Below we evaluate retrievable diffuser systems by reviewing several common primary types of units.
Simple drop-type assembly with a small diameter pipe and “T” section at the bottom. Diffusers are mounted at the “T” section and are installed near one wall of the aeration basin.
This configuration creates a strong roll mix aeration pattern in the basin size fluid schematics shown in Figure 1.
- The roll configuration dramatically reduces oxygen transfer as much as 25%.
- Proper mixing may be difficult to maintain unless the basin has a specific geometry conductive to roll mixing.
- Retrieval of the units is simple; however, reinstalling units with air inside the piping can be a major challenge.
- Typically used for small basins, small activated sludge plants and channel aeration.
Floating aeration systems that employ characteristics of a floating aeration pipe as an air header on the surface of the liquid.
The air header is fitted with feeder hoses, which deploy the diffusers at the desired elevation in the biological reactor, lagoon, or aeration basin.
There are two primary ways of configuring these systems:
- Floating air header (lateral) with hoses feeding diffuser units sitting on the floor of the aeration basins.
- Low-intensity aeration systems primarily use this configuration.
- Each diffuser is connected to a float-and-rope assembly on the surface of the basin to allow individual access for inspection and maintenance. Floating air header (lateral) system with diffusers suspended from the floor of the basin.
- Floating air header (lateral) system with diffusers suspended from the floor of the basin.
- This array is particularly economical for large basins and large lagoon installations with low food/mass (F/M) loading rates.
- Retrievable diffuser units in small waste treatment facilities with individual rubber hoses connecting each diffuser unit.
Air flow through the rubber hose is controlled by a valve at the air header, and the diffusers sit on the floor of the basin.
Large activated sludge systems and high intensity aeration systems can employ a retrievable aeration system similar to the EDI ModuleAir™ unit.
The ModuleAirTM is a large-diameter PVC or stainless steel pipe fed by a large diameter hose from a metal air header above the liquid surface. This unit is mounted on legs or feet to level the assembly and maintain the assembly and diffusers at the desired elevation. See Figure 2, next page.
To employ this device requires a level and stable floor, such as a concrete floor. Notable characteristics of the system are:
- Slightly reduced aeration efficiency compared to a complete grid configuration.
- An installed capital cost of 1.5 – 2 times that of the most economical grid diffuser system using floor-mounted diffusers.
- A typical need for a crane to lift the assemblies out of the aeration basin for inspection and maintenance.
Other specially-designed retrievable diffuser systems are available and configured to distinct project needs.
For customized design requirements, contact Environmental Dynamics International.
By offering easy access for maintenance, the proper use of retrievable aeration mixing systems can significantly increase the ability of diffusers to perform their aeration and mixing duties in water and wastewater systems. These systems can be custom-engineered and applied to each application as required.
The proper selection or application of these products is beyond the scope of this Technical Bulletin. Please contact Environmental Dynamics International for in-depth design considerations.