Activated Sludge Diffusion

Activated Sludge Diffusion

Activated sludge diffusion is a technology that involves collecting odorous air, directing it to the suction side of aeration blowers, and diffusing it into activated sludge basins. The odors are removed by a combination of mechanisms including absorption, adsorption, condensation, and biological oxidation in the basins.

The process is relatively simple to implement into new designs or where aeration blowers and diffusers already exist.

There are a number of plants in the U.S. using this process with excellent results on moderate to high strength odors. Typical odor removal efficiencies are reported in the 95 – 99% range, with hydrogen sulfide removal efficiencies exceeding 99%.

FRP Fan with inlet filter and moisture trap

Advantages include low capital and operating costs (if aeration blowers and diffusers already exist), no chemical handling or storage, no spent media disposal, and the process can handle wide fluctuations in hydrogen sulfide and other reduced sulfur compound loadings.

Disadvantages include potential corrosion of unprotected steel blowers, inlet filters and piping, and a build-up of a “tar-like” substance (probably grease) on internal components of the blowers has been reported. These disadvantages can be minimized or eliminated through the use of inlet components constructed from corrosion resistant materials such as FRP or stainless steel. The “tar-like” substance can be removed by routine steam cleaning or use of a grease-cutting solvent.

Applicable Treatment Processes

All liquid treatment plant processes, sludge thickening, sludge dewatering.

Major Design Considerations

Minimize treated volumes

Volumes can be minimized by covering individual sources, as opposed to treating entire room volumes, etc.


Utilize corrosion-resistant materials such as FRP or stainless steel for aeration blower inlet components. The aeration blowers should be constructed of stainless steel and installed with inlet filters and moisture traps.


Fine bubble diffusers will provide higher odor removal efficiencies than coarse bubble diffusers, particularly with high hydrogen sulfide loadings.