Home - Aeration & Mixing Systems - Diffused Gas Technology

Description

    Diffused aeration systems depend on the principal of eduction of fluid through the displacement created by rising bubbles to generate mixing within the tank. Eduction occurs at the elevation of the bubble emittance point, areas below this discharge elevation have little velocity and mixing influence.  Fine bubble and coarse bubble diffusion systems will have different mixing characteristics due to their different bubble mass and should be accounted for in the system design evaluation. 

    The amount of mixing energy produced with a gas diffusion system is directly related to the submergence depth of the liquid and the mass of the gas being diffused.  The deeper the liquid the more momentum is generated in the vertical path upward.  This mixing energy is defined through the velocity gradient of this momentum path (for more information on velocity gradient mixing design go to the Mixing Technology page.)  The configuration of the mixing system depends on the following variables; constant or variable operating depth, tank geometry, solids concentrations within the liquid, and the method of diffused gas applied (refer to the Technical Documents download area for specific design guideline documents).

The Tideflex Diffuser

    The Tideflex® Coarse Bubble Diffuser has the capability to locate the emittance point of the bubbles at the very bottom of the tank resulting in complete mixing from the water surface to the tank floor.  The principal of operation of the Tideflex diffuser is simple: positive air pressure opens the valve allowing forward flow. Reverse differential pressure seals the bills, preventing backflow into the manifold piping. The elastomer duckbill will even seal around entrapped solids. Conventional stainless steel tube diffusers have fixed diameter holes that cannot prevent backflow or fouling, and their 12" to 24" length causes them to break at the connection to the air manifold piping.

    For diffused aeration systems, hydrostatic head provides the differential pressure for closure. Many wastewater treatment facilities are intentionally turning off the air supply to sludge tanks and digesters to allow the sludge to settle to the bottom for a decanting period, then remove the supernatant liquid which results in a thicker sludge. Thickening of the sludge reduces the hydraulic loading to the sludge processing equipment resulting in significant cost savings. This process operational mode now employed by most facilities requires that the diffuser units have backflow elimination capabilities. Standard ‘open orifice’ type diffusers will quickly clog when subjected to the decanting operations and settled sludge compacting into the air holes. These type units were designed for continual airflow operation – this approach is no longer practical for today’s methods of wastewater treatment.

Fine Bubble Assemblies with Internal Duckbill Check Valves

    Fine Bubble diffuser membranes provide a seal against backflow of liquids when the membrane retracts back around the support tube when the internal pressure is turned off, these membranes are not indestructable and if they become damaged over the operational life the membrane can loose it's ability to provide backflow prevention. Tideflex Technologies fine bubble diffusers are equipped with an internal Tideflex Duckbill Check Valve to provide a fail-safe in the event a membrane becomes damaged. This allows for continued process operation without having to drain the tank and immediately address the problem diffuser(s) because of their potential for clogging the entire manifold section.

    The bottom mounted orientation allows for condensate to be automatically purged from the system. Each diffuser is connected to the tee assembly with a full port threaded connection; this allows for easy replacement of the diffuser unit with a spare tube which is pre-assembled with the membrane attached and stored as a spare unit ready for quick replacement. Fine bubble diffusers are inherently good oxygen generators but poor mixing devices, but when combined with coarse bubble diffusers within the same process the benefits of both (good mixing & good oxygen transfer) can be achieved. Refer to the technical document Combination Systems for a description of the Tideflex Technologies patented process and patented system.

US Patent No. 6,016,839 / 6,193,220 / 6,372,140 / 6,702,263
Canada Patent No. 2,366,252 / 2,385,902; United Kingdom Patent No. 2,326,603