Shear Tubes & Multi-Eductor Draft Tube (MEDT)
Aeration for aerobic digestion systems is critical, particularly in thicker solids applications. Insufficient aeration and mixing can cause odours and impact volatile solids reduction (VSR), resulting in increased costs.
Shear tubes, draught tubes, and MEDT, when combined with a TransMAX or MS Diffuser, provide exceptional mixing and aeration, up to 4 percent at a reduced blower horsepower requirement. This system aerates deep basins with side water depths of 20 to 50 feet (6 to 15 metres).
Shear tubes, draught tubes, and MEDT when combined with the TransMAX and MS diffuser aeration systems provides many operational advantages over conventional diffuser systems, in deep tanks and/or solids up to 4 percent. Other features and benefits include:
- Simplified diffuser maintenance that doesn’t require entering, draining, or taking tanks out of service, since the orifice assembly is accessible above the water surface
- No moving parts
- Ability to cycle the air on and off without plugging or fouling the diffusers
- Long service life (20 years and above)
- Economically converts anaerobic digesters and Imholf tanks to aerobic digesters
- Reduces blower discharge pressure
A shear tube is an open-ended cylindrical tube with a single drop MS or TransMAX diffuser mounted inside. A draught tube is an open-ended cylindrical tube with multiple MS or TransMAX diffusers mounted inside. The MEDT combines both the draught tube and shear tubes into one system.
Due to the differential pressure between the bottom of the tube and the highly aerated sludge at the top of the tube, sludge is drawn up inside the tube and discharged out the top. This causes a rolling circulation pattern within the system, moving out from each tube, down the depth of the water and back up the tube. The pumping action is similar to that of an airlift pump and has been quantified with test data. By bringing the full pumped volume into the confined area of the tube the velocity is maintained between 4 and 6 ft/sec, thereby reducing the viscosity of the thickened sludge.