Which of the following is NOT among the five common pieces of equipment used in suspended growth secondary biological treatment?

• A. Disinfection system
• B. Aeration tanks
• C. Final clarifiers
• D. Sludge pumps

Answer: (A)

In suspended growth secondary biological treatment, the focus is on providing oxygen and keeping biomass active so microorganisms can break down organic matter, then separating the treated water from the solids. The equipment that supports this is the aeration tanks where the biological process happens, the aeration equipment (such as diffusers and blowers) that supplies air for the biological activity, the final clarifiers where solids settle out from the treated water, and the sludge handling pumps that move return sludge back to the reactor and remove excess sludge for disposal or digestion. A disinfection system, while essential for reducing pathogens, is not part of this secondary biological treatment stage; it’s used after secondary treatment in disinfection or tertiary stages. So it’s not among the common pieces of equipment for this process.