Which form of activated sludge must have primary clarifiers?

The form of activated sludge that must have primary clarifiers is conventional activated sludge. This process relies heavily on the effective removal of solids and organic matter before the aeration stage. Primary clarifiers serve to settle out larger suspended solids from the incoming wastewater, reducing the organic load that enters the aeration tanks.

In the context of conventional activated sludge, the removal of these solids is crucial because it helps prevent the overload of the biological treatment system, allowing the microorganisms to effectively digest the remaining organic material. Without primary clarification, the system might face issues such as increased aeration demand and a less efficient treatment process due to excess solids competing with the microorganisms.

While other forms of activated sludge, such as extended aeration and contact stabilization, utilize variations in aeration time and processes, they do not strictly require primary clarifiers as a component of their design. They might have different operational methods or can sometimes deal with untreated solids differently, potentially recycling a portion of the solids back into the system. Thin-layer contact, on the other hand, focuses more on the surface area for microbial growth and may also operate without a primary clarifier.

Thus, the requirement of primary clarifiers in the conventional activated sludge process underscores its need for preprocessing of influent to ensure