrostatic head against the exterior of the unit produces closure of the discharge opening preventing the waste sludge from entering the diffuser and piping system.
When the airflow to a mixing system is discontinued the solids within the process will settle to the bottom of the tank creating a concentrated blanket typically three times the density of the fluid during the mixing periods. Re-suspension of these settled and compacted solids after the anoxic period is critical to prevent solids accumulation within the tank. Solids remaining on the bottom for extended periods will move from an anoxic state to an anaerobic state and produce less desirable by-products such as hydrogen sulfide gas and methane gas. For more design considerations relating to sludge mixing go to 'Mixing and Oxygenation of Waste Sludge'. The Tideflex diffusers are oriented with the tip of the diffuser close to the tank bottom so that the air discharged from the units provides an educted upward path and a complete mixing loop from the floor of the tank to the liquid surface.
Mixing Dynamics of Diffused Aeration Systems
Complete mixing of a system using diffused aeration is achieved by maximizing the Depth of Influence of the hydraulic circulation loops within the tanks. The liquid area displaced by rising air bubbles creates an upward eduction of the fluid, this upward displacement of hydraulic mass must also return in downward velocities. This return circulation of the liquid will only extend to a depth equivalent to the elevation of the air bubble discharge from the diffuser. Areas below this elevation will have very low velocity and tend to become stagnant, therefore mounting the diffuser on the top side of the distribution piping is not recommended. In order to ensure adequate velocities and influence along the tank floor the discharge emittance point of the air from the diffuser must be located near the floor.
Distribution pipes with the Tideflex Technologies system can be installed with approximately 6 inches of clearance from the floor to prevent trapping of circulated solids. The Tideflex diffusers are oriented below the bottom elevation of the distribution pipes where the discharge emittance point is approximately 2 to 4 inches above the floor of the tank. This bottom discharge elevation ensures complete mix of the tank from the top water surface to the bottom surface of the tank. Blowers utilized in wastewater treatment are high volume / low pressure units (8 to 10 psi average); they have just enough pressure to emit the air at the submergence depth. As air is emitted from the diffuser it immediately begins to travel to the surface driven by it’s buoyancy force. In hydraulic flow applications the Tideflex diffuser can enhance velocity at the discharge but with low pressure blower systems directional velocity of discharged air is not achievable. Therefore, the tip of the Tideflex diffuser is located just above the floor surface to start the path of upward air flow as low in the tank as possible.
Coarse Bubble Diffuser Check Valve Prevents Backflow of Solids
The Tideflex diffuser incorporates backflow prevention of wastewater through the discharge opening when airflow is discontinued, this is achieved by the hydrostatic force against the outside surface of the bill portion of the diffuser forcing the discharge slit to seal closed. The deeper the submergence the greater the sealing force applied to close the diffuser. The diffuser discharge opening consists of an elongated slit which will open proportionally to the air flow pressure applied, this variable slit area provides self cleaning of any sludge particles which were instantaneously pinched and held in the bill flare at the time of closure.