Which treatment unit is not dependent on aerobic bacteria for its efficiency?

The treatment unit that is not dependent on aerobic bacteria for its efficiency is the primary settling unit. This unit operates primarily on the principle of gravity to remove suspended solids from wastewater. During the primary treatment process, wastewater flows into this unit where the heavier solids settle to the bottom, forming sludge, while lighter materials, such as oils and grease, float to the surface and can be skimmed off.

Unlike aerated systems, such as trickling filters and activated sludge reactors, which rely on aerobic bacteria to break down organic matter, the primary settling unit does not facilitate biological treatment. Instead, it is focused on the physical separation of solids and does not require the presence of bacteria to function effectively. Secondary clarifiers assist in the settling process after biological treatment, but they too require aerobic conditions to function optimally. Therefore, the primary settling unit stands out for its distinct operational mechanism that does not involve aerobic microbial action.