Typical preliminary treatment processes include screening, grinding, grit removal, grease removal, pre-aeration and

• A. Aeration
• B. Grit Removal
• C. Disinfection
• D. Flow Equalization

Answer: (D)

Flow equalization is included in typical preliminary treatment because the first stage of treatment aims to remove large debris and to smooth out the flow entering the plant. By leveling inflow, you prevent sudden surges from rain or industrial discharge from overwhelming primary clarifiers and subsequent treatment units, which helps maintain a more consistent, efficient process downstream. This makes downstream operations—such as sludge handling, digestion, and aeration—work more reliably and with fewer disturbances.

Aeration is associated with biological treatment rather than the physical, head-end work of preliminary treatment, and disinfection occurs later in the process. Grit and grease removals are already listed among the preliminary steps, so flow equalization best completes the set by addressing variability in flow itself.